Measurement of exclusive pion pair production in proton-proton collisions at $\sqrt{s} = 7$ TeV with the ATLAS detector

TL;DR

This paper reports the first measurement of exclusive pion pair production in proton-proton collisions at 7 TeV using the ATLAS detector, demonstrating proton tagging and providing cross-section data for theoretical comparison.

Contribution

It introduces the first use of proton tagging to measure exclusive hadronic final states at the LHC and provides new cross-section measurements for pion pair production.

Findings

Measured cross sections of 4.8 μb and 9 μb in two kinematic regions.

Demonstrated the feasibility of exclusive hadronic final state measurements at the LHC.

Compared experimental results with theoretical models.

Abstract

The exclusive production of pion pairs in the process $pp\to pp\pi^+\pi^-$ has been measured at $\sqrt{s}$ = 7 TeV with the ATLAS detector at the LHC, using 80 $\mu$b$^{-1}$ of low-luminosity data. The pion pairs were detected in the ATLAS central detector while outgoing protons were measured in the forward ATLAS ALFA detector system. This represents the first use of proton tagging to measure an exclusive hadronic final state at the LHC. A cross-section measurement is performed in two kinematic regions defined by the proton momenta, the pion rapidities and transverse momenta, and the pion-pion invariant mass. Cross section values of $4.8 \pm 1.0 \text{(stat.)} + {}^{+0.3}_{-0.2} \text{(syst.)}\mu$b and $9 \pm 6 \text{(stat.)} + {}^{+2}_{-2}\text{(syst.)}\mu$b are obtained in the two regions; they are compared with theoretical models and provide a demonstration of the feasibility of measurements of this type.