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Kotchetkov, D.

Publications and source records attributed to Kotchetkov, D..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

The imaging Time-of-Propagation detector at Belle II

Here, we report on the construction, operation, and performance of the Time-of-Propagation detector with imaging used for the Belle II experiment running at the Super-KEKB e + e - collider. This detector is located in the central barrel region and uses Cherenkov light to provide particle identification among hadrons. The Cherenkov light is radiated in highly polished bars of synthetic fused silica (quartz) and transported to the ends of the bars via total internal reflection. One bar end is instrumented with finely segmented micro-channel-plate photomultiplier tubes to record the light, while the other end has a mirror attached to reflect the photons back to the instrumented end. Both the propagation times and hit positions of the Cherenkov photons are measured; these depend on the Cherenkov angle and together provide good discrimination among charged pions, kaons, and protons with momenta up to around 4 GeV/ c . To date, the detector has been used to record and analyze almost 600 fb −1 of Belle II data.

43 PARTICLE ACCELERATORS↗
DOE OSTI2021

Search for the dark photon in B 0 → A'A', A' → e + e – , μ + μ – , and π + π – decays at Belle

We present a search for the dark photon A' in the B 0 → A'A' decays, where A' subsequently decays to e + e – , μ + μ – , and π + π – . The search is performed by analyzing 772 × 10 6 $B$$\overline{B}$ events collected by the Belle detector at the KEKB e + e – energy-asymmetric collider at the Υ(4S) resonance. No signal is found in the dark photon mass range 0.01 GeV/c 2 ≤ m A' ≤ 2.62 GeV/c 2 , and we set upper limits of the branching fraction of B0 → A'A' at the 90% confidence level. The products of branching fractions, B(B 0 →A'A')×B(A'→e + e – ) 2 and B(B 0 →A'A')×B(A'→μ + μ – ) 2 , have limits of the order of 10 –8 depending on the A' mass. Furthermore, considering A' decay rate to each pair of charged particles, the upper limits of B(B 0 →A'A') are of the order of 10 –8 –10 –5 . From the upper limits of B(B 0 →A'A'), we obtain the Higgs portal coupling for each assumed dark photon and dark Higgs mass. The Higgs portal couplings are of the order of 10 –2 –10 –1 at m h' ≃m B 0 ± 40 MeV/c 2 and 10 –1 –1 at m h' ≃m B 0 ± 3 GeV/c 2 .

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Test of lepton flavor universality and search for lepton flavor violation in B → Kℓℓ decays

We present measurements of the branching fractions for the decays B → Kμ + μ - and B → Ke + e - , and their ratio (R K ), using a data sample of 711 fb -1 that contains 772 × 10 6 B$\bar{B}$ events. The data were collected at the Υ(4S) resonance with the Belle detector at the KEKB asymmetric-energy e + e - collider. The ratio R K is measured in five bins of dilepton invariant-mass-squared (q 2 ): q 2 $\epsilon$ (0.1, 4.0), (4.00, 8.12), (1.0, 6.0), (10.2, 12.8) and (> 14.18) GeV 2 /c 4 , along with the whole q 2 region. The R K value for q 2 $\epsilon$ (1.0, 6.0) GeV 2 /c 4 is 1.03$^{+0.28}_{-0.24}$ ± 0.01. The first and second uncertainties listed are statistical and systematic, respectively. All results for RK are consistent with Standard Model predictions. We also measure CP-averaged isospin asymmetries in the same q 2 bins. The results are consistent with a null asymmetry, with the largest difference of 2.6 standard deviations occurring for the q 2 $\epsilon$ (1.0, 6.0) GeV 2 /c 4 bin in the mode with muon final states. The measured differential branching fractions, dB/dq 2 , are consistent with theoretical predictions for charged B decays, while the corresponding values are below the expectations for neutral B decays. We have also searched for lepton-flavor-violating B → Kμ ± e ∓ decays and set 90% confidence-level upper limits on the branching fraction in the range of 10 -8 for B + → K + μ ± e ∓ , and B 0 → K 0 μ ± e ∓ modes.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗