Search Results (35)

Future $e^{+}{e}^{-}$ colliders are expected to play a fundamental role in measuring Standard Model (SM) parameters with unprecedented precision and in probing physics beyond the SM (BSM). This study investigates two-particle angular correlation distributions involving final-state SM charged hadrons. Unexpected correlation structures in these distributions is considered to be a hint for new physics perturbing the QCD partonic cascade and thereby modifying azimuthal and (pseudo)rapidity correlations. Using Pythia8 Monte Carlo generator and fast simulation, including selection cuts and detector effects, we study potential structures in the two-particle angular correlation function. We adopt the QCD-like Hidden Valley (HV) scenario as implemented in Pythia8 generator, with relatively light HV v-quarks (below about 100 GeV), to illustrate the potential of this method. Full article

This investigation examines the Dead Hot Map (DHM) method and timing calibration for Run 14 Au+Au collisions in the PHENIX experiment. The DHM method guarantees data integrity by identifying and omitting defective detector towers (nonfunctional, hot, and very hot towers) via a set of criteria and statistical evaluations. This procedure entails hit distribution analysis, pseudorapidity adjustments, and normalization, resulting in an enhanced map of functional detector components. Timing calibration mitigates the issues associated with time-of-flight measurement inaccuracies, such as slewing effects and inter-sector timing differences. Numerous corrections are implemented, encompassing slewing, tower-specific offsets, and sector-by-sector adjustments, resulting in a final resolution of 500 picoseconds for the electromagnetic calorimeter. These calibrations improve the accuracy of photon and ${\pi }^0$ measurements, essential for investigating quark–gluon plasma in high-energy nuclear collisions. Full article

The increased particle flux expected at the HL-LHC poses a serious challenge for the ATLAS detector performance, especially in the forward region. The High-Granularity Timing Detector (HGTD), featuring novel Low-Gain Avalanche Detector silicon technology, will provide pile-up mitigation and luminosity measurement capabilities, and augment the new all-silicon Inner Tracker in the pseudo-rapidity range from 2.4 to 4.0. Two double-sided layers will provide a timing resolution better than 50 ps/track for MIPs throughout the HL-LHC running period, and provide a new timing-based handle to assign particles to the correct vertex. The LGAD technology provides suitable gain to reach the required signal-to-noise ratio, and a granularity of 1.3 × 1.3 mm² (with 3.6 M channels in total). This paper presents the current status of the HGTD project with emphasis on the sensor development and module results. Full article

The possibility to search for long-lived axion-like particles (ALPs) decaying into photons is investigated in ultraperipheral PbPb collisions at the Large Hadron Collider (LHC). We propose a search strategy for low-mass ALPs using the LHCb and ALICE experiments. The ALP identification is performed by requiring the decay vertex be reconstructed outside the region where a primary vertex is expected, which strongly suppress the contribution associated with the decay of light mesons. We also use the fact that a fraction of the photons convert into electron–positron pairs, allowing the reconstruction of the particle decay position. We present the predictions for the pseudorapidity and transverse momentum distributions of the ALPs and photons. Moreover, predictions for the fiducial cross-sections, derived considering the characteristics of the ALICE and LHCb detectors, are presented for different values of the ALP mass and the ALP—photon coupling. Full article

This study explores the inelastic doubly differential transverse momentum spectra of the primary charged particles, $({\pi }^{+}+{\pi }^{-})$, $(K^{+}+K^{-})$ and $\left(p\overline{p}\right)$, as a function of observables associated with underlying event (UE) at $\sqrt{s}=13TeV$. The particle production is measured on the basis of different angular regions like toward, transverse and away, elucidated with respect to the direction of leading particle of an event. To study the thermal freeze-out parameters, the non-extensive Tsallis distribution function is used to extract the temperature $T_{eff}$ and chemical potential $\mu$, which provide a basis to explain the QCD matter. The Tsallis distribution function describes transverse momentum spectra in pseudorapidity region of $\left|\eta \right|<0.8$. It is observed that effective temperature $T_{eff}$ changes from away to towards and forward region. Full article

A joint study of multi-particle pseudo-rapidity correlations and event-by-event fluctuations in the distributions of secondary particles and fragments of the target nucleus and the projectile nucleus was carried out in order to search for correlated clusters of secondary particles. An analysis of the collisions of the sulfur nucleus with photoemulsion nuclei at an energy of 200 A·GeV is presented based on experimental data obtained at the SPS at CERN. The analysis of multi-particle correlations was performed using the Hurst method. A detailed analysis of each individual event showed that in events of complete destruction of a projectile nucleus with a high multiplicity of secondary particles, long-distance multi-particle pseudo-rapidity correlations are observed. The distribution of average pseudo-rapidity in such events differs significantly from others, as it is much narrower, and its average value is noticeably shifted towards lower values <η>. Full article

The High-Luminosity Large Hadron Collider (HL-LHC) project aims to improve the performance of the LHC by increasing the proton–proton collision luminosity. New physics discoveries will be possible starting in 2027. The HL-LHC aims to improve the integrated luminosity by a factor of 10 concerning the current running LHC’s design value. The HL-LHC project foresees delivering proton–proton collisions at 14 TeV CM (Center of Mass) energy providing the integrated luminosity to a value of 3 ab⁻¹ for the ATLAS and CMS experiments, 50 fb⁻¹ for LHCb, and 5 fb⁻¹ for ALICE. The increased integrated luminosity for the above LHC experiments will provide the potential to discover rare processes while improving these measurements’ signal-to-noise (S/N) ratio statistics. The ATLAS muon spectrometer has been upgraded to face the challenges of the luminosity at the HL-LHC run. The new sub-detectors are as follows: The New Small Wheel (NSW) has replaced the Cathode Strip Chambers (CSC) discs at the internal part of the ATLAS end cups. The new integrated small Monitored Drift Chambers (sMDT) with the Resistive Plate Chambers (RPC) are installed at the outer end of the ATLAS BI (Barrel Inner) layer, in the barrel–endcap transition region, at 1.0 < |η| < 1.3, where η is the pseudo-rapidity (pseudo-rapidity η is a commonly used spatial coordinate describing the angle of a particle relative to the beam axis, defined as $\eta =-ln\left[tan\left({\displaystyle \frac{\theta }{2}}\right)\right]$, where θ is the angle between the vector momentum $\overrightarrow{p}$ and the positive direction of the beam axis). The NSW is an innovative technological achievement, including the MicroMegas (MM) gas detectors in large areas and small-strip Thin Gap Chambers (sTGC), enabling high p_T (high p_T is the high value of the particles’ transverse momentum versus the beam collision axis) trigger and muon detection. The muon reconstruction, the background rate, other spectrometer parameters, and the NSW performance are also presented. Full article

After rapid approval and installation, the SND@LHC Collaboration was able to gather data successfully in 2022 and 2023. Neutrino interactions from ν_μs originating at the LHC IP1 were observed. Since muons constitute the major background for neutrino interactions, the muon flux entering the acceptance was also measured. To improve the rejection power of the detector and to increase the fiducial volume, a third Veto plane was recently installed. The energy resolution of the calorimeter system was measured in a test beam. This will help with the identification of ν_e interactions that can be used to probe charm production in the pseudo-rapidity range of SND@LHC (7.2 < η < 8.4). Events with three outgoing muons have been observed and are being studied. With no vertex in the target, these events are very likely from muon trident production in the rock before the detector. Events with a vertex in the detector could be from trident production, photon conversion, or positron annihilation. To enhance SND@LHC’s physics case, an upgrade is planned for HL-LHC that will increase the statistics and reduce the systematics. The installation of a magnet will allow the separation of ν_μ from ${\overline{\nu }}_{\mu }$ Full article

The present work presents a study of jet production in the central region ($\left|\eta \right|$ < 2.5) and the forward region (3 < $\left|\eta \right|$ < 5) in proton–proton collisions at different energies: $\sqrt{s}$ = 13.6 TeV, $\sqrt{s}$ = 20 TeV, and $\sqrt{s}$ = 27 TeV. These energies are the present and expected future energies of the Large Hadron Collider. In addition, the measurement of dijets—where the dijet selected is the one leading the jet in the central region and the second jet is the one with the sub-leading role in the forward region—was investigated with the same collision energies. Jets are reconstructed with the anti-kT (R = 0.5) algorithm in the transverse momentum range pT = 15–1000 GeV/c. Different Monte Carlo event generators were used: PYTHIA, HERWIG, and EPOS-LHC. The momentum, multiplicity, energy, pseudorapidity, and azimuthal angle of the jets were measured. In addition, the dijet multiplicity and the difference in the azimuthal angle were measured. The generation of events was carried out using the Rivet analysis framework. It is observed that, when the energy of the collision increases, the production of the jets in the central and forward regions and the dijets multiplicity increase; overall an agreement is observed between the three event generators. The disagreement between the different generators points to potential areas for development or additional study. Full article

In this study, we develop the colour string model of particle production, based on the multi-pomeron exchange scenario, to address the controversial origin of the flow signal measured in proton–proton inelastic interactions. Our approach takes into account the string–string interactions but does not include a hydrodynamic phase. We consider a comprehensive three-dimensional dynamics of strings that leads to the formation of strongly heterogeneous string density in an event. The latter serves as a source of particle creation. The string fusion mechanism, which is a major feature of the model, modifies the particle production and creates azimuthal anisotropy. Model parameters are fixed by comparing the model distributions with the ATLAS experiment proton–proton data at the centre-of-mass energy $\sqrt{s}=13$ TeV. The results obtained for the two-particle angular correlation function, $C(\Delta \eta ,\Delta \varphi )$, with $\Delta \eta$ and $\Delta \varphi$ differences in, respectively, pseudorapidities and azimuthal angles between two particles, reveal the resonance contributions and the near-side ridge. Model calculations of the two-particle cumulants, $c_2\left\{2\right\}$, and second order flow harmonic, $v_2\left\{2\right\}$, also performed using the two-subevent method, are in qualitative agreement with the data. The observed absence of the away-side ridge in the model results is interpreted as an imperfection in the definition of the time for the transverse evolution of the string system. Full article

From a recently found family of analytic, finite and accelerating 1+1-dimensional solutions to perfect fluid relativistic hydrodynamics, we derive simple and powerful formulae to describe the rapidity and pseudorapidity density distributions. By introducing a new scaling function, we notice that the rapidity distribution data of the different experiments all collapse into a single curve. This data-collapsing (or -scaling) behaviour in the rapidity distributions suggests that high-energy $p+p$ collisions may be described as collective systems. Full article

SND@LHC is designed to perform measurements with neutrinos produced at the LHC in the pseudo-rapidity range of $7.2<\eta <8.4$. The experiment is located 480 m downstream of the ATLAS interaction point in the TI18 tunnel. The detector is a hybrid system composed of an 830 kg target made from 1 mm thick tungsten plates interleaved with nuclear emulsion films, electronic trackers also acting as an electromagnetic calorimeter, a hadronic calorimeter and a muon identification system. The detector is able to distinguish three neutrino flavours using the emulsion detector which can identify primary electrons and taus in charged current neutrino interactions. This capability allows probing heavy flavour forward production at the LHC, which even LHCb cannot access. The LHC CM energy corresponds to the ${10}^{17}$ eV astronomical energy region, which is of interest for future detectors. The SND@LHC’s capabilities and current status are reported in this document. Full article

In 2018, in preparation for the Beam Energy Scan II, the STAR detector was upgraded with the Event Plane Detector (EPD). The instrument enhanced STAR’s capabilities in centrality determination for fluctuation measurements, event plane resolution for flow measurements, and in triggering overall. Due to its fine radial granularity, it can also be utilized to measure pseudorapidity distributions of the produced charged primary particles, in EPD’s pseudorapidity coverage of $2.15<\left|\eta \right|<5.09$. As such a measurement cannot be done directly, the response of the detector to the primary particles has to be understood well. The detector response matrix was determined via Monte Carlo simulations, and corrected charged particle pseudorapidity distributions were obtained in Au + Au collisions at the center of mass collision energies $\sqrt{s_{{}_{NN}}}$ = 19.6 and 27.0 GeV using an iterative unfolding procedure. Several systematic checks of the method were also done. Full article

In this paper, using the concept of multi-pomeron exchange, we develope a Monte Carlo model of interacting quark–gluon strings acting as particle-emitting sources aimed at describing inelastic proton–proton interactions at high energies. The implemented 3D (three-dimensional) dynamics of colour string formation resulted in their finite length in the rapidity space and in the fluctuating event-by-event spatial density. Thus, this results in string cluster formation because of the fusion mechanism and the appearance of long-range multiplicity and mean transverse momentum (mean-$p_T$) correlations in rapidity. We study, via the pseudorapidity dependence, the sensitivity to the details of the 3D dynamical formation of strings for several observables such as the forward–backward correlation coefficient value, strongly intensive quantity, $\mathrm{\Sigma }$, and the “almost” strongly intensive observable, the variance, ${\sigma }_C^2$, of the distribution of the asymmetry coefficient, C. The strongly intensive quantity $\mathrm{\Sigma }$ is used in this study to suppress trivial statistical fluctuations in the number of particles emitting similar types of sources and to reveal the intrinsic fluctuations of a single source. We demonstrate the connection between $\mathrm{\Sigma }$ and such often used observables as cumulants, factorial cumulants, and ${\sigma }_C^2$. We stress the importance of the contribution of “short” strings and the event asymmetry of the initial conditions on the long-range correlation measures. We argue that string cluster formation because of the fusion mechanism explains the collective effects seen in multiplicity and transverse momentum–multiplicity, $⟨p_T⟩$–N, long-range correlation functions. Full article

The SND@LHC detector experiment is located at the Large Hadron Collider (LHC), about 480 m downstream of the ATLAS interaction point. The detector is designed to measure, for the first time ever, high-energy neutrinos produced at the LHC in the pseudorapidity region of $7.2<\eta <8.4$, which is inaccessible to other LHC experiments. The detector comprises a hybrid system that incorporates multiple components. The detector includes a 830 kg target composed of tungsten plates arranged in alternating layers with nuclear emulsion and electronic trackers: this arrangement functions as an electromagnetic calorimeter. Following the electromagnetic calorimeter, there is a hadronic calorimeter and a muon identification system. The detector possesses the ability to differentiate interactions involving all three neutrino flavours, enabling investigations into the physics of heavy flavour production in the forward region. This research is particularly significant for future circular colliders and high-energy astrophysical neutrino experiments. Furthermore, the detector has the ability to search for the scattering of Feebly Interacting Particles. The detector started operating during the LHC Run 3, and it collected a total of ∼39 fb${}^{-1}$ in 2022. The detector aims to collect approximately 250 fb${}^{-1}$ in the whole of Run 3. Full article