Sneha Malde

Abstract:

The ratio of branching fractions R(D∗-)≡B(B0→D∗-τ+ντ)/B(B0→D∗-μ+νμ) is measured using a data sample of proton-proton collisions collected with the LHCb detector at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 fb-1. The τ lepton is reconstructed with three charged pions in the final state. A novel method is used that exploits the different vertex topologies of signal and backgrounds to isolate samples of semitauonic decays of b hadrons with high purity. Using the B0→D∗-π+π-π+ decay as the normalization channel, the ratio B(B0→D∗-τ+ντ)/B(B0→D∗-π+π-π+) is measured to be 1.97±0.13±0.18, where the first uncertainty is statistical and the second systematic. An average of branching fraction measurements for the normalization channel is used to derive B(B0→D∗-τ+ντ)=(1.42±0.094±0.129±0.054)%, where the third uncertainty is due to the limited knowledge of B(B0→D∗-π+π-π+). A test of lepton flavor universality is performed using the well-measured branching fraction B(B0→D∗-μ+νμ) to compute R(D∗-)=0.291±0.019±0.026±0.013, where the third uncertainty originates from the uncertainties on B(B0→D∗-π+π-π+) and B(B0→D∗-μ+νμ). This measurement is in agreement with the Standard Model prediction and with previous measurements.

Abstract:

AbstractWe report the measurements of theCP-violating parameters inBs0 → Ds∓K±decays observed inppcollisions, using a data set corresponding to an integrated luminosity of 3.0 fb−1recorded with the LHCb detector. We measureCf= 0.73 ± 0.14 ± 0.05,AfΔΓ = 0.39 ± 0.28 ± 0.15,$$ {A}_{\overline{f}}^{\varDelta \varGamma }=0.31\pm 0.28\pm 0.15 $$Af¯ΔΓ=0.31±0.28±0.15,Sf= −0.52 ± 0.20 ± 0.07,$$ {S}_{\overline{f}}=-0.49\pm 0.20\pm 0.07 $$Sf¯=−0.49±0.20±0.07, where the uncertainties are statistical and systematic, respectively. These parameters are used together with the world-average value of theBs0mixing phase, −2βs, to obtain a measurement of the CKM angle γ fromBs0 → Ds∓K±decays, yieldingγ = (128− 22+ 17)°modulo 180°, where the uncertainty contains both statistical and systematic contributions. This corresponds to 3.8σevidence forCPviolation in the interference between decay and decay after mixing.