Analysis of the resonant components in Bs->J/\psi\pi+\pi-
  The decay Bs->J/\psi\pi+\pi- can be exploited to study CP violation. A detailed understanding of its structure is imperative in order to optimize its usefulness. An analysis of this three-body final state is performed using a 1.0/fb sample of data produced in 7 TeV pp collisions at the LHC and collected by the LHCb experiment. A modified Dalitz plot analysis of the final state is performed using both the invariant mass spectra and the decay angular distributions. The \pi+\pi- system is shown to be dominantly in an S-wave state, and the CP-odd fraction in this Bs decay is shown to be greater than 0.977 at 95% confidence level. In addition, we report the first measurement of the J/\psi\pi+\pi- branching fraction relative to J/\psi\phi\ of (19.79 +/- 0.47 +/- 0.52)%. 
The LHCb collaboration: R. Aaij, C. Abellan Beteta, B. Adeva, M.   Adinolfi, C. Adrover, A. Affolder, Z. Ajaltouni, J. Albre...
hep-ex