Search

In this paper, we propose a new experiment method to check contribution of chiral magnetic effect (CME). With experimental data of DIS involving transversely polarized proton, we have calculated the 3-D charge density inside the polarized proton, which is found to have a significant violation to spherical symmetry. Then we have calculated the property of electromagnetic field (E-M field) generated by a single transversely polarized proton ($p^{\uparrow}$). Based on them, the E-M field generated in small collision system $p^{\uparrow}+A$ are studied. We find that the orientation of this E-M field has a significant dependence on the polarization direction of the proton, and the correlator ($\Delta\gamma$ ) has also significant dependence on the angle between reaction plane and polarization direction. As background contribution are canceled comparing two collision geometry schemes, only contribution of CME is remained., Comment: 5 pages, 8 figures

Recent experiments show that $\Delta\gamma$, an observable designed for detecting the chiral magnetic effect (CME), in small collision system $p+A$ is similar with that in heavy ion collision $A+A$. This brings a challenge to the existence of CME because it is believed that there is no azimuthal correlation between the orientation of the magnetic field ($\Phi_B$) and the participant plane ($\Phi_2$) in small collision system. In this work, we introduce three charge density models to describe the inner charge distributions of proton and neutron, and calculate the electric and magnetic fields produced in small $p+A$ collisions at both RHIC and LHC energies. Our results show that the contribution of the single projectile proton to the magnetic field is the main source after average over all participants. The azimuthal correlation between $\Phi_B$ and $\Phi_2$ is small but not vanished. And due to the huge fluctuation of fields strength, the magnetic-field contribution to $\Delta\gamma$ could be large., Comment: 14 pages, 13 figures

The hot and dense matter generated in heavy-ion collisions contains intricate vortical structure in which the local fluid vorticity can be very large. Such vorticity can polarize the spin of the produced particles. We study the event-by-event generation of the so-called thermal vorticity in Au + Au collisions at energy region $\sqrt{s}=7.7-200$ GeV and calculate its time evolution, spatial distribution, etc., in a multiphase transport (AMPT) model. We then compute the spin polarization of the $\Lambda$ and $\bar{\Lambda}$ hyperons as a function of $\sqrt{s}$, transverse momentum $p_T$, rapidity, and azimuthal angle. Furthermore, we study the harmonic flow of the spin, in a manner analogous to the harmonic flow of the particle number. The measurement of the spin harmonic flow may provide a way to probe the vortical structure in heavy-ion collisions. We also discuss the spin polarization of $\Xi^0$ and $\Omega^-$ hyperons which may provide further information about the spin polarization mechanism of hadrons., Comment: V2: 8 pages, 10 figures, references updated, published version

The isobaric collisions of $^{96}_{44}$Ru + $^{96}_{44}$Ru and $^{96}_{40}$Zr + $^{96}_{40}$Zr 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 $dN/d\eta$, $p_T$ spectra, elliptic flow ($v_2$), and particularly possible CME signals in Ru + Ru and Zr + Zr collisions at $\sqrt{s_{_{\rm NN}}}$ = 200 GeV. 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 $dN/d\eta$, $p_T$ spectra, and $v_2$ 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., Comment: 8 pages, 10 figures; final published version

We employ a 3+1D anomalous hydrodynamics with initial condition generated by HIJING to simulate the chiral vortical effect and the chiral magnetic effect in heavy-ion collisions. This allows us to calculate the charge-dependent two-particle correlations with respect to the reaction plane at different collision energies and centralities. We then compare the computed results with the experimental data and give discussions on the possible background effects., Comment: 4 pages, 2 figures, as a contribution to the proceedings for Quark Matter 2017

We give a numerical simulation of the generation of the magnetic field and the charge-separation signal due to the chiral magnetic effect (CME) --- the induction of an electric current by the magnetic field in a parity-odd matter --- in the collisions of isobaric nuclei, $^{96}_{44}$Ru + $^{96}_{44}$Ru and $^{96}_{40}$Zr + $^{96}_{40}$Zr, at $\sqrt{s_{\rm NN}}=200$ GeV. We show that such collisions provide an ideal tool to disentangle the CME signal from the possible elliptic-flow driven background effects. We also discuss some other effects that can be tested by using the isobaric collisions., Comment: Proceedings of XXVIth International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2017)

In a noncentral heavy-ion collision, the two colliding nuclei have finite angular momentum in the direction perpendicular to the reaction plane. After the collision, a fraction of the total angular momentum is retained in the produced hot quark-gluon matter and is manifested in the form of fluid shear. Such fluid shear creates finite flow vorticity. We study some features of such generated vorticity, including its strength, beam energy dependence, centrality dependence, and spatial distribution., Comment: V1: 4 pages,3 figures. Contribution to the Proceedings of SQM2016, Berkeley, California, USA, June 27 - July 01, 2016

The quark-gluon matter produced in relativistic heavy-ion collisions may contain local domains in which P and 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 RHIC and the ALICE Collaboration at the 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. In this Letter, we show that the collisions of isobaric nuclei, $^{96}_{44}$Ru + $^{96}_{44}$Ru and $^{96}_{40}$Zr + $^{96}_{40}$Zr, provide an ideal tool to disentangle the CME signal from the background effects. Our simulation demonstrates that the two collision types at $\sqrt{s_{\rm NN}}=200$ 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 $20-60\%$., Comment: V1: 4 pages, 4 figures

We study the event-by-event generation of flow vorticity in RHIC Au + Au collisions and LHC Pb + Pb collisions by using the HIJING model. Different definitions of the vorticity field and velocity field are considered. A variety of properties of the vorticity are explored, including the impact parameter dependence, the collision energy dependence, the spatial distribution, the event-by-event fluctuation of the magnitude and azimuthal direction, and the time evolution. In addition, the spatial distribution of the flow helicity is also studied., Comment: V2: 31 pages, 16 figures; new discussion added to the end of Sec.VI, references updated

Multiple scattering and induced parton splitting lead to a medium modification of the QCD evolution for jet fragmentation functions and the final hadron spectra. Medium-induced parton splittings not only lead to energy loss of leading partons and suppression of leading hadron spectra, but also modify the flavor composition of a jet due to induced flavor conversion via gluon emission, quark pair production and annihilation. Through a numerical study of the medium-modified QCD evolution, leading $K^-$ strange meson spectra are found to be particularly sensitive to the induced flavor conversion in semi-inclusive deeply inelastic scatterings (SIDIS) off a large nucleus. The induced flavor conversion can lead to increased number of gluons and sea quarks in a jet and, as a consequence, enhance the leading $K^-$ spectra to counter the effect of parton energy loss in SIDIS with large momentum fractions $x_B$ where the struck quarks are mostly valence quarks of the nucleus., Comment: 8 pages in RevTex, 8 figures final published version

The non-central Cu + Au collisions can create strong out-of-plane magnetic fields and in-plane electric fields. By using the HIJING model, we study the general properties of the electromagnetic fields in Cu + Au collisions at 200 GeV and their impacts on the charge-dependent two-particle correlator $\gamma_{q_1q_2}=<\cos(\phi_1+\phi_2-2\psi_{RP})>$ (see main text for definition) which was used for the detection of the chiral magnetic effect (CME). Compared with Au + Au collisions, we find that the in-plane electric fields in Cu + Au collisions can strongly suppress the two-particle correlator or even reverse its sign if the lifetime of the electric fields is long. Combining with the expectation that if $\gamma_{q_1q_2}$ is induced by elliptic-flow driven effects we would not see such strong suppression or reversion, our results suggest to use Cu + Au collisions to test CME and understand the mechanisms that underlie $\gamma_{q_1q_2}$., Comment: V1: 7 pages, 8 figures. V2: Add 2 new figures. Published version

We develop a Monte-Carlo event generator based on combination of a parton production formula including the effects of parton saturation (called the DHJ formula) and hadronization process due to the Lund string fragmentation model. This event generator is designed for the description of hadron productions at forward rapidities and in a wide transverse momentum range in high-energy proton-proton collisions. We analyze transverse momentum spectra of charged hadrons as well as identified particles; pion, kaon, (anti-)proton at RHIC energy, and ultra-forward neutral pion spectra from LHCf experiment. We compare our results to those obtained in other models based on parton-hadron duality and fragmentation functions., Comment: 10 pages, 9 figures

Initial conditions are required to solve medium modified DGLAP (mDGLAP) evolution equations for modified fragmentation functions due to multiple scatterings and parton energy loss. Such initial conditions should in principle include energy loss for partons at scale $Q_0$ above which mDGLAP evolution equations can be applied. Several models for the initial condition motivated by induced gluon bremsstrahlung in perturbative QCD are used to calculate the modified fragmentation functions in nuclear medium and to extract the jet transport parameter $\hat q$ from fits to experimental data in deeply inelastic scattering (DIS) off nuclei. The model with a Poisson convolution of multiple gluon emissions is found to provide the overall best $\chi^2$/d.o.f. fit to the HERMES data and gives a value of $\hat q_0 \approx 0.020 \pm 0.005$ GeV$^2$/fm at the center of a large nucleus., Comment: 9 pages in RevTex, 9 figures

Multiple hard and semi-hard parton scatterings in high-energy $p+A$ collisions involve multi-parton correlation in both momentum and flavor inside the projectile proton which will lead to modification of the final hadron spectra relative to that in $p+p$ collisions. Such modification of final hadron transverse momentum spectra in $p+A$ collisions is studied within HIJING 2.1 Monte Carlo model which includes nuclear shadowing of the initial parton distributions and transverse momentum broadening. Multi-parton flavor and momentum correlation inside the projectile are incorporated through flavor and momentum conservation which are shown to modify the flavor content and momentum spectra of final partons and most importantly lead to suppression of large $p_{T}$ hadron spectra in $p+A$ collisions at both RHIC and LHC energies., Comment: 4 pages, 3 figures, talk given at the 5th international conference on Hard and Electromagnetic Probes of High Energy nuclear Collisions (Hard Probes 2012)

Multiple parton scatterings in high-energy p+A collisions involve multi-parton correlation inside the projectile and color coherence of multiple jets which will lead to nuclear modification of final hadron spectra relative to that in p+p collisions. Such modification of final hadron spectra in p+A collisions is studied within HIJING 2.1 model which includes initial parton shadowing, transverse momentum broadening, parton flavor and momentum correlation inside the projectile through flavor and momentum conservation and fragmentation of multiple jets. They are shown to modify the partonic flavor content of final jets and momentum spectra of final hadrons in p+A collisions at the Large Hadron Collider., Comment: 4 pages in RevTex with 4 figures, LHC pPb collision energy is changed to 5TeV and additional figures are added

We compute the electromagnetic fields generated in heavy-ion collisions by using the HIJING model. Although after averaging over many events only the magnetic field perpendicular to the reaction plane is sizable, we find very strong magnetic and electric fields both parallel and perpendicular to the reaction plane on the event-by-event basis. We study the time evolution and the spatial distribution of these fields. Especially, the electromagnetic response of the quark-gluon plasma can give non-trivial evolution of the electromagnetic fields. The implications of the strong electromagnetic fields on the hadronic observables are also discussed., Comment: v1: 16 pages, 7 figures. v2: typos corrected, 2 new figures added, discussion in Sec.IV extended, matches published version

The spatial configuration of initial partons in high-multiplicity proton-proton scatterings at 14 TeV is assumed as three randomly positioned "hot spots". The parton momentum distribution in the hot spots is calculated by HIJING2.0 with some modifications. This initial condition causes not only large eccentricity $\epsilon_2$ but also triangularity $\epsilon_3$ and the correlation of $\epsilon_2-\epsilon_3$ event-plane angles. The final elliptic flow $v_2$, triangular flow $v_3$, and the correlation of $v_2-v_3$ event-plane angles are calculated by using the parton cascade model BAMPS to simulate the space-time parton evolution. Our results show that the $v_2-v_3$ correlation is different from that of $\epsilon_2-\epsilon_3$. This finding indicates that translations of different Fourier components of the initial spatial asymmetry to the final flow components are not independent. A dynamical correlation between the elliptic and triangular flow appears during the collective expansion., Comment: 7 pages, 12 figures

Within the framework of generalized factorization of higher-twist contributions, including modification to splitting functions of both quark and gluon, we get and numerically resolve the medium-modified DGLAP (mDGLAP) evolution equations. With Woods-Saxon nuclear geometry and Hirano 3D ideal hydrodynamic simulations of hot medium, we study the medium modified fragmentation functions (mFF) in DIS and Au+Au collisions in RHIC. Our calculation imply that the parton density in hot medium produced in RHIC is about 30 times larger than cold nucleon., Comment: The proceedings of Hard Probes 2010 including 4 pages and 3 figures

The recently published first measurement of charged hadron multiplicity density at mid-rapidity $dN_{ch}/d\eta=1584 \pm 4 ({\rm stat.}) \pm 76 ({\rm sys.})$ in central $Pb+Pb$ collisions at $\sqrt{s} = 2.76$ TeV by the ALICE Experiment at LHC is in good agreement with the HIJING2.0 prediction within the experimental errors and theoretical uncertainties. The new data point is used to carry out a combined fit together with the RHIC data to reduce the uncertainty in the gluon shadowing parameter $s_{g}$ which controls the overall magnitude of gluon shadowing at small fractional momentum $x$ in HIJING2.0 model. Predictions on the centrality dependence of charged hadron multiplicity density at mid-rapidity with reduced uncertainty are given for $Pb+Pb$ collisions at $\sqrt{s}=2.76$ and 5.5 TeV. The centrality dependence is surprisingly independent of the colliding energy as compared to RHIC energy for most of centralities starting at $N_{\rm part}=50$ (100) at $\sqrt{s}=2.76$ (7) TeV. However, it becomes stronger in peripheral collisions at higher colliding energies., Comment: 4 pages in ReVTex with 4 figures, version accepted for publication in Phys. Lett. B

The HIJING (Heavy-ion Jet Interaction Generator) Monte Carlo model is updated with the latest parton distributions functions (PDF) and new set of the parameters in the two-component mini-jet model that controls total $p+p$ cross section and the central pseudorapity density. We study hadron spectra and multiplicity distributions using the HIJING 2.0 model and compare to recent experimental data from $p+p$ collisions at the LHC energies. We also give predictions of hadron production in $p+p$, $p+Pb$ and $Pb+Pb$ collisions at the full LHC energy., Comment: 9 pages in RevTex with 11 postscript figures, updated with new results and some new data are included in comparison. The title is changed in this version

Within the framework of generalized factorization of higher-twist contributions to semi-inclusive cross section of deeply inelastic scattering off a large nucleus, multiple parton scattering leads to an effective medium-modified fragmentation function and the corresponding medium-modified DGLAP evolution equations. We extend the study to include gluon multiple scattering and induced quark-antiquark production via gluon fusion . We numerically solve these medium-modified DGLAP (mDGLAP) evolution equations and study the scale ($Q^2$), energy ($E$), length ($L$) and jet transport parameter ($\hat q$) dependence of the modified fragmentation functions for a jet propagating in a uniform medium with finite length (a "brick" problem). We also discuss the concept of parton energy loss within such mDGLAP evolution equations and its connection to the modified fragmentation functions. With a realistic Wood-Saxon nuclear geometry, we calculate the modified fragmentation functions and compare to experimental data of DIS off large nuclei. The extracted jet transport parameter at the center of a large nucleus is found to be $\hat q_{0}=0.024\pm0.008$ GeV$^{2}$/fm., Comment: 21 pages in RevTex with 19 figures (some contents are added in this version)

Partons produced in the early stage of non-central heavy-ion collisions can develop a longitudinal fluid shear because of unequal local number densities of participant target and projectile nucleons. Under such fluid shear, local parton pairs with non-vanishing impact parameter have finite local relative orbital angular momentum along the direction opposite to the reaction plane. Such finite relative orbital angular momentum among locally interacting quark pairs can lead to global quark polarization along the same direction due to spin-orbital coupling. Local longitudinal fluid shear is estimated within both Landau fireball and Bjorken scaling model of initial parton production. Quark polarization through quark-quark scatterings with the exchange of a thermal gluon is calculated beyond small-angle scattering approximation in a quark-gluon plasma. The polarization is shown to have a non-monotonic dependence on the local relative orbital angular momentum dictated by the interplay between electric and magnetic interaction. It peaks at a value of relative orbital angular momentum which scales with the magnetic mass of the exchanged gluons. With the estimated small longitudinal fluid shear in semi-peripheral $Au+Au$ collisions at the RHIC energy, the final quark polarization is found to be small $|P_q|<0.04$ in the weak coupling limit. Possible behavior of the quark polarization in the strong coupling limit and implications on the experimental detection of such global quark polarization at RHIC and LHC are also discussed., Comment: 28 pages,11 figures