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Proceedings, 2019, HQ 2018

Hot Quarks 2018—Workshop for Young Scientists on the Physics of Ultrarelativistic Nucleus-Nucleus Collisions

Texel, The Netherlands | 7–14 September 2018

Volume Editors:
Javier Albacete (Universidad de Granada, Spain)
Jana Bielcikova (Nuclear Physics Inst., Academy of Sciences, Czech Republic)
Alessandro Grelli (Utrecht University & NIKHEF, Netherlands)
Jiangyong Jia (Stony Brook University & BNL, USA)
Jorge Noronha (University of Sao Paulo, Brazil)
Hannah Elfner (nee Petersen) (GSI, Goethe University & FIAS, Germany)
Lijuan Ruan (Brookhaven National Laboratory, USA)
Sevil Salur (Rutgers University, USA)
Bjoern Schenke (Brookhaven National Laboratory, USA)
Anthony Timmins (University of Houston, USA)


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Cover Story (view full-size image) The 8th edition of the Workshop for Young Scientists on the Physics of Ultrarelativistic [...] Read more.
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Open AccessProceedings
Direct Photon Measurements with the ALICE Experiment at the LHC
Published: 3 April 2019
Viewed by 353 | PDF Full-text (908 KB)
Abstract
In high-energy hadron collisions, direct photons can be produced in various processes and are of particular interest to study the hot QCD medium since they escape it without being affected. These proceedings present the latest ALICE experiment results concerning direct photon production in [...] Read more.
In high-energy hadron collisions, direct photons can be produced in various processes and are of particular interest to study the hot QCD medium since they escape it without being affected. These proceedings present the latest ALICE experiment results concerning direct photon production in proton-proton (pp), proton-lead (p–Pb) and lead-lead (Pb–Pb) collisions. All measurements agree with pQCD calculations at high transverse momentum (pT) and show no direct photon excess at low pT in small systems while a low-pT signal is found in central Pb–Pb collisions. Full article
Open AccessProceedings
Can Baryon Stopping Be Understood within a Hadronic Transport Approach
Published: 4 April 2019
Viewed by 303 | PDF Full-text (323 KB)
Abstract
The changing shape of the rapidity spectrum of net protons over the SPS energy range is still lacking theoretical understanding. In this work, a model for string excitation and string fragmentation is implemented for the description of high energy collisions within a hadronic [...] Read more.
The changing shape of the rapidity spectrum of net protons over the SPS energy range is still lacking theoretical understanding. In this work, a model for string excitation and string fragmentation is implemented for the description of high energy collisions within a hadronic transport approach. The free parameters of the string model are tuned to reproduce the experimentally measured particle production in proton-proton collisions. With the fixed parameters we advance to calculations for heavy ion collisions, where the shape of the proton rapidity spectrum changes from a single peak to a double peak structure with increasing beam energy in the experiment. We present calculations of proton rapidity spectra at different SPS energies in heavy ion collisions. Qualitatively, a good agreement with the experimental findings is obtained. In a future work, the formation process of string fragments will be studied in detail aiming to quantitatively reproduce the measurement. Full article
Open AccessProceedings
Multiplicity Dependence of the Jet Structures in pp Collisions at LHC Energies
Published: 4 April 2019
Cited by 1 | Viewed by 238 | PDF Full-text (279 KB)
Abstract
We study the charged event multiplicity dependence of the jet structure in pp collisions. We present evidence for jet shape modification due to multi-parton interactions using PYTHIA and HIJING++ Monte Carlo (MC) event generators as an input to our analysis. We introduce a [...] Read more.
We study the charged event multiplicity dependence of the jet structure in pp collisions. We present evidence for jet shape modification due to multi-parton interactions using PYTHIA and HIJING++ Monte Carlo (MC) event generators as an input to our analysis. We introduce a characteristic jet size measure which is independent of the choice of simulation parameters, parton distribution functions, jet reconstruction algorithms and even of the presence or absence of multi-parton interactions. We also investigate heavy-flavor jets and show the sensitivity of the multiplicity-differential jet structure to flavor-dependent fragmentation. Full article
Open AccessProceedings
HIJING, a Heavy Ion Jet INteraction Generator for the High-Luminosity Era of the LHC and Beyond
Published: 10 April 2019
Cited by 1 | Viewed by 274 | PDF Full-text (532 KB)
Abstract
HIJING++ (Heavy Ion Jet INteraction Generator) is the successor of the widely used original HIJING, developed almost three decades ago. While the old versions (1.x and 2.x) were written in FORTRAN, HIJING++ was completely rewritten in C++. During the development we keep in [...] Read more.
HIJING++ (Heavy Ion Jet INteraction Generator) is the successor of the widely used original HIJING, developed almost three decades ago. While the old versions (1.x and 2.x) were written in FORTRAN, HIJING++ was completely rewritten in C++. During the development we keep in mind the requirements of the high-energy heavy-ion community: the new Monte Carlo software have a well designed modular framework, therefore any future modifications are much easier to implement. It contains all the physical models that were also present in it’s predecessor, but utilizing modern C++ features it also includes native thread based parallelism, an easy-to-use analysis interface and a modular plugin system, which makes room for possible future improvements. In this paper we summarize the results of our performance tests measured on 2 widely used architectures. Full article
Open AccessProceedings
Testing a Best-Fit Hydrodynamical Model Using PCA
Published: 10 April 2019
Viewed by 278 | PDF Full-text (256 KB)
Abstract
Recently, a comprehensive Bayesian analysis was performed to simultaneously extract the values of a number of hydrodynamic parameters necessary for compatibility with a limited set of experimental data from the LHC. In this work, this best-fit model is tested against newly measured experimental [...] Read more.
Recently, a comprehensive Bayesian analysis was performed to simultaneously extract the values of a number of hydrodynamic parameters necessary for compatibility with a limited set of experimental data from the LHC. In this work, this best-fit model is tested against newly measured experimental flow results not included in the original work, namely the principal components of the two-particle correlation matrix in transverse momentum. The results from simulations show a good numerical agreement with data obtained by the CMS Collaboration. Full article
Open AccessProceedings
Centrality Dependence of Deuteron Production in PbPb Collisions at 2.76 TeV via Hydrodynamics and Hadronic Afterburner
Published: 10 April 2019
Viewed by 242 | PDF Full-text (374 KB)
Abstract
The deuteron binding energy is only 2.2 MeV. At the same time, its yield in Pb+Pb collisions at sNN = 2.76 TeV corresponds to a thermal yield at the temperature around 155 MeV, which is too hot to keep deuterons bound. [...] Read more.
The deuteron binding energy is only 2.2 MeV. At the same time, its yield in Pb+Pb collisions at sNN = 2.76 TeV corresponds to a thermal yield at the temperature around 155 MeV, which is too hot to keep deuterons bound. This puzzle is not completely resolved yet. In general, the mechanism of light nuclei production in ultra-high energy heavy ion collisions remains under debate. In a previous work we suggest a microscopic explanation of the deuteron production in central ultra-relativistic Pb+Pb collisions, the main mechanism being ppn $ pd reactions in the hadronic phase of the collision. We use a state-of-the-art hybrid approach, combining relativistic hydrodynamics for the hot and dense stage and hadronic transport for a later, more dilute stage. Deuteron rescattering in the hadronic stage is implemented explicitly, using its experimentally measured vacuum cross-sections. In these proceedings we extend our previous work to non-central collisions, keeping exactly the same methodology and parameters. We find that our approach leads to a good description of the measured deuteron transverse momentum spectra at centralities up to 40%, and underestimates the amount of deuterons at low transverse momentum at higher centralities. Nevertheless, the coalescence parameter B2, measured by ALICE collaboration, is reproduced well in our approach even for peripheral collisions. Full article
Open AccessProceedings
Low-Shear QCD Plasma from Perturbation Theory
Published: 10 April 2019
Cited by 1 | Viewed by 249 | PDF Full-text (349 KB)
Abstract
We argue that the inferred ratio of shear viscosity to entropy density of the quark-gluon plasma, h/s < 0.5 near the deconfinement temperature Tc, can be understood from perturbative QCD. To rebut opposite views, we first show that the existing leading order result [...] Read more.
We argue that the inferred ratio of shear viscosity to entropy density of the quark-gluon plasma, h/s < 0.5 near the deconfinement temperature Tc, can be understood from perturbative QCD. To rebut opposite views, we first show that the existing leading order result should not be expanded in logarithms. After then settling the question of scale for the running coupling, we establish a temperature dependence of h/s which agrees well with constraints from hydrodynamics. Full article
Open AccessProceedings
Review of Critical Point Searches and Beam-Energy Studies
Published: 10 April 2019
Viewed by 336 | PDF Full-text (281 KB)
Abstract
I give an introductory overview of the search for the critical point in the phase diagram of QCD in the context of heavy-ion collisions from a theoretical perspective. The focus is on static and dynamic critical physics and the corresponding properties of particle [...] Read more.
I give an introductory overview of the search for the critical point in the phase diagram of QCD in the context of heavy-ion collisions from a theoretical perspective. The focus is on static and dynamic critical physics and the corresponding properties of particle number fluctuations as relevant examples of promising observables for signatures of a critical point in beam-energy scan experiments. Full article
Open AccessProceedings
Heavy Hadrons Production by Coalescence Plus Fragmentation in AA Collisions at RHIC and LHC
Published: 10 April 2019
Viewed by 253 | PDF Full-text (232 KB)
Abstract
The hadronization process of heavy hadrons with bottom and charm quarks, especially for baryons Λc, in a dense QGP medium is largely not understood. We present within a coalescence plus fragmentation model the predictions for D0 and Λc spectra [...] Read more.
The hadronization process of heavy hadrons with bottom and charm quarks, especially for baryons Λ c , in a dense QGP medium is largely not understood. We present within a coalescence plus fragmentation model the predictions for D 0 and Λ c spectra and the related baryon to meson ratios at RHIC and LHC. We will discuss how our model can predict values for Λ c / D 0 of the order of O(1), which is much larger than the expectations from fragmentation, and in agreement whit early data from STAR collaboration. Furthermore in the same scheme can be predicted a baryon to meson ratio Λ c / D 0 in pp collisions assuming that at the LHC top energies there can be the formation of QGP matter. The results show a considerable volume effects that significantly reduce the ratios, but still predict quite larger values with respect to fragmentation, in agreement with recent data from ALICE in pp collisions. Full article
Open AccessProceedings
Production of Open-Charm Hadrons in AuAu Collisions at √sNN = 200 GeV Mesured by the STAR Experiment
Published: 10 April 2019
Cited by 1 | Viewed by 218 | PDF Full-text (2989 KB)
Abstract
Charm quarks are primarily produced at the early stages of ultra-relativistic heavy-ion collisions and can therefore probe the quark-gluon plasma throughout its whole evolution. Final-state open-charm hadrons are commonly used to experimentally study the charm quark interaction with the medium. Thanks to the [...] Read more.
Charm quarks are primarily produced at the early stages of ultra-relativistic heavy-ion collisions and can therefore probe the quark-gluon plasma throughout its whole evolution. Final-state open-charm hadrons are commonly used to experimentally study the charm quark interaction with the medium. Thanks to the excellent secondary vertex resolution provided by the Heavy Flavor Tracker, STAR is able to directly reconstruct D ± , D 0 , D s , and Λ c ± via their hadronic decay channels. The topological cuts for signal extraction are optimized using supervised machine learning techniques. In these proceedings, we present an overview of recent open charm results from the STAR experiment. The nuclear modification factors of open-charm mesons and Λ c ± /D 0 ratio are shown as functions of transverse momentum and collision centrality. Full article
Open AccessProceedings
Coherence Effects in Multiple Medium-Induced Radiation
Published: 11 April 2019
Viewed by 254 | PDF Full-text (694 KB)
Abstract
In the first part of this work we study the color coherence phenomenon by considering the well-known quark-antiquark antenna with an in-medium hard gluon emission and an extra very soft emission outside it—double antenna. By discussing the coherence effects in terms of the [...] Read more.
In the first part of this work we study the color coherence phenomenon by considering the well-known quark-antiquark antenna with an in-medium hard gluon emission and an extra very soft emission outside it—double antenna. By discussing the coherence effects in terms of the survival probability, we generalize previous studies of the antenna radiation to the case of more than two emitters. After providing support to the jet quenching picture with effective emitters in the QCD cascade, we present a novel setup of an antenna splitting inside the medium taking into account the finite formation time of the dipole, which turns out to be an important scale. We read into the role of coherence and the relevant time scales which control the scenario, while also providing theoretical support for vacuum-like emissions early in the medium. Finally, by mapping the spectrum of in-medium splittings through the corresponding kinematical Lund diagram, we appreciate regimes of a close correspondence to a semi-classical description. Full article
Open AccessProceedings
Non-Extensive Motivated Parton Fragmentation Functions
Published: 11 April 2019
Cited by 2 | Viewed by 243 | PDF Full-text (352 KB)
Abstract
A new form of fragmentation function is presented here, motivated by earlier non-extensive studies of jet fragmentation. We parametrized our Tsallis-like function on pion spectra and compared it to the most common fragmentation function parametrizations. It is shown that the new form is [...] Read more.
A new form of fragmentation function is presented here, motivated by earlier non-extensive studies of jet fragmentation. We parametrized our Tsallis-like function on pion spectra and compared it to the most common fragmentation function parametrizations. It is shown that the new form is in agreement with earlier parametrizations, furthermore, its scale evolution overlaps better with the experimental data. Full article
Open AccessProceedings
Testing the Reliability of the Soft-Gluon Approximation for High p Particles
Published: 11 April 2019
Viewed by 248 | PDF Full-text (291 KB)
Abstract
The soft-gluon approximation assumes that a high p parton propagating through dense QCD matter loses only a small amount of its energy via gluon radiation. This assumption is made in many different jet quenching approaches, which nevertheless predicted a sizable radiative energy [...] Read more.
The soft-gluon approximation assumes that a high p parton propagating through dense QCD matter loses only a small amount of its energy via gluon radiation. This assumption is made in many different jet quenching approaches, which nevertheless predicted a sizable radiative energy loss of such particles. This questions the reliability of this approximation, which must then be reconsidered. To address this issue, we relaxed the soft-gluon approximation within the DGLV formalism to the first order in opacity. The obtained analytical expressions are notably different from the soft-gluon case. Surprisingly the numerical effects that stem from waiving this assumption on fractional radiative energy loss and number of radiated gluons are small. Additionally, the effect on suppression is negligible, which can be intuitively understood by the cancellation of the opposite effects on the above mentioned variables. Consequently, our results surprisingly indicate that, contrary to the doubts mentioned above, the soft-gluon approximation remains well-founded within the DGLV formalism. We also investigate the effects of this assumption in the case of a dynamical medium, which suggests generality of the conclusions presented here. Full article
Open AccessProceedings
Forward-Backward Correlations and Multiplicity Fluctuations in Pb–Pb Collisions at √sNN = 2.76 TeV from ALICE at the LHC
Published: 11 April 2019
Viewed by 254 | PDF Full-text (2099 KB)
Abstract
This paper presents a comparative study of forward-backward correlations and multiplicity fluctuations in experimental data and in HIJING Monte Carlo simulations of Pb–Pb collisions at sNN=2.76 TeV. The analysis focuses on two observables: the forward-backward correlation coefficient b [...] Read more.
This paper presents a comparative study of forward-backward correlations and multiplicity fluctuations in experimental data and in HIJING Monte Carlo simulations of Pb–Pb collisions at s NN = 2 . 76 TeV. The analysis focuses on two observables: the forward-backward correlation coefficient b c o r r n - n and the strongly intensive quantity Σ . Results are discussed in the context of the dependence on centrality estimator and influence of event-by-event fluctuations of the geometry of the Pb–Pb collisions on the measured quantities. Full article
Open AccessProceedings
Fluctuations and Azimuthally Dependent Two-Particle Distributions
Published: 11 April 2019
Viewed by 222 | PDF Full-text (255 KB)
Abstract
The azimuthal dependence of the two-particle distribution, which reflects both the anisotropic flow of each particle and azimuthally sensitive correlations between the two particles, can be characterized with Fourier coefficients. We illustrate on a few idealized examples how the corresponding ”pair-flow coefficients” are [...] Read more.
The azimuthal dependence of the two-particle distribution, which reflects both the anisotropic flow of each particle and azimuthally sensitive correlations between the two particles, can be characterized with Fourier coefficients. We illustrate on a few idealized examples how the corresponding ”pair-flow coefficients” are affected by fluctuations of the single-particle anisotropic flow, even if genuine correlations are absent. Full article
Open AccessProceedings
Anisotropic Flow in the Few Collisions Regime: Application to Bottomonia
Published: 11 April 2019
Viewed by 174 | PDF Full-text (241 KB)
Abstract
Considering the kinetic Boltzmann equation in the limit of very few collisions, we study the evolution of the phase space distribution of bottomonia interacting with an expanding gas of massless partons. We investigate the scaling of the anisotropic flow coefficients on the initial [...] Read more.
Considering the kinetic Boltzmann equation in the limit of very few collisions, we study the evolution of the phase space distribution of bottomonia interacting with an expanding gas of massless partons. We investigate the scaling of the anisotropic flow coefficients on the initial eccentricities and the inverse Knudsen number, and compute their transverse momentum dependence. Full article
Open AccessProceedings
ψ(2S) Production in p-Pb and Pb-Pb Collisions with the ALICE Experiment
Published: 12 April 2019
Viewed by 227 | PDF Full-text (1856 KB)
Abstract
The inclusive production of the charmonium state ψ(2S) was studied in p-Pb and Pb-Pb collisions at sNN = 8.16 TeV and 5.02 TeV respectively, using the ALICE detector at the CERN LHC. The ψ(2S) [...] Read more.
The inclusive production of the charmonium state ψ ( 2 S ) was studied in p-Pb and Pb-Pb collisions at s NN = 8.16 TeV and 5.02 TeV respectively, using the ALICE detector at the CERN LHC. The ψ ( 2 S ) is less bound than the J / ψ and it represents an interesting probe for the study of cold nuclear matter effects in p-Pb collisions, while in the Pb-Pb system its formation can be strongly influenced by QGP production. The measurements are performed in different center-of-mass rapidity ranges, 2.03 < y cms < 3.53 and −4.46 < y cms < −2.96 for p-Pb collisions and 2.5 < y cms < 4.0 for Pb-Pb collisions, down to zero transverse momentum, through the ψ ( 2 S ) μ + μ - decay channel. The results are compared to those obtained for the J / ψ and with theoretical predictions. Full article
Open AccessProceedings
The Angantyr Model for Heavy-Ion Physics in PYTHIA8 †‡
Published: 12 April 2019
Viewed by 244 | PDF Full-text (248 KB)
Abstract
We have formulated a new model for collisions with nuclei, called Angantyr, which is now included in PYTHIA8 event generator. The model is inspired by the old Fritiof model, but also includes effects of hard partonic interactions. It uses a Glauber model to [...] Read more.
We have formulated a new model for collisions with nuclei, called Angantyr, which is now included in PYTHIA8 event generator. The model is inspired by the old Fritiof model, but also includes effects of hard partonic interactions. It uses a Glauber model to calculate the number of wounded nucleons, but includes fluctuations in the nucleon-nucleon(NN) interaction to separate non-diffractively and diffractively wounded nucleons. The MC simulates final states without assuming a thermalised plasma. In this manner we are providing an event generator to be used to simulate events from pp to AA with the same underlying physics approach. Collective effects due to high string density are not included in the present version, but will be added in future work. Full article
Open AccessProceedings
Measurement of Λc+ Baryon Production in p–Pb Collisions with ALICE at the LHC
Published: 12 April 2019
Viewed by 229 | PDF Full-text (285 KB)
Abstract
Charmed baryons and their corresponding baryon-to-meson ratios are important tools to understand hadronisation processes in the Quark-Gluon Plasma produced in heavy-ion collisions. Recent Run 2 measurements in p–Pb collisions at 5.02 TeV, performed with the ALICE experiment at the LHC, are presented and [...] Read more.
Charmed baryons and their corresponding baryon-to-meson ratios are important tools to understand hadronisation processes in the Quark-Gluon Plasma produced in heavy-ion collisions. Recent Run 2 measurements in p–Pb collisions at 5.02 TeV, performed with the ALICE experiment at the LHC, are presented and compared to theoretical model predictions. Full article
Open AccessProceedings
Multiplicity Dependence of Heavy-Flavour Correlations with Charged Particle and Collective Effects in p–Pb Collisions at √sNN = 5.02 TeV with ALICE at LHC
Published: 12 April 2019
Viewed by 223 | PDF Full-text (1746 KB)
Abstract
Azimuthal correlation studies of heavy-flavour particles with charged particles in p–Pb collisions can give an insight into the cold nuclear matter effects on heavy-quark production and hadronization into heavy-flavour jets. Multiplicity-dependent measurements of angular correlations of heavy-flavour particles with charged hadrons allow us [...] Read more.
Azimuthal correlation studies of heavy-flavour particles with charged particles in p–Pb collisions can give an insight into the cold nuclear matter effects on heavy-quark production and hadronization into heavy-flavour jets. Multiplicity-dependent measurements of angular correlations of heavy-flavour particles with charged hadrons allow us to investigate the collective behavior of the system and the initial state effects on heavy flavour hadron production. In addition, they can reveal possible modifications of the heavy-quark fragmentation and hadronization at different multiplicities. We present ALICE measurements of azimuthal correlations of prompt D-mesons with charged hadrons as a function of the multiplicity in p–Pb collisions at s NN = 5.02TeV. Moreover, the elliptic flow ( v 2 ) of heavy-flavour hadron decay electrons in high-multiplicity p–Pb collisions at s NN = 5.02 TeV, obtained using correlations with charged particles, is reported. Full article
Open AccessProceedings
Event Plane Dependence of Jet-Hadron Correlations in Au–Au Collisions at √sNN = 200 GeV with the STAR Detector at RHIC
Published: 12 April 2019
Viewed by 223 | PDF Full-text (250 KB)
Abstract
The phenomenon of jet quenching indicates that partons lose energy as they traverse the hot dense medium. By restricting a trigger jet in azimuth relative to the event plane, we are given another tool, which allows us to study the path length dependence [...] Read more.
The phenomenon of jet quenching indicates that partons lose energy as they traverse the hot dense medium. By restricting a trigger jet in azimuth relative to the event plane, we are given another tool, which allows us to study the path length dependence of medium modifications. Measurements of angular correlations relative to the event plane between reconstructed R = 0 . 4 full jets and charged hadrons are presented in mid-peripheral Au–Au collisions at s N N = 200 GeV with the STAR detector at RHIC. A robust and precise method, known as the Reaction Plane Fit (RPF) method is used to remove the complex, flow-dominated heavy-ion background from the correlation functions. Quantified through yield ratios, we study the event plane dependence of jet-correlated yields. The yield ratios are compared to prior measurements made by the ALICE Collaboration in Pb–Pb collisions at s N N = 2 . 76 TeV. With increased statistics and smaller uncertainties, the results from STAR show a similar conclusion to that of ALICE, that within uncertainties this measurement shows no significant path length dependence of medium modifications. Full article
Open AccessProceedings
Kaon Isospin Fluctuations in ALICE at the LHC
Published: 12 April 2019
Viewed by 217 | PDF Full-text (355 KB)
Abstract
The first measurements of isospin fluctuations in the kaon sector is presented in Pb-Pb collisions at sNN = 2.76 TeV. A robust statistical observable was used to extract the isospin fluctuations of neutral and charged kaons as a function of collision [...] Read more.
The first measurements of isospin fluctuations in the kaon sector is presented in Pb-Pb collisions at s N N = 2.76 TeV. A robust statistical observable was used to extract the isospin fluctuations of neutral and charged kaons as a function of collision centrality. The results show a significant variation in the behaviour of ν d y n in data when compared to Monte-Carlo models such as HIJING and AMPT. The deviation from 1/n scaling in data indicates possible isospin fluctuation in the kaon sector in heavy ion collisions. Full article
Open AccessProceedings
Mesonic Resonance Production in p–Pb, Pb–Pb and Xe–Xe Collisions with ALICE at the LHC
Published: 15 April 2019
Viewed by 237 | PDF Full-text (279 KB)
Abstract
We report recent measurements of mesonic resonance production in pp, p–Pb, Pb–Pb and Xe–Xe collision systems with the ALICE detector at LHC energies. Integrated particle yields, mean transverse momenta and particles ratios of mesonic resonances like ρ(770)0, K*(892)0 and [...] Read more.
We report recent measurements of mesonic resonance production in pp, p–Pb, Pb–Pb and Xe–Xe collision systems with the ALICE detector at LHC energies. Integrated particle yields, mean transverse momenta and particles ratios of mesonic resonances like ρ(770)0, K*(892)0 and Φ(1020) as a function of the charged particle multiplicity are presented. These measurements allow us to have better understanding of properties of the hadronic medium and hadrochemistry of the particle production from large ( Pb–Pb and Xe–Xe) to small systems ( pp, p–Pb). The flavour dependence of parton energy loss is also studied by measuring the nuclear modification factor, RAA in Pb–Pb at √sNN = 2.76 and 5.02 TeV and Xe–Xe at √sNN = 5.44 TeV collisions. Full article
Open AccessProceedings
Dielectron Production in Proton–Proton Collisions at √s =7 TeV with ALICE
Published: 15 April 2019
Viewed by 251 | PDF Full-text (469 KB)
Abstract
The ALICE Collaboration measured dielectron production as a function of the invariant mass (mee), the pair transverse momentum (pT,ee) and the pair distance of closest approach (DCAee) in pp collisions at s [...] Read more.
The ALICE Collaboration measured dielectron production as a function of the invariant mass ( m ee ), the pair transverse momentum ( p T , ee ) and the pair distance of closest approach ( DCA ee ) in pp collisions at s = 7 TeV. Prompt and non-prompt dielectron sources can be separated with the DCA ee , which will give the opportunity in heavy-ion collisions to identify thermal radiation from the medium in the intermediate-mass range dominated by contributions from open-charm and beauty hadron decays. The charm and beauty total cross sections are extracted from the data by fitting the spectra with two different MC generators, i.e., PYTHIA a leading order event generator and POWHEG a next-to-leading order event generator. Significant model dependences are observed, reflecting the sensitivity of this measurement to the heavy-flavour production mechanisms. Full article
Open AccessProceedings
Thermodynamics and Fluctuations-Correlations of Conserved Charges in a Hadron Resonance Gas Model with Attractive and Repulsive Interaction within S-Matrix Formalism
Published: 15 April 2019
Viewed by 272 | PDF Full-text (253 KB)
Abstract
We have extended the hadron resonance gas (HRG) model by including the effect of both attractive and repulsive interaction in the scattering matrix (S-matrix) formalism. The attractive part of the interaction is calculated using K-matrix formalism while the repulsive part is included by [...] Read more.
We have extended the hadron resonance gas (HRG) model by including the effect of both attractive and repulsive interaction in the scattering matrix (S-matrix) formalism. The attractive part of the interaction is calculated using K-matrix formalism while the repulsive part is included by fitting to experimental phase shifts. We have calculated various thermodynamics quantities like pressure, energy density, entropy density etc. A good agreement between our calculations and the hadronic phase of the lattice QCD (LQCD) simulations is observed. We have also calculated fluctuations and correlations for various conserved charges like baryon, strangeness and electric charge. In the present model, χ B 2 , χ B S 11 and C B S agree well with the LQCD data. Full article
Open AccessProceedings
Improved Event Mixing for Resonance Yield Extraction
Published: 15 April 2019
Viewed by 207 | PDF Full-text (516 KB)
Abstract
Resonance particles, such as the K*(892) meson, are reconstructed from the invariant mass (Minv) distribution of possible particle pairs. To extract the yield with the highest precision, the combinatorial background must be determined as precisely as possible. An event-mixed [...] Read more.
Resonance particles, such as the K*(892) meson, are reconstructed from the invariant mass (M i n v ) distribution of possible particle pairs. To extract the yield with the highest precision, the combinatorial background must be determined as precisely as possible. An event-mixed M i n v distribution is often used to describe the combinatorial background. However, this distribution will not contain the mini-jet-like structures present inside an event. This analysis introduces a new re-weighing scheme, where two M i n v distributions of like-sign particles in the same-event and in mixed-events are used to correct the mixed-event background estimate for the mini-jet-like structure. Using PYTHIA 8.2 generated proton-proton collisions at s NN = 5.02 TeV, it is shown that the new method can be used to more accurately describe the combinatorial background. Full article
Open AccessProceedings
Simulations of Energy Losses in the Bulk Nuclear Medium Using Hydrodynamics on the Graphics Cards (GPU)
Published: 15 April 2019
Viewed by 222 | PDF Full-text (734 KB)
Abstract
We are developing a software for energy loss simulation which is affected by jets in the nuclear matter described by relativistic hydrodynamics. Our program uses a Cartesian coordinate system in order to provide high spatial resolution for the analysis of jets propagation in [...] Read more.
We are developing a software for energy loss simulation which is affected by jets in the nuclear matter described by relativistic hydrodynamics. Our program uses a Cartesian coordinate system in order to provide high spatial resolution for the analysis of jets propagation in nuclear matter. In this work, we use 7th order WENO numerical algorithm which is resistant to numerical oscillations and diffusions. For simulating energy losses in the bulk nuclear medium, we develop efficient hydrodynamic simulation program for parallel computing using Graphics Processing Unit (GPU) and Compute Unified Device Architecture (CUDA). It allows us to prepare event-by-event simulations in high computing precision in order to study jet modifications in the medium and event-by-event simulations of fluctuating initial conditions. In our simulation, we start the hydrodynamic simulation from generation initial condition based on the UrQMD model in order to simulate comparable nucleus-nucleus interaction in the RHIC and LHC energies. The main part of this simulation is the computation of hydrodynamic system evolution. We present obtained energy density distributions which can be compared to experimental results. Full article
Open AccessProceedings
Multiplicity Dependence of Heavy-Flavour Hadron Decay Electron Production in Collisions at √sNN = 8.16 Measured with ALICE at the LHC
Published: 15 April 2019
Viewed by 213 | PDF Full-text (486 KB)
Abstract
A Large Ion Collider Experiment (ALICE) at the Large Hadron collider (LHC) is a heavy-ion dedicated experiment designed to study nuclear matter at extreme condition of high temperature and high density at which quarks are deconfined and give rise to a new state [...] Read more.
A Large Ion Collider Experiment (ALICE) at the Large Hadron collider (LHC) is a heavy-ion dedicated experiment designed to study nuclear matter at extreme condition of high temperature and high density at which quarks are deconfined and give rise to a new state of matter known as Quark Gluon Plasma (QGP). Heavy flavours (charm and beauty), are produced in the initial stages of hadronic collisions in hard scattering processes and therefore are effective probes to study the QGP. In this contribution, recent measurements of the production of electrons from heavy-flavour hadron decays, their nuclear modification factor and the self-normalised yield measured up to 14 in collisions at √sNN = 8.16 TeV collected in LHC Run2 in 2016 are presented. Full article
Open AccessProceedings
Overview on Heavy-Flavour at RHIC and LHC
Published: 16 April 2019
Viewed by 250 | PDF Full-text (350 KB)
Abstract
The PHENIX and STAR Collaborations at the Relativistic Heavy-Ion Collider and ALICE, CMS, ATLAS and LHCb Collaborations at the Large Hadron Collider have measured the production of charmonium and bottonium states as well as open heavy flavor hadrons via their hadronic and semi-leptonic [...] Read more.
The PHENIX and STAR Collaborations at the Relativistic Heavy-Ion Collider and ALICE, CMS, ATLAS and LHCb Collaborations at the Large Hadron Collider have measured the production of charmonium and bottonium states as well as open heavy flavor hadrons via their hadronic and semi-leptonic decays at mid-rapidity and in the semi-muonic decay channel at forward rapidity in pp, p–A and A–A collisions in an energy domain that ranges from s = 0.2 TeV to s = 13 TeV in pp collisions and from s NN = 0.2 TeV to s NN = 5.02 TeV in A–A collisions. In this contribution the latest experimental results will be reviewed. Full article
Open AccessProceedings
Quarkonia Production and Dissociation in a Langevin Approach
Published: 17 April 2019
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Abstract
We aim to describe the process of dissociation and recombination of quarkonia in the quark-gluon plasma. Therefore we developed a model which allows to observe the time evolution of a system with various numbers of charm-anticharm-quark pairs at different temperatures. The motion of [...] Read more.
We aim to describe the process of dissociation and recombination of quarkonia in the quark-gluon plasma. Therefore we developed a model which allows to observe the time evolution of a system with various numbers of charm-anticharm-quark pairs at different temperatures. The motion of the heavy quarks is realized within a Langevin approach. We use a simplified version of a formalism developed by Blaizot et al. in which an Abelian plasma is considered where the heavy quarks interact over a Coulomb like potential. We have demonstrated, that the system reaches the expected thermal distribution in the equilibrium limit. Full article
Open AccessProceedings
Diffusion of Conserved Charges in Relativistic Heavy Ion Collisions
Published: 17 April 2019
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Abstract
We discuss the diffusion currents occurring in a dilute system and show that the charge currents do not only depend on gradients in the corresponding charge density, but also on the other conserved charges in the system—the diffusion currents are therefore coupled. Gradients [...] Read more.
We discuss the diffusion currents occurring in a dilute system and show that the charge currents do not only depend on gradients in the corresponding charge density, but also on the other conserved charges in the system—the diffusion currents are therefore coupled. Gradients in one charge thus generate dissipative currents in a different charge. In this approach, we model the Navier-Stokes term of the generated currents to consist of a diffusion coefficient matrix, in which the diagonal entries are the usual diffusion coefficients and the off-diagonal entries correspond to the coupling of different diffusion currents. We evaluate the complete diffusion matrix for a specific hadron gas and for a simplified quark-gluon gas, including baryon, electric and strangeness charge. Our findings are that the off-diagonal entries can range within the same magnitude as the diagonal ones. Full article
Open AccessProceedings
Direct Photons at the PHENIX Experiment: From Large to Small Systems
Published: 17 April 2019
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Abstract
Direct photons are a unique probe to study the properties of the medium created in heavy ion collisions. Low transverse momentum (pT) direct photons are of special interest since thermal photons are supposed to be dominant, while at high p [...] Read more.
Direct photons are a unique probe to study the properties of the medium created in heavy ion collisions. Low transverse momentum ( p T ) direct photons are of special interest since thermal photons are supposed to be dominant, while at high p T direct photons come from initial hard scattering (pQCD). PHENIX has observed a large excess of direct photon yield as well as large azimuthal anisotropy at low p T in Au+Au collisions at the c.m.s energy per nucleon pair s N N = 200 GeV. The mechanism to produce a large direct photon yield with a large elliptic anisotropy ( v 2 ) is not well understood yet. PHENIX has made systematic measurements of direct photons with different collision energies and system configurations. It has been found that direct photon yield d N γ / d η is proportional to charge particle multiplicity ( d N c h / d η ) 1 . 25 . This behavior holds for beam energies measured both at RHIC and at the LHC in large systems. This scaling suggests that there is a transition from p+p to A+A system which could be understood with the analysis of smaller systems like p+Au and d+Au. Full article
Open AccessProceedings
Photons as Probes of Gluon Saturation in Dilute + Dense Collisions
Published: 18 April 2019
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Abstract
We use the Color Glass Condensate (CGC) effective field theory (EFT) to calculate inclusive photon production to leading order qgqγ, (LO), and next-to leading order ggqq¯γ (NLO) at LHC energies. These processes [...] Read more.
We use the Color Glass Condensate (CGC) effective field theory (EFT) to calculate inclusive photon production to leading order q g q γ , (LO), and next-to leading order g g q q ¯ γ (NLO) at LHC energies. These processes dominate the photon production at small-x , where x 0 . 01 in the target and projectile protons. We show that the NLO contribution dominates at values of x typical at the LHC, since its cross-section is sensitive to the gluon distributions in both protons. We perform a comparison of our results to the available inclusive photon data, from ATLAS and CMS at center-of-mass energies of 2 . 76 and 7 TeV . This data lies in the range k > 20 GeV . We show that for this range, the k -factorized cross-section converges to the full CGC EFT result, and can be used for the comparison. We find that it gives good agreement with experimental results. Our results are to be considered as a first step towards constraining unintegrated gluon distributions, which will be continued for larger systems, where coherent scatterings are enhanced. Full article
Open AccessProceedings
Studies of Heavy Flavor Jets Using D0-Hadron Correlations in Azimuth and Pseudorapidity in Au Au Collisons at 200 GeV at the STAR Experiment
Published: 19 April 2019
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Abstract
Heavy flavor (HF) quarks (charm, bottom) are important probes of the medium produced in relativistic heavy-ion collisions because they are formed in the early stage and propagate throughout the lifetime of the system. HF-meson spectra and azimuthal anisotropy (v2) measurements [...] Read more.
Heavy flavor (HF) quarks (charm, bottom) are important probes of the medium produced in relativistic heavy-ion collisions because they are formed in the early stage and propagate throughout the lifetime of the system. HF-meson spectra and azimuthal anisotropy ( v 2 ) measurements have been reported by experiments at RHIC and the LHC, and they suggest strong interactions of HF quarks with the medium. D 0 -hadron correlations on relative pseudorapidity and azimuth ( Δ η , Δ ϕ ) provide a method for disentangling correlation structures on ( Δ η , Δ ϕ )—allowing for separation of structures related to jets and bulk phenomena directly, with the D 0 serving as a proxy for a charm jet. In these proceedings, we present 2D D 0 -hadron angular correlations as a function of centrality in Au + Au collisions at s N N = 200 GeV. These data reveal a jet-like, peaked structure at ( Δ η , Δ ϕ ) = (0, 0) (near-side), and a Δ η -independent azimuthal harmonic modulation. Here, we focus on the evolution of the near-side peak’s yield and widths on ( Δ η , Δ ϕ ) as a function of centrality and compare them to results from light flavor correlations. Full article
Open AccessProceedings
Characterising Charm Jet Properties with Azimuthal Correlations of D Mesons and Charged Particles with ALICE at the LHC
Published: 19 April 2019
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Abstract
Charm quarks are produced via hard parton scattering in ultra-relativistic heavy-ion collisions, hence are ideal probes to study a possible de-confined state of matter, known as Quark Gluon Plasma (QGP). The angular correlation of a meson containing a charm quark with other charged [...] Read more.
Charm quarks are produced via hard parton scattering in ultra-relativistic heavy-ion collisions, hence are ideal probes to study a possible de-confined state of matter, known as Quark Gluon Plasma (QGP). The angular correlation of a meson containing a charm quark with other charged particles in heavy-ion collisions can help in studying the properties of QGP. Similar studies in pp collisions can give insight about the charm production mechanism while in p-Pb collisions could provide essential information to disentangle final-state QGP-induced modifications from effects caused by cold nuclear matter. In this proceedings, the results are presented for p-Pb collisions at s NN = 5.02 TeV and pp collisions at s = 13 TeV, so far the highest available energy at the LHC. The results are compared with Monte Carlo (MC) simulations using PYTHIA and POWHEG event generators and with pp collision results at s = 7 TeV. Full article
Open AccessProceedings
Anisotropic Hydrodynamics for Au-Au Collisions at 200 GeV
Published: 24 April 2019
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Abstract
In this proceedings, we review the basics of quasiparticle anisotropic hydrodynamics (aHydroQP). Then we present phenomenological comparisons between 3+1d quasiparticle anisotropic hydrodynamics and experimental data from RHIC experiments at 200 GeV Au-Au collisions. We show that 3+1d aHydroQP model is able to describe [...] Read more.
In this proceedings, we review the basics of quasiparticle anisotropic hydrodynamics (aHydroQP). Then we present phenomenological comparisons between 3+1d quasiparticle anisotropic hydrodynamics and experimental data from RHIC experiments at 200 GeV Au-Au collisions. We show that 3+1d aHydroQP model is able to describe the experimental results quite well using smooth Glauber initial conditions for many heavy-ion collision observables. Full article
Open AccessProceedings
Open Bottom Production in Au Au Collisions at √sNN = 200 GeV with the STAR Experiment
Published: 24 April 2019
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Abstract
In these proceedings, we present measurements of open bottom hadron production through multiple decay channels in Au + Au collisions at sNN = 200 GeV by the STAR experiment. Specifically, measurements of nuclear modification factors for electrons, J/ψ, and [...] Read more.
In these proceedings, we present measurements of open bottom hadron production through multiple decay channels in Au + Au collisions at s NN = 200 GeV by the STAR experiment. Specifically, measurements of nuclear modification factors for electrons, J / ψ , and D 0 from open bottom hadron decays, enabled by the Heavy Flavor Tracker, are shown. A large suppression for non-prompt J / ψ and non-prompt D 0 are observed at high transverse momenta. On the other hand, there seems to be less suppression for electrons from bottom hadron decays than for those from charm hadron decays at ∼ 2 σ significance level. Full article
Open AccessProceedings
Locating the QCD Critical Point Using Holographic Black Holes
Published: 29 April 2019
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Abstract
It has been shown that holographic black holes, constructed to mimic the equation of state of QCD computed on the lattice at finite temperature and zero density, display critical behavior at large baryonic chemical potential. In this proceedings, we discuss the mapping of [...] Read more.
It has been shown that holographic black holes, constructed to mimic the equation of state of QCD computed on the lattice at finite temperature and zero density, display critical behavior at large baryonic chemical potential. In this proceedings, we discuss the mapping of holographic black holes into the QCD phase diagram and the emergence of the critical point and the first order phase transition line. Full article
Open AccessProceedings
Measurements of Anisotropic Flow in Xe–Xe Collisions at √sNN = 5.44 TeV Using the ALICE Detector
Published: 29 April 2019
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Abstract
These proceedings summarise the first measurements of anisotropic flow coefficients vn, 2n4, for inclusive charged particles at mid-rapidity in Xe–Xe collisions at sNN=5.44TeV. The results are compared with those [...] Read more.
These proceedings summarise the first measurements of anisotropic flow coefficients v n , 2 n 4 , for inclusive charged particles at mid-rapidity in Xe–Xe collisions at s NN = 5 . 44 TeV . The results are compared with those from Pb–Pb collisions at s NN = 5 . 02 TeV , in order to test the initial state (IS) models and transport properties. The resulting differences in v 2 and v 3 between the two systems are consistent with two different hydrodynamical models. Moreover, it is expected that the ratios between v n and their corresponding eccentricities for n = 2 , 3 scale with transverse density. This is observed for some IS models, except for some deviations in central collisions. These results assist in constraining the initial state as well as the hydrodynamical propagation of the system. Full article
Open AccessProceedings
Study of Azimuthal Anisotropy of High-pT Charged Particles in Au Au Collisions at √sNN = 200 GeV with RHIC-PHENIX
Published: 29 April 2019
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Abstract
We study the path length dependence of energy-loss in the Quark Gluon Plasma (QGP) by measuring the azimuthal anisotropy coefficient and transverse momentum (pT) spectra for charged hadrons in Au + Au at sNN = 200 GeV at [...] Read more.
We study the path length dependence of energy-loss in the Quark Gluon Plasma (QGP) by measuring the azimuthal anisotropy coefficient and transverse momentum ( p T ) spectra for charged hadrons in Au + Au at s N N = 200 GeV at the RHIC-PHENIX experiment. To estimate the strength of the energy-loss as a function of p T , we use the Δ p T which is the difference of p T which provide the same yields at in-plane and out-of-plane directions. The results indicate that there are different structures between low- p T and high- p T regions. At high- p T , the size of Δ p T increases as the centrality goes up. We also calculate the difference of the path length of in-plane and out-of-plane directions for each centrality. The difference of the path length increases along with the centrality and the tendency is the same with the Δ p T results. Full article
Open AccessProceedings
Study of in-Medium Energy Loss with Heavy-Flavour Correlations in pp and Pb-Pb Collisions with ALICE at the LHC
Published: 29 April 2019
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Abstract
The azimuthal correlations between heavy-flavour hadrons or heavy-flavour decay electrons with charged particles in Pb-Pb collisions give insight on the modification of charm-jet properties in nucleus-nucleus collisions and the mechanisms through which heavy quarks in-medium energy-loss takes place. Studies in pp collisions, besides [...] Read more.
The azimuthal correlations between heavy-flavour hadrons or heavy-flavour decay electrons with charged particles in Pb-Pb collisions give insight on the modification of charm-jet properties in nucleus-nucleus collisions and the mechanisms through which heavy quarks in-medium energy-loss takes place. Studies in pp collisions, besides constituting the necessary baseline for nucleus-nucleus measurements, are important for testing expectations from pQCD-inspired Monte Carlo generators. In ALICE heavy-flavour hadrons are studied via their fully reconstructed hadronic decays (D mesons and Λ c baryon), via semileptonic decays of charmed baryons ( Λ c , Ξ c ) and via leptons coming from heavy-flavour hadron decays. In particular in the central barrel, η < | 0 . 8 | , the electrons from heavy-flavour hadron decays are investigated. This proceeding will include the study of azimuthal correlations of D mesons with charged particles in pp collisions and heavy-flavour decay electrons with charged particles in pp and Pb-Pb collisions at different energies available at the LHC. The Experimental results will also be compared with the expectations from POWHEG and PYTHIA event generators. Full article
Open AccessProceedings
Bulk Observables within a Hybrid Approach for Heavy Ion Collisions with SMASH Afterburner
Published: 30 April 2019
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Abstract
We present a model of the dynamical evolution of relativistic heavy ion collisions, which combines second-order viscous hydrodynamics and microscopic transport. In particular, we present a hybrid approach with MUSIC hydrodynamics, and SMASH (Simulating Many Accelerated Strongly-interacting Hadrons) afterburner. In this work, we [...] Read more.
We present a model of the dynamical evolution of relativistic heavy ion collisions, which combines second-order viscous hydrodynamics and microscopic transport. In particular, we present a hybrid approach with MUSIC hydrodynamics, and SMASH (Simulating Many Accelerated Strongly-interacting Hadrons) afterburner. In this work, we focus on low- p T hadronic observables—identified hadron p T spectra and anisotropic flow coefficients. We also demonstrate how the hadronic chemistry is altered by the hadronic non-equilibrium dynamics, for example by baryon-antibaryon annihilation. The new MUSIC + SMASH hybrid approach is also compared to existing MUSIC + UrQMD results. Full article
Open AccessProceedings
Insight into Thermal Modifications of Quarkonia From a Comparison of Continuum-Extrapolated Lattice Results to Perturbative QCD
Published: 5 May 2019
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Abstract
In this work, we strive to gain insight into thermal modifications of charmonium and bottomonium bound states as well as the heavy quark diffusion coefficient. The desired information is contained in the spectral function which can not be calculated on the lattice directly. [...] Read more.
In this work, we strive to gain insight into thermal modifications of charmonium and bottomonium bound states as well as the heavy quark diffusion coefficient. The desired information is contained in the spectral function which can not be calculated on the lattice directly. Instead, the correlator given by an integration over the spectral function times an integration kernel is obtained. Extracting the spectral function is an ill-posed inversion problem and various different solutions have been proposed. We focus on a comparison to a spectral function obtained from combining perturbative and pNRQCD calculations. In order to get precise results, continuum extrapolated correlators originating from large and fine lattices are used. We first analyze the pseudoscalar channel since the absence of a transport peak simplifies the analysis. The knowledge gained from this is then used to extend the analysis to the vector channel, where information on heavy quark transport is encoded in the low frequency regime of the spectral function. The comparison shows a qualitatively good agreement between perturbative and lattice correlators. Quantitative differences can be explained by systematic uncertainties. Full article
Open AccessProceedings
Measurements of the Υ Meson Production in Au + Au Collisions by the STAR Experiment
Published: 5 May 2019
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Abstract
In ultra-relativistic heavy-ion collisions, creation of a novel state of matter, the quark-gluon plasma (QGP), has been observed. Suppressed production of quarkonia, caused by the colour screening of the binding force, has been proposed as a direct evidence of the QGP formation. At [...] Read more.
In ultra-relativistic heavy-ion collisions, creation of a novel state of matter, the quark-gluon plasma (QGP), has been observed. Suppressed production of quarkonia, caused by the colour screening of the binding force, has been proposed as a direct evidence of the QGP formation. At RHIC energies, other phenomena such as the regeneration and co-mover absorption, are expected to have a small effect for the bottomonium family, which makes Υ a cleaner probe of the screening effect compared to the J / ψ meson. In these proceedings, the latest measurements of the Υ production suppression in Au + Au collisions at s NN = 200 GeV via the di-muon and di-electron decay channels by the STAR experiment at RHIC are presented and compared with data from the LHC and theoretical calculations. Moreover, Υ production measurements in p + p and p + Au collisions are also reported, providing a baseline and a quantification of the cold nuclear matter effects, respectively. Full article
Open AccessProceedings
Anti- and Hyper-Nuclei Production at the LHC with ALICE
Published: 7 May 2019
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Abstract
At the Large Hadron Collider (LHC) a significant production of (anti-)(hyper-)nuclei is observed in proton-proton (pp), proton-lead (p-Pb) and lead-lead (Pb-Pb) collisions. The measurement of the production yields of light (anti-)nuclei is extremely important to provide insight into the production mechanisms of nuclear [...] Read more.
At the Large Hadron Collider (LHC) a significant production of (anti-)(hyper-)nuclei is observed in proton-proton (pp), proton-lead (p-Pb) and lead-lead (Pb-Pb) collisions. The measurement of the production yields of light (anti-)nuclei is extremely important to provide insight into the production mechanisms of nuclear matter, which is still an open question in high energy physics. The outstanding particle identification (PID) capabilities of the ALICE detectors allow the identification of rarely produced particles such as deuterons, 3 He and their antiparticles. From the production spectra measured for light (anti-)nuclei with ALICE, the key observables of the production mechanisms (antimatter/matter ratio, coalescence parameter, nuclei/protons ratio) are computed and compared with the available theoretical models. Another open question is the determination of the hypertriton lifetime: published experimental values show a lifetime shorter than the expected one, which should be close to that of the free Λ hyperon. Thanks to the high-resolution track reconstruction capabilities of the ALICE experiment, it has been possible to determine the hypertriton lifetime at the highest Pb-Pb collisions energy with the highest precision ever reached. Full article
Open AccessProceedings
Hydrodynamization Time Near a Critical Point From a Holographic Bjorken Flow
Published: 13 May 2019
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Abstract
This proceedings reviews recent progress in the study of far-from-equilibrium hydrodynamization process of strongly interacting matter in the vicinity of a critical point. From a full non-linear evolution of a gravitational theory dual to a conformal strongly coupled plasma, and starting from a [...] Read more.
This proceedings reviews recent progress in the study of far-from-equilibrium hydrodynamization process of strongly interacting matter in the vicinity of a critical point. From a full non-linear evolution of a gravitational theory dual to a conformal strongly coupled plasma, and starting from a non-equilibrium initial state, it is verified that the time it takes for the plasma to acquire hydrodynamic behavior greatly increases near the critical point. Full article
Open AccessProceedings
Event Activity Measurements and Mid-Rapidity Correlations in 200 GeV pAu Collisions at STAR
Published: 13 May 2019
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Abstract
These proceedings report preliminary measurements of correlations between mid-rapidity charged tracks and high-rapidity event activity (EA) at STAR for sNN=200GeV p+Au collisions taken in 2015. These correlations are intriguing because they inform the current debate over use [...] Read more.
These proceedings report preliminary measurements of correlations between mid-rapidity charged tracks and high-rapidity event activity (EA) at STAR for s NN = 200 G e V p+Au collisions taken in 2015. These correlations are intriguing because they inform the current debate over use of the Glauber model in “small” systems (here meaning p+A or d+A and denoted as “s+A”) and have implications for calculating nuclear modification and quenching observables in these systems. The results support concerns about centrality binning in p+Au collisions, and as such motivate using ratios of semi-inclusive, as opposed to fully inclusive, jet spectra to look for jet enhancement or suppression. Full article
Open AccessProceedings
Dielectron Production in pp Collisions at √s = 13 TeV Measured in a Dedicated Low Magnetic-Field Setting with ALICE
Published: 13 May 2019
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Abstract
The low-mass dielectron production in pp collisions at s = 13 TeV was measured by ALICE with a reduced field of the ALICE central barrel solenoid magnet. This increases the reconstruction efficiency of low-pT electrons and allows a better electron background [...] Read more.
The low-mass dielectron production in pp collisions at s = 13 TeV was measured by ALICE with a reduced field of the ALICE central barrel solenoid magnet. This increases the reconstruction efficiency of low- p T electrons and allows a better electron background rejection while simultaneously giving the opportunity to access a similar phase space as covered by the AFS experiment at the Intersecting Storage Rings at CERN. There, an excess of dielectron pairs over the expectation from known dielectron sources was measured at low invariant mass and small pair transverse momenta in pp collisions at s = 63 GeV in 1987. It is shown how the ALICE dielectron analysis of the pp pilot runs at s = 13 TeV with B=0.2 T is adapted to the reduced-field configuration. Preliminary results are compared to the published reference data recorded with the nominal field, to illustrate the benefits of the low magnetic-field setting. Finally, the invariant-mass and pair-transverse-momentum distributions are compared to the AFS measurement to address a possible excess at low m ee and p T , ee . Full article

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Open AccessObituary
In Memoriam Dr. André Mischke
Published: 22 April 2019
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Abstract
André Mischke, a former organizer of the Hot Quarks international workshop, passed away at the age of 46 on Thursday 8 November 2018 due to a severe illness he fought for over a year. [...] Full article
Open AccessMeeting Report
Hot Quarks 2018—Workshop for Young Scientists on the Physics of Ultrarelativistic Nucleus–Nucleus Collisions, Texel, The Netherlands, 7–14 September 2018
Published: 22 April 2019
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Abstract
The 8th edition of the Workshop for Young Scientists on the Physics of Ultrarelativistic [...] Full article
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