32 research outputs found
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
Measurement of branching fractions for decays and search for a narrow resonance in the final state
We report an observation of the and decays using pairs collected at the resonance with the Belle detector at the KEKB asymmetric-energy collider. We obtain the branching fractions and . We search for a new narrow charmonium(-like) state in the mass spectrum and find no significant excess. We set upper limits on the product of branching fractions, , at where a -odd partner of may exist, at and assuming their known mass and width, and over a range from 3.8 to . The obtained upper limits at 90% confidence level for , , and are , , and , respectively
Silicon Photomultiplier Research and Development Studies for the Large Size Telescope of the Cherenkov Telescope Array
The Cherenkov Telescope Array (CTA) is the the next generation facility of
imaging atmospheric Cherenkov telescopes; two sites will cover both
hemispheres. CTA will reach unprecedented sensitivity, energy and angular
resolution in very-high-energy gamma-ray astronomy. Each CTA array will include
four Large Size Telescopes (LSTs), designed to cover the low-energy range of
the CTA sensitivity (20 GeV to 200 GeV). In the baseline LST design, the
focal-plane camera will be instrumented with 265 photodetector clusters; each
will include seven photomultiplier tubes (PMTs), with an entrance window of 1.5
inches in diameter. The PMT design is based on mature and reliable technology.
Recently, silicon photomultipliers (SiPMs) are emerging as a competitor.
Currently, SiPMs have advantages (e.g. lower operating voltage and tolerance to
high illumination levels) and disadvantages (e.g. higher capacitance and cross
talk rates), but this technology is still young and rapidly evolving. SiPM
technology has a strong potential to become superior to the PMT one in terms of
photon detection efficiency and price per square mm of detector area. While the
advantage of SiPMs has been proven for high-density, small size cameras, it is
yet to be demonstrated for large area cameras such as the one of the LST. We
are working to develop a SiPM-based module for the LST camera, in view of a
possible camera upgrade. We will describe the solutions we are exploring in
order to balance a competitive performance with a minimal impact on the overall
LST camera design.Comment: 8 pages, 5 figures. In Proceedings of the 34th International Cosmic
Ray Conference (ICRC2015), The Hague, The Netherlands. All CTA contributions
at arXiv:1508.0589
Evidence of and search for double-charmonium production in and decays
Using data samples of and
events collected with the Belle detector, a first experimental
search has been made for double-charmonium production in the exclusive decays
, where , , , , and . No significant signal is
observed in the spectra of the mass recoiling against the reconstructed
or except for the evidence of production with a
significance of for . The
measured branching fraction \BR(\Upsilon(1S)\rightarrow J/\psi+\chi_{c1}) is
. The
confidence level upper limits on the branching fractions of the other modes
having a significance of less than are determined. These results are
consistent with theoretical calculations using the nonrelativistic QCD
factorization approach.Comment: 12 pages, 4 figures, 1 table. The fit range was extended to include
X(4160) signal according to referee's suggestions. Other results unchanged.
Paper was accepted for publication as a regular article in Physical Review
Particle identification performance of the prototype aerogel RICH counter for the Belle II experiment
We have developed a new type of particle identification device, called an aerogel ring imaging Cherenkov (ARICH) counter, for the Belle II experiment. It uses silica aerogel tiles as Cherenkov radiators. For detection of Cherenkov photons, hybrid avalanche photo-detectors (HAPDs) are used. The designed HAPD has a high sensitivity to single photons under a strong magnetic field. We have confirmed that the HAPD provides high efficiency for single-photon detection even after exposure to neutron and -ray radiation that exceeds the levels expected in the 10-year Belle II operation. In order to confirm the basic performance of the ARICH counter system, we carried out a beam test at the using a prototype of the ARICH counter with six HAPD modules. The results are in agreement with our expectations and confirm the suitability of the ARICH counter for the Belle II experiment. Based on the in-beam performance of the device, we expect that the identification efficiency at is 97.4% and 4.9% for pions and kaons, respectively. This paper summarizes the development of the HAPD for the ARICH and the evaluation of the performance of the prototype ARICH counter built with the final design components
Measurement of two-particle correlations of hadrons in ▫▫ collisions at Belle
The measurement of two-particle angular correlation functions in high-multiplicity e+e− collisions at √s=10.52 GeV is reported. In this study, the 89.5 fb−1 of hadronic e+e− annihilation data collected by the Belle detector at KEKB are used. Two-particle angular correlation functions are measured in the full relative azimuthal angle (Δϕ) and three units of pseudorapidity (Δη), defined by either the electron beam axis or the event-shape thrust axis, and are studied as a function of charged-particle multiplicity. The measurement in the thrust axis analysis, with mostly outgoing quark pairs determining the reference axis, is sensitive to the region of additional soft gluon emissions. No significant anisotropic collective behavior is observed with either coordinate analyses. Near-side jet correlations appear to be absent in the thrust axis analysis. The measurements are compared to predictions from various event generators and are expected to provide new constraints to the phenomenological models in the low-energy regime
Search for B decays to final states with the η c meson
We report a search for B decays to selected final states with the ηc meson: B± → K±ηcπ+π−, B± → K±ηcω, B± → K±ηcη and B± → K±ηcπ0. The analysis is based on 772 × 10^6 B¯B pairs collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. We set 90% confidence level upper limits on the branching fractions of the studied B decay modes, independent of intermediate resonances, in the range (0.6–5.3)×10^−4. We also search for molecular-state candidates in the D^0 ¯D^∗0 − ¯D^0D^∗0, D^0 ¯D^0 + ¯D^0D^0 and D^∗0¯D^∗0 + ¯D^∗0D^∗0 combinations, neutral partners of the Z(3900)± and Z(4020)±, and a poorly understood state X(3915) as possible intermediate states in the decay chain, and set 90% confidence level upper limits on the product of branching fractions to the mentioned intermediate states and decay branching fractions of these states in the range (0.6–6.9)×10^−5