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

The SHiP Collaboration

Abstract

Di-muon events emanating from a replica of the SHiP target at the CERN SPS contain a clear signal of $J/ψ$~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 $σ(J/ψ)/A$ including the branching ratios of $J/ψ$ decays into muons, $B_{μμ}$: $B_{μμ}σ(J/ψ)/A=(1.18~\pm~0.04~\pm~0.10)~\rm{nb}$/nucleon. This is to be compared to the NA50 extrapolated result (using a much thinner target): $B_{μμ}σ(J/ψ)/A=(0.99~\pm~0.04)~\rm{nb}$/nucleon. Within the systematic errors, no significant enhancement due to secondary production of $J/ψ$ inside the target is observed. An upper limit of possible contributions from cascade collisions of $<32\%$ is obtained.

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

Abstract

Di-muon events emanating from a replica of the SHiP target at the CERN SPS contain a clear signal of ~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, , with the largest overlap with the NA50 measurement, , we obtain the production cross-section per nucleon including the branching ratios of decays into muons, : /nucleon. This is to be compared to the NA50 extrapolated result (using a much thinner target): /nucleon. Within the systematic errors, no significant enhancement due to secondary production of inside the target is observed. An upper limit of possible contributions from cascade collisions of is obtained.

Paper Structure

This paper contains 8 sections, 2 equations, 29 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Data and MC samples
  3. Track reconstruction and energy-loss corrections
  4. ${\mathrm{J}\xspace / \uppsi\xspace }$ reconstruction and selection
  5. Cross-section as function of rapidity and $\cos \Theta_{\mathrm{CS}}$
  6. Summary
  7. Appendix
  8. Primary vertex

Figures (29)

  • Figure 1: Reconstructed invariant mass of opposite and same sign combinations, top Monte Carlo simulation, bottom data.
  • Figure 2: Reconstructed invariant mass of opposite sign combinations in the Monte Carlo simulation for different sources.
  • Figure 3: Momentum, transverse momentum and $y_{\mathrm{cm}}$ of ${\mathrm{J}\xspace / \uppsi\xspace }$ in the Monte Carlo simulation. For Pythia v6, there is little difference between primary and secondary ${\mathrm{J}\xspace / \uppsi\xspace }$ production.
  • Figure 4: First (top) and last (bottom) tracker station measurement in $x$(left)- and $y$(right)-projection for reconstructed tracks from ${\mathrm{J}\xspace / \uppsi\xspace }$ muons, with both tracks identified as muons with the RPCs. Monte Carlo simulation (magenta), data (blue).
  • Figure 5: Energy loss of a muon traveling through the $1.5$ m target and $2.4$ m iron as function of the muon momentum. The mean and RMS are shown. Monte Carlo simulation.
  • ...and 24 more figures