Takayoshi Ohshima

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 B^+ ¿ ¿K^+

We report the first observation of the charmless hyperonic B decay, B+-->LambdaLambdaK+, using a 140 fb(-1) data sample recorded at the Upsilon(4S) resonance with the Belle detector at the KEKB (e+)(e-) collider. The measured branching fraction is B(B+-->LambdaLambdaK+) = (2.91(+0.90)(-0.70) +/- 0.38) x 10(-6). We also perform a search for the related decay mode B+-->LambdaLambdapi+, but do not find a significant signal. We set a 90% confidence-level upper limit of B(B+-->LambdaLambdapi+) < 2.8 x 10(-6).

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.

Test result of time-of-propagation Cherenkov counter

Abstract A new concept concerning Cherenkov detector for particle identification by means of measuring both the Time-of-Propagation (TOP) and horizontal emission angle ( Φ ) of Cherenkov photons is described here. Some R&D works are also reported.

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

By shortening the distance between the photocathode and the first dynode to 1 mm and using a finer mesh size of 2500 lines/in. with , a 24 anode linear-array of fine-mesh photomultiplier tube has produced a clear single-photon peak in its pulse-height distribution under a strong magnetic field of , and provided of transit time spread (TTS) and 85% of photoelectron detection efficiency.

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

Abstract R&D results on a 24-anode linear-array fine-mesh photomultiplier tube (L24-PMT) are reported. Under a magnetic field of B ⩽1 and 1.5 T , we have attained a transit time spread of σ =100 and 150 ps , respectively, as well as a photoelectron collection efficiency of 85%.

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

The Central Drift Chamber of the BELLE detector at the KEK B-factory is a cylindrical wire chamber device that uses a helium-based gas and aluminum field wires and is situated in a 1.5 T magnetic field. The transverse momentum resolution for charged tracks with 1.0 GeV/c transverse momentum is 0.35%. This paper describes the chambers configuration and performance.

Test of charge-to-time conversion and multi-hit TDC technique for the BELLE CDC readout

We tested a new CDC readout scheme utilizing a Charge-to-Time conversion (QTC) technique and multi-hit TDC to record both time and charge information. The new scheme is planned to be used in the BELLE experiment at the KEK B-Factory. We built a prototype Shaper/QTC board and examined the performance with a beam test. This new scheme worked successfully. We obtained the same spatial and dEdx resolutions as those using an ordinary TDC and ADC readout scheme.

Z-trigger system with the BELLE Central Drift Chamber

Abstract We describe the design and performance of a fast Z -trigger system with the BELLE Central Drift Chamber. It utilizes z -position information from the axial/stereo wire hits as well as the cathode strip. This system is essential to reduce the false trigger rate from caused by the spent electrons or positrons interacting with the material around the beam pipe. We tested the performance of the system using cosmic rays in a magnetic field of 1.5 T, provided by a superconducting solenoid. The trigger efficiency was 98% for a single track passing through the interaction region. This trigger was effective in rejecting tracks originating from points more than 10 cm away from the interaction point.

Examination of T/CP Invariance in the e^+e^-τ^+τ^- Reaction

We propose a method to examine the T/CP invariance of the heaviest lepton, tau, by means of a triple-momentum correlation for the reaction e^+e^- -->tau^+tau^-, tau --> e/mu nu nubar during the course of the B-Factory experimental program. An unprecedented high sensitivity could be obtained without requiring a high integrated luminosity.