Searches for a nucleon decay into a charged anti-lepton (e^+ or {mu}^+) plus a light meson ({pi}^0, {pi}^-, {eta}, {rho}^0, {rho}^-, {omega}) were performed using the Super-Kamiokande I and II data. Twelve nucleon decay modes were searched for. The t
otal exposure is 140.9 kiloton cdot years, which includes a 91.7 kiloton cdot year exposure (1489.2 live days) of Super-Kamiokande-I and a 49.2 kiloton cdot year exposure (798.6 live days) of Super-Kamiokande-II. The number of candidate events in the data was consistent with the atmospheric neutrino background expectation. No significant evidence for a nucleon decay was observed in the data. Thus, lower limits on the nucleon partial lifetime at 90% confidence level were obtained. The limits range from 3.6 times 10^31 to 8.2 times 10^33 years, depending on the decay modes.
A new application-specific integrated circuit (ASIC), the high-speed charge-to-time converter (QTC) IWATSU CLC101, provides three channels, each consisting of preamplifier, discriminator, low-pass filter, and charge integration circuitry, optimized f
or the waveform of a photomultiplier tube (PMT). This ASIC detects PMT signals using individual built-in discriminators and drives output timing signals whose width represents the integrated charge of the PMT signal. Combined with external input circuits composed of passive elements, the QTC provides full analog signal processing for the detectors PMTs, ready for further processing by time-to-digital converters (TDCs). High-rate (>1MHz) signal processing is achieved by short-charge-conversion-time and baseline-restoration circuits. Wide-range charge measurements are enabled by offering three gain ranges while maintaining a short cycle time. QTC chip test results show good analog performance, with efficient detection for a single photoelectron signal, four orders of magnitude dynamic range (0:3mV ~ 3V; 0:2 ~ 2500 pC), 1% charge linearity, 0.2 pC charge resolution, and 0.1 ns timing resolution. Test results on ambient temperature dependence, channel isolation, and rate dependence also meet specifications.
