Sneha Malde

Abstract:

We report a study of the suppressed B-→DK-π+π- and favored B-→Dπ-π+π- decays, where the neutral D meson is detected through its decays to the K π± and CP -even K+K- and π+π- final states. The measurement is carried out using a proton-proton collision data sample collected by the LHCb experiment, corresponding to an integrated luminosity of 3.0 fb-1. We observe the first significant signals in the CP -even final states of the D meson for both the suppressed B-→DK-π+π- and favored B-→Dπ-π+π- modes, as well as in the doubly Cabibbo suppressed D→K+π- final state of the B-→Dπ-π+π- decay. Evidence for the suppressed decay B-→DK-π+π-, with D→K+π-, is also presented. From the observed yields in the B-→DK-π+π-, B-→Dπ-π+π- and their charge conjugate decay modes, the most probable value of the weak phase γ corresponds to γ=(74-19+20)°. This is one of the most precise single-measurement determinations of γ to date.

Abstract:

Using a pp collision data sample corresponding to an integrated luminosity of 3.0  fb^{-1}, collected by the LHCb detector, we present the first search for the strangeness-changing weak decay Ξ_{b}^{-}→Λ_{b}^{0}π^{-}. No b hadron decay of this type has been seen before. A signal for this decay, corresponding to a significance of 3.2 standard deviations, is reported. The relative rate is measured to be f_{Ξ_{b}^{-}}/f_{Λ_{b}^{0}}B(Ξ_{b}^{-}→Λ_{b}^{0}π^{-})=(5.7±1.8_{-0.9}^{+0.8})×10^{-4},where f_{Ξ_{b}^{-}} and f_{Λ_{b}^{0}} are the b→Ξ_{b}^{-} and b→Λ_{b}^{0} fragmentation fractions, and B(Ξ_{b}^{-}→Λ_{b}^{0}π^{-}) is the branching fraction. Assuming f_{Ξ_{b}^{-}}/f_{Λ_{b}^{0}} is bounded between 0.1 and 0.3, the branching fraction B(Ξ_{b}^{-}→Λ_{b}^{0}π^{-}) would lie in the range from (0.57±0.21)% to (0.19±0.07)%.

Abstract:

A search for the rare decay of a B0 or Bs0 meson into the final state J/ψγ is performed, using data collected by the LHCb experiment in pp collisions at s=7 and 8 TeV, corresponding to an integrated luminosity of 3 fb-1. The observed number of signal candidates is consistent with a background-only hypothesis. Branching fraction values larger than 1.5×10-6 for the B0→J/ψγ decay mode are excluded at 90% confidence level. For the Bs0→J/ψγ decay mode, branching fraction values larger than 7.3×10-6 are excluded at 90% confidence level; this is the first branching fraction limit for this decay.

Abstract:

The forward-backward charge asymmetry for the process qq̅ → Z/γ^∗ → μ⁺μ⁻ is measured as a function of the invariant mass of the dimuon system. Measurements are performed using proton proton collision data collected with the LHCb detector at √s=7 and 8 TeV, corresponding to integrated luminosities of 1 fb⁻¹ and 2 fb⁻¹ respectively. Within the Standard Model the results constrain the effective electroweak mixing angle to be
sin²θ^eff_W = 0.23142 ± 0.00073 ± 0.00052 ± 0.00056,
where the first uncertainty is statistical, the second systematic and the third theoretical. This result is in agreement with the current world average, and is one of the most precise determinations at hadron colliders to date.