Observation of Time-Reversal Violation in the B[superscript 0] Meson System

Abstract

Although CP violation in the B meson system has been well established by the B factories, there has been no direct observation of time-reversal violation. The decays of entangled neutral B mesons into definite flavor states (B[superscript 0] or B̅[superscript 0]), and J/ψK[subscript L][superscript 0] or cc̅ K[subscript S][superscript 0] final states (referred to as B+ or B-), allow comparisons between the probabilities of four pairs of T-conjugated transitions, for example, B̅[superscript 0]→B[subscript -] and B_→B̅[superscript 0], as a function of the time difference between the two B decays. Using 468×10[superscript 6] BB̅ pairs produced in Υ(4S) decays collected by the BABAR detector at SLAC, we measure T-violating parameters in the time evolution of neutral B mesons, yielding ΔS[subscript T]+=-1.37±0.14(stat)±0.06(syst) and ΔS[subscript T[superscript]]-=1.17±0.18(stat)±0.11(syst). These nonzero results represent the first direct observation of T violation through the exchange of initial and final states in transitions that can only be connected by a T-symmetry transformation.