Malcolm John

Abstract:

Using pp collision data corresponding to an integrated luminosity of 8.5  fb^{-1} recorded by the LHCb experiment at center-of-mass energies of sqrt[s]=7, 8, and 13 TeV, the observation of an excited B_{c}^{+} state in the B_{c}^{+}π^{+}π^{-} invariant-mass spectrum is reported. The observed peak has a mass of 6841.2±0.6(stat)±0.1(syst)±0.8(B_{c}^{+})  MeV/c^{2}, where the last uncertainty is due to the limited knowledge of the B_{c}^{+} mass. It is consistent with expectations of the B_{c}^{*}(2^{3}S_{1})^{+} state reconstructed without the low-energy photon from the B_{c}^{*}(1^{3}S_{1})^{+}→B_{c}^{+}γ decay following B_{c}^{*}(2^{3}S_{1})^{+}→B_{c}^{*}(1^{3}S_{1})^{+}π^{+}π^{-}. A second state is seen with a global (local) statistical significance of 2.2σ (3.2σ) and a mass of 6872.1±1.3(stat)±0.1(syst)±0.8(B_{c}^{+})  MeV/c^{2}, and is consistent with the B_{c}(2^{1}S_{0})^{+} state. These mass measurements are the most precise to date.

Abstract:

A search for charge-parity (CP) violation in D0→K−K+ and D0→π−π+ decays is reported, using pp collision data corresponding to an integrated luminosity of 5.9 fb−1 collected at a center-of-mass energy of 13 TeV with the LHCb detector. The flavor of the charm meson is inferred from the charge of the pion in D∗(2010)+→D0π+ decays or from the charge of the muon in ¯B→D0μ−¯νμX decays. The difference between the CP asymmetries in D0→K−K+ and D0→π−π+ decays is measured to be ΔACP=[−18.2±3.2(stat)±0.9(syst)]×10−4 for π-tagged and ΔACP=[−9±8(stat)±5(syst)]×10−4 for μ-tagged D0 mesons. Combining these with previous LHCb results leads to ΔACP=(−15.4±2.9)×10−4, where the uncertainty includes both statistical and systematic contributions. The measured value differs from zero by more than 5 standard deviations. This is the first observation of CP violation in the decay of charm hadrons.

Abstract:

An amplitude analysis of B 0 → (π + π − )(K + π − ) decays is performed in the two-body invariant mass regions 300 < m(π + π − ) < 1100 MeV/c 2 , accounting for the ρ 0 , ω, f 0 (500), f 0 (980) and f 0 (1370) resonances, and 750 < m(K + π − ) < 1200 MeV/c 2 , which is dominated by the K * (892) 0 meson. The analysis uses 3 fb −1 of proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The CP averages and asymmetries are measured for the magnitudes and phase differences of the con- tributing amplitudes. The CP-averaged longitudinal polarisation fractions of the vector-vector modes are found to be f˜ρK*0 = 0.164 ± 0.015 ± 0.022 and f˜ωK*0 = 0.68 ± 0.17 ± 0.16, and their CP asymmetries, AρK*0 = −0.62 ± 0.09 ± 0.09 and AωK*0 = −0.13 ± 0.27 ± 0.13, where the first uncertainty is statistical and the second systematic.[Figure not available: see fulltext.].