J/ψ pair production at the Tevatron with s1/2=1.96 TeV

We study the J/ψ pair production issue at the Fermilab Tevatron Run II with a center-of-mass energy of s^1/2=1.96TeV. Both the color-singlet and color-octet production mechanisms are considered. Our results show that the transverse momentum （pT） scaling behaviors of the double J/ψ differential cross-sections in the color-singlets and color-octets deviate distinctively from each other while pT is larger than 8GeV, and with a luminosity of 5fb^-1 , the J/ψ pair events from the color-singlet scheme are substantially measurable in the Tevatron experiments, even with a certain lower transverse momentum cut. Hence the Tevatron is still a possible platform to check the heavy quarkonium production mechanism.     

Exploring J/ψ Production Mechanism at the Future Electron-Ion Collider

We propose to use transverse momentum p_T distribution of J/ψ production at the future Electron Ion Collider(EIC) to explore the production mechanism of heavy quarkonia in high energy collisions.We apply QCD and QED collinear factorization to the production of a cc pair at high p_T,and non-relativistic QCD factorization to the hadronization of the pair to a J/ψ.We evaluate J/ψ p_T-distribution at both leading and next-to-leading order in strong coupling,and show that production rates for various color-spin channels of a cc pair in electronhadron collisions are very different from that in hadron-hadron collisions,which provides a strong discriminative power to determine various transition rates for the pair to become a J/ψ.We predict that the J/ψ produced in electron-hadron collisions is likely unpolarized,and the production is an ideal probe for gluon distribution of colliding hadron(or nucleus).We find that the J/ψ production is dominated by the color-octet channel,providing an excellent probe to explore the gluon medium in large nuclei at the EIC.     

Centrality dependence of pT spectra for identified hadrons in Au+Au and Cu+Cu collisions at √sNN= 200GeV

The centrality dependence of transverse momentum spectra for identified hadrons at midrapidity in Au+Au collisions at √s_NN= 200GeV is systematically studied in a quark combination model. The p_T spectra of π^±, K^±, p(p) and Λ(Λ) in different centrality bins and the nuclear modification factors (R_CP) for these hadrons are calculated. The centrality dependence of the average collective transverse velocity 〈β(r)〉 for the hot and dense quark matter is obtained in Au+Au collisions, and it is applied to a relative smaller Cu+Cu collision system. The centrality dependence of p_T spectra and the R_CP for π⁰, K_s⁰ and Λ in Cu+Cu collisions at √s_NN= 200GeV are well described. The results show that 〈β(r)〉 is only a function of the number of participants N_part and it is independent of the collision system.     

O(α_sv~2) correction to J/ψ plus η_c production in e~+e~- annihilation at √s=10.6 GeV

Based on the nonrelativistic QCD factorization approach, O(α_sv2) corrections to J/ψ plus η_c production in m e⁺e^- annihilation at √s=10.6 ≥v are calculated in this work. The numerical results show that the correction at α_sv2 order is only about a few percent of the total theoretical result. This indicates that the perturbative expansions become convergent and that a higher order correction will be smaller. The uncertainties from the long-distance matrix elements, renormalization scale and the measurement in the experiment are also discussed. Our result is in agreement with the previous result by Jia.     

Transverse momentum spectra in high-energy nucleus-nucleus, proton-nucleus and proton-proton collisions

The transverse momentum distributions of final-state particles produced in nucleus-nucleus (AA), proton-nucleus (pA), and proton-proton (pp) collisions at high energies are investigated using a multisource ideal gas model. Our calculated results show that the contribution of hard emission can be neglected in the study of transverse momentum spectra of charged pions and kaons produced in Cu-Cu collisions at √s_NN=22.5 GeV. And if we consider the contribution of hard emission, the transverse momentum spectra of p and p produced in Cu-Cu collisions at √s_NN=22.5 GeV, K_s⁰ produced in Pb-Pb collisions at 158 A GeV, J/ψ particles produced in p-Pb collisions at 400 GeV and π⁺ , K⁺, p produced in proton-proton collisions at √s=200 GeV, can be described by the model, especially in the tail part of spectra.     

NaI （Tl） calorimeter calibration and simulation for Coulomb sum rule experiment in Hall-A at Jefferson Lab

A precision measurment of inclusive electron scattering cross sections is carried out at Jefferson Lab in the quasi-elastic region for ⁴He, ¹²C, ⁵⁶Fe and ²⁰⁸Pb targets. The longitudinal (R_L) and transverse (R_T) response functions of the nucleon need to be extracted precisely in the momentum transfer range 0.55 GeV/c≤|q|≤1.0 GeV/c. To achieve the above goal, a NaI (Tl) calorimeter is used to distinguish good electrons from background, including pions and low energy electrons rescattered from the walls of the spectrometer magnets. Due to a large set of kinematics and changes in HV settings, a number of calibrations are performed for the NaI (Tl) detector. Corrections for a few blocks of NaI (Tl) with bad or no signal are applied. The resolution of the NaI (Tl) detector after calibration reached (δE)/√E ≈ 3% at E=1 GeV. The performance of the NaI (Tl) detector is compared with a simulation. The good calibration and background analysis for the NaI(Tl) detector are very important for the reduction of the systematic error of cross sections and the separation of R_L and R_T.     

Energy loss of charm quarks from J/ψ production incold nuclear matter

J/ψ suppression in p-A collisions is studied by considering the nuclear effects on parton distribution, energy loss of beam proton and the finial state energy loss of color octet cc. The leading-order computations for J/ψ production cross-section ratios R_W/Be(x_F) are presented and compared with the selected E866 experimental data with the cc remaining colored on its entire path in the medium. It is shown that the combination of the different nuclear effects accounts quite well for the observed J/ψ suppression in the experimental data. It is found that the J/ψ suppression on R_W/Be(x_F) from the initial state nuclear effects is more important than that induced by the energy loss of color octet cc in the large x_F region. Whether the cc pair energy loss is linear or quadratic with the path length is not determined. The obtained cc pair energy loss per unit path length α=2.78±0.81 GeV/fm, which indicates that the heavy quark in cold nuclear matter can lose more energy compared to the outgoing light quark.     

Projectile fragment emission in the fragmentation of ~(56)Fe on C,Al and CH_2 targets at 471 A MeV

The emission angle and the transverse momentum distributions of projectile fragments produced in the fragmentation of ⁵⁶Fe on CH₂, C and Al targets at 471 A MeV are measured. It is found that for the same target, the average value and width of the angular distribution decrease with an increase of the projectile fragment charge; for the same projectile fragment, the average value of the distribution increases and the width of the distribution decreases with increasing the target charge number. The transverse momentum distribution of a projectile fragment can be explained by a single Gaussian distribution and the averaged transverse momentum per nucleon decreases with the increase of the charge of projectile fragment. The cumulated squared transverse momentum distribution of a projectile fragment can be explained well by a single Rayleigh distribution. The temperature parameter of the emission source of the projectile fragment, calculated from the cumulated squared transverse momentum distribution, decreases with the increase of the size of the projectile fragment.     

π-J/ψ correlation and elliptic flow parameter v2 of charmed mesons at RHIC energy

We study the correlation between the trigger π and the associated J/ψ on near and away sides in Au+Au collisions at √s_NN=200 GeV. In the region of trigger momentum p_t>4 GeV/c, the π spectrum is composed of thermal-shower and shower-shower recombinations in the frame work of the recombination model. We consider the azimuthal anisotropy in the quenched hard parton distribution and then calculate the elliptic flow parameter v₂ of charmed mesons (J/ψ, D⁰ and D_s) for different centralities.     

Photoproduction of J/ψ in non-single-diffractive p+p collisions

Significant enhancements of J/ψ production at very low transverse momenta were recently observed by the ALICE and STAR collaborations in peripheral hadronic A+A collisions. The anomalous excess points to coherent photon-nucleus interactions in violent hadronic heavy-ion collisions, which were conventionally studied only in ultra-peripheral collisions. Assuming that the coherent photoproduction is the underlying mechanism responsible for the excess observed in peripheral A+A collisions, its contribution in p+p collisions with nuclear overlap, i.e. nonsingle-diffractive collisions, is of particular interest. In this paper, we perform a calculation of exclusive J/ψ photoproduction in non-single-diffractive p+p collisions at the RHIC and LHC energies based on the pQCD motivated parametrization using the world-wide experimental data, which could be further employed to improve the precision of the phenomenological calculations for photoproduction in A+A collisions. The differential rapidity and transverse momentum distributions of J/ψ from photoproduction are presented. In comparison with the J/ψ production from hadronic interactions, we find that the contribution of photoproduction is negligible.     

Nuclear modification factor for J/ψ production in nucleus-nucleus collisions

The STAR Collaboration has offered an eminent nuclear modification factor of J/ψ at high p_T and midrapidity produced in Cu-Cu collisions at √s_NN=200 GeV. Recalling a prediction, we can understand that the feature of high-p_T nuclear modification factor is related to cc produced by 2 → 1 and 2 → 2 partonic processes in deconfined matter, particularly in the prethermal stage and to the recombination of c and c. The nuclear modification factor at high p_T is sensitive to the earliest form of deconfined matter that does not have a temperature.     

Cold nuclear matter effects on J/ψ production in d-Au collisions

The medium modifications of J/ψ production in d-Au collisions at √s_NN=200 GeV are studied in the Glauber model. By means of the c.m. energy loss parameter per collision studied in Drell-Yan process, taking account of the inhomogeneous shadowing effect, we find that the initial-state energy loss effect can be ignored in d-Au collisions at mid-rapidity. Then, the final-state J/ψ absorption effect is also considered and the theoretical results are in good agreement with the recent experimental data given by PHENIX. Finally, the experimental results of J/ψ production in d-Pb collisions are also predicted at RHIC and LHC energies respectively.     

Simulation of energy scan of pion interferometry in central Au+Au collisions at relativistic energies

We present a systematic analysis of two-pion interferometry for the central Au+Au collisions at √s_NN=3, 5, 7, 11, 17, 27, 39, 62, 130 and 200 GeV/c with the help of a multiphase transport (AMPT) model. Emission source-size radius parameters R_long, R_out, R_side and the chaotic parameter λ are extracted and compared with the experimental data. Transverse momentum and azimuthal angle dependencies of the HBT radii are also discussed for central Au+Au collisions at 200 GeV/c. The results show that the HBT radii in central collisions do not change much above 7 GeV/c. For central collisions at 200 GeV/c, the radii decrease with the increasing of transverse momentum p_T but are not sensitive to the azimuthal angle. These results provide a theoretical reference for the energy scan program of the RHIC-STAR experiment.     

Emissions of fragments and mesons produced in heavy-ion collisions at CSR and related energies

Using a multisource ideal gas (MSIG) model, we reconstruct the transverse emission source in the momentum space for light fragments produced in reactions ⁸⁶Kr-¹²⁴Sn at 25 MeV/nucleon and b=7—10 fm based on the theoretical predictions of the Isospin-Dependent Quantum Molecular Dynamics (IDQMD) model. We show that the MSIG model can reasonably describe the IDQMD-predicted results for the azimuthal distribution and the transverse momentum dependence of elliptic flow v₂ and fourth-order anisotropic flow v₄ but can only qualitatively describe the transverse momentum spectra. The azimuthal distributions of nuclear fragments produced in heavy-ion collisions at intermediate energies are studied by the MSIG model. The calculated results are compared and found to be in agreement with the experimental data of Ca-Ca, Nb-Nb, and Au-Au collisions at 150—800 MeV/nucleon beam energies. Meanwhile, the angular distributions of pions and kaons produced in heavy-ion collisions at the low-energy end (1—2 GeV/nucleon) of high energies are investigated by the MSIG model, too. The calculated results are compared and found to be in agreement with the experimental data of the KaoS Collaboration.     

J/ψ Inclusive Photon Spectrum at BESIII

With a 15M J/ψ inclusive Monte Carlo sample, the absolute branching fraction of J/ψ→γ\η' from the J/ψ inclusive photon spectrum is measured to be Br(J/ψ→γ\η')=(4.68±0.08±0.27)×10^-3, which is in good agreement with the input value. The J/ψ→γf_J(2220) is also searched for using the same sample. Under our assumptions, the statistical significances of J/ψ→γf_J(2220) are larger than 7\σ.     

Drell-Yan dilepton production in relativistic heavy-ion collisions at RHIC

We investigate the lepton pair production with the Drell-Yan process in relativistic heavy ion collisions by computing the double differential cross section dσ/dM²dy and dσ/dM²dx_F at the next-to-leading order in p+Au and Au+Au collisions with √s_NN =200 GeV at RHIC. The resulting nuclear modification factors R^pAu and R^AuAu show strong sensitivity to the cold nuclear matter (CNM) effects and could probe the CNM effects at a very wide region of the longitudinal momentum fraction x. The variation of R with the invariant mass M, the rapidity y and the Feynman variable x_F is shown and we find that the nuclear modification factor for the double differential cross section could be smaller than 0.4 in some kinematic regions of high-energy nucleus-nucleus reactions at RHIC.     

Temperature dependence of quarks and gluon vacuum condensate in the Dyson-Schwinger Equations at finite temperature

Based on the Dyson-Schwinger Equations (DSEs), the two-quark vacuum condensate, the four-quark vacuum condensate, and the quark gluon mixed vacuum condensate in the non-perturbative QCD vacuum state are investigated by solving the DSEs with rainbow truncation at zero- and finite-temperature, respectively. These condensates are important input parameters in QCD sum rule with zero and finite temperature, and in studying hadron physics, as well as predicting the quark mean squared momentum m₀²-also called quark virtuality in the QCD vacuum state. The present calculated results show that these physical quantities are almost independent of the temperature below the critical point temperature T_c=131 MeV, and above T_c the chiral symmetry is restored. For comparison we calculate the temperature dependence of the "in-hadron condensate" for pion. At the same time, we also calculate the ratio of the quark gluon mixed vacuum condensate to the two-quark vacuum condensate by using these condensates, and the unknown quark mean squared momentum in the QCD vacuum state has been obtained. The results show that the ratio m₀²(T) is almost flat in the temperature region from 0 to T_c, although there are drastic changes of the quark vacuum condensate and the quark gluon mixed vacuum condensate at the region. Our predicted ratio comes out to be m₀²(T)=2.41 GeV² at the Chiral limit, which is consistent with other theory model predictions, and strongly indicates the significance that the quark gluon mixed vacuum condensate has played in the virtuality calculations.     

Perturbative QCD for J/ψ inclusive production via initial state radiation in e~+e~- collisions

The process e+e-→J/ψ+X with the center-of-mass(CM)energy in the range from 3.7 to 10.6 GeV is calculated up to the next-to-leading order(NLO)in quantum chromodynamics(QCD).At 10.6 GeV,the result is consistent with the experimental result from Belle.However,the predictions are much smaller than the background in the measurements at BESIII in the low CM energy range from 3.7 to 4.6 GeV.This indicates that the convergence of the QCD perturbative expansion becomes worse as the CM energy is closer to the inclusive J/ψ production threshold.For a further study of the QCD mechanism of J/ψ production in e~+e~-collisions with different CM energies,the initial state radiation effect of e~+e~-→J/ψ +gg and e~+e~-→J/ψ+cc are calculated in QCD NLO.The results are plotted and the number of events for different CM energy bins are provided for SuperKEKB.This provides a method to precisely test the validity of perturbative predictions for J/ψ production in future measurements.     

Thermal production of charmonia in Pb-Pb collisions at (sNN)~(1/2)= 5.02 TeV

This work uses the Boltzmann transport model to study the thermal production of J/ψ and ψ(2S) in the quark gluon plasma(QGP) produced by (sNN)~(1/2)=5.02 TeV Pb-Pb collisions.The J/ψ nuclear modification factors are studied in detail alongside the mechanisms of primordial production and the recombination of charm and anti-charm quarks in the thermal medium.The ψ(2S) binding energy is much smaller in the hot medium compared to the ground state;thus,ψ(2S) with middle to low p_T can be thermally regenerated in the later stages of QGP expansions,enabling ψ(2S) to inherit larger collective flows from the bulk medium.We quantitatively study the nuclear modification factors of both J/ψ and ψ(2S) in different centralities and transverse momentum bins for (sNN)~(1/2)=5.02 TeV PbPb collisions.