Exclusive and semi-exclusive $\pi^{+}\pi^{-}$ production in proton-proton collisions at $\sqrt{s} =$ 7 TeV

Abstract

A measurement is presented of the exclusive and semi-exclusive production of charged pion pairs in proton-proton collisions, $\mathrm{ p p }\to\mathrm{ p }({\mathrm{p}^*} )+ \pi^{+}\pi^{-}+ \mathrm{ p } ({\mathrm{p}^*} )$, where the $\pi^{+} \pi^{-}$ pair is emitted at central rapidities, and the scattered protons stay intact ($\mathrm{p}$) or diffractively dissociate (${\mathrm{p}^*}$) without detection. The measurement is performed with the CMS detector at the LHC, using a data sample corresponding to an integrated luminosity of 450 $\mu$b$^{-1}$ collected at a center-of-mass energy of 7 TeV. The dipion cross section, measured for single-pion transverse momentum $p_{\mathrm{T}} >$ 0.2 GeV/$c$ and rapidity $|{y}| 0.2 GeV and rapidity abs(y)<2, is 26.5 +/- 0.3 (stat) +/- 5.0 (syst) +/- 1.1 (lumi) microbarns. The differential cross sections measured as a function of the invariant mass, pt, and y of the pion pair, and as a function of single-pion pt, are compared to phenomenological predictions