Measurement of di-muons from 400 GeV/c protons interacting in a thick molybdenum/tungsten target

TL;DR

This study measures J/psi di-muon production from 400 GeV/c protons hitting a thick molybdenum/tungsten target, comparing results with simulations and previous experiments to analyze production rates and secondary effects.

Contribution

First measurement of J/psi production in a thick target with detailed comparison to Monte Carlo simulations and prior thin-target data.

Findings

Measured J/psi production cross-section per nucleon: 1.18 nb with uncertainties.

Results agree with Pythia v8 simulations within errors.

No significant enhancement from secondary J/psi production inside the target.

Abstract

Di-muon events emanating from a replica of the SHiP target at the CERN SPS contain a clear signal of $J/{\psi}$~production. The production rate is in reasonable agreement with Monte Carlo simulations based on Pythia v8. For the interval in rapidity defined in the center of mass, $y_{cm}$, with the largest overlap with the NA50 measurement, $0.3 < y_{cm} < 0.6$, we obtain the production cross-section per nucleon $\sigma(J/{\psi})/A$ including the branching ratios of $J/{\psi}$ decays into muons, $B_{\mu\mu}$: $B_{\mu\mu}\sigma(J/{\psi})/A=(1.18~\pm~0.04~\pm~0.10)~\rm{nb}$/nucleon. This is to be compared to the NA50 extrapolated result (using a much thinner target): $B_{\mu\mu}\sigma(J/{\psi})/A=(0.99~\pm~0.04)~\rm{nb}$/nucleon. Within the systematic errors, no significant enhancement due to secondary production of $J/{\psi}$ inside the target is observed. An upper limit of possible contributions from cascade collisions of $<32\%$ is obtained.