We report measurements of partial branching fractions of inclusive charmless semileptonic B-meson decays at the endpoint of the electron momentum spectrum. The measurements are made in six ...overlapping momentum intervals that have lower bounds ranging from 1.9 to 2.4 GeV/c and a common upper bound of 2.6 GeV/c, as measured in the centre of mass frame. The results are based on a sample of 29 million BB¯ pairs, accumulated by the Belle detector at the KEKB asymmetric e+e− collider operating on the ϒ(4S) resonance. In the momentum interval ranging from 1.9 to 2.6 GeV/c we measure the partial branching fraction ΔB(B→Xueνe)=(8.47±0.37±1.53)×10−4, where the first error is statistical and the second is systematic. A prediction of the partial rate R=(21.69±3.62−1.98+2.18)|Vub|2 ps−1 in this momentum interval based on theory is calculated with input HQET parameters that have been derived from Belle's measurement of the B→Xsγ photon energy spectrum, where the first error is due to the uncertainty on HQET parameters and the second error is from theory. Using both ΔB(B→Xueνe) and R we find |Vub|=(5.08±0.47±0.42−0.23+0.26)×10−3, where the first error is from the partial branching fraction, and the second and third errors are from uncertainties in R.
For future upgrade of the Belle detector at the KEK B-factory we are developing a proximity focusing ring imaging Cherenkov detector using aerogel as a radiator. We present results from recent beam ...tests using 4times4 array of the flat-panel multi-anode PMTs. We introduce a new design, so called "dual radiator" scheme to improve the performance. In this design, we image Cherenkov photons from two aerogel radiators with different refractive indices. The results of the beam tests show that the photoelectron yield can be increased without significant deterioration in the angular resolution, leading to 4.8sigma K/pi separation at 4 GeV/c. We also discuss multi-radiator RICH, which consists of more than two radiators.
Currently, we are working on the program of the Belle detector upgrade, and the Cherenkov ring imaging counter with silica aerogel radiator (aerogel-RICH) is the most promising candidate for the ...particle identification device (PID) at the endcap section of the BELLE detector, where a threshold-type aerogel Cherenkov counter is occupied at present, in order to further expand pi-K separation capabilities at higher momentum region. Refractive index of silica aerogel should be around /spl sim/1.05 to match our PID requirement and must possess high optical transparency. Based upon our experience, new production technique has been developed to make high transparent aerogels with hydrophobicity. In this method, new chemical solvent, DMF (di-methyl formamide), is introduced and various conditions such as a mixing ratio of solvent as well as catalyst are optimized. As a result, aerogels with transmission length longer than 40 mm at 400 nm wavelength are successfully obtained. The optical quality is also confirmed in a series of beam tests, and we have observed Cherenkov photon yields significantly increased. We also produced multi-layer aerogels, where two layers with different refractive index are stacked as one sample. This can be used as a radiator to increase Cherenkov photons without stacking radiators by focusing Cherenkov photons. In this talk, details of the aerogel production method are described and high optical performance is also demonstrated.
Using aerogel as radiator and the BURLE 85011 multianode microchannel plate PMT for photon detection, a proximity focusing Cherenkov ring imaging detector has been constructed and tested in the KEK .../spl pi/2 beam. The aim was to experimentally study the performance of the photon detector, in particular its ability to efficiently detect single photons.
A high precision study of the process γγ→pp¯ has been performed using a data sample of 89 fb−1 collected with the Belle detector at the KEKB e+e− collider. The cross section of pp¯ production has ...been measured at two-photon center-of-mass (c.m.) energies between 2.025 and 4.0 GeV and in the c.m. angular range of |cosθ∗|<0.6. Production of γγ→ηc→pp¯ is observed and the product of the two-photon width of the ηc and its branching ratio to pp¯ is determined.
We report measurements of branching fractions for B --> K pi and B --> pi pi decays based on a data sample of 449 x 10(6) BBover pairs collected at the Upsilon(4S) resonance with the Belle detector ...at the KEKB asymmetric-energy e(+)e(-) collider. We also measure the ratios of partial widths for B-->Kpi decays, namely R(c) identical with 2Gamma(B(+) --> K(+) pi(0))/Gamma(B(+) --> K(0) pi(+)) = 1.08+/-0.06+/-0.08 and R(n) identical with Gamma(B(0) --> K(+) pi(-))/2 Gamma(B(0) --> K(0) pi(0)) = 1.08+/-0.08+/-0.08, where the first and the second errors are statistical and systematic, respectively. These ratios are sensitive to enhanced electroweak penguin contributions from new physics; the new measurements are, however, consistent with standard model expectations.
We have searched for neutrinoless τ lepton decays into three charged leptons using an 87.1fb−1 data sample collected with the Belle detector at the KEKB e+e− collider. Since the number of signal ...candidate events is compatible with that expected from the background, we set 90% confidence level upper limits on the branching fractions in the range (1.9–3.5)×10−7 for various decay modes τ−→ℓ−ℓ+ℓ− where ℓ represents e or μ.
PDF
