Photoproduction of J/ψ with forward hadron tagging in hadronic collisions

Abstract

We study the photoproduction of J/ψ using the NRQCD formalism with forward hadron tagging at the Large Hadron Collider. We estimate the total cross sections and event rates with and without nuclear shadowing effects in high energy proton-proton, proton-nucleus and nucleus-nucleus collisions. Our results show that the processes which involve J/ψ photoproduction depend on the choice of forward detector acceptances ξ. Under some precise cut of p J/ψ T and z J/ψ kinematic variables, we find that the distributions of photoproduction of J/ψ are led by the Fock state 1 S1 . The total cross sections and event rates will be smaller if the nuclear shadowing effects are considered. The processes give a crucial photoproduction signature at the LHC with forward detector acceptances. The exploration and the detection of the interactions will be useful for studying the mechanism of heavy quarkonium production. I. INTRODUCTIONSince the discovery of heavy quarkonia in the mid-1970s, their production and decay become reliable tools to improve our understanding of theoretical aspects of quantum chromodynamics (QCD) from the hard region, where the strong interaction is realized with a large momentum transfer, to the soft region, where the strong interaction is carried out with a small momentum transfer. These production and decay of heavy quarkonia are studied under the non-relativistic quantum chromodynamics (NRQCD) due to the large mass of heavy quarks (m c ∼ 1.5 GeV, m b ∼ 4.75 GeV). The full description of the theoretical framework was proposed by Bodwin, Braaten and Lepage(BBL) [1]. It factorizes the quarkonium production in terms of short distance QCD cross sections and long distance matrix elements (LDMEs). The former can be pertubatively evaluated in series of the running coupling constant α s while the latter is the probability for a heavy QQ pair with spin S, orbital angular momentum L, total angular momentum J, and color multiplicity a = 1 (color-singlet), 8 (color-octet) to evolve into a physical heavy quarkonium state. The value of LDMEs can either be calculated by utilizing non-perturbative methods or extracted phenomenologically from data [2], i.e., QCD lattice simulations or measurements in some production processes. The QQ pair is generated from the partonic interaction at short distances in color singlet (CS) or in color-octet (CO) states and hadronizes into physical CS observable by emitting soft gluons non-perturbatively. The effect of LDME contribution has a hierarchically ordered scaling with v [3], v being the nonrelativistic velocity of Q orQ in the QQ rest frame. The essence of this theory can now be systematically shortened by the double expansion in powers of α s and v. A lot of phenomenological approaches of this framework are meticulously narrated in Refs [4,5,7,8], taking into account the complete and spanned structure of the QQ Fock space by the state n = 2S+1 L (a) J . However, the golden age of the NRQCD theory has been to address the limitations of the early proposed models from which it establishes...

Hard diffractive ηc,b hadroproduction at the LHC

“…[n]|0 is the long-distance matrix element which describes the hadronization of the QQ heavy pair into the physical observable quarkonium state η c or η b . The σ(gg → QQ[n]) denotes the short-distance cross sections for the partonic process gg → QQ[n], which is found by operating the covariant projection method [52,53]. The Fock state n are given as follows:…”