Observation of Time Reversal Violation in the $B^0$ Meson System

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^0

or

\bar{B}^0

), and

J/\psi K_S^0

or

c\bar{c} K_S^0

final states (referred to as

B_+

or

B_-

), allow comparisons between the probabilities of four pairs of T-conjugated transitions, for example,

\bar{B}^0 \rightarrow B_-

and

B_- \rightarrow \bar{B}^0

, as a function of the time difference between the two B decays. Using 468 million

B\bar{B}

pairs produced in

\Upsilon(4S)

decays collected by the BABAR detector at SLAC, we measure T-violating parameters in the time evolution of neutral B mesons, yielding

\Delta S_T^+ = -1.37 \pm 0.14 (stat.) \pm 0.06 (syst.)

and

\Delta S_T^- = 1.17 \pm 0.18 (stat.) \pm 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.

Note:

7 pages, 3 postscript figures, 1 table, appendix with 4 pages containing supplementary material. Accepted by Phys. Rev. Lett

11.30.Er
13.25.Hw
14.40.Nd
time reversal: violation
B0 anti-B0: mixing
B0: hadronic decay
CP: violation
entanglement
electron positron: annihilation
B0: pair production

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Figures(18)

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