Phenomenological analysis of associated production of $Z^0+b$ in the $b \rightarrow J/ψX$ decay channel at the LHC

TL;DR

The paper analyzes associated production of a Z^0 boson with heavy flavour through the b→J/ψX decay channel at the LHC, focusing on disentangling single-parton scattering (SPS) and double-parton scattering (DPS) contributions. It performs a next-to-leading order QCD calculation with MadGraph5_aMC@NLO, including parton showering and hadronization via Pythia8, and compares predictions to ATLAS data for non-prompt J/ψ+Z production at √s = 8 TeV. The results show SPS contributions closely match the data in the ATLAS fiducial and inclusive regions, constraining DPS and allowing a lower bound on σ_eff around 5 mb (68% CL) and 2.3 mb (95% CL). The study emphasizes substantial QCD corrections and highlights the need for reduced experimental and theoretical uncertainties and more statistics to robustly extract DPS and probe gluon correlations.

Abstract

The ATLAS collaboration recently reported on the first observation of associated-production of a $Z^0$ boson with a $J/ψ$. We recently claimed that the corresponding yield of the {\it prompt} $J/ψ$ was dominated by double parton scatterings in the ATLAS acceptance with a somewhat small value of $σ_{\rm eff}$. We also found out that single parton scatterings were only dominant at large transverse momenta. We present here the first phenomenological analysis of another part of the ATLAS data sample, namely of a $Z^0$ boson plus a {\it non-prompt} $J/ψ$. Our study is performed at next-to-leading order in $α_s$ and includes parton-shower effects via the {\sc\small MadGraph5_aMC@NLO} framework. We find out that the data, unlike the case of prompt $J/ψ+Z^0$, do not hint at significant DPS contributions. Owing to the current experimental and theoretical uncertainties, there is still a room for these but with a lower limit of $σ_{\rm eff}$ close to 5 mb. We stress the importance of QCD corrections to account for the ATLAS data.

Figures (3)

• Figure 1: Total cross section ratio $^{np}R(J/\psi+Z)$ for the non-prompt $J/\psi+Z$ production at 8 TeV LHC.
• Figure 2: Differential cross section/distributions for non-prompt $J/\psi +Z$ production: $p_T$ distribution of $J/\psi$ (a) and azimuthal angle distribution (b).
• Figure 3: Extractions of $\sigma_{\rm eff}$ from quarkonium associated production Lansberg:2016rcxLansberg:2014swaAbazov:2014qbaATLAS:2016eiiAbazov:2015fbl and jet production Aad:2013bjmAbe:1993rvAbe:1997xkAbazov:2009gcChatrchyan:2013xxa processes at the Tevatron and the LHC. The symbol "np" in the legend refers to non-prompt $J/\psi$, otherwise it refers to prompt $J/\psi$. The lower limit (green arrow) $\sigma_{\rm eff}\ge 5.0$ mb is determined from the present analysis of the ATLAS non-prompt $J/\psi+Z$ sample Aad:2014kba. The upper limit of $\sigma_{\rm eff}\le 8.2$ mb in D0 $J/\psi+\Upsilon$Abazov:2015fbl is refined in Ref. Shao:2016wor.