Search

This study explores the chiral magnetic effect (CME) in ultra-relativistic heavy-ion collisions. The CME, observed as back-to-back charge separation along the magnetic field axis, is investigated using the newly developed sliding dumbbell method (SDM) applied to Au + Au events at a centre-of-mass energy s NN = 200 GeV generated by the AMPT model with string melting configuration. The CME-like signal is externally injected in the events by flipping charges of pairs of particles perpendicular to the reaction plane. The study reports a significant enhancement of the CME-sensitive 3-particle γ correlator in events with high back-to-back charge separation, in a given collision centrality. Additionally, a linear relationship is observed between the | γ | correlator for the same-sign charge pairs and positive charge asymmetry ( ⟨ A + ⟩ ) across the dumbbell in CME-enriched sub-samples. Furthermore, the fraction of CME in Δ γ (difference between the opposite and same sign γ correlators) is presented across different collision centralities having different percentages of externally injected CME-like signal. Overall, the research aims to understand and detect the CME through innovative experimental method and detailed analysis of the event structure. [ABSTRACT FROM AUTHOR]

We study the two-pion Hanbury Brown–Twiss correlation functions for a partially coherent source constructed with the emission points and momenta of the identical pions generated by a multiphase transport model. A coherent emission length is introduced, the effects of which on the two-pion interferometry results in central Au-Au collisions at sNN=200 GeV, central Pb-Pb collisions at sNN=2.76 TeV, and p-p collisions at s=13 TeV are investigated. It is found that the effect of coherent emission length reduces the two-pion correlation functions in the nucleus–nucleus collisions, leading to an average decrease of chaoticity parameter by approximately 15% in the high transverse momentum range. However, the influence of coherent emission length on the two-pion correlation functions in the p-p collisions is small, while the effect of coherent emission length on the chaoticity parameter is almost independent of the transverse momentum of pion pair in the p-p collisions.

Electromagnetic radiations are one of the potential probes to study the initial state of the hot and dense quark-gluon plasma (QGP) produced during the collision of heavy nuclei at relativistic energies. Photons are emitted throughout the lifetime of the evolving system and carry undistorted information from the production point to the detector. The observation of large anisotropic flow of charged particles provides a strong confirmation of QGP formation and collective behaviour of the produced matter in these collisions. However, the theoretical model calculations which explain the hadronic spectra and anisotropic flow successfully, underpredict the experimental data of elliptic as well as triangular flow of photons by a large margin. This discrepancy between data and theory results is known as direct photon puzzle. In this article, we review the anisotropic flow of photons calculated using hydrodynamical model framework for different collision systems and beam energies. In addition, we propose some new ideas which can be valuable for understanding direct photon puzzle. [ABSTRACT FROM AUTHOR]

The transverse momentum spectra of Λ c + baryons and D 0 mesons produced in proton–lead (p–Pb) collisions at the center-of-mass energy per nucleon pair s NN = 5 TeV (more exactly 5.02 TeV), D 0 + D ¯ 0 , D + + D - , D s + + D s - , and D ∗ + + D ∗ - (exactly D ∗ (2010) + + D ∗ (2010) - ) mesons produced in proton–proton (pp) collisions at the center-of-mass energy s = 5 and 13 TeV, Λ b 0 baryons and B ¯ 0 mesons produced in pp collisions at s = 7 and 8 TeV, as well as B + + B - mesons produced in pp collisions at s = 7 and 13 TeV measured by the LHCb collaboration in forward (backward) rapidity range are described by two models. The first model is based on the superposition of two Schwinger mechanisms, and the second one is based on the superposition of Tsallis statistics and inverse power law. The experimental data are fitted by the two two-component models. Then, the free parameters which depend on rapidity are extracted and analyzed. [ABSTRACT FROM AUTHOR]

Several elastic scattering angular distributions of C from target nuclei of A ≥ 39 are analyzed to extract theWoods-Saxon potential parameters with the fixed imaginary potential and Coulomb radius parameters. Using the best fitted diffuseness parameters, the correlations of the real part parameters with A + A and incident energy are revealed, and the systematic Woods-Saxon potential parameters are presented for nucleus-nucleus interaction. The proposed potential parameters can reproduce not only the elastic scattering angular distributions induced by C, but also many elastic scattering angular distributions induced by the projectiles other than C, thus providing important inputs for the study of nuclear reactions of heavy-ion systems. [ABSTRACT FROM AUTHOR]

In this article, we present the results of our investigations on the projectile's lightest fragment (proton) multiplicity and probability distributions with Kr emulsion collision at around 1 A GeV. The multiplicity and normalized multiplicity of projectile's lightest fragment (proton) are correlated with the compound particles, shower particles, black particles, grey particles; alpha (helium nucleus) fragments and heavily ionizing charged particles. It is found that projectile's lightest fragment (proton) is strongly correlated with compound particles and shower particles rather than other particles and the average multiplicity of projectile's lightest fragment (proton) increases with increasing compound, shower and heavily ionizing charge particles. Normalized projectile's lightest fragment (proton) is strongly correlated with compound particles, shower particles and heavily ionizing charge particles. The multiplicity distribution of the projectile's lightest fragment (proton) emitted in the Kr + emulsion interaction at around 1 A GeV with different target has been well explained by KNO scaling. The mean multiplicity of projectile's lightest fragments (proton) depends on the mass number of the projectile and does not significantly dependent of the projectile energy. The mean multiplicity of projectile's lightest fragment (proton) increases with increasing the target mass number. [ABSTRACT FROM AUTHOR]

We investigate the centrality dependence of charged-particle pseudorapidity density distributions in Cu-Cu collisions at high energy. In a thermal model, the particle-production contributions are classified according to the different origin of sources formed in the collisions. Comparing with the experimental data measured at RHIC energies, it is found that the improved model can describe the pseudorapidity density distributions over a broad pseudorapidity range and the changes of source-location parameters depend on collision centralities. [ABSTRACT FROM AUTHOR]

The transverse momentum spectra of charged particles produced in Au + Au collisions at the relativistic heavy ion collider and in Pb + Pb collisions at the large hadron collider with different centrality intervals are described by the multisource thermal model which is based on different statistic distributions for a singular source. Each source in the present work is described by the Tsallis distribution and the Boltzmann distribution, respectively. Then, the interacting system is described by the (two-component) Tsallis distribution and the (two-component) Boltzmann distribution, respectively. The results calculated by the two distributions are in agreement with the experimental data of the Solenoidal Tracker At Relativistic heavy ion collider, Pioneering High Energy Nuclear Interaction eXperiment, and A Large Ion Collider Experiment Collaborations. The effective temperature parameters extracted from the two distributions on the descriptions of heavy-ion data at the relativistic heavy ion collider and large hadron collider are obtained to show a linear correlation. [ABSTRACT FROM AUTHOR]

The target fragmentation in 60A and 200A GeV 16O interactions with emulsion nuclei is analyzed. The validity of the nuclear limiting fragmentation hypothesis is confirmed at ultrarelativistic energies. The emission mechanism of the fast target proton (grey particle) is investigated in terms of the multiplicity characteristics. The anisotropy ratio and asymmetry parameter, while found to be independent of the projectile size or incident energy, are dependent on the target size and system centrality. This dependence is insignificant for heavy targets and in more central regions, where constancy exists. In this species, the system of the grey particle emission cannot exhibit the optimum symmetry or asymmetry between the forward and backward hemispheres. It is seen that these target protons originate from two emission sources in the earlier stage of the target fragmentation. One them emits nucleons isotropically in the 4π space. The other is the main emission source, which emits nucleons, in the forward hemisphere only, as a result of the binary nucleon-nucleon collisions and (or) intranuclear cascade. [ABSTRACT FROM AUTHOR]

This paper presents an analysis on fractality of compound hadrons (pions + protons) and shower particles produced in heavy ion interactions initiated by 12C and 24Mg beams at incident energy 4.5A GeV and 32S beam at incident energy 200A GeV. G-moments analysis in emission angle (cos θ) space reveals multifractality in both compound hadrons and pion emission process. The degree of multifractality has been assessed using the Levy stability index. Moreover this analysis also suggests nonthermal phase transition in multiparticle production for both cases. [ABSTRACT FROM AUTHOR]

We report an experimental measurement on the multiplicity of slow target-associated particles in the forward and backward hemispheres in the interactions of 4He ions with emulsion nuclei at 2.1A and 3.7A GeV. The results indicate that the target fragment multiplicity does not depend on the incident kinetic energy. The dominant feature characterizing the multiplicity distributions of black and grey particles, in both forward and backward hemispheres, is exponential decay shaped curves, with the exception of the most central collisions and heavy target sizes. The results favor the nuclear limiting fragmentation hypothesis in the energy range beyond 1 GeV. [ABSTRACT FROM AUTHOR]

The multiplicity distribution of the target-evaporated black particles emitted in the interactions of 16O beams with emulsion nuclei at 60A and 200A GeV in both the forward and backward hemispheres are examined. The asymmetry parameters, the forward-backward ratios as well as multiplicity distribution moments are evaluated. The investigated scaled variances and the second Mueller moments are observed to indicate the strongly correlated emission of target-evaporated black particles in the forward direction. The ratio of entropy to average multiplicity of target fragments is evaluated, and is found to be energy-independent in both the forward and backward hemispheres. [ABSTRACT FROM AUTHOR]

The present paper deals with the interactions of 16O and 28Si nuclei with emulsion heavy target nuclei (silver (Ag) and bromine (Br)) at 4.5A GeV/ c. The results have been analyzed to identify interesting characteristics of the total disintegration (TD) events produced in these interactions. Events having a number of heavily ionizing particles Nh ≥ 28 have been selected in this study. The integral multiplicity distributions for the disintegrated particles from the target nuclei have been used to separate the inelastic interactions with the free hydrogen (H), the light (CNO), and the heavy (AgBr) nuclei. The average multiplicities of the different secondary particles emitted in these interactions have been compared with the corresponding ones of different projectiles nearly at the same momentum. The average multiplicity of the grey particles is found to increase with the mass of the projectile, while the average multiplicity of the black particles is found to decrease with increasing mass of the projectile; this result agrees with the prediction of the fireball model. Also, the dependence of the shower, grey, and black particles produced in the TD events on the mass of the projectile has been studied. Moreover, the dependence of the probability of the TD for the projectile mass as well as the target fragments has also been discussed. The results show that the multiplicity distributions of the shower, grey, and black particles present a Gaussian distribution. Finally, the linear dependence of the grey and compound multiplicities on the black, heavy, and shower particles has also been observed. [ABSTRACT FROM AUTHOR]

This work presents the analysis of ring-like and jet-like events in terms of factorial correlations of S-Ag/Br interactions at 200 A GeV. The investigation reveals that the correlated moments increase with decreasing bin-bin separation D, following power law, which suggests the presence of an intermittent nature of self-similar dynamical fluctuation pattern for ring-like and jet-like events. The analysis further shows that the strength of the non-statistical fluctuations is larger for ring- like events than those of jet-like events i.e. correlations in bins are more pronounced in case of ring-like events. However, ring-like events are consistent with the predictions of the α-model, but jet-like events are not. [ABSTRACT FROM AUTHOR]

In this experiment, 32S interaction with emulsion nuclei is examined at 3.7A and 200A GeV. Backward relativistic hadron production seems to be an exact decay system, depending on the target size. For emulsion nuclei, the decay constant of this system nearly equals 1.3. Independent of the projectile size and energy, the backward relativistic hadrons are produced with probability values of ∼20%-30%. For projectile nuclei with mass numbers greater than or equal to 6 and at any incident energy, the average multiplicity of these backward hadrons tends to a saturation value of ∼0.4. Regarding the multiplicity range of forward relativistic hadrons, reaching 60 hadrons per event at 3.7A GeV and extending to ∼400 hadrons per event at 200A GeV, energy plays a fundamental role in forward relativistic hadron production. The results strongly support the assumption that relativistic hadrons are created as a result of energy from participant nucleons. [ABSTRACT FROM AUTHOR]

In this paper, we present the intermittency and the erraticity analyses of the distributions of charged particles produced in 28Si-Ag/Br interaction at incident energy 14.5 A GeV. The experimental results are compared with a Monte Carlo simulation using ultra-relativistic quantum molecular dynamics (UrQMD) model. The experimental data show the presence of a nonstatistical component in the produced charged-particle density. Neither the UrQMD simulation nor the purely statistical simulation was found to match the experimental data. The present set of results are compared to those obtained in similar measurements from earlier high-energy nucleus-nucleus experiments. [ABSTRACT FROM AUTHOR]

Breakup temperatures were deduced from double ratios of isotope yields for target spectators produced in the reaction 197Au + 197Au at 1000 MeV per nucleon. Pairs of 3,4He and 6,7Li isotopes and pairs of 3,4He and H isotopes (p, d and d, t) yield consistent temperatures after feeding corrections, based on the quantum statistical model, are applied. The temperatures rise with decreasing impact parameter from 4 MeV for peripheral to about 10 MeV for the most central collisions. The good agreement with the breakup temperatures measured previously for projectile spectators at an incident energy of 600 MeV per nucleon confirms the universality established for the spectator decayat relativistic bombarding energies. The measured temperatures also agree with the breakup temperatures predicted by the statistical multifragmentation model. For these calculations a relation between the initial excitation energy and mass was derived which gives good simultaneous agreement for the fragment charge correlations. The energy spectra of light charged particles, measured at τlab = 150°, exhibit Maxwellian shapes with inverse slope parameters much higher than the breakup temperatures. The statistical multifragmentation model, because Coulomb repulsion and sequential decay processes are included, yields light-particle spectra with inverse slope parameters higher than the breakup temperatures but considerably below the measured values. The systematic behavior of the differences suggests that they are caused by light-charged-particle emission prior to the final breakup stage. [ABSTRACT FROM AUTHOR]