Prospects for observation of double parton scattering with four-muon final states at LHCb

TL;DR

This work evaluates the feasibility of observing double parton scattering (DPS) in four-muon final states at LHCb, focusing on two channels: double Drell–Yan (DDY) and double $J/\psi$ production. DPS is modeled as two independent hard scatterings, with cross sections related to two single DY processes via $d\sigma_{\rm DPS}^{\mathrm{DDY}} = \frac{d\sigma_{\rm SPS}^{\mathrm{DY}}\,d\sigma_{\rm SPS}^{\mathrm{DY}}}{2\,\sigma_{\rm eff}}$ using $\sigma_{\rm eff}=14.5$ mb, while the SPS background includes both double and single resonance diagrams; the analysis applies LHCb muon acceptance and mass cuts to separate DPS from SPS. The study finds DDY DPS cross sections at 14 TeV to be small (order $0.1-0.2$ fb) with limited signal-to-background improvement, whereas the double $J/\psi$ channel yields larger rates and better discrimination, making it a promising DPS observable. The results highlight the complementary information provided by quark-antiquark initiated DDY and gluon-gluon initiated $J/\psi$ pairs for probing double parton distributions, and suggest extending to other resonances (e.g., $\Upsilon$) to map the scale dependence of DPS.

Abstract

We study the prospects for observing double parton scattering through four-muon final states, forming two opposite-sign muon pairs, in the LHCb experiment in pp collisions at 14 TeV centre of mass energy. We consider two special cases, namely double Drell-Yan and J/psi-pair production. The kinematic properties and prospects for observing these processes are discussed. We find that the production rate depends strongly on the origin of the four muons, while many kinematic properties can be used to help identify the presence of double parton scattering events.

Figures (12)

• Figure 1: Example Feynman diagram for the DPS double Drell--Yan process.
• Figure 2: Example Feynman diagrams for the SPS double Drell--Yan process. (a) "double resonance"--type diagrams, where both virtual photons are attached to the initial state quarks, and (b) "single resonance"--type diagrams, where only one virtual photon is attached to the quark line.
• Figure 3: The DPS and SPS single $\mu$ distributions in (a) $\eta$ and (b) $p_{T}$ for the process $pp \to \gamma^* \gamma^* \to \mu^+\mu^- \mu^+\mu^-$ at the LHC with 14 TeV.
• Figure 4: (a) The DPS and SPS differential distributions in the $p_{T}$--balance variable $S$ for the $\mu^+\mu^-$ combination that minimises $S$, and (b) comparison of the DPS differential distributions for the "right", obtained by minimizing $S$, and "wrong" $\mu^+\mu^-$ pairs with the theoretical distribution obtained by always pairing a $\mu^+\mu^-$ pair from the same $\gamma^*$ together. In plot (b), the top (bottom) three keys correspond to parton shower simulations without (including) intrinsic $p_{T}$ smearing.
• Figure 5: The DPS and SPS differential distributions in the angle $\Delta \phi$ between the two $\mu^+$ for the process $pp \to \gamma^* \gamma^* \to \mu^+\mu^- \mu^+\mu^-$ at the LHC with 14 TeV.