Analysis of the resonant components in B0->J/\psi pi+pi-

TL;DR

This paper investigates the resonant components in B0->J/psi pi+pi- decays to improve understanding of CP violation effects, providing new measurements of decay fractions, resonance contributions, and setting limits on f0(980) resonance production.

Contribution

It presents the first detailed analysis of the final state composition in B0->J/psi pi+pi- decays, including resonance identification and upper limits on f0(980) production, enhancing CP violation studies.

Findings

Significant production of f0(500) and rho(770) resonances was observed.

No evidence for f0(980) resonance was found, setting an upper limit on its production.

Measured the branching fraction of B0->J/psi pi+pi- as (3.97 +/-0.09+/- 0.11 +/- 0.16)x10^{-5}.

Abstract

Interpretation of CP violation measurements using charmonium decays, in both the B0 and Bs systems, can be subject to changes due to "penguin" type diagrams. These effects can be investigated using measurements of the Cabibbo-suppressed B0->J/\psi pi+pi- decays. The final state composition of this channel is investigated 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 is performed using both the invariant mass spectra and the decay angular distributions. An improved measurement of the B0->J/\psi pi+pi- branching fraction of (3.97 +/-0.09+/- 0.11 +/- 0.16)x10^{-5} is reported where the first uncertainty is statistical, the second is systematic and the third is due to the uncertainty of the branching fraction of the decay B- -> J/\psi K- used as a normalization channel. In the J/\psi pi+pi- final state significant production of f0(500) and rho(770) resonances is found, both of which can be used for CP violation studies. In contrast evidence for the f0(980) resonance is not found, thus establishing the first upper limit on the branching fraction product B(B0->J/\psi f0(980) x B(f0(980)-> pi+ pi-) < 1.1x10^{-6}, leading to an upper limit on the absolute value of the mixing angle of the f0(980)$ with the f0(500) of <31 degrees, both at 90% confidence level.