H. Yuta

Cosmic-ray test of the installed endcap RPC modules in BELLE detector

In BELLE detector at KEKB, the resistive plate counter (RPC) modules were constructed for the muon trigger and K/sub L//sup 0/ detection. The endcap quadrant consisting of 14 superlayer RPC modules alternating with 47 mm thick iron plates and the 112 endcap modules have been installed in BELLE detector. We study on the tracking performance of the installed endcap RPC modules using by cosmic-ray test for the whole BELLE detector system.

Neutron sensitivity of the endcap RPC modules in Belle detector

The primary purpose in the Belle experiment at the asymmetric-energy e/sup =/e/sup -/ collider at the High-Energy Accelerator Research Organization (KEK B factory) is the measurement of charge conjugation and parity (CP) violation in B meson decays. The K/sub L/ mesons and muons (KLM) detector was designed to identify K/sub L/s and muons in this experiment. Since October 2001, the luminosity in the KEK B accelerator has been remarkably improved. The data on B meson decay are successfully collected in the Belle detector. In contrast with the high luminosity operations of the accelerator, however, the high background rate leading to a lower detection efficiency has been observed in the endcap KLM detector. For present and future high luminosity operations, we have to identify the background source and consider the shielding. To identify the background source, the background data sampled from e/sup +/e/sup -//spl rarr//spl mu//sup +//spl mu//sup -/ events were investigated and the simulations of the sensitivity of the endcap KLM detector to neutrons and /spl gamma/s as the background sources were performed using the Geant4 simulation toolkit. The comparisons of the simulations with the experimental data are presented.

Detection of Muons, and K//sup 0/sub L// Mesons from e+e- collisions using the endcap RPC module in the Belle detector

The BELLE experiment at KEKB has collected beam collision data from 1 June through 4 August 1999, corresponding to an integrated luminosity of 25 pb -1 , and the data contain approximately 10,000 e + e - -> μ + μ - events and 50,000 hadronic events. Using those events, we study the performance of the endcap RPC modules in the BELLE detector. The study shows that the endcap RPC modules perform quite well in detecting muons and K 0 L mesons.

Signal observation from a pulsed ionization chamber filled with tetramethyl germanium

Ionization signals from 207Bi conversion electrons were observed in a pulsed ionization chamber filled with purified tetramethylgermanium liquid. The free ion yield at zero field was measured as 0.57. The lifetimes of drifting electrons in the liquid were measured as 0.99, 3.99 and 4.32 µs for increasing purification cycles.

Performance of endcap RPC for the BELLE at KEK

The Resistive Plate Counters (RPC) has been provided for K/sub L//sup 0/ and muon detection in the BELLE experiment at KEK. The glass RPCs have been extensively tested using single cosmic-ray muons. We report on the performance of the endcap RPC with emphasis on detection efficiency and multiple hits of readout strips.

A study of non-flammable gas mixture for resistive plate counter

The RPC (resistive plate counter) has good time and position resolution. These factors make it an attractive candidate for trigger system at collider experiment. The standard gas mixtures (Ar+iso-C/sub 4/H/sub 10/+Freon) used in RPC are very flammable when leaked into air. In view of safety issue,we have studied non-flammable gas of Ar+CO/sub 2/+iso-C/sub 4/H/sub 10/+Freon as a function of ratio Ar:CO/sub 2/ allowed in non-flammable gas mixtures for the RPC with ABS electrodes. The basic performance of the various mixtures have been measured; singles (untriggered) count rate, detection efficiency and charge spectra versus operating voltage. We have found a set of non-flammable mixtures of the kind of Ar+CO/sub 2/+Freon contained less than /spl sim/8.4% of iso-C/sub 4/H/sub 10/ for K/sub L//muon counter of KEK B-factory at KEK.

A search for a freonless gas mixture for glass RPC

We have operated successfully the glass Resistive Plate Counters in the streamer mode at BELLE experiment by using a nonflammable gas mixture of argon 30%, butane-silver 8% and freon. HFC-134a 62%. This freon is non-ozone depleting freon, but having a high global warming potential, 1300 times higher than that of CO/sub 2/. Freon gases might be unusable in the near future. We tested a performance of glass RPC operated in the streamer mode with the alternative gas mixtures of argone, butane, CO/sub 2/ and/or O/sub 2/ gases, and found an efficiency of about 90%.

Radiation damage to tetramethlysilane and tetramethlygermanium ionization chambers

Two detector media suitable for a warm liquid ionization chamber filled with tetramethylsilane (TMS) and tetramethylgermanium (TMG) were exposed to /spl gamma/-radiation from a /sup 60/Co source up to a dose of 579 Gray and 902 Gray, respectively. The electron lifetimes and the free ion yields were measured as a function of accumulated radiation dose. A similar behavior of the electron lifetimes and the free ion yields with increasing radiation dose was observed between the TMS and TMG ionization chambers. >

Study of streamer size measurements using CCD camera system

We report on a study of correlation between readout pulses and lights of streamer produced in the glass resistive plate chamber (RPC) with six Ar gas mixtures (Ar/butane-silver/HFC134a). The streamer pulse produced by cosmic-ray are analyzed as a function of Ar/HFC134a mixing ratio using a digital oscilloscope. The streamer image due to the lights from the streamer is taken by using an image intensifier and a CCD camera. The average streamer size become larger linearly with increase Ar gas mixing ratio. The Ar/HFC134a ratio dependence of the charge and intensity were studied. The analysis of the light image of streamer might be useful for us to design the pickup pad width for the readout.

Free ion yields for tetramethylsilane and tetramethylgermanium

The free ion yields from /sup 207/Bi conversion electrons were measured as a function of applied electric field using ionization chambers filled with tetramethylsilane (TMS) and tetramethylgermanium (TMG). The distributions for thermalization lengths of electrons were calculated by using Gaussian and exponential forms. The total free ion yields considering the impurity effect in liquid, and the thermalization lengths of electrons in TMS and TMG were determined to be 3.35+or-0.49, 3.42+or-0.56 and 165+or-18 AA, 185+or-24 AA, respectively.<<ETX>>