Study of Rare B Meson Decays at Belle

In this paper, we briefly review results on rare decays of $B$ mesons from the Belle experiment, based on 10.4 fb$^{-1}$ data collected on the $\Upsilon$(4S) resonance. The topics include measurements of Cabibbo suppressed decays $B \to D^{(*)} K^{(*)}$, charmless two-body decays $B \to \pi\pi$, $K\pi$, $KK$ and $B \to \eta^{'} h (h = K^+, \pi^+, K^0)$, and a search for flavor changing neutral current decays $B \to K^{(*)} \ell^{+} \ell^{-}$.Comment: 21 pages, 8 figures, Contribution to the Proceedings of the 4th International Workshop on B Physics and CP Violation (BCP4), February 19-23, 2001, Ise-Shima, Japa

Study of a nonhomogeneous aerogel radiator in a proximity focusing RICH detector

The use of a nonhomogeneous aerogel radiator, i.e. one consisting of layers with different refractive indices, has been shown to improve the resolution of the Cherenkov angle measured with a proximity focusing RICH detector. In order to obtain further information on the performance of such a detector, a simple model has been used to calculate the resolution and search for optimal radiator parameters.Comment: Submitted to Nucl. Instr. Met

The Event Timing Finder for the Central Drift Chamber Level-1 Trigger at the Belle II experiment

The level-1 trigger system of the Belle II experiment is designed to select physics events of interest with almost 100% efficiency for hadronic events. In terms of event timing decision, the level-1 trigger is required to have an accuracy of less than 10 ns. The Central Drift Chamber (CDC) level-1 trigger provides the event timing information as one of the level-1 timing sources. We developed the new algorithm to measure the event timing with an accuracy of about 10 ns based on the CDC hit timing. Two-dimensional charged track reconstruction by Hough transformation was utilized to reduce high background hits. We used a new-developed general-purpose FPGA board (Universal Trigger board 4) for this module for the first time. We report the performance of the new algorithm using e$^+$e$^−$ collision data collected in 2020

Development of a multi-pixel photon sensor with single-photon sensitivity

A multi-pixel photon sensor with single-photon sensitivity has been developed, based on a technology of a hybrid photo-detector (HPD) consisting of a photocathode and a multi-pixel avalanche diode (MP-AD). The developed HPD has a proximity focused structure, where a photocathode and an MP-AD are facing each other with a small gap of 2.5 mm. The MP-AD, which has an effective area of 16x16 mm2 composed of 8x8 pixels, has been specially designed for the HPD. The gain of the HPD reaches 5x10^4, sufficiently high to detect single photons with a timing resolution better than 100 ps. Number of photoelectrons up to four can be clearly identified in a pulse-height spectrum as distinct peaks, thanks to the low noise characteristics of the HPD. It is also demonstrated that the HPD can be operated with good performance in a magnetic field as high as 1.5 TComment: 39 pages, 22 figures, submitted to Nucl. Intr. and Meth.

Production of doubly strange hypernuclei via {\Xi}- doorways in the 16O(K-, K+) reaction at 1.8 GeV/c

We examine theoretically production of doubly strange hypernuclei, 16 {\Xi}-C and 16 {\Lambda}{\Lambda}C, in doublecharge exchange 16O(K-, K+) reactions using a distorted-wave impulse approximation. The inclusive K+ spectrum at the incident momentum pK- = 1.8 GeV/c and scattering angle {\theta}lab = 0^{\circ} is estimated in a one-step mechanism, K-p \to K+{\Xi}- via {\Xi}- doorways caused by a {\Xi}-p-{\Lambda}{\Lambda} coupling. The calculated spectrum in the {\Xi}- bound region indicates that the integrated cross sections are on the order of 7-12 nb/sr for significant 1- excited states with 14C(0+, 2+) \otimes s{\Lambda}p{\Lambda} configurations in 16 {\Lambda}{\Lambda}C via the doorway states of the spin-stretched 15N(1/2-, 3/2-) \otimes s{\Xi}- in 16 {\Xi}-C due to a high momentum transfer q{\Xi}- \approx 400 MeV/c. The {\Xi}- admixture probabilities of these states are on the order of 5-9%. However, populations of the 0+ ground state with 14C(0+) \otimes s2{\Lambda} and the 2+ excited state with 14C(2+) \otimes s2 {\Lambda} are very small. The sensitivity of the spectrum on the {\Xi}N-{\Lambda}{\Lambda} coupling strength enables us to extract the nature of {\Xi}N-{\Lambda}{\Lambda} dynamics in nuclei, and the nuclear (K-, K+) reaction can extend our knowledge of the S = -2 world.Comment: 10 pages, 3 figure