A novel type of proximity focusing RICH counter with multiple refractive index aerogel radiator

A proximity focusing ring imaging Cherenkov detector, with the radiator consisting of two or more aerogel layers of different refractive indices, has been tested in 1-4 GeV/c pion beams at KEK. Essentially, a multiple refractive index aerogel radiator allows for an increase in Cherenkov photon yield on account of the increase in overall radiator thickness, while avoiding the simultaneous degradation in single photon angular resolution associated with the increased uncertainty of the emission point. With the refractive index of consecutive layers suitably increasing in the downstream direction, one may achieve overlapping of the Cherenkov rings from a single charged particle. In the opposite case of decreasing refractive index, one may obtain well separated rings. In the former combination an approximately 40% increase in photon yield is accompanied with just a minor degradation in single photon angular resolution. The impact of this improvement on the pion/kaon separation at the upgraded Belle detector is discussed.Comment: submitted to Nucl. Instr. Meth.

Search for lepton-flavor-violating τ→ℓV0\tau\to\ell V^0 decays at Belle

We have searched for neutrinoless $\tau$ lepton decays into $\ell$ and $V^0$, where $\ell$ stands for an electron or muon, and $V^0$ for a vector meson ($\phi$, $\omega$, $K^{*0}$, $\bar{K}^{*0}$ or $\rho^0$), using 543 fb$^{-1}$ of data collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. No excess of signal events over the expected background has been observed, and we set upper limits on the branching fractions in the range $(5.9-18) \times 10^{-8}$ at the 90% confidence level. These upper limits include the first results for the $\ell \omega$ mode as well as new limits that are significantly more restrictive than our previous results for the $\ell \phi$, $\ell K^{*0}$, $\ell \bar{K}^{*0}$ and $\ell \rho^0$ modes.Comment: 7 pages, 16 figure

Measurements of time-dependent CP violation in B^0 -> psi(2S) K_S decays

We report improved measurements of time-dependent CP violation parameters for B^0(\bar{B}^0) -> psi(2S) K_S. This analysis is based on a data sample of 657x10^6 BBbar pairs collected at the Y(4S) resonance with the Belle detector at the KEKB energy-asymmetric e+e- collider. We fully reconstruct one neutral B meson in the psi(2S) K_S CP-eigenstate decay channel, and the flavor of the accompanying B meson is identified to be either B^0 or \bar{B}^0 from its decay products. CP violation parameters are obtained from the asymmetries in the distributions of the proper-time intervals between the two B decays: S (psi(2S) K_S) = +0.72 +/- 0.09(stat) +/- 0.03(syst), A (psi(2S) K_S) = +0.04 +/- 0.07(stat) +/- 0.05(syst). These results are in agreement with results from measurements of B^0 -> J/psi K^0.Comment: 6 pages, 4 figures, presented at 2007 Lepton-Photon Symposium (BELLE-CONF-0770). Modified version published in PRD(RC

Observation of B^0 \to D^{*-} \tau^+ \nu_{\tau} decay at Belle

We report an observation of the decay $B^0\to D^{*-} \tau^+ \nu_{\tau}$ in a data sample containing $535\times10^6$ $B\bar{B}$ pairs collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We find a signal with a significance of 5.2 standard deviations and measure the branching fraction $\mathcal{B}(B^0\to D^{*-} \tau ^+ \nu_{\tau})=(2.02 ^{+0.40}_{-0.37} (stat) \pm 0.37 (syst))$. This is the first observation of an exclusive $B$ decay with a $b \to c \tau \nu_{\tau}$ transition.Comment: 6 pages, 3 figures, submitted to Phys. Rev. Let

Measurement of the ratio B(D0->pi+pi-pi0)/B(D0->K-pi+pi0) and the time-integrated CP asymmetry in D0->pi+pi-pi0

We report a high-statistics measurement of the relative branching fraction B(D0->pi+pi-pi0)/B(D0->K-pi+pi0) using a 532 fb^{-1} data sample collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. The measured value of the relative branching fraction is B(D0->pi+pi-pi0)/B(D0->K-pi+pi0) = (10.12 +/- 0.04(stat) +/- 0.18(syst))x10^{-2} which has an accuracy comparable to the world average. We also present a measurement of the time-integrated CP asymmetry in D0->pi+pi-pi0 decay. The result, A_{CP} = (0.43 +/- 1.30)%, shows no significant CP violation.Comment: 15 pages, 11 figures, submitted to Physics Letters

Development of Advanced Photon Calibrator for KAGRA

The KAGRA cryogenic gravitational-wave observatory has begun joint observation with the worldwide gravitational waves detector network. Precise calibration of the detector response is essential for the parameter estimation of gravitational wave sources. The photon calibrator is the main calibrator in LIGO, Virgo and KAGRA, and we used this calibrator in joint observation 3 on 2020 April with GEO600 in Germany. KAGRA improved the system for joint observation 3 with three unique points: high laser power, power stabilization system, and remote beam position control. KAGRA employs the 20 W laser and divides it into two beams injected on the mirror surface. By using a high-power laser, we can calibrate the response at the kHz region. To control the power of each laser independently, we also installed an optical follower servo for each beam power stabilization. By controlling the optical path of the photon calibrater beam positions with pico-motors, we were able to characterize the rotation response of the detector. We also installed a telephoto camera and QPD to monitor beam position and controlled beam position to optimize mirror response. In this paper, we discussed the statistical error with the result of the relative power noise measurement. We also discussed systematic errors about the power calibration model of photon calibrator and simulation of elastic deformation effect with the finite element analysis.Comment: 16 pages, 10 figure

Improved search for D^0 mixing using semileptonic decays at Belle

A search for mixing in the neutral D meson system has been performed using semileptonic D0 -> K(*)- e+ \nu and D0 -> K(*)- \mu+ \nu decays. Neutral D mesons from D*+ -> D0 \pi_s^+ decays are used and the flavor at production is tagged by the charge of the slow pion. The measurement is performed using 492 fb^-1 of data recorded by the Belle detector. From the yield of right-sign and wrong-sign decays arising from non-mixed and mixed events, respectively, we measure the ratio of the time-integrated mixing rate to the unmixed rate to be R_M = (1.3 +- 2.2 +- 2.0) x 10^-4. This corresponds to an upper limit of R_M < 6.1 x 10^-4 at the 90% C.L.Comment: 20 pages, 16 figures, 8 tables; accepted by PRD; changes from previous version: minor rewording

Shower development of particles with momenta from 15 GeV to 150 GeV in the CALICE scintillator-tungsten hadronic calorimeter

We present a study of showers initiated by electrons, pions, kaons, and protons with momenta from 15 GeV to 150 GeV in the highly granular CALICE scintillator-tungsten analogue hadronic calorimeter. The data were recorded at the CERN Super Proton Synchrotron in 2011. The analysis includes measurements of the calorimeter response to each particle type as well as measurements of the energy resolution and studies of the longitudinal and radial shower development for selected particles. The results are compared to Geant4 simulations (version 9.6.p02). In the study of the energy resolution we include previously published data with beam momenta from 1 GeV to 10 GeV recorded at the CERN Proton Synchrotron in 2010.Comment: 35 pages, 21 figures, 8 table

Measurement of the cross-section and charge asymmetry of WW bosons produced in proton-proton collisions at s=8\sqrt{s}=8 TeV with the ATLAS detector

This paper presents measurements of the $W^+ \rightarrow \mu^+\nu$ and $W^- \rightarrow \mu^-\nu$ cross-sections and the associated charge asymmetry as a function of the absolute pseudorapidity of the decay muon. The data were collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS experiment at the LHC and correspond to a total integrated luminosity of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the 1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured with an uncertainty between 0.002 and 0.003. The results are compared with predictions based on next-to-next-to-leading-order calculations with various parton distribution functions and have the sensitivity to discriminate between them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables, submitted to EPJC. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13