arXiv subjects

Ben-Wei Zhang

Publications and source records attributed to Ben-Wei Zhang.

At least 91 records · Page 5Linked to original sources

arXiv2019

Probing cold nuclear matter effects with the productions of isolated-$γ$ and $γ$+jet in p$+$Pb collisions at $\sqrt{s_{NN}}=$ 8.16 TeV

We investigate the cold nuclear matter (CNM) effects on the productions of the isolated prompt photon and $γ+$jet in proton-lead collisions at $\rm 8.16$ TeV under the next-to-leading order (NLO) perturbative quantum chromodynamics calculations with four parametrizations for nuclear parton distribution functions (nPDFs), i.e. DSSZ, EPPS16, nCTEQ15, nIMParton. Our theoretical calculations provide good descriptions of pp baseline in the ATLAS collaboration and make predictions for future experimental results at $\rm p$+$\rm Pb$ collisions. We calculate the dependence of the nuclear modification factor of isolated prompt photon on transverse momentum $\rm p_T^γ$ and pseudo-rapidity $η^γ$ at very forward and backward rapidity regions, and demonstrate that the forward-to-backward yield asymmetries $\rm Y_{\rm pPb}^{\rm asym}$ as a function of $\rm p_T^γ$ with different nPDFs parametrizations have diverse behaviors. Furthermore, the nuclear modification factor of isolated-$γ+$jet $\rm R_{\rm pPb}^{γJet}$ as a function of $γ+$jet's pseudo-rapidity $η_{γ\rm Jet}=\frac{1}{2}(η_γ+η_{\rm Jet})$ at different average transverse momentum $\rm p_T^{\rm avg}=\frac{1}{2}(\rm p_T^γ+\rm p_T^{\rm Jet})$ has been discussed, which can facilitate a tomography study of CNM effects with precise locations in a rather wide kinematic region by varying the transverse momenta and rapidities of both isolated photon and jet in p+A collisions.

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arXiv2018

Parton energy loss effect on Z+jet production in high-energy nuclear collisions

We give a report of medium modification of Z+jet correlations in Pb+Pb collisions at the Large Hadron Collider using Sherpa to generate initial Z+jet at next-leading-order matrix element matched parton shower, and the Linear Boltzmann Transport Model for jet propagation in the expanding quark-gluon-plasma. Our numerical calculations show excellent agreement with all available observables of Z+jet simultaneously in both proton + proton and Pb+Pb collisions. Our results can well explain the shift of momentum asymmetry $x_{jZ}=p_T^{jet}/p_T^Z$ as well as its mean values, the suppression of the jet yields per Z trigger $R_{jZ}$ and the modification of azimuthal angle correlation $Δϕ_{jZ}$. We also demonstrate that it is the energy loss effect on multi-jets from high-order corrections that leads to the suppression of the Z+jet correlation at small azimuthal angle difference $Δϕ_{jZ}$ and at small $x_{jZ}$. The jet shape reflecting transverse momentum distribution inside the jet is also calculated, which indicates that large fraction of jet energy is carried away from the jet axis in Pb+Pb collisions.

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arXiv2018

The production of $b\bar{b}$ dijet in heavy-ion collisions at the LHC

We report our recent theoretical calculations for $b\bar{b}$ dijet production in high-energy nuclear collisions. The NLO+parton shower (PS) event generator SHERPA has been employed to provide the pp baseline of $b\bar{b}$ dijet production. A framework which combines Langevin transport equation to describe the evolution of heavy quarks and the higher-twist scheme to consider the inelastic energy loss of both light and heavy partons has been implemented. Within this framework, we present the theoretical result of transverse momentum imbalance $x_J=p_{T1}/p_{T2}$ both for inclusive dijet and $b\bar{b}$ dijet in Pb+Pb collision at 5.02 TeV. The energy loss of b jet would shift $x_J$ to smaller value relative to p+p reference which is consistent with the CMS data. In addition, we show the medium modification for angular correlation of $b\bar{b}$ dijet in A+A collision at $\sqrt{s_{NN}}=5.02$~TeV. We observe a stronger suppression in small $Δϕ=|ϕ_{b1}-ϕ_{b2}|$ region where the gluon splitting processes dominate relative to large $Δϕ$ region. The difference leads to a modest suppression on near side ($Δϕ\sim 0$) and enhancement on away side ($Δϕ\simπ$).

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arXiv2018

Jet tomography in high-energy nuclear collisions

When an energetic parton traversing the QCD medium, it may suffer multiple scatterings and lose energy. This jet quenching phenomenon may lead to the suppression of leading hadron productions as well as medium modifications of full jet observables in heavy-ion collisions. In this talk we discuss the nuclear modification factors and yield ratios of identified meson such as $η$, $ρ^0$, $ϕ$, $ω$, and $K^0_{\rm S}$ as well as $π$ meson at large $p_T$ in A+A collisions at the next-to-leading order (NLO) with high-twist approach of parton energy loss. Then we discuss a newly developed formalism of combing NLO matrix elements and parton shower (PS) for initial hard production with parton energy loss in the QGP, and its application in investigating massive gauge boson ($Z^0$/$W^{\pm}$) tagged jet productions and $b\bar{b}$ dijet correlations in Pb+Pb at the LHC.

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arXiv2018

HIJING++, a Heavy Ion Jet INteraction Generator for the High-luminosity Era of the LHC and Beyond

HIJING++ (Heavy Ion Jet INteraction Generator) is the successor of the widely used original HIJING, developed almost three decades ago. While the old versions (1.x and 2.x) were written in FORTRAN, HIJING++ was completely rewritten in C++. During the development we keep in mind the requirements of the high-energy heavy-ion community: the new Monte Carlo software have a well designed modular framework, therefore any future modifications are much easier to implement. It contains all the physical models that were also present in it's predecessor, but utilizing modern C++ features it also includes native thread based parallelism, an easy-to-use analysis interface and a modular plugin system, which makes room for possible future improvements. In this paper we summarize the results of our performance tests measured on 2 widely used architectures.

physics.comp-ph↗

arXiv2018

Production of $ρ^{0}$ meson with large $p_T$ at NLO in heavy-ion collisions

Production of large transverse momentum $ρ^{0}$ meson in high-energy nuclear collisions is investigated for the first time at the next-leading-order in the QCD improved parton model. The $ρ^0$ fragmentation functions (FFs) in vacuum at any scale $Q$ are obtained, by evolving a newly developed initial parametrization of $ρ^0$ FFs at a scale $\rm Q_{0}^2=1.5\ GeV^2$ from a broken SU(3) model through NLO DGLAP equations. The numerical simulations of $p_{\rm T}$ spectra of $ρ^{0}$ meson in the elementary $\rm p+p$ collisions at NLO give a decent description of STAR $\rm p+p$ data. In $\rm A+A$ reactions the jet quenching effect is taken into account with the higher-twist approach by the medium-modified parton FFs due to gluon radiation in the quark-gluon plasma, whose space-time evolution is described by a (3+1D) hydrodynamical model. The nuclear modification factors for $ρ^{0}$ meson and its double ratio with $π^\pm$ nuclear modification in central $\rm Au+Au$ collisions at the RHIC are calculated and found to be in good agreement with STAR measurement. Predictions of $ρ^{0}$ nuclear modification and the yield ratio $ρ^0/π^0$ in central Pb+Pb at the LHC are also presented. It is shown that the ratio $ρ^0/π^0$ in central Pb+Pb will approach to that in p+p reactions when $p_{\rm T}>12$~GeV.

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arXiv2018

Z+jet correlation with NLO-matched parton-shower and jet-medium interaction in high-energy nuclear collisions

The impact of jet quenching on $Z^0$-tagged jets in relativistic heavy-ion collisions at the Large Hadron Collider (LHC) is investigated. We employ Sharpa Monte Carlo program that combines next-to-leading order matrix elements with matched resummation of parton shower to compute the initial $Z^0$+jet production. The Linear Boltzmann Transport (LBT) model is then used to simulate the propagation, energy attenuation of and medium response induced by jet partons in the quark-gluon plasma. With both higher-order corrections and matched soft/collinear radiation as well as a sophisticated treatment of parton energy loss and medium response in LBT, our numerical calculations can provide the best description so far of all available observables of $Z^0$+jet simultaneously in both p+p and Pb+Pb collisions, in particular, the shift of the distribution in transverse momentum asymmetry $x_{\rm jZ}=p_T^{\rm jet}/p_T^Z$, the modification of azimuthal angle correlation in $Δϕ_{\rm{j}Z}=|ϕ_{\rm jet}-ϕ_Z|$ and the overall suppression of average number of $Z^0$-tagged jets per boson $R_{\rm jZ}$ at $\sqrt s =5.02$ TeV as measured by the CMS experiment. We also show that higher-order corrections to $Z^0$+jet production play an indispensable role in understanding $Z^0$+jet azimuthal angle correlation at small and intermediate $Δϕ_{\rm jZ}$, and momentum imbalance at small $x_{\rm jZ}$. Jet quenching of the sub-leading jets is shown to lead to suppression of $Z^0$+jet correlation at small azimuthal angle difference $Δϕ_{\rm jZ}$ and at small $x_{\rm jZ}$.

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arXiv2018

Nuclear suppression of $ϕ$ meson yields with large $p_T$ at the RHIC and the LHC

We calculate $ϕ$ meson transverse momentum spectra in p+p collisions as well as their nuclear suppressions in central A+A collisions both at the RHIC and the LHC in LO and NLO with the QCD-improved parton model. We have included the parton energy loss effect in hot/dense QCD medium with the effectively medium-modified $ϕ$ fragmentation functions in the higher-twist approach of jet quenching. The nuclear modification factors of $ϕ$ meson in central Au+Au collisions at the RHIC and central Pb+Pb collisions at the LHC are provided, and a nice agreement of our numerical results at NLO with the ALICE measurement is observed. Predictions of yield ratios of neutral mesons such as $ϕ/π^0$, $ϕ/η$ and $ϕ/ρ^0$ at large $p_T$ in relativistic heavy-ion collisions are also presented for the first time.

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arXiv2018

Z+jet productions in heavy-ion collisions

We report a systematic study of Z+jet correlation in Pb+Pb collisions at the LHC by combining the next-leading-order matrix elements calculations with matched parton shower in Sherpa for the initial Z+jet production, and Linear Boltzmann transport Model for jet propagation in the expanding quark-gluon-plasma. Our numerical results can well explain CMS measurements on Z+jet correlation in Pb+Pb collisions: the shift of $p_T$ imbalance $x_{jZ}=p_T^{jet}/p_T^Z$ and their mean values, the suppression of the average number of jet partners per Z boson $R_{jZ}$, as well as the modification of azimuthal angle correlations $Δϕ_{jZ}$. We also demonstrate that high-order corrections play a significant role in the understanding of Z+jet correlations at high energies.

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arXiv2018

First Results with HIJING++ on High-energy Heavy Ion Collisions

We present preliminary results with HIJING++ (3.1.1) for identified hadron production in high-energy heavy ion collisions at LHC energies. The recently developed HIJING++ version is based on the latest version of PYTHIA8 and contains all the nuclear effects that have been included in the HIJING2.552, which will be improved by a new version of the shadowing parametrization and jet quenching module. Here, we summarize the structure and the speed gain due to parallelization of the new program code, also presenting some comparison between experimental data.

hep-ph↗

arXiv2017

Chiral phase transition in linear sigma model with non-extensive statistical mechanics

From the non-extensive statistical mechanics, we investigate the chiral phase transition at finite temperature $T$ and baryon chemical potential $μ_B$ in the framework of the linear sigma model. The corresponding non-extensive distribution, based on Tsallis' statistics, is characterized by a dimensionless non-extensive parameter, $q$, and the results in the usual Boltzmann-Gibbs case are recovered when $q\to 1$. The thermodynamics of the linear sigma model and its correspodning phase diagram are analysed. At high temperature region, the critical temperature $T_c$ is shown to decrease with increasing $q$ from the phase diagram in the $(T,~μ)$ plane. However, larger values of $q$ causes the rise of $T_c$ at low temperature but high chemical potential. Moreover, it is found that $μ$ different from zero corresponds to a first-order phase transition while $μ=0$ to a crossover one. The critical endpoint (CEP) carries higher chemical potential but lower temperature with $q$ increasing due to the non-extensive effects.

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arXiv2017

Generalized Ensemble Theory with Non-extensive Statistics

The non-extensive canonical ensemble theory is reconsidered with the method of Lagrange multipliers by maximizing Tsallis entropy, with the constraint that the normalized term of Tsallis' $q-$average of physical quantities, the sum $\sum p_j^q$, is independent of the probability $p_i$ for Tsallis parameter $q$. The self-referential problem in the deduced probability and thermal quantities in non-extensive statistics is thus avoided, and thermodynamical relationships are obtained in a consistent and natural way. We also extend the study to the non-extensive grand canonical ensemble theory and obtain the $q$-deformed Bose-Einstein distribution as well as the $q$-deformed Fermi-Dirac distribution. The theory is further applied to the generalized Planck law to demonstrate the distinct behaviors of the various generalized $q$-distribution functions discussed in literature.

cond-mat.stat-mech↗

arXiv2017

First Results with HIJING++ in High-Energy Heavy-Ion Collisions

First calculated results with the new HIJING++ are presented for identified hadron production in high-energy heavy ion collisions. The recently developed HIJING++ version is based on the latest version of PYTHIA8 and contains all the nuclear effects has been included in the HIJING2.552, which will be improved by a new version of the shadowing parametrization and jet quenching module. Here, we summarize the major changes of the new program code beside the comparison between experimental data for some specific high-energy nucleus-nucleus collisions.

hep-ph↗

arXiv2017

Medium modification of averaged jet charge in heavy-ion collisions

Jet charge characterizes the electric charge distribution inside a jet. In this talk we make the first theoretical study of jet charge in high-energy nuclear collisions and calculate numerically the medium alternations of jet charge due to parton energy loss in the quark-gluon plasma. The parton multiple scattering in hot/dense QCD medium is simulated by a modified version of PYQUEN Monte Carlo model with 3+1D ideal hydrodynamical evolution of the fireball. Our preliminary results show that the averaged jet charge is significant modified in A+A collisions relative to that in p+p. The different features of quark jet charge and gluon jet charge in heavy-ion collisions, and the sensitivity of jet charge modifications to flavour dependence of energy loss are observed, which could then be used to discriminate quark and gluon jet as well as their energy loss patterns in heavy-ion collisions.

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arXiv2016

Study of W and Z Boson Production in Proton-Lead Collisions at the LHC with KP Nuclear Parton Distributions

We present a detailed study of the (pseudo)rapidity distributions of massive vector bosons produced in p+p and p+Pb collisions at the LHC within the next-to-leading order approximation in perturbative quantum chromodynamics. In particular, we discuss the impact of different cold nuclear matter effects on this process using the nuclear parton distributions calculated from the microscopic model developed by Kulagin and Petti (KP). This model was successfully applied to study nuclear effects in the deep-inelastic scattering and the Drell-Yan reactions off various (fixed) target nuclei. Results are compared with the recent CMS and ATLAS p+Pb data with \sqrt{s}=5.02 TeV per two colliding nucleons. We found an excellent agreement between the predictions of the KP model and the recent LHC data on W+- and Z0 production in p+Pb collisions, including the differential cross sections, the forward-backward asymmetries, and W charge asymmetry. We also discuss the sensitivity of the current and future LHC data to the underlying mechanisms responsible for the nuclear modifications of parton density functions.

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arXiv2016

Productions of $η$, $ρ^0$ and $ϕ$ at large transverse momentum in Heavy ion Collisions

The suppression of the productions of the $η$ meson in relativistic heavy-ion collisions and its ratio of $η/π^0$ are computed theoretically in the framework of the perturbative QCD(pQCD) to confront the experimental data which matches well. We explore how the hadron production ratios as$η/π^0$ would further disclose the informations of the production suppressions due to the energy loss of the energetic jet that propagating though the QGP medium. Also, we present our further studies on vector mesons such as $ρ^0$ and $ϕ$ within the same framework. The theoretical predictions based on pQCD are thus firstly given which give a decent description on the experimental measurements. It paved the way to the uniformly understanding of the strong suppression of single hadron productions at large transverse momentum which is a convincing evidence of the jet quenching effect.

hep-ph↗

arXiv2016

Probing cold nuclear matter effects with weak gauge boson production in ultra-relativistic heavy-ion collisions

Within the framework of pQCD, we systematically study the $W^{\pm}/Z^0$ boson production as a probe of cold nuclear matter effects and nuclear parton distributions in p+Pb and Pb+Pb collisions at the LHC and future colliders. A detailed analysis at partonic level is performed. Moreover, with a semi-microscopic KP model of NPDFs, in which several nuclear effects (e.g. Fermi motion and nuclear binding, the off-shell correction, the nuclear coherent correction, and the nuclear meson correction) are included, we study the vector boson rapidity distribution in p+Pb collisions at the LHC, and a very good agreement with the latest data is found, including the $W$-boson charge asymmetry.

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arXiv2015

Quantifying jet transport properties via large $p_T$ hadron production

Nuclear modification factor $R_{AA}$ for large $p_T$ single hadron is studied in a next-to-leading order (NLO) perturbative QCD (pQCD) parton model with medium-modified fragmentation functions (mFFs) due to jet quenching in high-energy heavy-ion collisions. The energy loss of the hard partons in the QGP is incorporated in the mFFs which utilize two most important parameters to characterize the transport properties of the hard parton jets: the jet transport parameter $\hat q_{0}$ and the mean free path $λ_{0}$, both at the initial time $τ_0$. A phenomenological study of the experimental data for $R_{AA}(p_{T})$ is performed to constrain the two parameters with simultaneous $χ^2/{\rm d.o.f}$ fits to RHIC as well as LHC data. We obtain for energetic quarks $\hat q_{0}\approx 1.1 \pm 0.2$ GeV$^2$/fm and $λ_{0}\approx 0.4 \pm 0.03$ fm in central $Au+Au$ collisions at $\sqrt{s_{NN}}=200$ GeV, while $\hat q_{0}\approx 1.7 \pm 0.3$ GeV$^2$/fm, and $λ_{0}\approx 0.5 \pm 0.05$ fm in central $Pb+Pb$ collisions at $\sqrt{s_{NN}}=2.76$ TeV. Numerical analysis shows that the best fit favors a multiple scattering picture for the energetic jets propagating through the bulk medium, with a moderate averaged number of gluon emissions. Based on the best constraints for $λ_{0}$ and $τ_0$, the estimated value for the mean-squared transverse momentum broadening is moderate which implies that the hard jets go through the medium with small reflection.

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