Indication for Double Parton Scatterings in W + Prompt J/Psi Production at the LHC

TL;DR

This paper investigates the production of prompt J/psi and W bosons at the LHC, providing evidence for double-parton scattering contributions by comparing NLO theoretical predictions with experimental data.

Contribution

It presents the first NLO study of SPS contributions in the Colour-Evaporation Model for J/psi + W production, highlighting the significance of DPS effects.

Findings

SPS NLO CEM predictions underestimate ATLAS data by 3.1 sigma.

DPS contributions are larger than initially assumed by ATLAS.

Results are consistent with observed azimuthal distributions and other J/psi production data.

Abstract

We re-analyse the associated production of a prompt J/psi and a W boson in pp collisions at the LHC following the results of the ATLAS Collaboration. We perform the first study of the Single-Parton-Scattering (SPS) contributions at the Next-to-Leading Order (NLO) in alpha_s in the Colour-Evaporation Model (CEM), an approach based on the quark-hadron-duality. Our study provides clear indications for Double-Parton-Scattering (DPS) contributions, in particular at low transverse momenta, since our SPS CEM evaluation, which can be viewed as a conservative upper limit of the SPS yields, falls short compared to the ATLAS experimental data by 3.1 standard deviations. We also determine a finite allowed region for sigma_eff, inversely proportional to the size of the DPS yields, corresponding to the otherwise opposed hypotheses, namely our NLO CEM evaluation and the LO direct Colour-Singlet (CS) Model contribution. In both cases, the resulting DPS yields are significantly larger than that initially assumed by ATLAS based on jet-related analyses but is consistent with their observed raw-yield azimuthal distribution and with their prompt J/psi+J/psi and Z + prompt J/psi data.