Malcolm John

Abstract:

Search for the lepton-flavour violating decay D⁰ → e^±μ^∓

A search for the lepton-flavour violating decay D⁰ → e^±μ^∓ is made with a dataset corresponding to an integrated luminosity of 3.0 fb⁻¹ of proton–proton collisions at centre-of-mass energies of 7 TeV and 8 TeV, collected by the LHCb experiment. Candidate D⁰ mesons are selected using the decay D^∗+ → D⁰π⁺ and the D⁰ → e^±μ^∓ branching fraction is measured using the decay mode D⁰ → K⁻π⁺ as a normalization channel. No significant excess of D⁰ → e^±μ^∓ candidates over the expected background is seen, and a limit is set on the branching fraction, 𝓑(D⁰ → e^±μ^∓) < 1.3 × 10⁻⁸, at 90% confidence level. This is an order of magnitude lower than the previous limit and it further constrains the parameter space in some leptoquark models and in supersymmetric models with R-parity violation.

Abstract:

First observation of the decay B_s⁰ → K_S⁰K^∗(892)⁰ at LHCb

A search for B_(s)⁰ → K_S⁰K^∗(892)⁰ decays is performed using pp collision data, corresponding to an integrated luminosity of 1.0 fb⁻¹, collected with the LHCb detector at a centre-of-mass energy of 7 TeV. The B_s⁰ → K_S⁰K^∗(892)⁰ decay is observed for the first time, with a significance of 7.1 standard deviations. The branching fraction is measured to be
𝓑(B_s⁰ → K̅⁰K^∗(892)⁰) + 𝓑(B_s⁰ → K⁰K̅^∗(892)⁰)=(16.4 ± 3.4 ± 2.3) × 10⁻⁶,
where the first uncertainty is statistical and the second is systematic. No evidence is found for the decay B⁰ → K_S⁰K^∗(892)⁰ and an upper limit is set on the branching fraction, 𝓑(B⁰ → K̅⁰K^∗(892)⁰) + 𝓑(B⁰ → K⁰K̅^∗(892)⁰) < 0.96 × 10⁻⁶, at 90 % confidence level. All results are consistent with Standard Model predictions.

Abstract:

The Dalitz plot analysis technique is used to study the resonant substructures of B−→D+π−π− decays in a data sample corresponding to 3.0  fb−1 of pp collision data recorded by the LHCb experiment during 2011 and 2012. A model-independent analysis of the angular moments demonstrates the presence of resonances with spins 1, 2 and 3 at high D+π− mass. The data are fitted with an amplitude model composed of a quasi-model-independent function to describe the D+π− S wave together with virtual contributions from the D∗(2007)0 and B*0 states, and components corresponding to the D∗2(2460)0, D∗1(2680)0, D∗3(2760)0 and D∗2(3000)0 resonances. The masses and widths of these resonances are determined together with the branching fractions for their production in B−→D+π−π− decays. The D+π− S wave has phase motion consistent with that expected due to the presence of the D∗0(2400)0 state. These results constitute the first observations of the D∗3(2760)0 and D∗2(3000)0 resonances, with significances of 10σ and 6.6σ, respectively.

Abstract:

A model-dependent amplitude analysis of the decay B0 → D(KS0π+π−)K∗0 is performed using proton-proton collision data corresponding to an integrated luminosity of 3.0 fb−1, recorded at √s=7 and 8 TeV by the LHCb experiment. The CP violation observables x± and y±, sensitive to the CKM angle γ, are measured to bex−=−0.15±0.14±0.03±0.01,y−=0.25±0.15±0.06±0.01,x+=0.05±0.24±0.04±0.01,y+=−0.65−0.23+0.24±0.08±0.01, where the first uncertainties are statistical, the second systematic and the third arise from the uncertainty on the D → KS0π+π− amplitude model. These are the most precise measurements of these observables. They correspond to γ = (80−22+21)° and rB0=0.39±0.13, where rB0 is the magnitude of the ratio of the suppressed and favoured B0 → DK+π− decay amplitudes, in a Kπ mass region of ±50 MeV around the K*(892)0 mass and for an absolute value of the cosine of the K*0 decay angle larger than 0.4.[Figure not available: see fulltext.]