P. Krizan

An improved upper limit on the ντ-mass from the decay π−→π−π−π−π+π+ντ

Abstract Using the ARGUS detector at the e + e − storage ring DORIS II, we have observed the decay τ − → π − π − π − π + π + ν τ in tau-pair events produced at center-or-mass energies between 9.4 and 10.6 GeV. From the 5π invariant mass distribution we derive an upper limit of m ( ν τ ) c 2 at the 95% confidence level. The branching ratio for this decay channel is found to be (0.064±0.023±0.01)%.

An Improved Upper Limit on the tau-neutrino Mass from the Decay tau- ---> pi- pi- pi- pi+ pi+ tau-neutrino

Abstract Using the ARGUS detector at the e + e − storage ring DORIS II, we have observed the decay τ − → π − π − π − π + π + ν τ in tau-pair events produced at center-or-mass energies between 9.4 and 10.6 GeV. From the 5π invariant mass distribution we derive an upper limit of m ( ν τ ) c 2 at the 95% confidence level. The branching ratio for this decay channel is found to be (0.064±0.023±0.01)%.

PHOTON DETECTORS FOR THE HERA-B RICH

Abstract Results of tests of different position-sensitive photon detectors for the HERA-B RICH are given. It is observed, that the CsI-MWPC cannot be routinely produced and maintained with sufficiently high quantum efficiency and that the TMAE detector loses anode wire gain too quickly. The third candidate, the H-6568 Hamamatsu multianode PMT, seems to meet all the requirements necessary for photon detection in the HERA-B RICH.

Measurement of the polarization in the decay B ---> J / psi K*

Abstract Polarization in the exclusive decay B → J/ψK ∗ was measured using the ARGUS detector at the e+e− storage ring DORIS II. The ratio of the transverse to the total decay width was found to be ΓT/Γ = 0.03±0.16±0.15. This measurement demonstrates that the B 0 → J/ψK ∗0 decay channel can be effectively used for CP violation studies.

Recent progress in Cerenkov counters

The paper reviews recent progress in individual components of Cerenkov counters, as well as the performance of installed detector systems.

Aging and rejuvenation of a TMAE+methane multiwire photon detector

A UV sensitive multiwire photon detector has been tested as a possible candidate for the HERA-B RICH detector. The main obstacle to using such a TMAE+Methane filled gas detector in a high rate experiment appears to be rapid aging in the form of prohibitive loss of chamber gas gain. A special circuit has been designed for heating the anode wires in-situ with elevated currents, thus evaporating the polymer deposits. Heating almost completely recovers the initial gain, but this rejuvenation is unfortunately of short duration. Nevertheless, the cells exposed to periodic heat treatments have an average gain considerably higher than the non-heated cells.

Amplitude analysis of e+e- => Y(nS)pi+pi- at sqrt(s)=10.865 GeV

We report results on studies of the e+e- annihilation into three-body Y(nS)pi+pi- (n=1,2,3) final states including measurements of cross sections and the full amplitude analysis. The cross sections measured at sqrt(s)=10.865 GeV and corrected for the initial state radiation are sigma(e+e-=>Y(1S)pi+pi-)=(2.27+-0.12+-0.14) pb, sigma(e+e-=>Y(2S)pi+pi-)=(4.07+-0.16+-0.45) pb, and sigma(e+e-=>Y(3S)pi+pi-)=(1.46+-0.09+-0.16) pb. Amplitude analysis of the three-body Y(nS)pi+pi- final states strongly favors I^G(J^P)=1^+(1^+) quantum-number assignments for the two bottomonium-like Zb+- states, recently observed in the Y(nS)pi+- and hb(mP)pi+- (m=1,2) decay channels. The results are obtained with a

Studies of a proximity focusing RICH with aerogel radiator for Belle II experiment

121.4 1/fb data sample collected with the Belle detector at the KEKB asymmetric-energy e+e- collider.

Search for neutrinoless

For the Belle II experiment, we are developing a proximity focusing ring imaging Cherenkov counter using a silica aerogel as a radiator. Recently, a new aerogel fabrication method, called “pin-hole drying”, was invented and remarkably improved optical transparency has been realized in the region of refractive index larger than 1.05. For the photo-detector, we have developed a 144-channel Hybrid Avalanche Photo-Detector with Hamamatsu Photonics K. K. The HAPD has excellent single photon detection performance, 5 × 5 mm2 position resolution and immunity to magnetic field. The tolerance to the neutron irradiation up to 5 × 1011 neutron/cm2 has been confirmed. In November 2009, we have performed a test beam experiment at KEK for a prototype A-RICH counter with 6 HAPDs and aerogel tiles produced by the “pin-hole drying” method. We successfully observed a clear Cherenkov ring image and obtained the single photon Cherenkov angle resolution of 13.5 mrad and 15.3 detected photoelectrons. This result corresponds to more than 6σ K/π separation at 4 GeV/c and fulfills the requirement for the Belle II.

\tau

AbstractUpper limits on branching ratios for six neutrinoless leptonic, 16 semileptonic, two radiative-leptonic, two radiative-hadronic and three purely hadronic τ decays have been determined. The results improve over previously published ones by about a factor of two. For the first time the lepton and baryon number violating decays