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.
Highlights
The CP violation measurements using neutral B meson decays into J=c mesons are of prime importance both for determinations of Standard Model parameters and searching for physics beyond the Standard Model
The decay rate for these J=c modes is dominated by the color-suppressed tree level diagram, an example of which is shown for B"0 decays in Fig. 1(a), while penguin processes, an example of which is shown in Fig. 1(b), are expected to be suppressed
The decay B"0 ! J=c þÀ, with J=c ! þÀ, can be described by four variables. These are taken to be the invariant mass squared of J=c þ (s12 m2ðJ=c þÞ), the invariant mass squared of þÀ (s23 m2ðþÀÞ), where we use label 1 for J=c, 2 for þ, and 3 for À, the J=c helicity angle (J=c ), which is the angle of the þ in the J=c rest frame with respect to the J=c direction in the B"0 rest frame, and the angle between the J=c and þÀ decay planes () in the B"0 rest frame
Summary
The CP violation measurements using neutral B meson decays into J=c mesons are of prime importance both for determinations of Standard Model parameters and searching for physics beyond the Standard Model. Final states containing vector resonances, such as the ð770Þ, can be analyzed in a similar manner as was done for the decay B"0s ! (a) Tree level and (b) penguin diagram examples for B"0 decays into J=c KS0. (a) Tree level and (b) penguin diagram for B"0 decays into J=c þÀ. In this paper the J=c þ and þÀ mass spectra and decay angular distributions are used to determine the resonant and nonresonant components. This differs from a classical Dalitz-plot analysis [12] because one of the particles in the final state, the J=c meson, has spin 1 and its three decay amplitudes must be considered. We report on the resonant structure and the CP content of the final state
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