QED contribution to the production of J/ψ+c\bar{c}+X at the Tevatron and LHC

TL;DR

The paper addresses the challenge of understanding J/ψ hadroproduction within NRQCD by examining the J/ψ+c c̄ channel and specifically quantifying the QED contribution and its interference with QCD. Using NRQCD factorization and focusing on the color-singlet 3S1 cc̄ state, the authors compute polarized and unpolarized observables for pp( p̄ ) → J/ψ+c c̄+X at Tevatron and LHC, including two classes of QED diagrams and their interference with the α_s^4 QCD contribution. They find that QED effects are small at low p_t but significantly enhance high-p_t distributions (≈1.5× at Tevatron p_t=50 GeV and ≈1.9× at LHC p_t=100 GeV) and drive J/ψ polarization toward transverse at large p_t; the QED–QCD interference is positive with a near-π/2 phase. Overall, photon-fragmentation QED contributions can materially affect high-p_t J/ψ production in hadron collisions, offering observable signatures to test NRQCD and photon-fragmentation dynamics at the LHC.

Abstract

We calculate α^{2}α_{s}^{2} order QED contribution to J/ψproduction in pp(\bar{p})\to J/ψ+c\bar{c} color-singlet process at the Tevatron and LHC in the framework of non-relativistic QCD. The contribution of the interference between the α^{2}α_{s}^{2} QED and α_{s}^{4} QCD is also taken into account. The J/ψproduction associated with a charm quark pair could be a measurable signal at hadron collider experiment. Our calculations show that by including the QED contribution, the p_{t} distribution is enhanced by a factor of 1.5 (1.9) at the Tevatron (LHC) at p_{t}=50 (100) GeV. In addition, the polarization of J/ψturns from unpolarized in all region to increasingly transverse when p_{t} becomes larger.

Figures (6)

• Figure 1: The typical Feynman diagrams for the $\alpha_{s}^{4}$ QCD part of $gg\to c\bar{c}[^3S_1,\underline{1}]+c+\bar{c}$.
• Figure 2: The typical Type I Feynman diagrams in the LO ($\alpha^{2}\alpha_{s}^2$) QED part of $gg\to c\bar{c}[^3S_1, \underline{1}]+c+\bar{c}$.
• Figure 3: The typical Type II Feynman diagrams of photon fragmentation in the LO ($\alpha^{2}\alpha_{s}^2$) QED part of $gg\to c\bar{c}[^3S_1, \underline{1}]+c+\bar{c}$.
• Figure 4: The typical Feynman diagrams of the LO process of $q\bar{q}\to c\bar{c}[^3S_1, \underline{1}]+c+\bar{c}$ for QCD and QED.
• Figure 5: (a): The $p_t$ distributions of the production rate for $J/\psi + c + \bar{c}$ hadroproduction at the Tevatron ($\sqrt{s}=$1.96TeV, $|y|<$0.6, 3GeV$<$pt$<$50GeV) and LHC ($\sqrt{s}=$14TeV, $|y|<$3, 3GeV$<$pt$<$100GeV). (b): the $p_t$ distributions of the "total" with $\mu_r=\mu_f=\mu$ dependence. Where the total refers to the sum of the QCD, QED and their interference results.