Measurement of exclusive pion pair production in proton-proton collisions at √s=7 TeV with the ATLAS detector

The exclusive production of pion pairs in the process pp -> pp pi(+)pi(-) has been measured at root s = 7TeV 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 forwardATLASALFAdetector system. This represents the first use of proton tagging to measure an exclusive hadronic final state at the LHC. Across-sectionmeasurement 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 +/- 1.0 (stat)(-0.2) (+0.3)(syst) mu b and 9 +/- 6 (stat)(-2)(+2) (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.