Exclusive pi+ pi- production at 7TeV

We report a measurement of the exclusive production of pairs of charged pions in proton-proton collisions, dominated by the process $pp \rightarrow p^{()} \pi^{+}\pi^{-} p^{()}$,where$\rm p^{()}$ stands for a diffractively dissociated proton, the ${\pi }^{+}{\pi }^{-}$ pair is emitted at central rapidities $y$, and the incident protons stay intact or dissociate without detection ${\rm p^{()}}$. 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 $\sqrt{s}$ = 7 TeV in 2010. The cross section measured in the phase space defined by pion transverse momentum $p_{\rm T}>0.2$GeV\mathrm{/}candrapidity$|y|< 2 $isfoundtobe$20.5~\pm~0.3~(\rm {stat})~(\pm~3.1~\rm {syst})~\pm$0.8(lumi)$\mu$b. The differential cross sections for ${\pi }^{+}{\pi }^{-}$ pairs as a function of the pion pair invariant mass, $p_{\mathrm{T}}$, and $y$, as well as a single-pion differential cross section as a function of pion $p_{\mathrm{T}}$ are also measured and compared to several phenomenological predictions.