The medium-temperature dependence of jet transport coefficient in high-energy nucleus-nucleus collisions

The medium-temperature T dependence of the jet transport coefficient̂q was studied via the nuclear modification factor RAA(p_(T))and elliptical flow parameter v_(2)(p_(T))for large transverse momentum p_(T) hadrons in high-energy nucleus-nucleus collisions.Within a next-to-leading-order perturbative QCD parton model for hard scatterings with modified fragmentation functions due to jet quenching controlled by q,we check the suppression and azimuthal anisotropy for large p_(T) hadrons,and extract q by global fits to RAA(pT)and v_(2)(pT)data in A+A collisions at RHIC and LHC,respectively.The numerical results from the best fits show that q∕T^(3) goes down with local medium-temperature T in the parton jet trajectory.Compared with the case of a constant q∕T^(3),the going-down T dependence of q∕T^(3) makes a hard parton jet to lose more energy near T_(c) and therefore strengthens the azimuthal anisotropy for large pT hadrons.As a result,v_(2)(p_(T))for large pT hadrons was enhanced by approximately 10%to better fit the data at RHIC/LHC.Considering the first-order phase transition from QGP to the hadron phase and the additional energy loss in the hadron phase,v_(2)(p_(T))is again enhanced by 5-10%at RHIC/LHC.

Transverse momentum balance of dijets in Xe+Xe collisions at the LHC

We present a theoretical study of the medium modifications of the p_(T)balance (x_(J)) of dijets in Xe+Xe collisions at■.The initial production of dijets was carried out using the POWHEG+PYTHIA8 prescription,which matches the next-toleading-order (NLO) QCD matrix elements with the parton shower (PS) effect.The SHELL model described the in-medium evolution of nucleus–nucleus collisions using a transport approach.The theoretical results of the dijet xJin the Xe+Xe collisions exhibit more imbalanced distributions than those in the p+p collisions,consistent with recently reported ATLAS data.By utilizing the Interleaved Flavor Neutralisation,an infrared-and-collinear-safe jet flavor algorithm,to identify the flavor of the reconstructed jets,we classify dijets processes into three categories:gluon–gluon (gg),quark–gluon (qg),and quark–quark (qq),and investigated the respective medium modification patterns and fraction changes of the gg,qg,and qq components of the dijet sample in Xe+Xe collisions.It is shown that the increased fraction of qg component at a small x_(J)contributes to the imbalance of the dijet;in particular,the q_(1)g_(2)(quark-jet-leading) dijets experience more significant asymmetric energy loss than the g_(1)q_(2)(gluon-jet-leading) dijets traversing the QGP.By comparing the■of inclusive,■ dijets in Xe+Xe collisions,we observe■.Moreover,ρ_(Xe),P_(b),the ratios of the nuclear modification factors of dijets in Xe+Xe to those in Pb+Pb,were calculated,which indicates that the yield suppression of dijets in Pb+Pb is more pronounced than that in Xe+Xe owing to the larger radius of the lead nucleus.

Jet Radius and Momentum Splitting Fraction with Dynamical Grooming in Heavy-Ion Collisions

We investigate the medium modifications of momentum splitting fraction and groomed jet radius with both dynamical grooming and soft drop algorithms in heavy-ion collisions.In the calculation,the partonic spectrum of initial hard scattering in p+p collisions is provided by the event generator PYTHIA8,and the energy loss of fast parton traversing in a hot/dense quantum-chromodynamic medium is simulated with the linear Boltzmann transport model.We predict the normalized distributions of the groomed jet radiusθ_(g)and momentum splitting fraction z_(g)with the dynamical grooming algorithm in Pb+Pb collisions at(sNN)~(1/2)=5.02 TeV,then compare these quantities in dynamical grooming at a=0.1,with that in soft drop at z_(out)=0.1 andβ=0.It is found that the normalized distribution ratios Pb+Pb/p+p with respect to z_(g)in z_(cut)=0.1,β=0 soft drop case are close to unity,those in a=0.1 dynamical grooming case show enhancement at small z_(g),and Pb+Pb/p+p with respect toθ_(g)in the dynamical grooming case demonstrate weaker modification than those in the soft drop counterparts.We further calculate the groomed jet number averaged momentum splitting fraction_(jets)and averaged groomed jet radius<θ_(g)>_(jets)in p+p and A+A for both grooming cases in three p_T~(ch jet)intervals,and find that the originally generated well balanced groomed jets will become more momentum imbalanced and jet size less narrowed due to jet quenching,and weaker medium modification of z_(g)andθ_(g)in the a=0.1 dynamical grooming case than in the soft drop counterparts.

Phenomenological study of the anisotropic quark matter in the two-flavor Nambu–Jona–Lasinio model

With the two-flavor Nambu–Jona–Lasinio (NJL) model, we carried out a phenomenological study on the chiral phase structure, mesonic properties, and transport properties of momentum-space anisotropic quark matter. To calculate the transport coefficients we utilized the kinetic theory in the relaxation time approximation, where the momentum anisotropy is embedded in the estimation of both the distribution function and relaxation time. It was shown that an increase in the anisotropy parameterξmay result in a catalysis of chiral symmetry breaking. The critical endpoint(CEP) is shifted to lower temperatures and larger quark chemical potentials asξincreases, and the impact of momentum anisotropy on the CEP temperature is almost the same as that on the quark chemical potential of the CEP. The meson masses and the associated decay widths also exhibit a significant ξ dependence. It was observed that the temperature behavior of the scaled shear viscosity η/T~3 and scaled electrical conductivity σ/T exhibited a similar dip structure, with the minima of both η/T~3 and σ/T shifting toward higher temperatures with increasing ξ. Furthermore,we demonstrated that the Seebeck coefficient S decreases when the temperature rises and its sign is positive, indicating that the dominant carriers for converting the temperature gradient to the electric field are up-quarks. The Seebeck coefficient S is significantly enhanced with a largeξfor a temperature below the critical temperature.

CEPC Technical Design Report

The Circular Electron Positron Collider(CEPC)is a large scientific project initiated and hosted by China,fostered through extensive collaboration with international partners.The complex comprises four accelerators:a 30 GeV Linac,a 1.1 GeV Damping Ring,a Booster capable of achieving energies up to 180 GeV,and a Collider operating at varying energy modes(Z,W,H,and tt).The Linac and Damping Ring are situated on the surface,while the subterranean Booster and Collider are housed in a 100 km circumference underground tunnel,strategically accommodating future expansion with provisions for a potential Super Proton Proton Collider(SPPC).The CEPC primarily serves as a Higgs factory.In its baseline design with synchrotron radiation(SR)power of 30 MW per beam,it can achieve a luminosity of 5×10^(34)cm^(-2)s^(-1)per interaction point(IP),resulting in an integrated luminosity of 13 ab^(-1)for two IPs over a decade,producing 2.6 million Higgs bosons.Increasing the SR power to 50 MW per beam expands the CEPC's capability to generate 4.3 million Higgs bosons,facilitating precise measurements of Higgs coupling at sub-percent levels,exceeding the precision expected from the HL-LHC by an order of magnitude.This Technical Design Report(TDR)follows the Preliminary Conceptual Design Report(Pre-CDR,2015)and the Conceptual Design Report(CDR,2018),comprehensively detailing the machine's layout,performance metrics,physical design and analysis,technical systems design,R&D and prototyping efforts,and associated civil engineering aspects.Additionally,it includes a cost estimate and a preliminary construction timeline,establishing a framework for forthcoming engineering design phase and site selection procedures.Construction is anticipated to begin around 2027-2028,pending government approval,with an estimated duration of 8 years.The commencement of experiments and data collection could potentially be initiated in the mid-2030s.

Z^(0)boson associated b-jet production in high-energy nuclear collisions

The production of vector boson tagged heavy quark jets potentially provides new tools to probe the jet quenching effect.In this paper,we present the first theoretical study on the angular correlations(ΔφbZ),transverse momentum imbalance(xbZ),and nuclear modification factor(IAA) of Z0boson tagged b-jets in heavy-ion collisions,which was performed using a Monte Carlo transport model.We find that the medium modification of theΔφbZfor Z0+b-jet has a weaker dependence on ΔφbZthan that for Z^(0)+jet,and the modification patterns are sensitive to the initial jet pTdistribution.Additionally,with the high purity of the quark jet in Z^(0)+(b-) jet production,we calculate the momentum imbalance xbZand the nuclear modification factor IAAof Z^(0)+b-jet in Pb+Pb collisions.We observe a smaller Δ<xjZ> and larger IAAof Z^(0)+b-jet in Pb+Pb collisions relative to those of Z^(0)+jet,which may be an indication of the mass effect of jet quenching and can be tested in future measurements.

Holographic energy loss near critical temperature in an anisotropic background

We study the energy loss of a quark moving in a strongly coupled quark gluon plasma under the influence of anisotropy.The heavy quark drag force,diffusion coefficient,and jet quenching parameter are calculated using the Einstein–Maxwell-dilaton model,where the anisotropic background is characterized by an arbitrary dynamical parameter A.Our findings indicate that as the anisotropic factor A increases,the drag force and jet quenching parameter both increase,while the diffusion coefficient decreases.Additionally,we observe that the energy loss becomes more significant when the quark moves perpendicular to the anisotropy direction in the transverse plane.The enhancement of the rescaled jet quenching parameters near critical temperature Tc,as well as drag forces for a fast-moving heavy quark is observed,which presents one of the typical features of quantum chromodynamics phase transition.

Hadron productions and jet substructures associated with Z^(0)/γ in Pb+Pb collisions at the LHC

We carry out a detailed study of medium modifications on Z^(0)/γ+hadron correlations as well as jet substructures in association with Z^(0)/γ in Pb+Pb collisions with √S_(NN)=5.02TeV at the LHC.We utilize the linear Boltzmann transport(LBT)model to simulate the jet-medium interactions and medium response,and an extended cluster hadronization model to investigate the nonperturbative transition of quarks and gluons into final hadrons in heavy-ion collisions.Including hadronization effect,we can well describe Z^(0)/γ+hadrons correlations and Z^(0)/γ-tagged jet substructures in both p+p and Pb+Pb collisions simultaneously.Medium modification on jet profile and jet fragmentation functions indicate that particles carrying a large fraction of the jet momentum are generally closely aligned with the jet axis,whereas low-momentum particles are observed to have a much broader angular distribution relative to jet axis in Pb+Pb collisions due to jet-medium interactions.In particular,we find that Z^(0)/γ-tagged hadron correlations are sensitive to the soft particles from the dense medium and medium response,while jet-substructures show weak dependence on those soft hadrons with only a fraction of them falling inside the jet area.

Transverse momentum balance and angular distribution of bb dijets in Pb+Pb collisions

In this study,the production of inclusive b-jet and bb dijets in Pb+Pb collisions has been investigated byconsidering the in-medium evolution of heavy and light quarks simultaneously.The initial hard processes of inclusiveb-jet and bb production are described using a next-to-leading order(NLO)plus parton shower Monte Carlo(MC)event generator,SHERPA,which can be well matched with the experimental data in p+p collisions.Theframework uses the Langevin transport model to describe the evolution of the bottom quark.Furthermore,the collisionalenergy loss and higher-twist description are considered to determine the radiative energy loss from both thebottom and light quarks.We compare the theoretical simulation of the inclusive jet and b-jet RAA in the Pb+Pb collisionsat√SNN=2:76 TeV with the experimental data and present the theoretical simulation of the momentum balanceof the bb dijet in the Pb+Pb collisions at 5.02 TeV along with recent CMS data for the first time.A similartrend to that seen in inclusive dijets is observed in bb dijets;the distribution of the production shifts to smaller xJ owingto the jet quenching effect.Finally,we report the prediction of the normalized azimuthal angle distribution of the bb dijet in the Pb+Pb collisions at 5.02 TeV.The medium-induced energy loss effect of the bb dijets will generallysuppress its production;however,the same side(ΔФ→0 region)suffers more energy loss than the far side(ΔФ→πregion),thus leading to suppression on the same side and enhancement on the far side in the normalized azimuthalangle distribution in A+A collisions.

Radial profile of bottom quarks in jets in high-energy nuclear collisions

Angular correlations between a heavy quark(HQ)and its tagged jet are potentially new tools to gain insight into the in-medium partonic interactions in relativistic heavy-ion collisions.In this work,we present the first theoretical study on the radial profiles of B mesons in jets in Pb+Pb collisions at the Large Hadron Collider(LHC).The initial production of a bottom quark tagged jet in p+p is computed by SHERPA,which matches the next-to-leading order matrix elements with contributions of parton showers,whereas the massive quark traversing the quark-gluon plasma is described by a Monte Carlo model,SHELL,which can simultaneously simulate light and heavy flavor in-medium energy loss within the framework of Langevin evolution.In p+p collisions,we find that at lower PQ/T the radial profiles of heavy flavors in jets are sensitive to the heavy quark mass.In 0-10%Pb+Pb collisions at√SNN=5.02 TeV,we observe an inverse modification pattern of the B meson radial profiles in jets at4PQ/T<20 GeV compared to those of D mesons:the jet quenching effects narrow the jet radial profiles of B mesons in jets while broadening those of D mesons in jets.We find that in A+A collisions,the contribution dissipated from the higher PQ/T>20 GeV region naturally has a narrower initial distribution and consequently leads to a narrower modification pattern of the radial profile;however the diffusion nature of the heavy flavor in-medium interactions will give rise to a broader modification pattern of the radial profile.These two effects consequently compete and offset with each other,and the b quarks in jets benefit more from the former and suffer less diffusion effect compared to that of c quarks in jets.These findings can be tested in the future experimental measurements at the LHC to gain better understanding of the mass effect of jet quenching.

Particle production at large p_(T) in Xe+Xe collisions with jet quenching using the higher twist approach

The production of π^(0),η,andφin the most central(0%-5%)Xe+Xe collisions at √s_(NN)=5.44 TeV is investigated in the framework of the perturbative QCD(pQCD)improved parton model at an accuracy of next-toleading order(NLO).The jet quenching effect is effectively incorporated by medium-modified fragmentation functions via the higher-twist approach.Predictions of the nuclear modification factors of π^(0),η,and φ as functions of the transverse momentum p_(T) are made with the jet transport parameter q_(0),which is extracted from the available experimental data of charged hadrons provided by ALICE and CMS.The particle ratios η/π^(0),φ/π^(0) as functions of p_(T) in Xe+Xe collisions at √s_(NN)=5.44 TeV as well as in 0%-5% Pb+Pb collisions at √s_(NN)=5.02 TeV are also presented.The numerical simulations of the scaled ratios of charged hadron production in the Xe+Xe 5.44 TeV system over those in the Pb+Pb 5.02 TeV system give a good description of the CMS data,and the scaled ratios of π^(0),η,and φ production coincide with the curve of charged hadron production.

p_(T) dispersion of inclusive jets in high-energy nuclear collisions

In this study,we investigate the impact of jet quenching on the p_(T) dispersion(p_(T)D)of inclusive jets(R=0.2)in central Pb+Pb(0%-10%)collisions at √s=2.76 TeV.The partonic spectrum in the initial hard scattering of elementary collisions is obtained by an event generator POWHEG+PYTHIA,which matches the next-to-leading order(NLO)matrix elements with parton showering,and the energy loss of a fast parton traversing through hot/dense QCD medium is calculated using Monte Carlo simulation within the Higher-Twist formalism of jet quenching in heavy-ion collisions.We present model calculations of the normalized p_(T)D distributions of inclusive jets in p+p and central Pb+Pb collisions at √s=2.76 TeV,which offer good descriptions of ALICE measurements.It is shown that the p_(T)D distributions of inclusive jets in central Pb+Pb collisions shift significantly to a higher p_(T)D region relative to those in p+p collisions.Thus,the nuclear modification ratio of the p_(T)D distributions of inclusive jets is smaller than unity in the small p_(T)D region and larger than one in the large p_(T)D region.This behavior is caused by a more uneven p_(T) distribution for jet constituents as well as the fraction alteration of quark/gluon initiated jets in heavy-ion collisions.The difference in p_(T)D distribution between groomed and ungroomed jets in Pb+Pb collisions is also discussed.

Probing cold nuclear matter effects with th e productions of isolated-γ and γ+jet in p+Pb collisions at (sNN)^(1/2)= 8.16 TeV

We investigate cold nuclear matter(CNM) effects on the productions of isolated prompt photons and +jet in proton-lead collisions at 8.16 TeV under next-to-leading order perturbative quantum chromodynamics calculations with four parameterizations for nuclear parton distribution functions(nPDFs), i.e., DSSZ, EPPS16, nCTEQ15, and nIMParton. Our theoretical calculations provide good descriptions of the pp baseline in the ATLAS collaboration and make predictions for future experimental results at p+Pb collisions. We calculate the dependence of the nuclear modification factor of isolated prompt photons on transverse momentum pу/T and pseudo-rapidity η~у at very forward and backward rapidity regions, and we demonstrate that the forward-to-backward yield asymmetries Yasym/pPb as a function of pу/T with different nPDF parameterizations have diverse behaviors. Furthermore, the nuclear modification factor of isolated-у+jet RуJet/pPb as a function of у+jet's pseudo-rapidity η_(уJet)=1/2(η_у+η_(Jet)) at different average transverse momenta pavg/T=1/2(pу/T+pJet/T) has been discussed. This can facilitate a tomographic study of CNM effects with precis locations in a rather wide kinematic region by varying the transverse momenta and rapidities of both isolated photons and jets in p+A collisions.

Physics perspectives of heavy-ion collisions at very high energy

Heavy-ion collisions at very high colliding energies are expected to produce a quark-gluon plasma(QGP) at the highest temperature obtainable in a laboratory setting. Experimental studies of these reactions can provide an unprecedented range of information on properties of the QGP at high temperatures. We report theoretical investigations of the physics perspectives of heavy-ion collisions at a future high-energy collider. These include initial parton production, collective expansion of the dense medium, jet quenching,heavy-quark transport, dissociation and regeneration of quarkonia, photon and dilepton production. We illustrate the potential of future experimental studies of the initial particle production and formation of QGP at the highest temperature to provide constraints on properties of strongly interaction matter.

Effect of momentum anisotropy on quark matter in the quark-meson model

We investigate the chiral phase structure of quark matter with spheroidal momentum-space anisotropy specified by one anisotropy parameter ξ in the 2+1 flavor quark-meson model.We find that the chiral phase diagram and the location of the critical endpoint(CEP) are significantly affected by the value of ξ.With an increase inξ,the CEP is shifted to lower temperatures and higher quark chemical potentials.In addition,the temperature of the CEP is more sensitive to the anisotropy parameter than the corresponding quark chemical potential,which is the opposite to that from the finite system volume effect.The effects of the momentum anisotropy on the thermodynamic properties and scalar(pseudoscalar) meson masses are also studied at the vanishing quark chemical potential.The numerical results reveal that an increase in ξ can hinder the restoration of chiral symmetry.We also find that shear viscosity and electrical conductivity decrease as ξ increases.However,the bulk viscosity exhibits a significant nontrivial behavior with ξ in the entire temperature domain of interest.

Jet charge in high-energy nuclear collisions

The averaged jet charge characterizes the electric charge of the initiating parton and provides a powerful tool to distinguish quark jets from gluon jets.We predict,for the first time,the medium modification of the averaged jet charge in the heavy-ion collisions at the LHC,where jet productions in p+p collisions are simulated by PYTHIA6,and the parton energy loss in QGP is calculated with two Monte Carlo models of jet quenching:PYQUEN and JEWEL.We found that the distribution of averaged jet charge is significantly suppressed by initial state isospin effects due to the participation of neutrons with zero electric charge during nuclear collisions.The considerable enhancement of the averaged jet charge in central Pb+Pb collisions is observed relative to peripheral collisions,since the jet quenching effect is more pronounced in central collisions.The distinct feature of the averaged jet charge between quark and gluon jets,along with the sensitivity of medium modifications on the jet charge to flavor dependence of the parton energy loss,could be very useful to discriminate the energy loss pattern between quark and gluon jets in heavy-ion collisions.