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Register a new user$J/psi$ polarization in the CGC+NRQCD approach
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We compute the $J/psi$ polarization observables $lambda_theta$, $lambda_phi$, $lambda_{thetaphi}$ in a Color Glass Condensate (CGC) + nonrelativistic QCQ (NRQCD) formalism that includes contributions from both color singlet and color octet intermediate states. Our results are compared to low $p_T$ data on $J/psi$ polarization from the LHCb and ALICE experiments on proton-proton collisions at center-of-mass energies of $sqrt{s}=7$ TeV and 8 TeV. Our CGC+NRQCD computation provides a better description of data for $p_T leq 15$ GeV relative to extant next-to-leading (NLO) calculations within the collinear factorization framework. These results suggest that higher order computations in the CGC+NRQCD framework have the potential to greatly improve the accuracy of extracted values of the NRQCD universal long distance matrix elements.
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Quarkonium production mechanism in high multiplicity small collision systems has recently been pursued in the color-glass-condensate (CGC) effective theory combined with non-relativistic QCD (NRQCD) factorization, allowing to study initial state interactions. Quarkonium polarization, potentially measured in future experiments, would help elucidate the quarkonium production mechanism at high multiplicities. In this paper, we provide predictions on $J/psi$ polarization parameters in high multiplicity proton-proton ($pp$) and proton-nucleus ($pA$) collisions within the CGC+NRQCD framework. Theoretical predictions are given for $J/psi$ rapidity $2.5< y_{J/psi}<4$, charged-particle multiplicity pseudorapidity $|eta_{ch} | <1$ and energies $sqrt{S}=13mathrm{~TeV}$ for $pp$, $sqrt{S}=8.16mathrm{~TeV}$ for $pA$ collisions. Considering two leptonic frame choices (Collins - Soper and helicity) we find a weak polarization of $J/psi$ that additionally decreases with growing event activities. No significant system size dependence between $pp$ and $pA$ collisions is obtained - this could be a new constraint to initial state interactions in small collision systems.
We present $Phi$- and $J/Psi$--nuclear bound state energies and absorption widths for some selected nuclei, using potentials in the local density approximation computed from an effective Lagrangian approach combined with the quark-meson coupling model. Our results suggest that these mesons should form bound states with all the nuclei considered provided that these mesons are produced in nearly recoilless kinematics.
Interpreting the J/psi suppression reported in nucleus--nucleus collisions at SPS and RHIC requires the quantitative understanding of cold nuclear matter effects, such as the inelastic rescattering of J/psi states in nuclei or the nuclear modification of parton densities. With respect to our former Glauber analysis, we include in the present work the new PHENIX d--Au measurements, and analyze as well all existing data using the EPS08 nuclear parton densities recently released. The largest suppression reported in the new PHENIX analysis leads in turn to an increase of sigma from 3.5 +/- 0.3 mb to 5.4 +/- 2.5 mb using proton PDF. The stronger x-dependence of the G^{A}/G^p ratio in EPS08 as compared to e.g. EKS98 shifts the cross section towards larger values at fixed target energies (x_2 ~ 0.1) while decreasing somehow the value extracted at RHIC (x_2 ~10^{-2}).
Using the data on coherent $J/psi$ photoproduction in Pb-Pb ultraperipheral collisions (UPCs) obtained in Runs 1 and 2 at the Large Hadron Collider (LHC), we determined with a good accuracy the nuclear suppression factor of $S_{Pb}(x)$ in a wide range of the momentum fraction $x$, $10^{-5} leq x leq 0.04$. In the small-$x$ region $x < 10^{-3}$, our $chi^2$ fit favors a flat form of $S_{Pb}(x) approx 0.6$ with approximately a 5% accuracy for $x=6 times 10^{-4} - 10^{-3} $ and a 25% error at $x=10^{-4}$. At the same time, uncertainties of the fit do not exclude a slow decrease of $S_{Pb}(x)$ in the small-$x$ limit. At large $x$, $S_{Pb}(x)$ is constrained to better than 10% precision up to $x=0.04$ and is also consistent with the value of $S_{Pb}(x)$ at $langle x rangle =0.042$, which we extract from the Fermilab data on the $A$ dependence of the cross section of coherent $J/psi$ photoproduction on fixed nuclear targets. The resulting uncertainties on $S_{Pb}(x)$ are small, which indicates the potential of the LHC data on coherent charmonium photoproduction in Pb-Pb UPCs to provide additional constraints on small-$x$ nPDFs. We explicitly demonstrate this using as an example the EPPS16 and nCTEQ16 nuclear parton distribution functions, whose uncertainties decrease severalfold after the Bayesian reweighting of the discussed UPC data.
We argue that the s-channel cut contribution to J/psi hadroproduction can be significantly larger than the usual cut contribution of the color-singlet mechanism, which is known to underestimate the experimental measurements. A scenario accounting for intermediate $cbar(c)$ interactions is proposed that reproduces the data at low- and mid-range transverse momenta P_T from the Fermilab Tevatron and BNL Relativistiv Heavy Ion Collider. The J/psi produced in this manner are polarized predominantly longitudinally.
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