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.     

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.     

J/ψ-N center of mass energy dependence of nuclear absorption effect on J/ψ production

In this paper, the J/ψ nuclear absorption effect is studied at RHIC and LHC energies with the EKS98 shadowing parameterizations. By assuming that the J/ψ absorption cross section, σ abs , increases with the charmonium-nucleon （J/ψ-N） center of mass energy, s J/ψN , it is found that σ abs should depend on x F （or y） at a certain center of mass energy per nucleon pair,s , especially at LHC energies. The theoretical results with the x F （or y）-dependence of the absorption effect are in good agreement with the experiment data from PHENIX in d-Au collisions and the predicted results will be examined by the forthcoming experimental data from LHC in d-Pb collisions. Finally, we also present baseline calculations of cold nuclear matter effects on J/ψ production in nucleus-nucleus （A-A） collisions and find that the x F （or y）-dependence of absorption effect is very small at both RHIC and LHC energies in A-A collisions.     

J/ψ Production in Ultra-Peripheral pp Collisions through aTwo-Photon Process

Using the photon spectrum of a high energy charged patton, we investigate the J/ψ production via the two photon interaction mechanism in ultra-peripheral pp collisions. It is shown that the contributions from the direct electromagnetic and the corresponding fragmentation processes are meaningful for the J/ψ productions in ultra-peripheral pp collisions at LHC energy.     

J/ψ-N center of mass energy dependence of nuclear absorption effect on J/ψ production

In this paper, the J/ψ nuclear absorption effect is studied at RHIC and LHC energies with the EKS98 shadowing parameterizations. By assuming that the J/ψ absorption cross section, σ abs , increases with the charmonium-nucleon (J/ψ-N) center of mass energy, s J/ψN , it is found that σ abs should depend on x F (or y) at a certain center of mass energy per nucleon pair,s , especially at LHC energies. The theoretical results with the x F (or y)-dependence of the absorption effect are in good agreement with the experiment data from PHENIX in d-Au collisions and the predicted results will be examined by the forthcoming experimental data from LHC in d-Pb collisions. Finally, we also present baseline calculations of cold nuclear matter effects on J/ψ production in nucleus-nucleus (A-A) collisions and find that the x F (or y)-dependence of absorption effect is very small at both RHIC and LHC energies in A-A collisions.     

Energy loss of charm quarks from J/ψ production in cold 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/ψproduction cross-section ratios RW/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 RW/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 Ge V/fm, which indicates that the heavy quark in cold nuclear matter can lose more energy compared to the outgoing light quark.     

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.     

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.     

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.     

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.     

Determination of the number of J/ψ events with inclusive J/ψ decays

A measurement of the number of J/ψ events collected with the BESⅢ detector in 2009 and 2012 is performed using inclusive decays of the J/ψ. The number of J/ψ events taken in 2009 is recalculated to be(223.7±1.4)×10~6, which is in good agreement with the previous measurement, but with significantly improved precision due to improvements in the BESⅢ software. The number of J/ψ events taken in 2012 is determined to be(1086.9±6.0)×10~6. In total, the number of J/ψ events collected with the BESⅢ detector is measured to be(1310.6±7.0)×106, where the uncertainty is dominated by systematic effects and the statistical uncertainty is negligible.     

A modified explanation of cold nuclear matter effects on J/ψ production in p+A collisions

A modified explanation of the cold nuclear matter(CNM) effects on J/ψ production in p+A collisions is presented in this paper.The advantage of the modified explanation is that all the CNM effects implemented in this model have clear physical origins and are mostly centered on the idea of multiple parton scattering.With the CNM effects presented in this paper, we calculated the nuclear modification factor Rp A in J/ψ production under different collision energies.The results are compared with the corresponding experiment data and the factors calculated with classic nuclear effects.The factors calculated with CNM effects presented in this paper can accurately reproduce almost all existing J/ψ measurements in p-A collisions, which is much better than results obtained with the factors calculated with classic nuclear effects.The new model is therefore a more suitable approach to explain CNM effects in the hardproduction of quarkonium.     

The Monte Carlo Generator for J／ψ Decays with Angular Distribution

We present a Monte Carlo scheme to generate events of J/ψ decays with angular distributions based on the acceptance-rejection sampling method. We test this scheme with J/ψ → pp and J/ψ → ∧∧ → ppπ^ π^-, and the results show that the input angular distributions are well reproduced, and efficiency of the HOWL generator of this scheme is also discussed.     

J/ψ→μ^＋μ^- reconstruction in the CMS experiment

In this paper the J/ψ→μ^＋μ^- reconstruction performance in the CMS experiment at the LHC is studied in detail by using B8→J/ψφ→μμKK events. The reconstruction efficiencies of J/ψ mesons and their decay muons are obtained as a function of the transverse momentum PT and the pseudo-rapidity η. We also study the muon trigger efficiency for this channel with the planned Level-1 trigger and High Level Trigger selection criteria. It was observed that the muon reconstruction efficiency decreases when the two decay muons have a small or large 3D angular separation, which further affects the overall J/ψ reconstruction efficiency.     

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

We study the m J/ψ pair production issue at the Fermilab Tevatron Run II with a center-of-mass energy of √s=1.96 TeV. Both the color-singlet and color-octet production mechanisms are considered. Our results show that the transverse momentum (p_T) scaling behaviors of the double m J/ψ differential cross-sections in the color-singlets and color-octets deviate distinctively from each other while p_T is larger than 8 GeV, and with a luminosity of 5 fb^-1, the m 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.     

粲夸克对在质子-原子核碰撞J/ψ 产生过程中的能量损失

高能重离子碰撞热核环境中J/ψ产额的压低被认为是夸克胶子等离子体生成的重要信号。研究冷核物质中各种核效应对J/ψ 形成过程的影响,是准确理解热核环境中核效应对J/ψ产额压低机制的重要途径。研究了质子-原子核碰撞J/ψ 产生过程中初态部分子分布函数的核效应、入射质子的能量损失效应、以及末态粲夸克对能量损失效应对J/ψ 粒子产额的压低作用,对质子-原子核碰撞J/ψ产生过程的微分截面比R_Fe/Be(xF)进行了领头阶的唯象分析,并与E866 实验数据中代表J/ψ粒子在靶核外产生的实验数据进行比较,获取了粲夸克对的能量损失值(3.81±1.71) GeV/fm。研究结果表明,部分子分布函数的核效应对截面比RFe=Be(xF) 的压低作用在xF > 0区域是随着xF 的增大而增大的;末态粲夸克对的能量损失效应是影响J= 粒子产额压低的重要核效应;当xF较大时(0:65≤xF≤0.92),初态入射质子的能量损失效应在对微分截面比R_Fe/Be(xF)的压低中起了主要作用。J/ψ suppression observed in hot nuclear matter from heavy-ion collisions is considered as a most reliable signature for the formation of Quark-Gluon Plasma. The study about the nuclear effects on J/ψ production in cold nuclear matter provides an important tool for clarifying the conventional nuclear suppression mechanism in heavy-ion collisions. J/ψ suppression in p-A collisions is studied by considering the nuclear effects on parton distribution, the energy loss of beam proton in initial state, and the finial state energy loss of c¯c pair.The leading-order computations for J/ψ production cross-section ratios RFe=Be(xF) are presented and compared with the selected E866 experimental data with the J/ψ production occurring outside the nucleus, the obtained energy loss of the color octet is (3.81±1.71) GeV/fm. It is found that the nuclear suppression from the nuclear effects on the parton distribution functions becomes larger as the increase of xF in the range xF > 0,the J/ψ suppression on R_Fe/Be(xF) induced by the energy loss of color octet c¯c is an important nuclear effect, in the region 0:656xF 60:92, the energy loss of beam proton in initial state is the dominant mechanism which causes a reduction of the J/ψ yield.     

J/ψ→μ+μ- reconstruction in the CMS experiment

In this paper the J/ψ→μ+μ- reconstruction performance in the CMS experiment at the LHC is studied in detail by using B5→ J/ψψ →μμКК events. The reconstruction efficiencies of J/ψ mesons and their decay muons are obtained as a function of the transverse momentum PT and the pseudo-rapidity η. We also study the muon trigger efficiency for this channel with the planned Level-1 trigger and High Level Trigger selection criteria. It was observed that the muon reconstruction efficiency decreases when the two decay muons have a small or large 3D angular separation, which further affects the overall J/ψ reconstruction efficiency.     

Double Diffractive Process Factorization from ηc and γ Associated Production at Tevatron and LHC

We present a study of associated ηc and γ double diffractive production in p-p collision based on Ingelman-Schlein model, and the framework of non-relativistic QCD factorization formalism for quarkonia production. The predic-tion of ηc and γ is more reliable than J/ψ production, because the associated ηc and γ production is a pure color-octetprocess, and the dominant contribution comes from color octet 1So(8) subprocess, which is related to the color octet matrixelement of 1So(8) of J/ψ by the heavy quark spin symmetry and the large PT J/ψ production data. We find that the ratioof diffractive to inclusive cross sections is independent of the values of color octet matrix elements, but is sensitive to thegluon factor of the Pomeron and renormalized Pomeron flux factors. So experimental measurement of this ratio can giveus more information of the nature of Pomeron and test the assumption of hard diffractive factorization in hadron-hadron collisions.