Search

Charge separation induced by the chiral magnetic effect has suggested that some P- or CP-odd metastable domains could be produced in a QCD vacuum in the early stage of relativistic heavy-ion collisions. Based on a multiphase transport model, our results suggest that a domain-based scenario with final state interactions can describe the solenoidal tracker at RHIC (STAR) detector measurements of both same- and opposite-charge azimuthal angle correlations, (cos(<φα + φβ)), in Au + Au collisions at √SNN = 200 GeV. The occupancy factor of the total volume of domains over the fireball volume is small, which indicates that the size and number of metastable domains should be relatively small in the early stage of a quark-gluon plasma. [ABSTRACT FROM AUTHOR]

Within a multi-phase transport (AMPT) model with the string melting mechanism and imported initial electric quadrupole moment, the difference between the elliptic flow of positive and negative pions is calculated. The slope parameter r of the linear dependence of Δv2=v2(π-)-v2(π+)on Ach=(N+-N-)/(N++N-) is yielded owing to the parton cascade, which converts the initial electric quadrupole distribution into the final charge-dependent elliptic flow. The slope parameter r is found to be increased by the hadronization given by the coalescence, and decreased by the resonance decays. The slope parameter r is very sensitive to both the initial electric quadrupole percentage and centrality bin and consequently a helpful constraint on the quadrupole moment of the chiral magnetic wave is obtained for Au + Au collisions at the top RHIC energy. [ABSTRACT FROM AUTHOR]

Azimuthal anisotropies of reconstructed jets [vjetn(n=2,3)] have been investigated in Pb+Pb collisions at the center of mass energy √sNN= 2.76 TeV within a framework of a multiphase transport (AMPT) model. The vjet2 is in good agreement with the recent ATLAS data. However, the vjet3 shows a smaller magnitude than vjet2, and approaches zero at a larger transverse momentum. It is attributed to the path-length dependence in which the jet energy loss fraction depends on the azimuthal angles with respect to different orders of event planes. The ratio vjetn/en increases from peripheral to noncentral collisions, and vjetn increases with the initial spatial asymmetry (en) for a given centrality bin. These behaviors indicate that the vjetn is produced by the strong interactions between jet and the partonic medium with different initial geometry shapes. Therefore, azimuthal anisotropies of reconstructed jet are proposed as a good probe to study the initial spatial fluctuations, which are expected to provide constraints on the path-length dependence of jet quenching models [ABSTRACT FROM AUTHOR]

Within a multiphase transport model, medium modifications of differential jet shapes are investigated in Pb+Pb collisions at √sNN = 2.76 TeV. The differential jet shapes are significantly modified by the strong interactions between jets and a partonic medium in Pb+Pb collisions relative to that in p + p collisions. The modifications are slightly weakened by the hadronization of coalescence, but strengthened by resonance decays in hadronic rescatterings. Subleading jets display larger medium modifications than leading jets, especially in central Pb + Pb collisions with large dijet asymmetries. These behaviors of medium modifications of differential jet shapes reflect a dynamical evolution of redistribution of jet energy inside a quenched jet cone in high-energy heavy-ion collisions. [ABSTRACT FROM AUTHOR]

Based on a multiphase transport model, the measured jet fragmentation function ratio of Pb + Pb collisions to p + p collisions in CERN Large Hadron Collider experiments is decomposed into two parts, corresponding to the two contributions of jet hadronization from fragmentation and coalescence. The results suggest an existence of distinct competitions between two jet hadronization mechanisms for different £ = ln( 1 /z) ranges in different centrality bins. The jet fragmentation functions for different types of hadrons (mesons and baryons) are proposed as a good probe to study the competition between fragmentation and coalescence for the jet hardonization in high-energy heavy-ion collisions. [ABSTRACT FROM AUTHOR]

Within a multiphase transport (AMPT) model, dijet asymmetry is studied in Pb + Pb collisions at √sNN = 2.76 TeV. It is found that a large dijet asymmetry (Aj) is produced by strong interactions between jets and partonic matter. It is demonstrated that hadronization and final-state hadronic rescatterings have little effect on Aj. The final Aj is found to be driven by both initial Aj and partonic jet energy loss, which is consistent with an increasing jet energy loss in a hot and strongly interacting partonic medium in more central Pb + Pb collisions. [ABSTRACT FROM AUTHOR]

In the framework of a multi-phase transport model, initial fluctuations in the transverse parton density lead to all orders of harmonic flows. Hadron-triggered azimuthal correlations include all contributions from harmonic flows, hot spots, and jet-medium excitations, which are isolated by using different initial conditions. We found that different physical components dominate different pseudorapidity ranges of dihadron correlations. Because γ-triggered azimuthal correlations can only be caused by jet-medium interactions, a comparative study of hadron- and γ-triggered azimuthal correlations can reveal more dynamics about jet-medium interactions. [ABSTRACT FROM AUTHOR]

The Hanbury-Brown Twiss (HBT) radii of Au+Au collisions at RHIC energy are investigated by a hydrodynamical expanding source with both shear (η) and bulk viscosities (ζ). With different height of the ratio of ζ to entropy density s, the ratio Rout/Rside of HBT radii can not describe the experimental data. But with large enough peak of ζ/s, the instability suggests that the source may clusterize which gives a hint to resolve the HBT puzzle. [ABSTRACT FROM AUTHOR]

Femtosecond laser-assisted cataract surgery performs the anterior capsulotomy, lens fragmentation, corneal incisions making and astigmatic limbal relaxing incision with femtosecond laser, which effectively reduces the complications of conventional phacoemulsification surgery and improves the postoperative visual quality of patients. It further improves the technology and effect of cataract surgery and has broad clinical application prospects. This paper compares pros and cons as well as the clinical values of femtosecond laser-assisted cataract surgery with conventional phacoemulsification surgery based on the overview of published articles.

We calculate the k-particle (k=2,4,6,8) azimuthal cumulants resulting from the conservation of transverse momentum. We find that c2{k}>0 and, depending on the transverse momenta, c2{k} can reach substantial values even for a relatively large number of particles. The impact of our results on the understanding of the onset of collectivity in small systems is emphasized. [ABSTRACT FROM AUTHOR]

We present predictions from the string melting version of a multiphase transport model on various observables in Pb+Pb collisions at √sNN=5.02TeV. We use the same version of the model as an earlier study that reasonably reproduced dN/dy, pT spectra and elliptic flow of charged pions and kaons at low-pT for central and semicentral heavy ion collisions at 200 GeV and 2.76 TeV. While we compare with the already-available centrality dependence data on charged particle dN/dη at mid-pseudorapidity in Pb+Pb collisions at 5.02 TeV, we make predictions on identified particle dN/dy, pT spectra, azimuthal anisotropies vn(n=2,3,4), and factorization ratios rn(ηa,ηb)(n=2,3) for longitudinal correlations. [ABSTRACT FROM AUTHOR]

The overall transverse momentum balance and the redistribution of the lost energy from hard jets for asymmetric dijet events in PbPb collisions at 2.76A TeV at the LHC is studied within a multiphase transport (AMPT) model. A detailed analysis is performed for the projected transverse momentum ⟨/p||T⟩ contributed from the final charged hadrons carrying different transverse momenta and emitted from different angular directions. We find that the transverse momentum projection ⟨/p||T⟩ in the leading jet direction is mainly contributed by hard hadrons (pT>8.0GeV/c) in both peripheral and central PbPb collisions, while the opposite direction in central collisions is dominated by soft hadrons (pT=0.5-2.0GeV/c). The study of in-cone and out-of-cone contributions to ⟨/p||T⟩ shows that these soft hadrons are mostly emitted at large angles away from the dijet axis. Our AMPT calculation is in qualitative agreement with the CMS measurements and the primary mechanism for the energy transported to large angles in the AMPT model is the elastic scattering at the partonic stage. Future studies including also inelastic processes should be helpful in understanding the overestimation of the magnitudes of in-cone and out-of-cone imbalances from our AMPT calculations, and shed light on different roles played by radiative and collisional processes in the redistribution of the lost energy from hard jets. [ABSTRACT FROM AUTHOR]

The isobaric collisions of 9644Ru+9644Ru and 9640Zr+9640Zr have recently been proposed to discern the charge separation signal of the chiral magnetic effect (CME). In this article, we employ the string melting version of a multiphase transport model to predict various charged-particle observables, including dN/dη,pT spectra, elliptic flow (v2), and particularly possible CME signals in Ru + Ru and Zr + Zr collisions at √sNN=200GeV. Two sets of the nuclear structure parametrization have been explored, and the difference between the two isobaric collisions appears to be small, in terms of dN/dη,pT spectra, and v2 for charged particles. We mimic the CME by introducing an initial charge separation that is proportional to the magnetic field produced in the collision, and study how the final-state interactions affect the CME observables. The relative difference in the CME signal between the two isobaric collisions is found to be robust, insensitive to the final-state interactions. [ABSTRACT FROM AUTHOR]

Because the properties of the QCD phase transition and the chiral magnetic effect (CME) depend on the number of quark flavors (Nf) and quark mass, relativistic heavy-ion collisions provide a natural environment to investigate the flavor features if quark deconfinement occurs. We introduce an initial two-flavor or three-flavor dipole charge separation into a multiphase transport (AMPT) model to investigate the flavor dependence of the CME. By taking advantage of the recent ALICE data of charge azimuthal correlations with identified hadrons, we attempt to disentangle two-flavor and three-flavor CME scenarios in Pb+Pb collisions at 2.76 TeV. We find that the experimental data show a certain potential to distinguish the two scenarios, therefore we further suggest to collect more data to clarify the possible flavor dependence in future experiments. [ABSTRACT FROM AUTHOR]

We calculate the electromagnetic fields generated in small systems by using a multiphase transport (AMPT) model. Compared to A+A collisions, we find that the absolute electric and magnetic fields are not small in p+Au and d+Au collisions at energies available at the BNL Relativistic Heavy Ion Collider and in p+Pb collisions at energies available at the CERN Large Hadron Collider. We study the centrality dependencies and the spatial distributions of electromagnetic fields. We further investigate the azimuthal fluctuations of the magnetic field and its correlation with the fluctuating geometry using event-by-event simulations. We find that the azimuthal correlation ?cos2(?B-?2)? between the magnetic field direction and the second-harmonic participant plane is almost zero in small systems with high multiplicities, but not in those with low multiplicities. This indicates that the charge azimuthal correlation ?cos(?a+?ß-2?RP)? is not a valid probe to study the chiral magnetic effect (CME) in small systems with high multiplicities. However, we suggest searching for possible CME effects in small systems with low multiplicities. [ABSTRACT FROM AUTHOR]

The quark-gluon matter produced in relativistic heavy-ion collisions may contain local domains in which parity (P) and combined charge conjugation and parity (CP) symmetries are not preserved. When coupled with an external magnetic field, such P- and CP-odd domains will generate electric currents along the magnetic field--a phenomenon called the chiral magnetic effect (CME). Recently, the STAR Collaboration at the BNL Relativistic Heavy Ion Collider (RHIC) and the ALICE Collaboration at the CERN Large Hadron Collider (LHC) released data of charge-dependent azimuthal-angle correlators with features consistent with the CME expectation. However, the experimental observable is contaminated with significant background contributions from elliptic-flow-driven effects, which makes the interpretation of the data ambiguous. We show that the collisions of isobaric nuclei, 96Ru44+96Ru44 and 96Zr40+96Zr40, provide an ideal tool to disentangle the CME signal from the background effects. Our simulation demonstrates that the two collision types at √=sNN=200 GeV have more than 10% difference in the CME signal and less than 2% difference in the elliptic-flow-driven backgrounds for the centrality range of 20-60%. [ABSTRACT FROM AUTHOR]

Fluctuations in the initial transverse energy-density distribution lead to anisotropic flows as observed in central high-energy heavy-ion collisions. Studies of longitudinal fluctuations of the anisotropic flows can shed further light on the initial conditions and dynamical evolution of the hot quark-gluon matter in these collisions. Correlations between anisotropic flows with varying pseudorapidity gaps in Pb + Pb collisions at the CERN Large Hadron Collider are investigated using both an event-by-event (3 + 1)-dimensional ideal hydrodynamical model with fluctuating initial conditions and a multiphase transport (AMPT) Monte Carlo model for high-energy heavyion collisions. Anisotropic flows at different pseudorapidities are found to become significantly decorrelated with increasing pseudorapidity gaps due to longitudinal fluctuations in the initial states of heavy-ion collisions. The longitudinal correlation of the elliptic flow shows a strong centrality dependence while the correlation of the triangular flow is independent of the centrality. Longitudinal fluctuations as a source of the decorrelation are further shown to consist of a twist or gradual rotation in flow angles between the forward and backward direction and additional fluctuations on top of the twist. Within the AMPT model, longitudinal correlations of anisotropic flows are also found to depend on the value of partonic cross sections. The implications of constraining the initial conditions and shear viscosity to entropy density ratio of the partonic matter in high-energy heavy-ion collisions are also discussed. [ABSTRACT FROM AUTHOR]

A new subevent cumulant method was recently developed, which can significantly reduce the nonflow contributions in long-range correlations for small systems compared to the standard cumulant method. In this work, we study multiparticle cumulants in p + Pb collisions at √sNN = 5.02 TeV with a multiphase transport model (AMPT), including two- and four-particle cumulants (c2{2} and c2{4}) and symmetric cumulants [SC(2,3) and SC(2,4)]. Our numerical results show that v2{2} is consistent with the experimental data, while the magnitude of c2{4} is smaller than the experimental data, which may indicate that either the collectivity is underestimated or some dynamical fluctuations are absent in the AMPT model. For the symmetric cumulants, we find that the results from the standard cumulant method are consistent with the experimental data, but those from the subevent cumulant method show different behaviors. The results indicate that the measurements from the standard cumulant method are contaminated by nonflow effects, especially when the number of produced particles is small. The subevent cumulant method is a better tool to explore the real collectivity in small systems. [ABSTRACT FROM AUTHOR]