Color Evaporation Model Research Articles

Quarkonium production in high energy proton-nucleus collisions: CGC meets NRQCD

We study the production of heavy quarkonium states in high energy proton-nucleus collisions. Following earlier work of Blaizot, Fujii, Gelis, and Venugopalan, we systematically include both small $x$ evolution and multiple scattering effects on heavy quark pair production within the Color Glass Condensate (CGC) framework. We obtain for the first time expressions in the Non-Relativistic QCD (NRQCD) factorization formalism for heavy quarkonium differential cross sections as a function of transverse momentum and rapidity. We observe that the production of color singlet heavy quark pairs is sensitive to both "quadrupole" and "dipole" Wilson line correlators, whose energy evolution is described by the Balitsky-JIMWLK equations. In contrast, the color octet channel is sensitive to dipole correlators alone. In a quasi-classical approximation, our results for the color singlet channel reduce to those of Dominguez et. al. [1]. We compare our results to those obtained combining the CGC with the color evaporation model and point to qualitative differences in the two approaches.

Heavy quarkonium production in a strong magnetic field

It is well known that in noncentral heavy-ion collisions a transient strong magnetic field is generated in the direction perpendicular to the reaction plane. The maximal strength of this field is estimated to be $eB \sim m^2_{\pi} \sim 0.02 \text{GeV}^2$ at the RHIC and $eB \sim 15 m^2_{\pi} \sim 0.3 \text{GeV}^2$ at the LHC. We investigate the effects of a strong magnetic field on $B$ and $D$ mesons, focusing on the changes of the energy levels and the masses of the bound states. Using the Color Evaporation Model we discuss the possible changes in the production of $J/\psi$ and $\Upsilon$.

Improving the J/ψ Production Baseline at RHIC and the LHC

Abstract We assess the theoretical uncertainties on the inclusive J / ψ production cross section in the Color Evaporation Model (CEM) using values for the charm quark mass, renormalization and factorization scales obtained from a fit to the charm production data. We use our new results to provide improved baseline comparison calculations at RHIC and the LHC. We also study cold matter effects on J / ψ production at leading relative to next-to-leading order in the CEM within this approach.

Transverse single spin asymmetry ine+p↑→e+J/ψ+Xand transverse momentum dependent evolution of the Sivers function

We extend our analysis of transverse single spin asymmetry in electroproduction of $J/\ensuremath{\psi}$ to include the effect of the scale evolution of the transverse momentum dependent (TMD) parton distribution functions and gluon Sivers function. We estimate single spin asymmetry for JLab, HERMES, COMPASS, and eRHIC energies using the color evaporation model of charmonium production, using an analytically obtained approximate solution of TMD evolution equations discussed in the literature. We find that there is a reduction in the asymmetry compared with our predictions for the earlier case considered by us, wherein the ${Q}^{2}$ dependence came only from DGLAP evolution of the unpolarized gluon densities and a different parametrization of the TMD Sivers function was used.

Heavy quark pair production in high-energy pA collisions: Quarkonium

Quarkonium production in high-energy proton (deuteron)–nucleus collisions is investigated in the color glass condensate framework. We employ the color evaporation model assuming that the quark pair produced from dense small-x gluons in the nuclear target bounds into a quarkonium outside the target. The unintegrated gluon distribution at small Bjorken x in the nuclear target is treated with the Balitsky–Kovchegov equation with running coupling corrections. For the gluons in the proton, we examine two possible descriptions, unintegrated gluon distribution and ordinary collinear gluon distribution. We present the transverse momentum spectrum and nuclear modification factor for J/ψ production at RHIC and LHC energies, and those for ϒ(1S) at LHC energy, and discuss the nuclear modification factor and the momentum broadening by changing the rapidity and the initial saturation scale.

MARTINI event generator for heavy quarks: Initialization, parton evolution, and hadronization

We present additions to the MARTINI event generator for examining heavy quarks and quarkonia in heavy-ion collisions. All stages of a heavy-ion collision affect the observables associated with heavy quarks: the initial phase space of the heavy quarks are sampled with pythia8.1, the heavy quarks are evolved using Langevin dynamics and a 3+1-dimensional hydrodynamical description of the heavy-ion collision, and are fragmented and hadronized using a modified version of the color evaporation model that takes into account nontrivial evolution in position space, as well as the possibility of recombinant quarkonium production in heavy-ion collisions. We use this to re-examine the production of quarkonium at the Relativistic Heavy Ion Collider (RHIC), and anticipating vertex detection we predict yields of ${B}_{c}$ mesons at RHIC and the Large Hadron Collider.

Sivers effect and transverse single spin asymmetry ine+p↑→e+J/ψ+X

We discuss the possibility of using electroproduction of $J/\psi $ as a probe of gluon Sivers function by measuring single spin asymmetry (SSA) in experiments with transversely polarized protons and electron beams. We estimate SSA for JLab, HERMES, COMPASS and eRHIC energies using the color evaporation model of charmonium production and find asymmetry up to 25% for certain choices of model parameters which have been used earlier for estimating SSA in the SIDIS and Drell-Yan processes.

SIVERS ASYMMETRY IN e + p↑ → e + J/ψ + X

A recent investigation of the single spin asymmetry (SSA) in low virtuality electroproduction/photoproduction of J/ψ in color evaporation model is presented. It is shown that the asymmetry is sizable and can be used as a probe for the still unknown gluon Sivers function.

The dependence of J/ψ-nucleon inelastic cross section on the Feynman variable

By means of two typical sets of nuclear parton distribution functions, meanwhile taking account of the energy loss of the beam proton and the nuclear absorption of the charmonium states traversing the nuclear matter in the uniform framework of the Glauber model, a leading order phenomenological analysis is given in the color evaporation model of the E866 experimental data on J/ψ production differential cross section ratios RFe/Be(xF). It is shown that the energy loss effect of beam proton on RFe/Be(xF) is more important than the nuclear effects on parton distribution functions in the high Feynman variable xF region. It is found that the J/ψ-nucleon inelastic cross section depends on the Feynman variable xF and increases linearly with xF in the region xF > 0.2.

Measurement of the differential cross-sections of inclusive, prompt and non-prompt [formula omitted] production in proton–proton collisions at [formula omitted

The inclusive J / ψ production cross-section and fraction of J / ψ mesons produced in B-hadron decays are measured in proton–proton collisions at s = 7 TeV with the ATLAS detector at the LHC, as a function of the transverse momentum and rapidity of the J / ψ , using 2.3 pb −1 of integrated luminosity. The cross-section is measured from a minimum p T of 1 GeV to a maximum of 70 GeV and for rapidities within | y | < 2.4 giving the widest reach of any measurement of J / ψ production to date. The differential production cross-sections of prompt and non-prompt J / ψ are separately determined and are compared to Colour Singlet NNLO ⋆ , Colour Evaporation Model, and FONLL predictions.

Υcross section inp+pcollisions ats=200 GeV

We report on a measurement of the Upsilon(1S+2S+3S) -> e+e- cross section at midrapidity in p+p collisions at sqrt(s)=200 GeV. We find the cross section to be 114 +/- 38 (stat.) +23,-24 (syst.) pb. Perturbative QCD calculations at next-to-leading order in the Color Evaporation Model are in agreement with our measurement, while calculations in the Color Singlet Model underestimate it by 2 sigma. Our result is consistent with the trend seen in world data as a function of the center-of-mass energy of the collision and extends the availability of Upsilon data to RHIC energies. The dielectron continuum in the invariant mass range near the Upsilon is also studied to obtain a combined cross section of Drell-Yan plus (b b-bar) -> e+e-.

Transverse momentum broadening of vector boson production in high energy nuclear collisions

We calculate in perturbative QCD the transverse momentum broadening of vector boson production in high energy nuclear collisions. We evaluate the effect of initial-state parton multiple scattering for the production of the Drell-Yan virtual photon and W/Z bosons. We calculate both the initial- and final-state multiple scattering effect for the production of heavy quarkonia and their transverse momentum broadening in both nonrelativistic QCD and the color evaporation model of quarkonium formation. We find that J/{psi} and {upsilon} broadening in hadron-nucleus collision is close to 2C{sub A}/C{sub F} times the corresponding Drell-Yan broadening, which gives a good description of existing Fermilab data. Our calculations are also consistent with Relativistic Heavy Ion Collider data on J/{psi} broadening in relativistic heavy ion collisions. We predict the transverse momentum broadening of vector boson (J/{psi}, {upsilon}, and W/Z) production in relativistic heavy ion collisions at the Large Hadron Collider and discuss the role of the vector boson broadening in diagnosing medium properties.

J/ψ, ψ′ AND ϒ PRODUCTION AT HADRON COLLIDERS: A REVIEW

We give an overview of the present status of knowledge of the production of J/ψ, ψ′ and ϒ in high-energy hadron collisions. We first present two early models, namely the Color-Singlet Model (CSM) and the Color-Evaporation Model (CEM). The first is the natural application of pQCD to quarkonium production and has been shown to fail dramatically to describe experimental data, the second is its phenomenological counterpart and was introduced in the spirit of the quark–hadron duality in the late 1970's. Then, we expose the most recent experimental measurements of J/ψ, ψ′ and ϒ prompt and direct production at nonzero pTfrom two high-energy hadron colliders, the Tevatron and RHIC. In a third part, we review six contemporary models describing J/ψ, ψ′ and ϒ production at nonzero pT.

Comparison of the color-evaporation model and the nonrelativistic QCD factorization approach in charmonium production

We compare the color-evaporation model (CEM) and nonrelativistic QCD (NRQCD) factorization predictions for inclusive quarkonium production. Using the NRQCD factorization formulas for quarkonium production and for perturbative QQ-bar production, we deduce relationships that are implied by the CEM between the nonperturbative NRQCD matrix elements that appear in the factorization formula for quarkonium production. These relationships are at odds with the phenomenological values of the matrix elements that have been extracted from the Tevatron data for charmonium production at large transverse momentum. A direct comparison of the CEM and NRQCD factorization predictions with the CDF charmonium production data reveals that the CEM fits to the data are generally unsatisfactory, while the NRQCD factorization fits are generally compatible with the data. The inclusion of k_T smearing improves the CEM fits substantially, but significant incompatibilities remain. The NRQCD factorization fits to the chi_c data indicate that multiple gluon radiation is an essential ingredient in obtaining the correct shape of the cross section as a function of p_T.

Color-evaporation-model calculation ofe+e−→J/ψ+cc¯+Xats=10.6 GeV

Measurements by the Belle Collaboration of the cross section for inclusive J/psi production in e^+e^- annihilation have been a serious challenge to current heavy-quarkonium theory. Especially, the measured cross sections for exclusive J/psi+eta_c and inclusive J/psi+cc-bar+X differ from nonrelativistic QCD predictions by an order of magnitude. In order to check if other available alternative theory can resolve such a large discrepancy, we calculate the cross section for inclusive J/psi+cc-bar+X based on the color-evaporation model. As a phenomenological model, the color-evaporation model is still employed to predict cross sections for inclusive quarkonium production in various processes. Our results show that the color-evaporation-model prediction is even smaller than the nonrelativistic QCD prediction by an order of magnitude. The resultant color-evaporation-model prediction for J/psi+cc-bar+X fraction in the inclusive J/psi production cross section is 0.049, while the empirical value measured by the Belle Collaboration is 0.82.

O1-05-07 Behavioral benefits with continued donepezil treatment in Alzheimer's disease patients

We present a measurement of inclusive J/ψ production at mid-rapidity (|y|<1) in p+p collisions at a center-of-mass energy of s=200 GeV with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The differential production cross section for J/ψ as a function of transverse momentum (pT) for 0<pT<14 GeV/c and the total cross section are reported and compared to calculations from the color evaporation model and the non-relativistic Quantum Chromodynamics model. The dependence of J/ψ relative yields in three pT intervals on charged-particle multiplicity at mid-rapidity is measured for the first time in p+p collisions at s=200 GeV and compared with that measured at s=7 TeV, PYTHIA8 and EPOS3 Monte Carlo generators, and the Percolation model prediction.

Charmonium production in pp collisions at PHENIX

A preliminary measurement of the J/ψ production cross section in = 200 GeV pp collisions at PHENIX is presented. Using observations of the J/ψ → μ+μ− and J/ψ → e+e− decay channels, the total production cross section for J/ψ is found to be 3.8 ± 0.6 (stat.) ± 1.3 (sys.) µb. The measurement agrees well with predictions given by the colour evaporation model and non-relativistic QCD. Our one available data point for the differential pt cross section indicates that the colour octet production mechanisms dominate J/ψ production at RHIC.

Testing color evaporation in photon-photon production ofJ/ψat CERN LEP II

The DELPHI Collaboration has recently reported the measurement of J/Psi production in photon-photon collisions at LEP II. These newly available data provide an additional proof of the importance of colored c bar{c} pairs for the production of charmonium because these data can only be explained by considering resolved photon processes. We show here that the inclusion of color octet contributions to the J/Psi production in the framework of the color evaporation model is able to reproduce this data. In particular, the transverse-momentum distribution of the J/Psi mesons is well described by this model.

Color evaporation description of inelastic photoproduction ofJ/ψat DESY HERA

The H1 Collaboration recently reported a new analysis of data on the inelastic photoproduction of $J/\ensuremath{\psi}$ mesons at DESY's HERA ep collider. We show that these new experimental results are well described by the color evaporation model for quarkonium production. Moreover, these new data require the introduction of resolved photon contributions in order to accommodate the results in the kinematic region where the fractional energy carried by the $J/\ensuremath{\psi}$ is small, demonstrating that colored perturbative $c\overline{c}$ states contribute to the production of a color singlet.

Soft and hard QCD dynamics in hadroproduction of charmonium

Both hard and soft QCD dynamics are important in charmonium production, as presented here through a next-to-leading order QCD matrix element calculation combined with the colour evaporation model. Observed $x_F$ and $p_\perp$ distributions of $J/\psi$ in hadroproduction at fixed target and $p\bar{p}$ collider energies are reproduced. Quite similar results can also be obtained in a more phenomenologically useful Monte Carlo event generator where the perturbative production of \ccbar pairs is instead obtained through leading order matrix elements and the parton shower approximation of the higher order processes. The soft dynamics may alternatively be described by the soft colour interaction model, originally introduced in connection with rapidity gaps. We also discuss the relative rates of different charmonium states and introduce an improved model for mapping the continuous \ccbar mass spectrum on the physical charmonium resonances.