Observation and studies of double J/psi production at the Tevatron

TL;DR

This paper reports the first measurement of double J/psi production at the Tevatron, distinguishing contributions from single and double parton scatterings, and determining the effective cross section related to parton spatial density.

Contribution

It provides the first separation of double J/psi production cross section into single and double parton scattering contributions at the Tevatron.

Findings

Measured double J/psi production cross section.

Separated contributions from single and double parton scatterings.

Determined the effective cross section σ_eff.

Abstract

We present the observation of doubly-produced $J/\psi$ mesons with the D0 detector at Fermilab in $p\bar{p}$ collisions at $\sqrt{s}=1.96$ TeV. The production cross section for both singly and doubly-produced $J/\psi$ mesons is measured using a sample with an integrated luminosity of 8.1fb$^{-1}$. For the first time, the double $J/\psi$ production cross section is separated into contributions due to single and double parton scatterings. Using these measurements, we determine the effective cross section $\sigma_{eff}$, a parameter characterizing an effective spatial area of the parton-parton interactions and related to the parton spatial density inside the nucleon.