PDF《Measurement of time-dependent CP》

85748 Garching

77 Toho University, Funabashi 274-8510

78 Department of Physics, Tohoku University, Sendai 980-8578

79 Earthquake Research Institute, University of Tokyo, Tokyo 113-0032

80 Department of Physics, University of Tokyo, Tokyo 113-0033

81 Tokyo Institute of Technology, Tokyo 152-8550

82 Tokyo Metropolitan University, Tokyo 192-0397

83 Virginia Polytechnic Institute and State University, Blacksburg, Virginia

24061 84 Wayne State University, Detroit, Michigan

48202 85 Yamagata University, Yamagata 990-8560

86 Yonsei University, Seoul 120-749 We report a measurement of time-dependent CP violation in B0 → K0 Sπ0 π0 decays using a data sample of

772 *

106 B ? B pairs collected by the Belle experiment running at the Υ(4S) resonance at the KEKB e+ e? collider. This decay proceeds mainly via a b → sd ? d penguin amplitude. The results are sin 2φe?

1 = 0.92+0.27 ?0.31 (stat.) ±0.11 (syst.) and A = 0.28 ± 0.21 (stat.) ±0.04 (syst.),

3 which are the most precise measurements of CP violation in this decay mode to date. The value for the CP-violating parameter sin 2φe?

1 is consistent with that obtained using decay modes proceeding via a b → c? cs tree amplitude. PACS numbers: 11.30.Er, 12.15.Hh, 13.25.Hw In the Standard Model (SM), CP violation in the quark sector is induced by a complex phase in the Cabibbo-Kobayashi-Maskawa (CKM) quark mixing ma- trix [1].At Υ(4S) → B ? B transitions, for neutral B meson decays into a CP eigenstate produced, the decay rate has a time dependence [2, 3] P(?t, q) = e?|?t|/τB0 4τB0 * (1)

1 + q S sin(?md?t) + A cos(?md?t) , where S and A are CP-violating parameters;

q =

1 for ? B0 decays and ?1 for B0 decays;

?t is the di?erence in decay times of the B0 and ? B0 mesons;

?md is the mass di?erence between the two mass eigenstates of the B0 - ? B0 system;

and τB0 is the B0 lifetime. As the B0 → K0 Sπ0 π0 decays proceeds mainly via a b → sd ? d penguin am- plitude, and the ?nal state is CP even [4], the SM ex- pectation is S ≈ ? sin 2φ1 and A ≈ 0, where φ1 = arg[(?VcdV ? cb)/(VtdV ? tb)]. Deviations from these expecta- tions could indicate new physics. The value of sin 2φ1 is well-measured using decays proceeding via a b → c? cs tree amplitude, and thus comparing our measurement of sin 2φe?

1 to the b → c? cs value [6, 7] provides a test of the SM [8]. We note that there is a b → u? us tree ampli- tude that also contributes to B0 → K0 Sπ0 π0 decays and can shift φe?

1 from φ1;

however, this amplitude is doubly Cabibbo-suppressed, and thus the resulting shift is very small [9]. Previo........