LHCb

Abstract:

A measurement is reported of the ratio of branching fractions R(J/ψ)=B(B_{c}^{+}→J/ψτ^{+}ν_{τ})/B(B_{c}^{+}→J/ψμ^{+}ν_{μ}), where the τ^{+} lepton is identified in the decay mode τ^{+}→μ^{+}ν_{μ}ν[over ¯]_{τ}. This analysis uses a sample of proton-proton collision data corresponding to 3.0  fb^{-1} of integrated luminosity recorded with the LHCb experiment at center-of-mass energies of 7 and 8 TeV. A signal is found for the decay B_{c}^{+}→J/ψτ^{+}ν_{τ} at a significance of 3 standard deviations corrected for systematic uncertainty, and the ratio of the branching fractions is measured to be R(J/ψ)=0.71±0.17(stat)±0.18(syst). This result lies within 2 standard deviations above the range of central values currently predicted by the standard model.

Abstract:

Abstract The ratios of the branching fractions of the decays Λ c +  → pπ − π +, Λ c +  → pK − K +, and Λ c +  → pπ − K + with respect to the Cabibbo-favoured Λ c +  → pK − π + decay are measured using proton-proton collision data collected with the LHCb experiment at a 7 TeV centre-of-mass energy and corresponding to an integrated luminosity of 1.0 fb−1: $$ \begin{array}{l}\frac{\mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{\pi}^{-}{\pi}^{+}\right)}{\mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{K}^{-}{\pi}^{+}\right)}=\left(7.44\pm 0.08\pm 0.18\right)\%,\hfill \\ {}\frac{\mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{K}^{-}{K}^{+}\right)}{\mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{K}^{-}{\pi}^{+}\right)}=\left(1.70\pm 0.03\pm 0.03\right)\%\hfill \\ {}\frac{\mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{\pi}^{-}{K}^{+}\right)}{\mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{K}^{-}{\pi}^{+}\right)}=\left(0.165\pm 0.015\pm 0.005\right)\%,\hfill \end{array} $$ ℬ Λ c + → p π − π + ℬ Λ c + → p K − π + = 7.44 ± 0.08 ± 0.18 % , ℬ Λ c + → p K − K + ℬ Λ c + → p K − π + = 1.70 ± 0.03 ± 0.03 % ℬ Λ c + → p π − K + ℬ Λ c + → p K − π + = 0.165 ± 0.015 ± 0.005 % , where the uncertainties are statistical and systematic, respectively. These results are the most precise measurements of these quantities to date. When multiplied by the world-average value for $$ \mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{K}^{-}{\pi}^{+}\right) $$ ℬ Λ c + → p K − π + , the corresponding branching fractions are $$ \begin{array}{l}\mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{\pi}^{-}{\pi}^{+}\right)=\left(4.72\pm 0.05\pm 0.11\pm 0.25\right)\times {10}^{-3},\hfill \\ {}\mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{K}^{-}{K}^{+}\right)=\left(1.08\pm 0.02\pm 0.02\pm 0.06\right)\times {10}^{-3},\hfill \\ {}\mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{\pi}^{-}{K}^{+}\right)=\left(1.04\pm 0.09\pm 0.03\pm 0.05\right)\times {10}^{-4},\hfill \end{array} $$ ℬ Λ c + → p π − π + = 4.72 ± 0.05 ± 0.11 ± 0.25 × 10 − 3 , ℬ Λ c + → p K − K + = 1.08 ± 0.02 ± 0.02 ± 0.06 × 10 − 3 , ℬ Λ c + → p π − K + = 1.04 ± 0.09 ± 0.03 ± 0.05 × 10 − 4 , where the final uncertainty is due to $$ \mathrm{\mathcal{B}}\left({\varLambda}_c^{+}\to p{K}^{-}{\pi}^{+}\right) $$ ℬ Λ c + → p K − π + .

Abstract:

Abstract A search for the lepton-flavour violating decays B s 0  → e ± μ ∓ and B 0 → e ± μ ∓ is performed based on a sample of proton-proton collision data corresponding to an integrated luminosity of 3 fb−1, collected with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The observed yields are consistent with the background-only hypothesis. Upper limits on the branching fraction of the B s 0  → e ± μ ∓ decays are evaluated both in the hypotheses of an amplitude completely dominated by the heavy eigenstate and by the light eigenstate. The results are $$ \frac{@}{@}\mathrm{\mathcal{B}}\left({B}_s^0\to {e}^{\pm }{\mu}^{\mp}\right)<6.3(5.4)\times 1{0}^{-9} $$ @ @ ℬ B s 0 → e ± μ ∓ < 6.3 5.4 × 1 0 − 9 and $$ \frac{@}{@}\mathrm{\mathcal{B}}\left({B}_s^0\to {e}^{\pm }{\mu}^{\mp}\right)<7.2(6.0)\times 1{0}^{-9} $$ @ @ ℬ B s 0 → e ± μ ∓ < 7.2 6.0 × 1 0 − 9 at 95% (90%) confidence level, respectively. The upper limit on the branching fraction of the B 0 → e ± μ ∓ decay is also evaluated, obtaining $$ \frac{@}{@}\mathrm{\mathcal{B}}\left({B}^0\to {e}^{\pm }{\mu}^{\mp}\right)<1.3(1.0)\times 1{0}^{-9} $$ @ @ ℬ B 0 → e ± μ ∓ < 1.3 1.0 × 1 0 − 9 at 95% (90%) confidence level. These are the strongest limits on these decays to date.

Abstract:

© 2018 authors. We report measurements of charm-mixing parameters based on the decay-time-dependent ratio of D0→K+π- to D0→K-π+ rates. The analysis uses a data sample of proton-proton collisions corresponding to an integrated luminosity of 5.0 fb-1 recorded by the LHCb experiment from 2011 through 2016. Assuming charge-parity (CP) symmetry, the mixing parameters are determined to be x′2=(3.9±2.7)×10-5, y′=(5.28±0.52)×10-3, and RD=(3.454±0.031)×10-3. Without this assumption, the measurement is performed separately for D0 and D0 mesons, yielding a direct CP-violating asymmetry AD=(-0.1±9.1)×10-3, and magnitude of the ratio of mixing parameters 1.00<|q/p|<1.35 at the 68.3% confidence level. All results include statistical and systematic uncertainties and improve significantly upon previous single-measurement determinations. No evidence for CP violation in charm mixing is observed.