Malcolm John

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.

Abstract:

A search for the rare decays B0s→μ+μ− and B0→μ+μ− is performed at the LHCb experiment using data collected in pp collisions corresponding to a total integrated luminosity of 4.4  fb−1. An excess of B0s→μ+μ− decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be B(B0s→μ+μ−)=(3.0±0.6+0.3−0.2)×10^−9, where the first uncertainty is statistical and the second systematic. The first measurement of the B0s→μ+μ− effective lifetime, τ(B0s→μ+μ−)=2.04±0.44±0.05  ps, is reported. No significant excess of B0→μ+μ− decays is found, and a 95% confidence level upper limit, B(B0→μ+μ−)<3.4×10^−10, is determined. All results are in agreement with the standard model expectations.

Abstract:

The Ξ+cK− mass spectrum is studied with a sample of pp collision data corresponding to an integrated luminosity of 3.3  fb^-1, collected by the LHCb experiment. The Ξ+cK− is reconstructed in the decay mode pK-π+. Five new, narrow excited Ω0c states are observed: the Ωc(3000)^0, Ωc(3050)^0, Ωc(3066)^0, Ωc(3090)^0, and Ωc(3119)^0. Measurements of their masses and widths are reported.