Eur. Phys. J. C 82, 283 (2022) We report on new flavor tagging algorithms developed to determine the
quark-flavor content of bottom ($B$) mesons at Belle II. The algorithms provide
essential inputs ...for measurements of quark-flavor mixing and charge-parity
violation. We validate and evaluate the performance of the algorithms using
hadronic $B$ decays with flavor-specific final states reconstructed in a data
set corresponding to an integrated luminosity of $62.8$ fb$^{-1}$, collected at
the $\Upsilon$(4$S$) resonance with the Belle II detector at the SuperKEKB
collider. We measure the total effective tagging efficiency to be
$\varepsilon_{\rm eff} = \big(30.0 \pm 1.2(\text{stat}) \pm
0.4(\text{syst})\big)\%$ for a category-based algorithm and $\varepsilon_{\rm
eff} = \big(28.8 \pm 1.2(\text{stat}) \pm 0.4(\text{syst})\big)\%$ for a
deep-learning-based algorithm.
We present measurements of the branching fraction, the polarization parameters and CP-violating asymmetries in B0→D∗+D∗− decays using a 140 fb−1 data sample collected at the ϒ(4S) resonance with the ...Belle detector at the KEKB energy-asymmetric e+e− collider. We obtain B(B0→D∗+D∗−)=0.81±0.08(stat)±0.11(syst)×10−3, R⊥=0.19±0.08(stat)±0.01(syst), R0=0.57±0.08(stat)±0.02(syst), S=−0.75±0.56(stat)±0.12(syst) and A=−0.26±0.26(stat)±0.06(syst). Consistency with Standard Model expectations is also discussed.
The Aerogel Ring Imaging Cherenkov (ARICH) counter serves as a particle identification device in the forward end-cap region of the Belle II spectrometer. It is capable of identifying pions and kaons ...with momenta up to \(4 \, {\rm GeV}/c\) by detecting Cherenkov photons emitted in the silica aerogel radiator. After the detector alignment and calibration of the probability density function, we evaluate the performance of the ARICH counter using early beam collision data. Event samples of \(D^{\ast +} \to D^0 \pi^+ (D^0 \to K^-\pi^+)\) were used to determine the \(\pi(K)\) efficiency and the \(K(\pi)\) misidentification probability. We found that the ARICH counter is capable of separating kaons from pions with an identification efficiency of \(93.5 \pm 0.6 \, \%\) at a pion misidentification probability of \(10.9 \pm 0.9 \, \%\). This paper describes the identification method of the counter and the evaluation of the performance during its early operation.
We have measured π+π− and K+K− production in two-photon collisions using 87.7fb−1 of data collected with the Belle detector at the asymmetric energy e+e− collider KEKB. The cross sections are ...measured to high precision in the two-photon center-of-mass energy (W) range between 2.4GeV<W<4.1GeV and angular region |cosθ∗|<0.6. The cross section ratio σ(γγ→K+K−)/σ(γγ→π+π−) is measured to be 0.89±0.04(stat.)±0.15(syst.) in the range of 3.0GeV<W<4.1GeV, where the ratio is energy-independent. We observe a sin−4θ∗ behavior of the cross section in the same W range. Production of χc0 and χc2 mesons is observed in both γγ→π+π− and γγ→K+K− modes.
Aging and rejuvenation of a TMAE+methane multiwire photon detector Korpar, S.; Krizan, P.; Stanovnik, A. ...
1998 IEEE Nuclear Science Symposium Conference Record. 1998 IEEE Nuclear Science Symposium and Medical Imaging Conference (Cat. No.98CH36255),
1998, Letnik:
1
Conference Proceeding
A UV sensitive multiwire photon detector has been tested as a possible candidate for the HERA-B RICH. The main obstacle to using such a TMAE+methane filled gas detector in a high rate experiment, ...appears to be rapid aging in the form of prohibitive loss of chamber gas gain. A special circuit has been designed for heating the anode wires in-situ with elevated currents, thus evaporating the polymer deposits. Heating almost completely recovers the initial gain, but this rejuvenation is unfortunately of short duration. Nevertheless, the cells exposed to periodic heat treatments have an average gain considerably higher than the non-heated cells.
We report the observation of B0 decays to the K+π−π0 final state using a data sample of 78 fb−1 collected by the Belle detector at the KEKB e+e− collider. With no assumptions about intermediate ...states in the decay, the branching fraction is measured to be (36.6−4.3+4.2±3.0)×10−6. We also search for B decays to intermediate two-body states with the same K+π−π0 final state. Significant B signals are observed in the ρ(770)−K+ and K*(892)+π− channels, with branching fractions of (15.1−3.3−1.5−2.1+3.4+1.4+2.0)×10−6 and (14.8−4.4−1.0−0.9+4.6+1.5+2.4)×10−6, respectively. The first error is statistical, the second is systematic and the third is due to the largest possible interference. Contributions from other possible two-body states will be discussed. No CP asymmetry is found in the inclusive K+π−π0 or ρ−K+ modes, and we set 90% confidence level bounds on the asymmetry of −0.12<ACP<0.26 and −0.18<ACP<0.64, respectively.
PDF
