J/psi Production: Tevatron and Fixed-Target Collisions

TL;DR

The paper analyzes J/ψ production within NRQCD across Tevatron and fixed-target collisions, incorporating $O(\alpha_s^4)$ color-singlet corrections and intrinsic $k_T$ smearing, followed by a NLO NRQCD analysis of fixed-target data. It fits color-octet matrix elements to Tevatron data and then tests universality by extracting a fixed-target octet parameter, highlighting how higher-order effects alter certain LDME values while leaving others relatively stable. The results indicate partial consistency with NRQCD universality but reveal substantial theoretical uncertainties and a remaining tension between Tevatron and fixed-target extractions, which may be alleviated by further higher-order corrections. Overall, the work strengthens the case for NRQCD-based descriptions of heavy quarkonium production while underscoring the need for more precise calculations to achieve full cross-experimental universality.

Abstract

In this talk I show the results of a fit of the NRQCD matrix elements to the CDF data for direct $J/ψ$ production, by including the radiative corrections to the colour-singlet channel and the effect of the $k_T$-smearing. Furthermore I perform the NLO NRQCD analysis of $J/ψ$ production in fixed-target proton-nucleon collisions and I fit the colour-octet matrix elements to the available experimental data. The results are compared to the Tevatron ones.

Figures (3)

• Figure 1: Different channels contributing to the $J\!/\!\psi$ production at the Tevatron. The NLO $^3S_1^{[1]}$ channel is given by the dashed curves ( $s_{\rm min} = M^2_J\!/\!\psi$J / ψ$$ (lower dash) and $s_{\rm min} = M^2_J\!/\!\psi$J / ψ$/20$ (upper dash) ). The fit of the colour-octet MEs to data are performed by considering the upper dashed curve. The resulting fitted curves are shown ( $^3S_1^{[8]}$ (dots) and $\Delta^{J/\psi}_8(3.5)$ (dotdash) ).
• Figure 2: Different contributions to $J\!/\!\psi$ production at the Tevatron. Dots: $\hbox{$^3S_1^{[8]}$}$. Dashes: $^1S_0^{[8]}$ + $\hbox{$^3P_J^{[8]}$}$. Dotdash: NLO $\hbox{$^3S_1^{[1]}$}$. The effect of $k_T$-smearing is included for three different values of $\langle k_T\rangle$ ($\langle k_T\rangle =0,1,1.5\; \hbox{$\mathrm{GeV}$}$). The results are given for three different sets of pdfs. The NLO $^3S_1^{[1]}$ effect is only included in the $\langle k_T\rangle=0$ case.
• Figure 3: Fits of the matrix element $\Delta^{J/\psi}_8(6.4)$ to the fixed-target proton-nucleon collisions data. Fits are performed for three sets of pdfs. The value of $\langle\cal{O}$O$^{J/\psi}_8(^3S_1$^3S_1$)\rangle$ is taken from the above Tevatron fits ( for any correspondent pdf ) with $\langle k_T\rangle=0$. ( The value of $\langle\cal{O}$O$^{J/\psi}_8(^3S_1$^3S_1$)\rangle$ is only sligtly affected by the intrinsic $k_T$ anyway. The indirect impact of the Tevatron $k_T$-smearing in the extraction of $\Delta^{J/\psi}_8(6.4)$ is not appreciable ).