M. Akatsu

Time-of-propagation Cherenkov counter for particle identification

Abstract We describe here a new concept of a Cherenkov detector for particle identification by means of measuring the Time-of-Propagation (TOP) of Cherenkov photons.

Observation of Large CP Violation and Evidence for Direct CP Violation in B0→π+π- Decays

We report the first observation of CP violation in B0-->pi(+)pi(-) decays based on 152x10(6) gamma (4S)-->BB decays collected with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. We reconstruct a B0-->pi(+)pi(-) CP eigenstate and identify the flavor of the accompanying B meson from its decay products. From the distribution of the time intervals between the two B meson decay points, we obtain A(pipi)=+0.58+/-0.15(stat)+/-0.07(syst) and S(pipi)=-1.00+/-0.21(stat)+/-0.07(syst). We rule out the CP-conserving case, A(pipi)=S(pipi)=0, at a level of 5.2 standard deviations. We also find evidence for direct CP violation with a significance at or greater than 3.2 standard deviations for any S(pipi) value.

Measurement of B^0_d-¯B^0_d Mixing Rate from the Time Evolution of Dilepton Events at the Y(4S)

We report a determination of the B(0)(d)-&B_(0)(d) mixing parameter Deltam(d) based on the time evolution of dilepton yields in Upsilon(4S) decays. The measurement is based on a 5.9 fb(-1) data sample collected by the Belle detector at KEKB. The proper-time difference distributions for same-sign and opposite-sign dilepton events are simultaneously fitted to an expression containing Deltam(d) as a free parameter. Using both muons and electrons, we obtain Deltam(d) = 0.463+/-0.008 (stat)+/-0.016 (syst) ps(-1). This is the first determination of Deltam(d) from time evolution measurements at the Upsilon(4S). We also place limits on possible CPT violations.

Progress report on Time-Of-Propagation counter—a new type of ring imaging Cherenkov detector

Abstract The Time-Of-Propagation (TOP) counter measures both the time and position information of radiated photons with high resolutions to distinguish the Cherenkov angles between different particle species. Current R&D status is reported. We also propose a further simplified version of the TOP-counter.

Observation of the D1(2420)→Dπ+π- decays

We report on the first observation of D{sub 1}{sup 0}(2420){yields}D{sup 0}{pi}{sup -}{pi}{sup +} and D{sub 1}{sup +}(2420){yields}D{sup +}{pi}{sup -}{pi}{sup +} decays (where the contribution from the dominant known D{sub 1}{yields}D*{pi} decay mode is excluded) in the B{sup -}{yields}D{sub 1}{sup 0}{pi}{sup -} and B{sup 0}{yields}D{sub 1}{sup +}{pi}{sup -} decays, respectively. The observation is based on 15.2x10{sup 7} BB events collected with the Belle detector at the KEKB collider. We also set 90% confidence level upper limits for the branching fractions of the four following decays: B{sup -}{yields}D{sub 1}{sup 0}{pi}{sup -}, D{sub 1}{sup 0}{yields}D*{sup 0}{pi}{sup -}{pi}{sup +}, B{sup 0}{yields}D{sub 1}{sup +}{pi}{sup -}, D{sub 1}{sup +}{yields}D{sup *+}{pi}{sup -}{pi}{sup +}, B{sup -}{yields}D{sub 2}*{sup 0}(2460){pi}{sup -}, D{sub 2}*{sup 0}{yields}D*{sup 0}{pi}{sup -}{pi}{sup +}, B{sup 0}{yields}D{sub 2}*{sup +}(2460){pi}{sup -}, D{sub 2}*{sup +}{yields}D{sup *+}{pi}{sup -}{pi}{sup +}.We report on the first observation of

Vidence for CP-violating asymmetries in B0→π +π- decays and constraints on the CKM angle φ2

D_1\to D\pi^+\pi^-

Development of a 24-anode linear-array fine-mesh PMT with 85% photoelectron detection efficiency and 100 ps TTS at

decays (where the contribution from the dominant known

Observation of B0→π0π0

D_1 \to D^* \pi

R&D report on fine-mesh multi-anode PMT with TTS = 100 ps under B ≤ 1 T

decay mode is excluded) in the

A high-resolution cylindrical drift chamber for the KEK B-factory

B\to D_1\pi