Prompt photon measurements in relativistic nuclear collisions serve as an essential comparative basis for heavy ion studies enabling the separation of medium induced effects. However, the identification of prompt photons is experimentally challenging due to substantial backgrounds from photons produced in hadron decays and jet fragmentation. Appropriate isolation criteria are applied to suppress these background contributions. We analyze prompt photon spectra using the JETPHOX framework to quantify the relative contributions of fragmentation and direct production mechanisms to the total photon yield. We perform a systematic study of the impact of isolation criteria on prompt photon production in relativistic nuclear collisions with emphasis on their dependence on beam energy and photon transverse momentum. The fragmentation contribution is found to be substantially large particularly for p_T < 15 GeV and the isolation criterion plays a crucial role in the analysis of prompt photons in that p_T region. A dynamical isolation criterion suppresses the fragmentation component more effectively than a fixed one in this region. Furthermore, the isolation criterion shows a stronger dependence on beam energy and photon p_T than on system size. These observations emphasize the importance of employing carefully selected and consistent isolation criteria when comparing experimental data with theoretical calculations especially for observables sensitive to fragmentation.

Compressed Baryonic Matter (CBM) is a fixed target experiment at the upcoming Facility for Anti-proton and Ion Research in Germany, having collision rates up to 10 MHz. Due to the proximity of the target and secondaries produced in absorbers, Muon Chambers (MuCh) of the CBM experiment will face a very high particle hit rate of up to 400 kHz/cm 2 in its first two stations. To cope with these particle rates, a Gas Electron Multiplier (GEM) detector will be used for the first two stations while, due to relatively lower particle rates, the last two stations will use a low resistivity Bakelite Resistive Plate Chamber (RPC) detector. The electronics of these two MuCh detectors need different dynamic ranges. A Silicon Tracking Station (STS) system made of 300 μm thick silicon micro-strip sensors will be installed upstream of the MuCh detector system. The sensors will be read out through multi-line micro-cables with fast electronics. The micro-strip sensors will be double-sided with a stereo angle of 7.5°, a strip width of 58 μm, and strip lengths between 20 and 120 mm requiring high-density readout. To meet the high rate and high density requirements of MuCh and STS, respectively, a specialized 128-channel readout ASIC with a dual-gain feature is designed. This is a highly configurable ASIC with about 30,000 configurable register bits which control various bias and threshold settings of the ASIC. To integrate this ASIC with both the detector systems, detailed testing and characterization of the ASIC are required. Due to the high number of configurable registers and several operating conditions, characterizing this ASIC is very challenging. This paper describes the optimization procedures of several configurable bias parameters in detail and also explains how this ASIC is integrated with both GEM and RPC detectors of the MuCh system.

In the year 2016, Resistive Plate Chambers (RPCs) were proposed to be used as muon detectors in the 3rd and 4th stations of the Muon Chamber (MuCh) detector set-up of the under construction Compressed Baryonic Matter (CBM) experiment at the Facility for Anti-proton and Ion Research (FAIR) in Darmstadt, Germany. Since then, sincere efforts are being given to develop suitable detectors for this purpose with major challenges being the capability to handle high particle rates and perform well under harsh radiation environments. We have developed and tested a real size RPC along with its dedicated PCB and electronics read-out chain in GIF++ under intense photon flux for its muon detection capability. In this manuscript, we have presented the test results of the RPC tested during November-2021 beam time in GIF++, CERN, Switzerland.

Elliptic flow measurements from two-, four-, and six-particle correlations are used to investigate flow fluctuations in collisions of U+U at sqrt[s_{NN}]=193  GeV, Cu+Au at sqrt[s_{NN}]=200  GeV and Au+Au spanning the range sqrt[s_{NN}]=11.5-200  GeV. The measurements show a strong dependence of the flow fluctuations on collision centrality, a modest dependence on system size, and very little if any, dependence on particle species and beam energy. The results, when compared to similar LHC measurements, viscous hydrodynamic calculations, and trento model eccentricities, indicate that initial-state-driven fluctuations predominate the flow fluctuations generated in the collisions studied.

The Muon Chamber (MuCh) is a sub-system of the Compressed Baryonic Matter (CBM) experiment for the detection of low-mass-vector mesons produced in high energy heavy ion collisions at beam energies ranging from 2 AGeV to 11 AGeV and decaying in the di-muon channel. MuCh consists of a segmented absorber and four detector triplet stations sandwiched between the absorber segments. At the 3rd and 4th stations of MuCh, Resistive Plate Chambers (RPCs) have been conceived for muon tracking. We have tested the performance of a low resistivity bakelite RPC prototype equipped with self-triggered front end electronics (MuCh-XYTER) for the CBM Muon Chamber. A systematic study on the muon detection efficiency and time resolution has been carried out in a high-rate photon background at the Gamma Irradiation Facility (GIF++) at CERN. The details of the measurement setup and the results are presented here.

An R&D programme has been going on at VECC, Kolkata with a low-resistive prototype bakelite RPC to be used in the CBM experiment at FAIR, Germany. It has been operated in an avalanche mode gas mixture to withstand the high flux environment of upcoming CBM experiment. A self-triggered front-end electronics PADI has been used to acquire the data. In this paper, the characterization of the detector such as IV characteristics, efficiency, and noise rate have been presented.

The STAR collaboration reports a measurement of the transverse single-spin asymmetries, A(N), for neutral pions produced in polarized proton collisions with protons (pp), with aluminum nuclei (pAl) and with gold nuclei (pAu) at a nucleon-nucleon center-of-mass energy of 200 GeV. Neutral pions are observed in the forward direction relative to the transversely polarized proton beam, in the pseudorapidity region 2.7 < eta < 3.8. Results are presented for pi(0)s observed in the STAR forward meson spectrometer electromagnetic calorimeter in narrow Feynman x (x(F)) and transverse momentum (p(T)) bins, spanning the range 0.17 < x(F) < 0.81 and 1.7 < p(T) < 6.0 GeV/c. For fixed x(F) < 0.47, the asymmetries are found to rise with increasing transverse momentum. For larger x(F), the asymmetry flattens or falls as p(T) increases. Parametrizing the ratio r(A) = A(N)(pA)/A(N)(pp) = A(P) over the kinematic range, the ratio r(A) is found to depend only weakly on A, with < P > = -0.027 +/- 0.005. No significant difference in P is observed between the low-p(T) region, p(T) < 2.5 GeV/c, where gluon saturation effects may play a role, and the high-p(T) region, p(T) > 2.5 GeV/c. It is further observed that the value of A(N) is significantly larger for events with a large-p(T) isolated pi(0) than for events with a nonisolated pi(0) accompanied by additional jetlike fragments. The nuclear dependence r(A) is similar for isolated and nonisolated pi(0) events.

Using event-by-event fluctuations, we study the diffusion parameters of net-charge, net-pion, net-kaon, and net-proton in the heavy-ion jet interaction generator (HIJING), and ultra-relativistic quantum molecular dynamics (UrQMD) models at different collision energies \sqsn available at BNL Relativistic Heavy Ion Collider (RHIC). The diffusion parameter ($\sigma$) of net-charge and identified particles are estimated in rapidity space at various \sqsn. It is observed that, the $\sigma$ values are independent of collision energies but emphasises the particle-species dependence of diffusion coefficient in the QGP medium. The present work on particle-species dependence of diffusion coefficient provides a baseline for comparison with the experimental data.

The global polarization of the $\\Lambda$ and $\\overline\\Lambda$ hyperons is measured for Pb-Pb collisions at $\\sqrt{s_{\\rm{NN}}}$ = 2.76 and 5.02 TeV recorded with the ALICE at the LHC. The results are reported differentially as a function of collision centrality and hyperon\u0027s transverse momentum ($p_{\\rm{T}}$) for the range of centrality 5-50%, $0.5 \u003c p_{\\rm{T}} \u003c5$ GeV/$c$, and rapidity $|y|\u003c0.5$. The hyperon global polarization averaged for Pb-Pb collisions at $\\sqrt{s_{\\rm{NN}}}$ = 2.76 and 5.02 TeV is found to be consistent with zero, $\\langle P_{\\rm{H}}\\rangle$ (%) $\\approx$ 0.01 $\\pm$ 0.06 (stat.) $\\pm$ 0.03 (syst.) in the collision centrality range 15-50%, where the largest signal is expected. The results are compatible with expectations based on an extrapolation from measurements at lower collision energies at RHIC, hydrodynamical model calculations, and empirical estimates based on collision energy dependence of directed flow, all of which predict the global polarization values at LHC energies of the order of 0.01%.

We study the fluctuations of net charge, net pion, net kaon, and net proton using the v(dyn) variable in the heavy-ion jet interaction generator (HIJING), ultrarelativistic quantum molecular dynamics (UrQMD), and hadron resonance gas (HRG) model at different collision energies root(NN)-N-s. It has been observed that the values of v(d)(yn) strongly depend on Delta eta in the HIJING and UrQMD models and are independent in the HRG model. The present work emphasizes the particle species dependence of net charge fluctuation strength and provides a baseline for comparison with the experimental data.

The chromo-electromagnetic field is produced due to the motion of partons in a quark–gluon plasma created by relativistic heavy-ion collisions. The fluctuations in the produced chromo-electromagnetic field are important, since they cause heavy quarks to gain energy in the low velocity limit. We study the effect of such fluctuations on heavy quark diffusion in quark–gluon plasma within the framework of Langevin dynamics under the background matter described by the ($$3+1$$)-dimensional relativistic viscous hydrodynamics. Theoretical calculations of the nuclear modification factor ($$R_{AA}$$) of heavy mesons (D and B mesons), with the effect of these fluctuations, are compared with experimental measurements in Au–Au collisions at $$\sqrt{s_{NN}} = 200$$ GeV by the STAR experiment at the BNL Relativistic Heavy Ion Collider (RHIC) and Pb–Pb collisions at $$\sqrt{s_{NN}} = 2.76$$ and 5.02 TeV by the ALICE and CMS experiments at the CERN Large Hadron Collider (LHC). In addition to that, the elliptic flow ($$v_2$$) of D-meson has been calculated in the same framework for Pb–Pb collisions at $$\sqrt{s_{NN}} = 2.76$$ and compared with ALICE measurements. We find a significant effect of these fluctuations in describing the measured $$R_{AA}$$ and $$v_2$$ of heavy flavour mesons at both RHIC and LHC energies.

We report systematic measurements of bulk properties of the system created in Au + Au collisions at root S-NN = 14.5 GeV recorded by the STAR detector at the Relativistic Heavy Ion Collider (RHIC). The transverse momentum spectra of pi(+/-), K-+/-, and p((p) over bar) are studied at midrapidity (vertical bar y vertical bar < 0.1) for nine centrality intervals. The centrality, transverse momentum (p(T)), and pseudorapidity (eta) dependence of inclusive charged particle elliptic flow (v(2)), and rapidity-odd charged particles directed flow (v(1)) results near midrapidity are also presented. These measurements are compared with the published results from Au + Au collisions at other energies, and from Pb Pb collisions at root S-NN = 2.76 TeV. The results at root S-NN = 14.5 GeV show similar behavior as established at other energies and fit well in the energy dependence trend. These results are important as the 14.5-GeV energy fills the gap in mu(B), which is of the order of 100 MeV, between root S-NN = 11.5 and 19.6 GeV. Comparisons of the data with UrQMD and AMPT models show poor agreement in general.

The Multi-gap Resistive Plate Chambers (MRPCs) are parallel plate gas detectors known for their excellent time resolution. High precision in timing measurements makes these detectors suitable for Time-Of-Flight (TOF) studies in several experiments. We have developed two nearly identical oil-free bakelite MRPCs. The time resolution measurements of these detectors with cosmic rays have been reported here.

We have calculated the temperature dependent drag and diffussion coefficients of heavy quarks and nuclear modification factor (R-AA) of heavy mesons (D and B mesons) by considering the energy gain due to chromo-electromagnetic field fluctuations along with collisional and radiative energy loss of charm and beauty quarks in the hot and dense deconfined medium of quarks and gluons created in relativistic heavy ion collisions. Our results are in good agreement with the experimentally measured RAA of D and B mesons by ALICE and CMS experiments at root s(NN) = 2.76 TeV and root s(NN) = 5.02 TeV.

The Multi-gap Resistive Plate Chambers (MRPCs) are parallel plate gas detectors known for their excellent time resolution. High precision in timing measurements makes these detectors suitable for Time-Of-Flight (TOF) studies in several experiments. We have developed two nearly identical oil-free bakelite MRPCs. The time resolution measurements of these detectors with cosmic rays have been reported here.

The Relativistic Heavy Ion Collider (RHIC) accelerates nuclei to ultra-relativistic velocities, producing some of the strongest known magnetic fields in the Universe (${10^{14}-10^{15}}$ Tesla). The highly Lorentz-contracted Coulomb fields of the nuclei generate a flux of linearly polarized quasi-real photons that can interact via the Breit-Wheeler process to produce electron-positron pairs (${\gamma\gamma \rightarrow e^+e^-}$). Experimental data presented in this article are consistent with Breit-Wheeler theory across all measured differentials. The detected pairs are produced predominantly at low transverse momentum ($P_{\perp}$) with a smooth invariant mass distribution, with the individual ${e^\pm}$ preferentially aligned along the beam direction, and with a 4th-order modulation in azimuth between the ${e^+e^-}$ pair and ${e^\pm}$ momenta. The $P_{\perp}$ spectrum broadens from large to small impact parameters. Our observation opens new opportunities to study Quantum Chromodynamics under extreme conditions and provides a new tool for interdisciplinary study of extreme electromagnetic fields.

We report on the first measurement of the charmed baryon $\Lambda_c^{\pm}$ production at midrapidity ($|y|$ $<$ 1) in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV collected by the STAR experiment at the Relativistic Heavy Ion Collider. The $\Lambda_c$/$D^0$ (denoting ($\Lambda_c^++\Lambda_c^-$)/($D^0+\bar{D^0}$)) yield ratio is measured to be 1.08 $\pm$ 0.16 (stat.) $\pm$ 0.26 (sys.) in the 0--20% most central Au+Au collisions for the transverse momentum ($p_T$) range 3 $<$ $p_T$ $<$ 6 GeV/$c$. This is significantly larger than the PYTHIA model calculations for $p+p$ collisions. The measured $\Lambda_c$/$D^0$ ratio, as a function of $p_T$ and collision centrality, is comparable to the baryon-to-meson ratios for light and strange hadrons in Au+Au collisions. Model calculations including coalescence hadronization for charmed baryon and meson formation reproduce the features of our measured $\Lambda_c$/$D^0$ ratio.