BRANCHING FRACTION AND TIME-DEPENDENT CP ASYMMETRY IN NEUTRAL B DECAYS TO PSI AND A NEUTRAL PION

Abstract

The invariance of physical laws under the combination of exchange of particles with antiparticles (charge conjugation, C) and reversal of coordinates (parity, P) is called CP symmetry. The violation of CP symmetry was first discovered in 1964 in the neutral kaon system, and is in general one of the great puzzles of particle physics. The recent observation of CP violation in the B meson system has been a simultaneous success for model predictions and experiment. The opportunity now exists to probe details of the underlying mechanisms. This thesis presents measurements of the branching fraction and time-dependent CP-violating asymmetry in neutral B decays to J/{psi}{pi}{sup 0}. The decay amplitude for this channel features both tree and penguin diagram contributions, the interference of which can yield a result for the asymmetry differing from that found in the ''golden mode'' B{sup 0} {yields} J/{psi} K{sub s}{sup 0}. Using the measured branching fraction and CP asymmetry, constraints are placed on the ratio of penguin to tree amplitudes in B{sup 0} {yields} J/{psi}{pi}{sup 0}. In addition, the impact on the CP asymmetry measurement in B{sup 0} {yields} J/{psi} K{sub s}{sup 0} is discussed. The results are presented for e{sup +}e{sup -} annihilation data collected with the BABAR detector on the {Upsilon}(4S) resonance at the PEP-II asymmetric-energy B Factory at SLAC. The measurement of the branching fraction, based on about 23 million B{bar B} pairs collected between October 1999 and October 2000, yields BF(B{sup 0} {yields} J/{psi}{pi}{sup 0}) = (2.0 {+-} 0.6 (stat) {+-} 0.2(syst)) x 10{sup -5}. With about 88 million B{bar B} pairs collected during the years 1999-2002, our results for the coefficients of the cosine and sine terms of the CP asymmetry are C{sub J/{psi}{pi}{sup 0}} = 0.38 {+-} 0.41 (stat) {+-} 0.09 (syst) and S{sub J/{psi}{pi}{sup 0}} = 0.05 {+-} 0.49 (stat) {+-} 0.16 (syst).