76655214
Hadron production in p+p, p+Pb, and Pb+Pb collisions with the HIJING 2.0 model at energies available at the CERN Large Hadron Collider
The Heavy-Ion Jet Interaction Generator (hijing) Monte Carlo model is updated with the latest parton distributions functions and a new set of the parameters in the two-component minijet model that controls the total p+p cross section and the central pseudorapity density. We study hadron spectra and multiplicity distributions using the hijing2.0 model and compare to recent experimental data from p+p collisions at the Large Hadron Collider (LHC) energies. We also give predictions of hadron production in p+p, p+Pb, and Pb+Pb collisions at the full LHC energy.
3066888
Global quark polarization in non-central A+A collisions
Partons produced in the early stage of non-central heavy-ion collisionscan 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 orbitalangular 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 left hbar P_q right hbar <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.
119244375
Elliptic and Triangular Flow and their Correlation in Ultrarelativistic High Multiplicity Proton Proton Collisions at 14 TeV
Abstract 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 ϵ 2 but also triangularity ϵ 3 and the correlation of ϵ 2 − ϵ 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 ϵ 2 − ϵ 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.
118024758
Nuclear modification of high-p_T hadron spectra in p+A collisions at LHC
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.
119191221
Modified DGLAP evolution for fragmentation functions in nuclei and QGP
Abstract 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 calculations imply that the parton density in the hot medium produced in RHIC is about 30 times larger than in a cold nucleus.
119188222
Gluon shadowing and hadron production in heavy-ion collisions at LHC
Abstract The recently published first measurement of charged hadron multiplicity density at mid-rapidity d N c h / d η = 1584 ± 4 ( stat. ) ± 76 ( sys. ) in central Pb + Pb collisions at 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 uncertainties are given for Pb + Pb collisions at s = 2.76 and 5.5 TeV. The centrality dependence is surprisingly independent of the colliding energy similar to that in Au + Au collisions at RHIC for most of centralities starting at N part = 50 (100) at s = 2.76 (7) TeV. However, it becomes stronger in peripheral collisions at higher colliding energies.
119306470
Understanding the flavor symmetry breaking and nucleon flavor-spin structure within the chiral quark model
In {chi}QM, a quark can emit Goldstone bosons. The flavor symmetry breaking in the Goldstone boson emission process is used to interpret the nucleon flavor-spin structure. In this paper, we study the inner structure of constituent quarks implied in {chi}QM caused by the Goldstone boson emission process in nucleon. From a simplified model Hamiltonian derived from {chi}QM, the intrinsic wave functions of constituent quarks are determined. Then the obtained transition probabilities of the emission of Goldstone boson from a quark can give a reasonable interpretation to the flavor symmetry breaking in nucleon flavor-spin structure.
124976148
Vector Coupling and Rho Meson in a Nonlocal Nambu-Jona-Lasinio Model*
A vector coupling term apart from the scalar and pseudoscalar terms, is introduced into the nonlocal quark-(anti-)quark interaction in an extended Nambu-Jona-Lasinio model to investigate the vector rho meson mode in the relativistic random phase approximation (RPA). It is shown that a favorable choice of the vector coupling to fit the empirical data has to be the same form as that of the original scalar and pseudoscalar ones but with a necessary negative sign.
53665229
LOW ENERGY SPECTRAL INDEX AND Ep EVOLUTION OF QUASI-THERMAL PHOTOSPHERE EMISSION OF GAMMA-RAY BURSTS
Recent observations by the Fermi satellite suggest that a photosphere emission component is contributing to the observed spectrum of many gamma-ray bursts (GRBs). One important question is whether the photosphere component can interpret the typical 'Band' function of GRBs with a typical low energy photon spectral index α ∼ –1. We perform a detailed study of the photosphere emission spectrum by progressively introducing several physical ingredients previously not fully incorporated, including the probability distribution of the location of a dynamically evolving photosphere, superposition of emission from an equal arrival time 'volume' in a continuous wind, the evolution of optical depth of a wind with finite but evolving outer boundary, as well as the effect of different top-hat wind luminosity (L{sub w} ) profiles. By assuming a comoving blackbody spectrum emerging from the photosphere, we find that for an outflow with a constant or increasing L{sub w} , the low-energy spectrum below the peak energy (E{sub p} ), can be modified to F {sub ν} ∼ ν{sup 1.5} (α ∼ +0.5). A softer (–1 < α < +0.5) or flat (α = –1) spectrum can be obtained during the L{sub w} decreasing phase or high-latitude-emission-dominated phase. We also study the evolutionmore » of E{sub p} as a function of wind and photosphere luminosity in this photosphere model. An E{sub p} – L tracking pattern can be reproduced if a certain positive dependence between the dimensionless entropy η and L{sub w} is introduced. However, the hard-to-soft evolution pattern cannot be reproduced unless a contrived condition is invoked. In order to interpret the Band spectrum, a more complicated photosphere model or a different energy dissipation and radiation mechanism is needed.« less
119474747
Extended Quark Potential Model from Random Phase Approximation
The quark potential model is extended to include the sea quark excitation using the random phase approximation (RPA). The effective quark interaction preserves the important Quantum Chromodynamics (QCD) properties -- chiral symmetry and confinement simultaneously. A primary qualitive analysis shows that the $\pi$ meson as a well-known typical Goldstone boson and the other mesons made up of valence $q\bar{q}$ quark pair such as the $\rho$ meson can also be described in this extended quark potential model.
118376948
Measuring the beaming angle of GRB 030329 by fitting the rebrightenings in its multiband afterglow
Multiple rebrightenings have been observed in the multiband afterglow of GRB 030329. In particular, a marked and quick rebrightening occurred at about t ∼ 1.2 × 10 5 s. Energy injection from late and slow shells seems to be the best interpreta- tion for these rebrightenings. Usually it is assumed that the energy is injected into the whole external shock. However, in the case of GRB 030329, the rebrightenings are so quick that the usual consideration fails to give a satisfactory fit to the observed light curves. Actually, since these late/slow shells freely coast in the wake of the external shock, they should be cold and may not expand laterally. The energy injection then should only occur at the central region of the external shock. Considering this effect, we numerically re-fit the quick rebrightenings observed in GRB 030329. By doing this, we were able to derive the beaming angle of the energy injection process. Our result, with a relative residual of only 5% - 10% during the major rebrightening, is bet- ter than any previous modeling. The derived energy injection angle is about 0.035. We assume that these late shells are ejected by the central engine via the same mechanism as those early shells that produce the prompt gamma-ray burst. The main difference is that their velocities are much slower, so that they catch up with the external shock relatively late and are manifested as the observed quick rebrightenings. If this were true, then the derived energy injection angle can give a good measure of the beaming angle of the prompt γ-ray emission. Our study may hopefully provide a novel method to measure the beaming angle of gamma-ray bursts.