Measurement of branching fractions for BtoJ/psietaKB to J/psi eta K decays and search for a narrow resonance in the J/psietaJ/psi eta final state

We report an observation of the $B^{pm } to J/psi eta K^{pm }$ and $B^0 to J/psi eta K^0_S$ decays using $772times 10^{6}Boverline {B}$ pairs collected at the $Upsilon (4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We obtain the branching fractions ${mathcal B}(B^{pm }rightarrow J/psi eta K^{pm })=(1.27pm 0.11(hbox {stat.})pm 0.11(hbox {syst.}))times 10^{-4}$ and ${mathcal B}(B^0to J/psi eta K^0_S)=(5.22 pm 0.78 (hbox {stat.}) pm 0.49 (hbox {syst.}))times 10^{-5}$. We search for a new narrow charmonium(-like) state $X$ in the $J/psi eta$ mass spectrum and find no significant excess. We set upper limits on the product of branching fractions, ${mathcal B}(B^pm to XK^pm){mathcal B}(X to J/psi eta)$, at $3872,hbox {MeV},c^{-2}$ where a $C$-odd partner of $X(3872)$ may exist, at $psi (4040)$ and $psi (4160)$ assuming their known mass and width, and over a range from 3.8 to $4.8,hbox {GeV},c^{-2}$. The obtained upper limits at 90% confidence level for $X^{Chbox {-}{rm odd}}(3872)$, $psi (4040)$, and $psi (4160)$ are $3.8times 10^{-6}$, $15.5times 10^{-6}$, and $7.4times 10^{-6}$, respectively

Pion wave function from lattice QCD vs. chiral quark models

We analyze the equal-time Bethe-Salpeter quark wave function of the pion obtained from a quenched lattice QCD calculation with delocalized quark interpolators. We find that the result agrees remarkably well with the predictions of the Nambu--Jona-Lasinio model in all channels. We choose the quenched lattice QCD, since it is closer to the large-Nc limit of the Nambu--Jona-Lasinio model. We also show how transversity information, relevant for the light-cone physics, can be obtained from our equal-time rest-frame lattice calculations.Comment: 7 pages, 2 figure

Slow control of the Belle II Aerogel Ring Imaging detector

Since 2018, an Proximity Focusing Aerogel Ring Imaging Detector (ARICH) efficiently separates hadrons in the forward end-cap of the Belle II spectrometer. Cherenkov photons emitted in the double-layer aerogel radiator are expanded in 16-cm space and detected on the photon detector, which consists of 420 hybrid avalanche photodiodes and rear readout electronics operating in threshold mode. Each of the sensors requires six different high voltages and a supply of four low voltages for the electronics. Because of the power dissipation, the system also includes a cooling system in which cold water circulates through the Al tubes thermally connected to the readout electronics. Reliable control of supply voltages and monitoring of environmental data and sensor status ensure stable operation of the ARICH detector and early response to sudden changes in current, single event disturbances, overheating, and other faults. In this paper, we introduce the ARICH’s slow control system and the data quality monitor used to track performance

Measurement of two-particle correlations of hadrons in ▫e+e−e^+ e^-▫ 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

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 $gamma$-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 $3.5,{rm GeV}/c$ 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

Search for the decay ▫Bs0toetaetaB_s^0 to eta eta▫

We report results from a search for the decay B0s→ηη using 121.4  fb−1 of data collected at the Υ(5S) resonance with the Belle detector at the KEKB asymmetric-energy e+e− collider. We do not observe any signal and set an upper limit on the branching fraction of 14.3×10−5 at 90% confidence level. This result represents a significant improvement over the previous most stringent limit

Measurement of the branching fraction and ▫CPCP▫ asymmetry for ▫BtobarD0piB to bar{D}^0 pi▫ decays

We measure the branching fractions and CP asymmetries for the decays B⁰ → D¯ 0π⁰ and B⁺ → D¯ 0π⁺, using a data sample of 772 × 10⁶ BB¯ pairs collected at the ϒ(4S) resonance with the Belle detector at the KEKB e⁺e− collider. The branching fractions obtained and direct CP asym-metries are B(B⁰ → D¯ 0π⁰)=[2.70 0.06(stat) 0.10(syst)]×10−⁴, B(B⁺ → D¯ 0π⁺)=[4.53 0.02(stat) 0.15(syst)]×10−³, ACP(B⁰ → D¯ 0π⁰)= [+0.42 2.05(stat) 1.22(syst)]%, and ACP(B⁺ → D¯ 0π⁺) = [+0.19 0.36(stat) 0.57(syst)]%. The measurements of B are the most precise to date and are in good agreement with previous results, as is the measurement of ACP(B⁺ → D¯ 0π⁺). The measurement of ACP for B⁰ → D¯ 0π⁰ is the first for this mode, and the value is consistent with Standard Model expectations