Научная группа: Belle Collaboration
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Search for a Light CP -odd Higgs Boson and Low-Mass Dark Matter at the Belle Experiment
(2019) Seong, I. S.; Vahsen, S. E.; Adachi, I.; Aihara, H.; Mizuk, R.; Pakhlov, P.; Zhukova, V.
© 2019 authors. Published by the American Physical Society. We report on the first Belle search for a light CP-odd Higgs boson, A0, that decays into low mass dark matter, χ, in final states with a single photon and missing energy. We search for events produced via the dipion transition (2S)→ (1S)π+π-, followed by the on-shell process (1S)→γA0 with A0→χχ, or by the off-shell process (1S)→γχχ. Utilizing a data sample of 157.3×106 (2S) decays, we find no evidence for a signal. We set limits on the branching fractions of such processes in the mass ranges MA0<8.97 GeV/c2 and Mχ<4.44 GeV/c2. We then use the limits on the off-shell process to set competitive limits on WIMP-nucleon scattering in the WIMP mass range below 5 GeV/c2.
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Observation of Transverse Lambda/(Lambda)over-bar Hyperon Polarization in e(+)e(-) Annihilation at Belle
(2019) Guan, Y.; Vossen, A.; Adachi, I.; Adamczyk, K.; Mizuk, R.; Pakhlov, P.; Zhukova, V.
We report the first observation of the spontaneous polarization of Lambda and (Lambda) over bar hyperons transverse to the production plane in e(+)e(-) annihilation, which is attributed to the effect arising from a polarizing fragmentation function. For inclusive Lambda/(Lambda) over bar production, we also report results with subtracted feed-down contributions from Sigma(0) and charm. This measurement uses a dataset of 800.4 fb(-1) collected by the Belle experiment at or near a center-of-mass energy of 10.58 GeV. We observe a significant polarization that rises with the fractional energy carried by the Lambda/(Lambda) over bar hyperon.
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Search for CP violation with kinematic asymmetries in the D-0 -> K+K- pi(+)pi(-) decay
(2019) Kim, J. B.; Won, E.; Adachi, I.; Aihara, H.; Mizuk, R.
We search for CP violation in the singly-Cabibbo-suppressed decay D-0 -> K+K-pi(+)pi(-) using data corresponding to an integrated luminosity of 988 fb(-1) collected by the Belle detector at the KEKB e(+)e(-). We measure a set of five kinematically dependent CP asymmetries, of which four asymmetries are measured for the first time. The set of asymmetry measurements can be sensitive to CP violation via interference between the different partial-wave contributions to the decay and performed on other pseudoscalar decays. We find no evidence of CP violation.
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Measurement of time-dependent CP violation in B0 → KS0 π0π0 decays
(2019) Yusa, Y.; Aihara, H.; Al, Said, S.; Asner, D. M.; Mizuk, R.
© 2019 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the »https://creativecommons.org/licenses/by/4.0/» Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP 3 . We report a measurement of time-dependent CP violation in B0→KS0π0π0 decays using a data sample of 772×106 BB pairs collected by the Belle experiment running at the ?(4S) resonance at the KEKB e+e- collider. This decay proceeds mainly via a b→sdd "penguin" amplitude. The results are sin2φ1eff=0.92-0.31+0.27 (stat.) ±0.11 (syst.) and A=0.28±0.21 (stat.) ±0.04 (syst.), which are the most precise measurements of CP violation in this decay mode to date. The value for the CP-violating parameter sin2φ1eff is consistent with that obtained using decay modes proceeding via a b→ccs "tree" amplitude.
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Observation of Xi(1620)(0) and Evidence for Xi(1690)(0) in Xi(+)(c) -> Xi(-) pi(+) pi(+) Decays
(2019) Sumihama, M.; Adachi, I.; Ahn, J. K.; Aihara, H.; Mizuk, R.; Pakhlov, P.; Zhukova, V.
We report the first observation of the double strange baryon Xi(1620)(0) in its decay to Xi(-) pi(+) via Xi(+)(c) -> Xi(-)pi(+)pi(+) decays based on a 980 fb(-1) data sample collected with the Belle detector at the KEKB asymmetricenergy e(+)e(-) collider. The mass and width are measured to be 1610.4 +/- 6.0(stat)(-4.2)(+6.1) (syst) MeV/c(2) and 59.9 +/- 4.8(stat)(-7.1)(+2.8)(syst) MeV, respectively. We obtain 4.0 sigma evidence of the Xi(1690)(0) with the same data sample. These results shed light on the structure of hyperon resonances with strangeness S = -2.
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Эксперимент BELLE по изучению структуры материи и свойств антиматерии. Международный эксперимент Belle был запущен на асимметричном электрон-позитронном коллайдере KEKB в научном центре КЕК (Цукуба, Япония) в 1999 году. За период работы до 2010 года ускоритель KEKB достиг рекордной светимости, и детектор Belle набрал более 1000 фбн ̶1 данных. Коллаборация Belle представила миру множество важнейших научных результатов. Среди них подтверждение механизма СР-нарушения, послужившее основанием для присуждения М. Кобаяши и Т. Маскаве Нобелевской премии по физике в 2008 году.