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LHCb Collaboration(Aaij, R. et al), Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., & Ruiz Vidal, J. (2022). Measurement of the B-s(0) -> mu(+)mu(-) decay properties and search for the B-0 -> mu(+)mu(-) and B-s(0) -> mu(+)mu(-) gamma decays. Phys. Rev. D, 105(1), 012010–34pp.
Abstract: An improved measurement of the decay B-s(0) -> mu(+)mu(-) and searches for the decays B-0 -> mu(+)mu(-) and B-s(0) -> mu(+)mu(-)gamma are performed at the LHCb experiment using data collected in proton-proton collisions at root s = 7, 8 and 13 TeV, corresponding to integrated luminosities of 1, 2 and 6 fb(-1), respectively. The B-s(0) -> mu(+)mu(-) branching fraction and effective lifetime are measured to be B(B-s(0) -> mu(+)mu(-)) = (3.09(-0.43-0.11)(+0.46+0.15)) x 10(-9) and tau(B-s(0) -> mu(+)mu(-)) = (2.07 +/- 0.29 +/- 0.03) ps, respectively, where the uncertain-ties include both statistical and systematic contributions. No significant signal for B-0 -> mu(+)mu(-) and B-s(0) -> mu(+)mu(-) gamma decays is found and the upper limits B(B-0 -> mu(+)mu(-)) < 2.6 x 10(-10) and B(B-s(0) -> mu(+)mu(-)gamma) 2.0 x 10(-9) at 95% confidence level are determined, where the latter is limited to the range m(mu mu) > 4.9 GeV/c(2). Additionally, the ratio between the B-0 -> mu(+)mu(-) and B-s(0) -> mu(+)mu(-) branching fractions is measured to be R mu+mu- < 0.095 at 95% confidence level. The results are in agreement with the Standard Model predictions.
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LHCb Collaboration(Aaij, R. et al), Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., & Ruiz Vidal, J. (2022). Measurement of the photon polarization in Lambda(0)(b) -> Lambda gamma decays. Phys. Rev. D, 105(5), L051104–11pp.
Abstract: The photon polarization in b -> s gamma transitions is measured for the first time in radiative b -baryon decays exploiting the unique spin structure of Lambda(0)(b)-> Lambda(gamma) decays. A data sample corresponding to an integrated luminosity of 6 fb(-1) collected by the LHCb experiment in pp collisions at a center-of-mass energy of 13 TeV is used. The photon polarization is measured to be alpha(gamma) = 0.82(-0.26-0.)(13)(+)(0.17+0.04), where the first uncertainty is statistical and the second systematic. This result is in agreement with the Standard Model prediction and previous measurements in b-meson decays. Charge-parity breaking effects are studied for the first time in this observable and found to be consistent with CP symmetry.
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LHCb Collaboration(Aaij, R. et al), Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., & Ruiz Vidal, J. (2022). Observation of the B-0 -> (D)over-bar*K-0(+) pi(-) and B-s(0) -> (D)over-bar*K-0(-)pi(+) decays. Phys. Rev. D, 105(7), 072005–22pp.
Abstract: The first observations of B-0 -> (D) over bar*(2007)K-0(+)pi(-) and B-s(0) -> (D) over bar*(2007)K-0(-)pi(+) decays are presented, and their branching fractions relative to that of the B ->( D) over bar* (2007)(0)pi(+)pi(-) decay are reported. These modes can potentially be used to investigate the spectroscopy of charm and charm-strange resonances and to determine the angle gamma of the Cabibbo-Kobayashi-Maskawa unitarity triangle. It is also important to understand them as a source of potential background in determinations of gamma from B+ -> DK+ and B-0 -> DK+pi(-) decays. The analysis is based on a sample corresponding to an integrated luminosity of 5.4 fb(-1 )of proton-proton collision data at 13 TeV center-of-mass energy recorded with the LHCb detector. The (D) over bar*(2007)(0) mesons are fully reconstructed in the (D) over bar (0)pi(0) and (D) over bar (0)gamma channels with the (D) over bar (0) -> K+pi(-) decay. A novel weighting method is used to subtract background while simultaneously applying an event-by-event efficiency correction to account for resonant structures in the decays.
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LHCb Collaboration(Aaij, R. et al), Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., Ruiz Vidal, J., et al. (2022). Measurement of the charm mixing parameter y(CP)-y(CP)(K pi) using two-body D-0 meson decays. Phys. Rev. D, 105(9), 092013–17pp.
Abstract: A measurement of the ratios of the effective decay widths of D-0 -> pi(-)pi(+) and D-0 -> K- K+ decays over that of D-0 -> K-pi(+) decays is performed with the LHCb experiment using proton-proton collisions at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb(-1). These observables give access to the charm mixing parameters y(CP)(pi pi) – y(CP)(K pi )and y(CP)(KK) -y(CP)(K pi), and are measured as y(CP)(pi pi) – y(CP)(K pi) = (6.57 +/- 0.53 +/- 0.16) x 10(-3), y(CP)(KK) – y(CP)(K pi) = (7.08 +/- 0.30 +/- 0.14) x 10(-3), where the first uncertainties are statistical and the second systematic. The combination of the two measurements is Y-CP – y(CP)(K pi) = (6.96 +/- 0.26 +/- 0.13) x 10(-3), which is four times more precise than the previous world average.
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Heavy Flavor Averaging Group(Amhis, Y. et al), & Oyanguren, A. (2023). Averages of b-hadron, c-handron, and t-lepton properties as of 2021. Phys. Rev. D, 107(5), 052008–365pp.
Abstract: This paper reports world averages of measurements of b-hadron, c-hadron, and τ-lepton properties obtained by the Heavy Flavor Averaging Group using results available before April 2021. In rare cases, significant results obtained several months later are also used. For the averaging, common input parameters used in the various analyses are adjusted (rescaled) to common values, and known correlations are taken into account. The averages include branching fractions, lifetimes, neutral meson mixing parameters, CP violation parameters, parameters of semileptonic decays, and Cabibbo-Kobayashi-Maskawa matrix elements.
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