Sneha Malde

Abstract:

A search for CP violation in the decay Λb0 → pK−μ+μ− is presented. This decay is mediated by flavour-changing neutral-current transitions in the Standard Model and is potentially sensitive to new sources of CP violation. The study is based on a data sample of proton-proton collisions recorded with the LHCb experiment, corresponding to an integrated luminosity of 3 fb^−1. The Λb0 → pK−μ+μ− decay is observed for the first time, and two observables that are sensitive to different manifestations of CP violation are measured, ΔACP ≡ ACP(Λ0b→pK−μ+μ−) − ACP(Λ0b→pK−J/ψ) and a aT-odd/CP, where the latter is based on asymmetries in the angle between the μ+μ− and pK− decay planes. These are measured to be ΔACP = (−3.5 ±5.0(stat) ±0.2(syst))×10^−2, aT-odd/CP = (1.2 ±5.0 (stat) ±0.7 (syst))×10^−2,and no evidence for CP violation is found.

Abstract:

The observation of the decay Ξ b − →J/ψΛK − is reported, using a data sample corresponding to an integrated luminosity of 3fb −1 , collected by the LHCb detector in pp collisions at centre-of-mass energies of 7 and 8TeV. The production rate of Ξ b − baryons detected in the decay Ξ b − →J/ψΛK − is measured relative to that of Λ b 0 baryons using the decay Λ b 0 →J/ψΛ. Integrated over the b-baryon transverse momentum p T < 25GeV/c and rapidity 2.0 < y < 4.5, the measured ratio is [Formula presented][Formula presented] =(4.19±0.29 (stat)±0.15 (syst))×10 −2 , where f Ξ b − and f Λ b 0 are the fragmentation fractions of b→Ξ b − and b→Λ b 0 transitions, and B represents the branching fraction of the corresponding b-baryon decay. The mass difference between Ξ b − and Λ b 0 baryons is measured to be M(Ξ b − )−M(Λ b 0 )=177.08±0.47 (stat)±0.16 (syst)MeV/c 2 .

Abstract:

A search for the rare decays B0s→ τþτ− and B0 → τþτ− is performed using proton–proton collision data collected with the LHCb detector. The data sample corresponds to an integrated luminosity of 3 fb^−1 collected in 2011 and 2012. The τ leptons are reconstructed through the decay τ− → π−π+π−ντ. Assuming no contribution from B0 → τþτ− decays, an upper limit is set on the branching fraction B(B0s → τ+τ−) < 6.8 × 10^−3 at the 95% confidence level. If instead no contribution from B0s → τ+τ− decays is assumed, the limit is B(B0 → τþτ−) < 2.1 × 10^−3 at the 95% confidence level. These results correspond to the first direct limit on B(B0s→ τ+τ−) and the world’s best limit on B(B0 → τ+τ−).

Abstract:

The production of J/ψ mesons in jets is studied in the forward region of proton-proton collisions using data collected with the LHCb detector at a center-of-mass energy of 13 TeV. The fraction of the jet transverse momentum carried by the J/ψ meson, z(J/ψ)≡p_{T}(J/ψ)/p_{T}(jet), is measured using jets with p_{T}(jet)>20  GeV in the pseudorapidity range 2.5<η(jet)<4.0. The observed z(J/ψ) distribution for J/ψ mesons produced in b-hadron decays is consistent with expectations. However, the results for prompt J/ψ production do not agree with predictions based on fixed-order nonrelativistic QCD. This is the first measurement of the p_{T} fraction carried by prompt J/ψ mesons in jets at any experiment.

Abstract:

A search for $CP$ violation in $D^{\pm}\rightarrow \eta^{\prime} \pi^{\pm}$ and $D^{\pm}_{s}\rightarrow \eta^{\prime} \pi^{\pm}$ decays is performed using proton-proton collision data, corresponding to an integrated luminosity of $3$ fb$^{-1}$, recorded by the LHCb experiment at centre-of-mass energies of $7$ and $8$ TeV. The measured $CP$-violating charge asymmetries are $A_{CP}(D^{\pm} \rightarrow \eta^{\prime} \pi^{\pm})=(-0.61\pm 0.72 \pm 0.53 \pm 0.12)\%$ and $A_{CP}(D^{\pm}_{s}\rightarrow \eta^{\prime} \pi^{\pm})=(-0.82\pm 0.36 \pm 0.22 \pm 0.27)\%$, where the first uncertainties are statistical, the second systematic, and the third are the uncertainties on the $A_{CP}(D^{\pm} \rightarrow K^0_S \pi^{\pm})$ and $A_{CP}(D^{\pm}_{s}\rightarrow \phi \pi^{\pm})$ measurements used for calibration. The results represent the most precise measurements of these asymmetries to date.