Observation of double 𝐽�/𝜓� meson production in 𝑝�⁢Pb collisions at √𝑠�NN=8.16 TeV

Abstract

The first observation of the concurrent production of two J=ψ mesons in proton-nucleus collisions is presented. The analysis is based on a proton-lead (pPb) data sample recorded at a nucleon-nucleon center-of-mass energy of 8.16 TeV by the CMS experiment at the CERN LHC and corresponding to an integrated luminosity of 174.6 nb−1. The two J=ψ mesons are reconstructed in their μþμ− decay channels with transverse momenta pT > 6.5 GeV and rapidity jyj < 2.4. Events where one of the J=ψ mesons is reconstructed in the dielectron channel are also considered in the search. The pPb → J=ψJ=ψ þ X process is observed with a significance of 5.3 standard deviations. The measured inclusive fiducial cross section, using the four-muon channel alone, is σðpPb → J=ψJ=ψ þ XÞ ¼ 22.0 8.9ðstatÞ 1.5ðsystÞ nb. A fit of the data to the expected rapidity separation for pairs of J=ψ mesons produced in single (SPS) and double (DPS) parton scatterings yields σpPb→J=ψJ=ψþX SPS ¼ 16.5 10.8ðstatÞ 0.1ðsystÞ nb and σpPb→J=ψJ=ψþX DPS ¼ 5.4 6.2ðstatÞ 0.4ðsystÞ nb, respectively. This latter result can be transformed into a lower bound on the effective DPS cross section, closely related to the squared average interparton transverse separation in the collision, of σeff > 1.0 mb at 95% confidence level.