arXiv subjects

Ben-Wei Zhang

Publications and source records attributed to Ben-Wei Zhang.

At least 109 records · Page 6Linked to original sources

arXiv2015

Probing Shadowed Nuclear Sea with Massive Gauge Bosons in the Future Heavy-Ion Collisions

The production of the massive bosons $Z^0$ and $W^{\pm}$ could provide an excellent tool to study cold nuclear matter effects and the modifications of nuclear parton distribution functions (nPDFs) relative to parton distribution functions (PDFs) of a free proton in high energy nuclear reactions at the LHC as well as in heavy-ion collisions (HIC) with much higher center-of mass energies available in the future colliders. In this paper we calculate the rapidity and transverse momentum distributions of the vector boson and their nuclear modification factors in p+Pb collisions at $\sqrt{s_{NN}}=63$TeV and in Pb+Pb collisions at $\sqrt{s_{NN}}=39$TeV in the framework of perturbative QCD by utilizing three parametrization sets of nPDFs: EPS09, DSSZ and nCTEQ. It is found that in heavy-ion collisions at such high colliding energies, both the rapidity distribution and the transverse momentum spectrum of vector bosons are considerably suppressed in wide kinematic regions with respect to p+p reactions due to large nuclear shadowing effect. We demonstrate that in the massive vector boson productions processes with sea quarks in the initial-state may give more contributions than those with valence quarks in the initial-state, therefore in future heavy-ion collisions the isospin effect is less pronounced and the charge asymmetry of W boson will be reduced significantly as compared to that at the LHC. Large difference between results with nCTEQ and results with EPS09 and DSSZ is observed in nuclear modifications of both rapidity and $p_T$ distributions of $Z^0$ and $W$ in the future HIC.

nucl-th↗

arXiv2015

$η$ meson production of high-energy nuclear collisions at NLO

The transverse momentum spectrum of $η$ meson in relativistic heavy-ion collisions is studied at the next-to-leading-order (NLO) within the perturbative QCD, where the jet quenching effect in the QGP is incorporated with the effectively medium-modified $η$ fragmentation functions using the higher-twist approach. We show that the theoretical simulations could give nice descriptions of PHENIX data on $η$ meson in both $\rm p+p$ and central $\rm Au+Au$ collisions at the RHIC, and also provide numerical predictions of $η$ spectra in central $\rm Pb+Pb$ collisions with $\sqrt{s_{NN}}=2.76$~TeV at the LHC. The ratios of $η/π^0$ in $\rm p+p$ and in central $\rm Au+Au$ collisions at $200$~GeV are found to overlap in a wide $p_T$ region, which matches well the measured ratio $η/ π^0$ by PHENIX. We demonstrate that, at the asymptotic region when $p_{T} \rightarrow \infty$ the ratios of $η/π^{0}$ in both $\rm Au+Au$ and $\rm p+p$ are almost determined only by quark jets fragmentation and thus approach to the one in $e^{+} e^{-}$ scattering; in addition, the almost identical gluon (quark) contribution fractions to $η$ and to $π$ result in a rather moderate variation of $η/π^{0}$ distribution at intermediate and high $p_T$ region in $\rm A+A$ relative to that in $\rm p+p$; while a slightly higher $η/π^{0}$ at small $p_T$ in $\rm Au+Au$ can be observed due to larger suppression of gluon contribution fraction to $π^{0}$ as compared to the one to $η$. The theoretical prediction for $η/ π^0$ at the LHC has also been presented.

nucl-th↗

arXiv2015

Productions of $Z^0$ and $W^+/W^-$ in Relativistic Heavy-Ion Collisions at the LHC

The productions of massive gauge bosons, $Z^0$ and $W^+/W^-$, in heavy-ion reactions at the LHC, provide an excellent tool to study the cold nuclear matter effects in high-energy nuclear collisions. In this paper we investigate $Z^0$ and $W^+/W^-$ productions in p+Pb and Pb+Pb at the LHC, at NLO and NNLO with DYNNLO incorporating the nuclear PDFs (nPDFs) parametrization sets EPS09 and DSSZ, within the framework of perturbative QCD. The numerical simulations of the transverse momentum spectra, rapidity dependence, and related nuclear modification factors for $Z^0$ and $W$ particles, as well as the charge asymmetry for W boson, are provided and tested against the latest experimental data. It is found that the theoretical results with EPS09 and DSSZ nPDFs can give good descriptions of the recent data on $Z^0$ and $W^{\pm}$ particles in p+Pb and Pb+Pb within the experimental error bars, though some differences between results with EPS09 and DSSZ can be observed, especially in the rapidity dependence of the $Z^0$ yield. Theoretical predictions for future measurements on $Z^0$ and $W$ in p+Pb and Pb+Pb collisions at the LHC are also provided.

nucl-th↗

arXiv2013

Momentum imbalance of isolated photon-tagged jet production at RHIC and LHC

In collisions of ultra-relativistic nuclei, photon-tagged jets provide a unique opportunity to compare jet production and modification due to parton shower formation and propagation in strongly-interacting matter at vastly different center-of-mass energies. We present first results for the cross sections of jets tagged by an isolated photon to ${\cal O}(α_{\rm em} α_s^2)$ in central Au+Au reactions with $\sqrt{s_{NN}}=200$ GeV at RHIC and central Pb+Pb reactions with $\sqrt{s_{NN}}=2.76$ TeV at LHC. We evaluate the increase in the transverse momentum imbalance of the observed $γ$+jet state, induced by the dissipation of the parton shower energy due to strong final-state interactions. Theoretical predictions to help interpret recent and upcoming experimental data are presented.

hep-ph↗

arXiv2012

Jet probes of QCD matter: single jets and dijets in heavy-ion collisions

Modifications of jets in the existence of a hot and dense QCD medium have recently attracted a lot of attentions. In this talk, we demonstrate how jet-medium interactions change the behavior of jets by offering examples of inclusive jet and dijet productions at $ {\cal O}(α_s^3)$ in heavy ion collisions including initial-state cold nuclear effects and especially the final-state parton energy loss effect. The suppression of inclusive jet spectrum varying with jet radii and a flatter dijet momentum imbalance as compared to those in hadron-hadron collisions are observed in high-energy nuclear collisions.

nucl-th↗

arXiv2012

Probing nuclear matter with jets

Jet physics in relativistic heavy ion collisions, which combines perturbative QCD jet production with quark and gluon energy loss and in-medium parton shower modification, has emerged as a powerful tool to probe the properties of strongly-interacting matter formed in high-energy nuclear reactions. We present selected results for the modification of jet cross sections and related observables in the ambiance of hot and/or dense nuclear medium. We focus on the inclusive jet spectrum and dijets [${\cal O}(α_s^3) $], and $Z^0/γ^*$ tagged jets [${\cal O}(G_Fα_s^2) $] in the framework of perturbative QCD.

nucl-th↗

arXiv2012

${\cal O}(α_s^3)$ analysis of inclusive jet and di-jet production in heavy ion reactions at the Large Hadron Collider

Jets physics in heavy ion reactions is an important new area of active research at the Relativistic Heavy Ion Collider (RHIC) and at the Large Hadron Collider (LHC) that paves the way for novel tests of QCD multi-parton dynamics in dense nuclear matter. At present, perturbative QCD calculations of hard probes in elementary nucleon-nucleon reactions can be consistently combined with the effects of the nuclear medium up to $ {\cal O}(α_s^3) $. While such accuracy is desirable but not necessary for leading particle tomography, it is absolutely essential for the new jet observables. With this motivation, we present first results and predictions to $ {\cal O}(α_s^3) $ for the recent LHC lead-lead (Pb+Pb) run at a center-of-mass energy of 2.76 TeV per nucleon-nucleon pair. Specifically, we focus on the suppression of the single and double inclusive jet cross sections. Our analysis includes not only final-state inelastic parton interactions in the QGP, but also initial-state cold nuclear matter effects and an estimate of the non-perturbative hadronization corrections. We demonstrate how an enhanced di-jet asymmetry in central Pb+Pb reactions at the LHC, recently measured by the ATLAS and CMS experiments, can be derived from these results. We show quantitatively that a fraction of this enhancement may be related to the ambiguity in the separation between the jet and the soft background medium and/or the diffusion of the parton shower energy away from the jet axis through collisional processes. We point to a suite of measurements that can help build a consistent picture of parton shower modification in heavy ion collisions at the LHC.

hep-ph↗

arXiv2012

Cold Nuclear Matter Effects on Dijet Productions in Relativistic Heavy-ion Reactions at LHC

We investigate the cold nuclear matter(CNM) effects on dijet productions in high-energy nuclear collisions at LHC with the next-to-leading order perturbative QCD. The nuclear modifications for dijet angular distributions, dijet invariant mass spectra, dijet transverse momentum spectra and dijet momentum imbalance due to CNM effects are calculated by incorporating EPS, EKS, HKN and DS param-etrization sets of parton distributions in nucleus . It is found that dijet angular distributions and dijet momentum imbalance are insensitive to the initial-state CNM effects and thus provide optimal tools to study the final-state hot QGP effects such as jet quenching. On the other hand, the invariant mass spectra and the transverse momentum spectra of dijet are generally enhanced in a wide region of the invariant mass or transverse momentum due to CNM effects with a feature opposite to the expected suppression because of the final-state parton energy loss effect in the QGP. The difference of EPS, EKS, HKN and DS parametrization sets of nuclear parton distribution functions is appreciable for dijet invariant mass spectra and transverse momentum spectra at p+Pb collisions, and becomes more pronounced for those at Pb+Pb reactions.

hep-ph↗

arXiv2011

Transport Model Studies of the Baryon-Rich Quark-Gluon Plasma formed in Heavy Ion Collisions

Heavy ion collisions in the low energy run at Relativistic Heavy Ion Collider (RHIC) and future Facility for Antiproton and Ion Research (FAIR) in Germany are expected to produce a quark-gluon plasma that has a finite baryon chemical potential, allowing thus the possibility to study the location of the critical endpoint in the QCD phase diagram. In this talk, using a multiphase transport model, that includes interactions in both initial partonic and final hadronic matters and the transition between these two phases of matter, we discuss the effects of partonic interactions on observables such as the elliptic flow that have played essential roles in studying the properties of the net baryon free quark-gluon plasma produced in heavy ion collisions at higher energies at RHIC. Also, we study the effect of density fluctuations due to a first-order transition between the quark-gluon plasma and hadronic matter on fluctuations of hadron mean transverse momentum and produced deuteron number as well as on two-pion correlations. We further discuss the possibility of studying the mechanism of charm energy loss in the baryon-rich quark-gluon plasma and the properties of phi mesons in hot-dense matter produced in these collisions.

nucl-th↗

arXiv2011

Full jet tomography of high-energy nuclear collisions

Parton energy loss in the hot QCD medium will manifest itself not only in leading hadron spectra but also in reconstructed jet productions in high-energy nucleus-nucleus collisions. In this paper we report on recent theoretical efforts in studying full jet observables in relativistic heavy-ion collisions by discussing the modifications of jet shapes, inclusive jet cross section and the vector boson accompanied jet production in the presence of the QGP-induced jet quenching.

nucl-th↗

arXiv2010

Jet tomography of high-energy nucleus-nucleus collisions at next-to-leading order

We demonstrate that jet observables are highly sensitive to the characteristics of the vacuum and the in-medium QCD parton showers and propose techniques that exploit this sensitivity to constrain the mechanism of quark and gluon energy loss in strongly-interacting plasmas. As a first example, we calculate the inclusive jet cross section in high-energy nucleus-nucleus collisions to ${\cal O}(α_s^3)$. Theoretical predictions for the medium-induced jet broadening and the suppression of the jet production rate due to cold and hot nuclear matter effects in Au+Au and Cu+Cu reactions at RHIC are presented.

hep-ph↗

arXiv2009

A light-cone wavefunction approach to open heavy flavor dynamics in QCD matter

We calculate the lowest order charm and beauty parton distribution functions in and fragmentation functions into D and B mesons using the operator definitions of factorized perturbative QCD. In the vacuum, we find the leading corrections that arise from the structure of the final-state hadrons. Quark-antiquark potentials extracted from the lattice are employed to demonstrate the existence of open heavy flavor bound-state solutions in the QGP in the vicinity of the critical temperature. We provide first results for the in-medium modification of the heavy quark distribution and decay probabilities in a co-moving plasma. In an improved perturbative QCD description of heavy flavor dynamics in the thermal medium, we combine D and B meson formation and dissociation with parton-level charm and beauty quark quenching to obtain predictions for the heavy meson and non-photonic electron suppression in Cu+Cu and Pb+Pb collisions at RHIC and the LHC, respectively.

hep-ph↗

arXiv2009

A study on the anomaly of $p$ over $π$ ratios in $Au+Au$ collisions with jet quenching

The ratios of $p/π$ at large transverse momentum in central $Au+Au$ collisions at RHIC are studied in the framework of jet quenching based on a next-to-leading order pQCD parton model. It is shown that theoretical calculations with a gluon energy loss larger than the quark energy loss will naturally lead to a smaller $p/π$ ratios at large transverse momentum in $Au+Au$ collisions than those in $p+p$ collisions at the same energy. Scenarios with equal energy losses for gluons and quarks and a strong jet conversion are both explored and it is demonstrated in both scenarios $p/π$ ratios at high $p_T$ in central $Au+Au$ collisions are enhanced and the calculated ratios of protons over pions approach to the experimental measurements. However, ${\bar p}/p$ in the latter scenario is found to fit data better than that in the former scenario.

hep-ph↗

arXiv2009

Direct photon production in d+A and A+A collisions at RHIC

Direct photon production in minimum bias d+Cu and d+Au and central Cu+Cu and Au+Au collisions at center of mass energies $\sqrt{s}=62.4$ GeV and 200GeV at RHIC is systematically investigated. We study the jet quenching effect, the medium-induced photon bremsstrahlung and jet-photon conversion in the hot QGP. We account for known cold nuclear matter effects, such as the isospin effect, the Cronin effect, shadowing and cold nuclear matter energy loss. It is shown that at high $p_T$ the nuclear modification factor for direct photons $R_{AA}^γ (p_T) < 1$ is dominated by cold nuclear matter effects and there is no evidence for large cross section amplification due to medium-induced photon bremsstrahlung and jet-photon conversion in the medium. Comparison of numerical simulations to experimental data also rules out large Cronin enhancement and incoherent photon emission in the QGP but the error bars in the current experimental data cannot provide further constraints on the magnitudes of other nuclear matter effects.

nucl-th↗

arXiv2009

Jet Observables of Parton Energy Loss in High-Energy Nuclear Collisions

While strong attenuation of single particle production and particle correlations has provided convincing evidence for large parton energy loss in the QGP, its application to jet tomography has inherent limitations due to the inclusive nature of the measurements. Generalization of this suppression to full jet observables leads to an unbiased, more differential and thus powerful approach to determining the characteristics of the hot QCD medium created in high-energy nuclear collisions. In this article we report on recent theoretical progress in calculating jet shapes and the related jet cross sections in the presence of QGP-induced parton energy loss. (i) A theoretical model of intra-jet energy flow in heavy-ion collisions is discussed. (ii) Realistic numerical simulations demonstrate the nuclear modification factor $R_{AA}(p_T)$ evolves continuously with the jet cone size $R^{\max}$ or the acceptance cut $ω_{\min}$ - a novel feature of jet quenching. The anticipated broadening of jets is subtle and most readily manifested in the periphery of the cone for smaller cone radii.

hep-ph↗

arXiv2008

A systematic study of direct photon production in heavy ion collisions

A theoretical derivation of photon bremsstrahlung, induced by the interactions of an energetic quark in a hot and dense quark-gluon plasma, is given in the framework of the reaction operator approach. For the physically relevant case of hard jet production, followed by few in-medium interactions, we find that the Landau-Pomeranchuk-Migdal suppression of the bremsstrahlung photon intensity is much stronger than in the previously discussed limit of on-shell quarks and a large number of soft scatterings. We present the first systematic study of direct photon production in minimum bias d+Cu and d+Au and central Cu+Cu and Au+Au heavy ion collisions at the Relativistic Heavy Ion Collider at center of mass energies of 62.4 GeV and 200 GeV. We find that the contribution of the final-state photon production at pT < 5 GeV is limited to 35%, and at high transverse momenta, the modification of the direct photon cross section is dominated by initial-state cold nuclear matter effects.

hep-ph↗

arXiv2008

The theory and phenomenology of jets in nuclear collisions

We review selected results from a recent in-depth study of jet shapes and jet cross sections in ultra-relativistic reactions with heavy nuclei at the LHC arXiv:0810.2807 [hep-ph]. We demonstrate that at the highest collider energies these observables become feasible as a new, differential and accurate test of the underlying QCD theory. Our approach allows for detailed simulations of the experimental acceptance/cuts that help isolate jets emerging from a dense QGP. We show for the first time that the pattern of stimulated gluon emission can be correlated with a variable quenching of the jet rates and provide an approximately model-independent approach to determining the characteristics of the medium-induced bremsstrahlung spectrum. The connection between such cross section attenuation and the in-medium jet shapes is elucidated.

hep-ph↗

arXiv2008

A theory of jet shapes and cross sections: from hadrons to nuclei

For jets, with great power comes great opportunity. The unprecedented center of mass energies available at the LHC open new windows on the QGP: we demonstrate that jet shape and jet cross section measurements become feasible as a new, differential and accurate test of the underlying QCD theory. We present a first step in understanding these shapes and cross sections in heavy ion reactions. Our approach allows for detailed simulations of the experimental acceptance/cuts that help isolate jets in such high-multiplicity environment. It is demonstrated for the first time that the pattern of stimulated gluon emission can be correlated with a variable quenching of the jet rates and provide an approximately model-independent approach to determining the characteristics of the medium-induced bremsstrahlung spectrum. Surprisingly, in realistic simulations of parton propagation through the QGP we find a minimal increase in the mean jet radius even for large jet attenuation. Jet broadening is manifest in the tails of the energy distribution away from the jet axis and its quantification requires high statistics measurements that will be possible at the LHC.

hep-ph↗