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BABAR Collaboration(Aubert, B. et al), Azzolini, V., Lopez-March, N., Martinez-Vidal, F., Milanes, D. A., & Oyanguren, A. (2010). Measurements of Charged Current Lepton Universality and vertical bar V-us vertical bar Using Tau Lepton Decays to e(-)(nu)over-bar(e)nu(tau), mu(-)(nu)over-bar(mu)nu(tau), pi(-)nu(tau), and K-nu(tau). Phys. Rev. Lett., 105(5), 051602–8pp.
Abstract: Using 467 fb(-1) of e(+)e(-) annihilation data collected with the BABAR detector, we measure B(tau(-)->mu(-)(nu) over bar (mu)nu(tau))/B(tau(-)-> e(-)(nu) over bar (e)nu(tau)) = (0.9796 +/- 0.0016 +/- 0.0036), B(tau(-)->pi(-)nu(tau))/B(tau(-)-> e(-)nu(e)nu(tau)) = (0.5945 +/- 0.0014 +/- 0.0061), and B(tau(-)-> K-nu(tau))/B(tau(-)-> e(-)nu(e)nu(tau)) = (0.03882 +/- 0.00032 +/- 0.00057), where the uncertainties are statistical and systematic, respectively. From these precision similar to measurements, we test the standard model assumption of μ- e and tau – μcharge current lepton universality and provide determinations of vertical bar V-us vertical bar experimentally independent of the decay of a kaon.
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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), Henry, L., Jashal, B. K., Martinez-Vidal, F., Oyanguren, A., Remon Alepuz, C., et al. (2022). J/psi photoproduction in Pb-Pb peripheral collisions at root S-NN=5 TeV. Phys. Rev. C, 105(3), L032201–10pp.
Abstract: The photoproduction of J/psi mesons at low transverse momentum is studied in peripheral lead-lead collisions collected by the LHCb Collaboration at a center-of-mass energy per nucleon pair of 5 TeV, corresponding to an integrated luminosity of 210 μb(-1). The J/psi candidates are reconstructed through the prompt decay into two muons of opposite charge in the rapidity region of 2.0 < y < 4.5. The results significantly improve previous measurements and are compared to the latest theoretical prediction.
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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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BABAR Collaboration(del Amo Sanchez, P. et al), Azzolini, V., Lopez-March, N., Martinez-Vidal, F., Milanes, D. A., & Oyanguren, A. (2010). Test of Lepton Universality in Y(1S) Decays at BABAR. Phys. Rev. Lett., 104(19), 191801–7pp.
Abstract: The ratio R-tau mu(Y(1S)) = Gamma Y(1S)->tau(+)tau(-)/Gamma(+)(-)(Y(1S)->mu)(mu) is measured using a sample of (121.8 +/- 1.2) x 10(6)Y(3S) events recorded by the BABAR detector. This measurement is intended as a test of lepton universality and as a search for a possible light pseudoscalar Higgs boson. In the standard model (SM) this ratio is expected to be close to 1. Any significant deviations would violate lepton universality and could be introduced by the coupling to a light pseudoscalar Higgs boson. The analysis studies the decays Y(3S) -> Y(1S)pi(+)pi(-), Y(1S) -> l(+)l(-), where l = mu, tau. The result, R-tau μ(Y(1S)) = 1.005 +/- 0.013(stat) +/- 0.022(syst), shows no deviation from the expected SM value, while improving the precision with respect to previous measurements.
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BABAR Collaboration(Lees, J. P. et al), Azzolini, V., Lopez-March, N., Martinez-Vidal, F., Milanes, D. A., & Oyanguren, A. (2010). Search for Charged Lepton Flavor Violation in Narrow Gamma Decays. Phys. Rev. Lett., 104(15), 151802–7pp.
Abstract: Charged-lepton flavor-violating processes are unobservable in the standard model, but they are predicted to be enhanced in several extensions to the standard model, including supersymmetry and models with leptoquarks or compositeness. We present a search for such processes in a sample of 99 x 10(6)Gamma(2S) decays and 117 x 10(6)Gamma(3S) decays collected with the BABAR detector. We place upper limits on the branching fractions B(Gamma(nS) --> e(+/-)tau(-/+)) and B(Gamma(n(S) --> mu(+/-)tau(-/+)) (n = 2, 3) at the 10(-6) level and use these results to place lower limits of order 1 TeV on the mass scale of charged-lepton flavor-violating effective operators.
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BABAR Collaboration(Aubert, B. et al), Azzolini, V., Lopez-March, N., Martinez-Vidal, F., Milanes, D. A., & Oyanguren, A. (2010). Measurement of vertical bar V-cb vertical bar and the Form-Factor Slope in (B)over-bar -> Dl(-) (nu)over-bar(l) Decays in Events Tagged by a Fully Reconstructed B Meson. Phys. Rev. Lett., 104(1), 011802–7pp.
Abstract: We present a measurement of the Cabibbo-Kobayashi-Maskawa matrix element vertical bar V-cb vertical bar and the form-factor slope rho(2) in (B) over bar -> Dl(-) (nu) over bar (l) decays based on 460 X 10(6) B (B) over bar events recorded at the Gamma(4S) resonance with the BABAR detector. (B) over bar -> Dl(-) (nu) over bar (l) decays are selected in events in which a hadronic decay of the second B meson is fully reconstructed. We measure B(B- -> D(0)l(-) (nu) over bar (l))/B(B- -> Xl(-) (nu) over bar (l)) = (0.255 +/- 0.009 +/- 0.009) and B((B) over bar (0) -> D(+)l(-) (nu) over bar (l))/B((B) over bar (0) -> Xl(-) (nu) over bar (l)) = (0.230 +/- 0.011 +/- 0.011), along with the differential decay distribution in (B) over bar -> Dl(-) (nu) over bar (l) decays. We then determine G(1)vertical bar V-cb vertical bar = 42.3 +/- 1.9 +/- 1.4) X 10(-3) and rho(2) = 1.20 +/- 0.09 +/- 0.04, where G(1) is the hadronic form factor at the point of zero recoil.
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BABAR Collaboration(Aubert, B. et al), Azzolini, V., Lopez-March, N., Martinez-Vidal, F., Milanes, D. A., & Oyanguren, A. (2010). Searches for Lepton Flavor Violation in the Decays tau(+/-) -> e(+/-)gamma and tau(+/-) -> mu(+/-)gamma. Phys. Rev. Lett., 104(2), 021802–7pp.
Abstract: Searches for lepton-flavor-violating decays of a tau lepton to a lighter mass lepton and a photon have been performed with the entire data set of (963 +/- 7) x 10(6) tau decays collected by the BABAR detector near the Y(4S), Y(3S) and Y(2S) resonances. The searches yield no evidence of signals and we set upper limits on the branching fractions of B(tau(+/-) -> e(+/-)gamma) < 3.3 X 10(-8) and B(tau(+/-) -> mu(+/-)gamma) < 4.4 X 10(-8) at 90% confidence level.
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