  A measurement is presented of the exclusive and semi-exclusive production of
charged pion pairs in proton-proton collisions, pp to p(p*) + $\pi^+\pi^-$ +
p(p*) here the $\pi^+\pi^-$ pair is emitted at central rapidities, and the
scattered protons stay intact (p) or diffractively dissociate (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 inverse
microbarns collected at a center-of-mass energy of 7 TeV. The dipion cross
section, measured for single-pion transverse momentum pt >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.
