Measurement of exclusive $\pi^{+} \pi^{-}$ production in proton-proton collisions at $\sqrt{s} = 7~\mathrm{TeV}$

We report a measurement of exclusive pion pair production in proton-proton collisions, dominated by $\mathrm{p} + \mathrm{p} \rightarrow \mathrm{p}^{(*)} + \pi^{+} \pi^{-} + \mathrm{p}^{(*)}$, where the $\pi^{+} \pi^{-}$ pair is produced at central rapidities $y$ and the incident protons stay intact or dissociate without being detected. The measurement is performed with the CMS detector at the LHC, using an integrated luminosity of $450~\mu \mathrm{b}^{-1}$ collected at a center-of-mass energy of $\sqrt{s} = 7~\mathrm{TeV}$ in 2010. The cross section measured in the phase space defined by $p_{T}(\pi)>0.2~\mathrm{GeV}/c$ and $|y(\pi)|< 2 $ is $20.5~\pm{0.3~(stat)}~\pm {3.1~(syst)}~\pm~{0.8~(lumi)}~\mu \mathrm{b}$. The differential $\pi^{+}\pi^{-}$ cross sections as a function of invariant mass, $p_{T}$, and $y$, and the single $\pi$ cross section as a function of $p_{T}$, are also shown and compared to model predictions.