Prompt J/psi production at the LHC

TL;DR

Prompt J/psi production at the LHC investigates how non-perturbative QCD dynamics shape quarkonium formation beyond the Colour Singlet Model. The study compares four approaches—COM (NRQCD), CEM, SCI, and GAL—tuned to Tevatron data, and extrapolates them to LHC energies to quantify theoretical uncertainties and the impact of higher-order pQCD via parton showers. Results show large model-to-model differences at 14 TeV, especially in the high-$p_T$ tail, and highlight the importance of higher-order $c\bar{c}$ production. Additionally, prompt J/psi constitutes a potentially significant background to CP-violation measurements in B decays, underscoring the need for improved understanding of prompt quarkonium production.

Abstract

Models with essential non-perturbative QCD dynamics for the production of charmonium are extrapolated to give predictions of prompt J/psi production at the LHC. Differences of up to an order of magnitude occurs, although the different models all describe the Tevatron data on high-pT charmonium. An important point is here the treatment of higher order perturbative QCD effects. We also discuss the large rate of prompt J/psi from these models as a background to CP violation studies.

Figures (4)

• Figure 1: Illustration of $c\bar{c}$ production processes in (a) leading order ($\alpha_s^2$) and (b) next-to-leading order ($\alpha_s^3$).
• Figure 2: Distribution in transverse momentum of prompt $J/\psi$ as observed by CDF and D0 Tevatron in $p\bar{p}$ interactions at the Tevatron and obtained in the CEM, SCI and GAL models.
• Figure 3: Differential cross sections in transverse momentum and rapidity for $J/\psi$ in $pp$ collisions at $\sqrt{s}=14$ TeV based on the CEM, SCI and GAL models. In all cases only $J/\psi$ with $p_{\perp}^{J/\psi}>10$ GeV and decaying into $\mu^+\mu^-$, which in (c, d) are required to be within the indicated rapidity coverage of the Atlas and lhc-b detectors, respectively. For comparison, the COM results from san1 is included in (c).
• Figure 4: Distribution in transverse momentum of prompt $J/\psi$ at (a) the Tevatron and (b) LHC ($|\eta|<2.5$ as for Atlas ) for the colour octet model (COM) based on NLO ${\cal O}(\alpha_s^3)$ matrix elements (from san1) and for the colour evaporation model (CEM) including $g\to c\bar{c}$ to all orders in the parton shower and in the 'NLO' approximation where only $c\bar{c}$ pairs from the first branching have been included. The result of this 'first branching' approximation applied to the soft colour interaction model (SCI) is also shown in (b).