Lepton Flavour Universality tests in BB decays as a probe for New Physics

In the Standard Model (SM), the coupling of the electroweak gauge bosons to the leptons is lepton flavour universal. Tests of this property constitute sensitive probes for new physics models that violate lepton flavour universality. Recent tests of lepton universality in rare $b\to s\ell\ell$ decays and semileptonic $b\to c\tau\bar{\nu}_\tau$ transitions have shown some tensions with the precise SM predictions. These proceedings summarise the latest results on lepton flavour universality from the LHCb experiment.Comment: 6 pages, 5 figures. Contribution to the proceedings of the 53th Rencontres de Moriond, Electroweak Session, 10-17 March 201

Latest results on rare decays from LHCb

Rare flavour changing neutral current decays are sensitive indirect probes for new effects beyond the Standard Model (SM). In the SM, these decays are forbidden at tree level and are therefore loop-suppressed. In SM extensions, new, heavy particles can significantly contribute and affect both their branching fractions as well as their angular distributions. The rare decay $B^0\to K^{*0}(\to K^+\pi^-)\mu^+\mu^-$ is of particular interest, since it gives access to many angular observables, allowing to model-independently test the operator structure of the decay. A previous analysis of the angular distributions of the final state particles showed interesting tensions with SM predictions using the data sample taken by the LHCb detector during 2011. These proceedings will summarize latest results on rare decays from the LHCb experiment with emphasis on the angular analysis of the decay $B^0\to K^{*0}\mu^+\mu^-$, using the full Run I data sample of the LHCb experiment.Comment: 8 pages, 7 figures. Contribution to the proceedings of the 50th Rencontres de Moriond, Electroweak Session, 14-21 March 201

Hermann Kant: Der Aufenthalt

Berlin: Rütten & Loening, 1977. 600 p. DM 10,80

First observation of a baryonic B+c decay

A baryonic decay of the B+c meson, B+c→J/ψpp¯π+, is observed for the first time, with a significance of 7.3 standard deviations, in pp collision data collected with the LHCb detector and corresponding to an integrated luminosity of 3.0  fb−1 taken at center-of-mass energies of 7 and 8 TeV. With the B+c→J/ψπ+ decay as the normalization channel, the ratio of branching fractions is measured to be B(B+c→J/ψpp¯π+)/B(B+c→J/ψπ+)=0.143+0.039−0.034(stat)±0.013(syst). The mass of the B+c meson is determined as M(B+c)=6274.0±1.8(stat)±0.4(syst)  MeV/c2, using the B+c→J/ψpp¯π+ channel

Measurement of CP violation parameters in B0→DK*0 decays

An analysis of B0→DK*0 decays is presented, where D represents an admixture of D0 and D¯0 mesons reconstructed in four separate final states: K−π+, π−K+, K+K− and π+π−. The data sample corresponds to 3.0  fb−1 of proton-proton collision, collected by the LHCb experiment. Measurements of several observables are performed, including CP asymmetries. The most precise determination is presented of rB(DK*0), the magnitude of the ratio of the amplitudes of the decay B0→DK+π− with a b→u or a b→c transition, in a Kπ mass region of ±50  MeV/c2 around the K∗(892) mass and for an absolute value of the cosine of the K*0 helicity angle larger than 0.4

Search for CP violation in D ± → K S 0 K ± and D s ± → K S 0 π ± decays

A search for CP violation in Cabibbo-suppressed D ± → K S 0 K ± and D s ± → K S 0 π ± decays is performed using pp collision data, corresponding to an integrated luminosity of 3 fb, recorded by the LHCb experiment. The individual CP-violating asymmetries are measured to be AD±CP→K0SK±=(+0.03±0.17±0.14)%AD±sCP→K0Sπ±=(+0.38±0.46±0.17)%, assuming that CP violation in the Cabibbo-favoured decays is negligible. A combination of the measured asymmetries for the four decay modes D (s) ± → K S 0 K ± and D (s) ± → K S 0 π ± gives the sum AD±→K0SK±CP+AD±s→K0Sπ±CP=(+0.41±0.49±0.26)%. In all cases, the first uncertainties are statistical and the second systematic. The results represent the most precise measurements of these asymmetries to date and show no evidence for CP violation

Study of η − η′ mixing from measurement of B (s) 0 → J/ψη(′) decay rates

A study of B and Bs meson decays into J/ψ η and J/ψ η′ final states is performed using a data set of proton-proton collisions at centre-of-mass energies of 7 and 8 TeV, collected by the LCHb experiment and corresponding to 3.0 fb−1 of integrated luminosity. The decay B0 → J/ψ η′ is observed for the first time. The following ratios of branching fractions are measured: B(B0→J/ψη′)B(B0s→ J/ψη′)=(2.28±0.65 (stat)±0.10 (syst)±0.13 (fs/fd))×10−2,B(B0→ J/ψη)B(B0s→ J/ψη)=(1.85±0.61 (stat)±0.09 (syst)±0.11 (fs/fd))×10−2, where the third uncertainty is related to the present knowledge of fs/fd, the ratio between the probabilities for a b quark to form a Bs or a B0 meson. The branching fraction ratios are used to determine the parameters of η − η′ meson mixing. In addition, the first evidence for the decay Bs → ψ(2S)η′ is reported, and the relative branching fraction is measured, B(B0s→ ψ(2S)η′)B(B0s→ J/ψη′)=(38.7±9.0 (stat)±1.3 (syst)±0.9(B))×10−2, where the third uncertainty is due to the limited knowledge of the branching fractions of J/ψ and ψ(2S) mesons

Measurement of indirect CP asymmetries in D0 → K−K+ and D0 → π−π+ decays using semileptonic B decays

Time-dependent CP asymmetries in the decay rates of the singly Cabibbo-suppressed decays D0 → K−K+ and D0 → π−π+ are measured in pp collision data corresponding to an integrated luminosity of 3.0 fb−1 collected by the LHCb experiment. The D0 mesons are produced in semileptonic b-hadron decays, where the charge of the accompanying muon is used to determine the initial state as D0 or D¯0. The asymmetries in effective lifetimes between D0 and D¯0 decays, which are sensitive to indirect CP violation, are determined to be AΓK−K+=−0.134±0.077−0.034−0.026%, AΓπ−π+=−0.092±0.145−0.033−0.025%, where the first uncertainties are statistical and the second systematic. This result is in agreement with previous measurements and with the hypothesis of no indirect CP violation in D0 decays