Search Results (32)

In ultra-relativistic heavy-ion collisions, the study of muons from kaon (K) and pion ($\pi$) decays provides insights into hadron production and propagation in the Quark–Gluon Plasma (QGP). This paper investigates muon yields from K and $\pi$ decays in Pb–Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV using a fast simulation method. We employ a fast Monte Carlo procedure to estimate muon yields from charged kaons and pions. The simulation involves generating pions and kaons with uniform $p_{\mathrm{T}}$ and y distributions, simulating their decay kinematics via PYTHIA, and reweighting to match the physical spectra. Our results show the transverse momentum distributions of muons from K and $\pi$ decays at forward rapidity ($2.5<y<4.0$) for different centrality classes. The systematic uncertainties are primarily from the mid-rapidity charged K/$\pi$ spectra and rapidity-dependent $R_{\mathrm{AA}}$ uncertainties. The muon yields from pion and kaon decays exhibit consistency across centrality classes in the $p_{\mathrm{T}}$ range of 3–10 GeV/c. This study contributes to understanding hadronic interactions and decay kinematics in heavy-ion collisions, offering references for investigating pion and kaon decay channels and hot medium effects. Full article

The potential correlation between the ordinary muon capture (OMC) on ¹³⁶Ba and $0\nu \beta \beta$ decay of ¹³⁶Xe is explored. For this, we compute $0\nu \beta \beta$-decay amplitudes for intermediate states in ¹³⁶Cs below 1 MeV of excitation and for angular-momentum values $J\le 5$ by using the proton–neutron quasiparticle random-phase approximation (pnQRPA) and nuclear shell model (NSM). We compare these amplitudes with the corresponding OMC rates, computed in a previous Universe article (Universe 2023, 9, 270) for the same energy and angular-momentum ranges. The obtained results suggest that an extension of the present analysis to a wider energy and angular-momentum region could be highly beneficial for probing the $0\nu \beta \beta$-decay nuclear matrix elements using experimental data on OMC rates to intermediate states of $0\nu \beta \beta$ decays. Full article

Searches for new particles beyond the Standard Model (SM) are an important task for the Large Hadron Collider (LHC). In this paper, we investigate the properties of the heavy non-SM Higgs bosons in the $\mu$-term extended Next-to-Minimal Supersymmetric Standard Model ($\mu$NMSSM). We scan the parameter space of the $\mu$NMSSM considering the basic constraints from Higgs data, dark matter (DM) relic density, and LHC searches for sparticles. And we also consider the constraints from the LZ2022 experiment and the muon anomaly constraint at the 2$\sigma$ level. We find that the LZ2022 experiment has a strict constraint on the parameter space of the $\mu$NMSSM, and the limits from the DM-nucleon spin-independent (SI) and spin-dependent (SD) cross-sections are complementary. Then, we discuss the exotic decay modes of heavy Higgs bosons decaying into SM-like Higgs bosons. We find that for doublet-dominated Higgs $h_3$ and $A_2$, the main exotic decay channels are $h_3\to Z{A}_1$, $h_3\to h_1{h}_2$, $A_2\to A_1{h}_1$, and $A_2\to Z{h}_2$, and the branching ratio can reach to about 23%, 10%, 35%, and 10% respectively. Full article

Muon collisions are considered a promising means for exploring the energy frontier, leading to a detailed study of the possible feasibility challenges. Beam intensities of the order of ${10}^{12}$ muons per bunch are needed to achieve the necessary luminosity, generating a high flux of secondary and tertiary particles from muons decay that reach both the machine elements and the detector region. To limit the impact of this background on the physics performance, tungsten shieldings have been studied. A machine learning-based approach to the geometry optimization of these shieldings will be discussed. Full article

The flavour anomalies are a set of experimental deviations from the Standard Model (SM) predictions in several observables involving decays of bottom quarks. In particular, tensions between theory and experiment in measurements involving a bottom quark decaying into a strange quark and a pair of muons have motivated much theoretical work to explore possible new physics explanations. This review summarises the tumultuous evolution of these tensions, focusing on the most recent experimental results and their implications for physics beyond the SM. We also discuss the prospects for future measurements and tests of the flavour anomalies at the LHC and other facilities. Full article

In this paper, the interactions of low-energy muons (E < 10 MeV) with natural silicon, the basic material of microelectronics, are studied by Geant4 and SRIM simulation. The study is circumscribed to muons susceptible to slowdown/stop in the target and able to transfer sufficient energy to the semiconductor to create single events in silicon devices or related circuits. The capture of negative muons by silicon atoms is of particular interest, as the resulting nucleus evaporation and its effects can be catastrophic in terms of the emission of secondary ionizing particles ranging from protons to aluminum ions. We investigate in detail these different nuclear capture reactions in silicon and quantitatively evaluate their relative importance in terms of number of products, energy, linear energy transfer, and range distributions, as well as in terms of charge creation in silicon. Finally, consequences in the domain of soft errors in microelectronics are discussed. Full article

Astrophysical plasma ejections (jets) are formed and powered by black holes that accrete material from their companion star in binary systems. Black hole X-ray binary systems constitute potential powerful galactic and extragalactic neutrino and gamma-ray sources. After being accelerated to highly relativistic velocities and subjected to various energy-consuming interactions, the lepto-hadronic content of the jets produces secondary particles such as pions and muons that decay to gamma-ray photons and neutrinos heading towards the Earth. In this work, we employ a jet emission model in order to predict the neutrino and gamma-ray integral fluxes emanating from some of the most investigated and prominent stellar black hole X-ray binary systems in the Milky Way, such as GRO J1655-40, Cygnus X-1, SS 433, and GRS 1915+105. For the sake of comparison, we also include an extragalactic system, namely, LMC X-1, located in the Large Magellanic Cloud. For the case of gamma-ray emissions, we also include absorption effects due to X-ray emission from the accretion disk and the black hole corona, as well as ultraviolet (UV) emission from the binary system’s companion star. Full article

Permanent electric dipole moments (EDMs) are excellent probes of physics beyond the Standard Model, especially on new sources of CP violation. The muon EDM has recently attracted significant attention due to discrepancies in the magnetic anomaly of the muon, as well as potential violations of lepton-flavor universality in B-meson decays. At the Paul Scherrer Institute in Switzerland, we have proposed a muon EDM search experiment employing the frozen-spin technique, where a radial electric field is exerted within a storage solenoid to cancel the muon’s anomalous spin precession. Consequently, the EDM signal can be inferred from the upstream-downstream asymmetry of the decay positron count versus time. The experiment is planned to take place in two phases, anticipating an annual statistical sensitivity of $3\times {10}^{-21}$$e·$cm for Phase I and $6\times {10}^{-23}$$e·$cm for Phase II. Going beyond ${10}^{-21}$$e·$cm will enable us to probe various Standard Model extensions. Full article

This experiment to search for the one of the charged lepton flavor-violating processes, muon-electron conversion, DeeMe, is being conducted at the J-PARC MLF H-Line in Japan. This experiment utilizes a pulsed proton beam from the Rapid Cycling Synchrotron (RCS). A graphite target is bombarded with a pulsed proton beam, negative pion production and pion-in-flight-decay to negative muon; then, the creation of muonic atoms is caused in the same pion production target. A converted electron is expected to be emitted after 1 ∼ 2 micro second-delayed timing. And two-body reaction of the new process, ${\mu }^{-}+(\mathrm{A},\mathrm{Z})\to e^{-}+(\mathrm{A},\mathrm{Z})$, results in 105 MeV monoenergetic electron. Thus, 1 ∼ 2 micro second-delayed 105 MeV monoenergetic electron is a searched signal. Electrons around 105 MeV are transported by the H-Line and analyzed using the dipole magnet (0.4 T) and four multi-wire proportional chambers (MWPCs). However, the burst pulse reaching ${10}^8$ charged particles/pulse attributable to the RCS pulse leads to significant dead time for the MWPC. Thus, the HV switching scheme is introduced to handle the prompt burst. The target single event sensitivity is ${10}^{-13}$. The H-Line construction was completed, and commissioning went well. The overview of the experiment and the current status are described in this article. Full article

The observation of lepton flavour violation (LFV) in the charged lepton sector would be an unambiguous sign of physics beyond the Standard Model (BSM), and thus, it is the channel of choice for many BSM searches. LFV searches in muon decays in particular benefit from the fact that muons can be easily produced at high rates. There is a global effort to search for LFV at high-intensity muon sources to which the upcoming Mu3e experiment at the Paul Scherrer Institute (PSI) will contribute. The Mu3e Collaboration aims to perform a background-free search for the LFV decay ${\mu }^{+}\to e^{+}{e}^{-}{e}^{+}$ with an unprecedented sensitivity in the order of 10⁻¹⁵ in the first phase of operation and 10⁻¹⁶ in the final phase—an improvement over the preceding SINDRUM experiment by four orders of magnitude. The high muon stopping rates and low momenta of the decay electrons make high demands on momentum and time resolution and on the data acquisition. The innovative experimental concept is based on a tracking detector built from novel ultra-thin silicon pixel sensors and scintillating fibres and tiles as well as online event reconstruction and filtering in real time. Full article

Time dilation (TD) is a principal concept in the special theory of relativity (STR). The Einstein TD formula is the relation between the proper time $t_0$ measured in a moving frame of reference with velocity v and the dilated time t measured by a stationary observer. In this paper, an integral approach is firstly presented to rededuce the Einstein TD formula. Then, the concept of TD is introduced and examined in view of the fractional calculus (FC) by means of the Caputo fractional derivative definition (CFD). In contrast to the explicit standard TD formula, it is found that the fractional TD (FTD) is governed by a transcendental equation in terms of the hyperbolic function and the fractional-order $\alpha$. For small v compared with the speed of light c (i.e., $v\ll c$), our results tend to Newtonian mechanics, i.e., $t\to t_0$. For v comparable to c such as $v=0.9994c$, our numerical results are compared with the experimental ones for the TD of the muon particles ${\mu }^{+}$. Moreover, the influence of the arbitrary-order $\alpha$ on the FTD is analyzed. It is also declared that at a specific $\alpha$, there is an agreement between the present theoretical results and the corresponding experimental ones for the muon particles ${\mu }^{+}$. Full article

Monitored neutrino beams are facilities where beam diagnostics enable the counting and identification of charged leptons in the decay tunnel of a narrow band beam. These facilities can monitor neutrino production at the single particle level (flux precision $<1$%) and provide information about the neutrino energy at the 10% level. The ENUBET Collaboration has demonstrated that lepton monitoring might be achieved not only by employing kaon decays but also by identifying muons from the ${\pi }^{+}\to {\mu }^{+}{\nu }_{\mu }$ decays and positrons from the decay-in-flight of muons before the hadron dump. As a consequence, beam monitoring can be performed using the ENUBET technique even when the kaon production yield is kinematically suppressed. This finding opens up a wealth of opportunities for measuring neutrino cross-sections below 1 GeV. In this paper, we investigate this opportunity at the European Spallation Source (ESS), which is an ideal facility to measure ${\nu }_{\mu }$ and ${\nu }_e$ cross-sections in the 0.2–1 GeV range. We also describe the planned activities for the design of this beam at the ESS within the framework of the ESS$\nu$SB+ design study, which was approved by the EU in July 2022. Full article

The main source of systematic uncertainty on neutrino cross-section measurements at the GeV scale originates from the poor knowledge of the initial flux. The goal of reducing this uncertainty to 1% can be achieved through the monitoring of charged leptons produced in association with neutrinos, by properly instrumenting the decay region of a conventional narrow-band neutrino beam. Large-angle muons and positrons from kaons are measured by a sampling calorimeter on the decay tunnel walls, while muon stations after the hadron dump can be used to monitor the neutrino component from pion decays. Furthermore, the narrow momentum width (<10%) of the beam provides a O (10%) measurement of the neutrino energy on an event-by-event basis, thanks to its correlation with the radial position of the interaction at the neutrino detector. The ENUBET project has been funded by the ERC in 2016 to prove the feasibility of such a monitored neutrino beam and, since 2019, ENUBET is also a CERN neutrino platform experiment (NP06/ENUBET). The breakthrough the project achieved is the design of a horn-less neutrino beamline that would allow for a 1% measurement of ${\nu }_e$ and ${\nu }_{\mu }$ cross-sections in about 3 years of data taking at CERN-SPS, using ProtoDUNE as far detector. Full article

In this work, we present a study of ordinary muon capture (OMC) on ${}^{136}$Ba, the daughter nucleus of ${}^{136}$Xe double beta decay (DBD). The OMC rates at low-lying nuclear states (below 1 MeV of excitation energy) in ${}^{136}$Cs are assessed by using both the interacting shell model (ISM) and proton–neutron quasiparticle random-phase approximation (pnQRPA). We also add chiral two-body (2BC) meson-exchange currents and use an exact Dirac wave function for the captured s-orbital muon. OMC can be viewed as a complementary probe of the wave functions in ${}^{136}$Cs, the intermediate nucleus of the ${}^{136}$Xe DBD. At the same time, OMC can be considered a powerful probe of the effective values of weak axial-type couplings in a 100 MeV momentum exchange region, which is relevant for neutrinoless DBD. The present work represents the first attempt to compare the ISM and pnQRPA results for OMC on a heavy nucleus while also including the exact muon wave function and the 2BC. The sensitivity estimates of the current and future neutrinoless DBD experiments will clearly benefit from future OMC measurements taken using OMC calculations similar to the one presented here. Full article

In special relativity, the time dilation formula has been obtained by particles propagation in a straight line trajectory relative to an observer in motion. Up to now, there are no available formulas for other possible trajectories of particles. However, this paper obtains formulas of time dilation for several trajectories of particle such as parabolic, elliptic, and circular and finds a relatively accurate trajectory. The obtained formulas are employed in order to analyze the time dilation of the muon particles decay. In this paper, it is found that the time dilation of the parabolic and the elliptical trajectories exceed the corresponding results utilizing the standard Lorentz-Einstein time dilation formula. Consequently, if we are able to control the trajectory of unstable particles by some external forces, then their life-times might be increased. Probably, the increase in lifetime via a curved trajectory occurs at lower relative velocity & acceleration energy if compared to the straight line trajectory. In addition, the circular trajectory leads to multiple values of time dilation at certain velocities of an observer in motion, which may give an interpretation of fluctuations of time dilation in quantum mechanics. The result arises from the present relatively accurate formula of time dilation that is very close to the experimental data of muon decay (CERN experiment) when it is compared to the result obtained by the Lorentz-Einstein formula. Finally, it may be concluded that the time dilation not only depends on relative velocity and acceleration energy of particles but also on curved trajectories. The present work may attract other researchers to study different trajectories. Full article