Narrow Results

We report on recent progress in testing the factorization formalism of non-relativistic quantum chromodynamics (NRQCD) at next-to-leading order (NLO) for J/ψ yield and polarization. We demonstrate that it is possible to unambiguously determine the leading color-octet (CO) long-distance matrix elements (LDMEs) in compliance with the velocity scaling rules through a global fit to experimental data of unpolarized J/ψ production in pp, , ep, γγ, and e⁺e^- collisions. Three data sets not included in the fit, from hadro-production and from photo-production in the fixed-target and colliding-beam modes, are nicely reproduced. The polarization observables measured in different frames at DESY HERA and CERN LHC reasonably agree with NLO NRQCD predictions obtained using the LDMEs extracted from the global fit, while measurements at the FNAL Tevatron exhibit severe disagreement. We demonstrate that the alternative LDME sets recently obtained, with different philosophies, in two other NLO NRQCD analyses of J/ψ yield and polarization also fail to reconcile the Tevatron polarization data with the other available world data.

Motivated by the recent measurements on nonleptonic J/ψ weak decays at BESIII and the potential prospects of J/ψ meson at the high-luminosity heavy-flavor experiments, the branching ratios of the two-body nonleptonic J/ψ → DP, DV decays are estimated quantitatively by considering the QCD radiative corrections to hadronic matrix elements with the QCD factorization approach. It is found that the Cabibbo favored , , decays have branching ratios ≳ 10^-10, which might be promisingly detectable in the near future.

Inspired by the recent measurements on two-body nonleptonic $J/\psi$ weak decay at BESIII, the charm-changing $J/\psi \to D_{s,d}V$ weak decays are studied with perturbative QCD approach, where $V$ denotes $\rho$ and $K^{\ast }$ vector mesons. It is found that branching ratio for $J/\psi \to D_s\rho$ decay can reach up to ${𝒪}(10^{-9})$, which is within the potential measurement capability of the future high-luminosity experiments.

We aggregate the transverse momentum spectra of $J/\psi$ mesons produced in high energy gold–gold (Au–Au), deuteron–gold ($d-$Au), lead–lead (Pb–Pb), proton–lead ($p$–Pb), and proton–(anti)proton ($p$–$p(\overline{p})$) collisions measured by several collaborations at the Relativistic Heavy Ion collider (RHIC), the Tevatron Proton–Antiproton Collider, and the Large Hadron Collider (LHC). The collision energy (the center-of-mass energy) gets involved in a large range from dozens of GeV to 13 TeV (the top LHC energy). We consider two participant or contributor partons, a charm quark and an anti-charm quark, in the production of $J/\psi$. The probability density of each quark is described by means of the modified Tsallis–Pareto-type function (the TP-like function) while considering that both quarks make suitable contributions to the $J/\psi$ transverse momentum spectrum. Therefore, the convolution of two TP-like functions is applied to represent the $J/\psi$ spectrum. We adopt the mentioned convolution function to fit the experimental data and find out the trends of the power exponent, effective temperature, and of the revised index with changing the centrality, rapidity, and collision energy. Beyond that, we capture the characteristic of $J/\psi$ spectrum, which is of great significance to better understand the production mechanism of $J/\psi$ in high energy collisions.