Malcolm John

Abstract:

The suppressed decay Λb0 → pπ−μ+μ−, excluding the J/ψ and ψ(2S) → μ+μ− resonances, is observed for the first time with a significance of 5.5 standard deviations. The analysis is performed with proton-proton collision data corresponding to an integrated luminosity of 3 fb−1 collected with the LHCb experiment. The Λb0 → pπ−μ+μ− branching fraction is measured relative to the Λb0 → J/ψ(→μ+μ−)pπ− branching fraction giving $\frac{\mathrm{\mathcal{B}}\left({\Lambda}_b^0\to p{\pi}^{-}{\mu}^{+}{\mu}^{-}\right)}{\mathrm{\mathcal{B}}\left({\Lambda}_b^0\to \mathrm{J}/\psi \left(\to {\mu}^{+}{\mu}^{-}\right)p{\pi}^{-}\right)}=0.044\pm 0.012\pm 0.007,$ where the first uncertainty is statistical and the second is systematic. This is the first observation of a b → d transition in a baryonic decay.

Abstract:

A search for the rare two-body charmless baryonic decay B + → pΛ¯ is performed with pp collision data, corresponding to an integrated luminosity of 3 fb −1 , collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. An excess of B + →pΛ¯ candidates with respect to background expectations is seen with a statistical significance of 4.1 standard deviations, and constitutes the first evidence for this decay. The branching fraction, measured using the B + →K S 0 π + decay for normalisation,(Formula Presented.)where the first uncertainty is statistical and the second systematic.[Figure not available: see fulltext.].

Abstract:

Two new algorithms for use in the analysis of pp collision are developed to identify the flavour of B0 mesons at production using pions and protons from the hadronization process. The algorithms are optimized and calibrated on data, using B0→ D−π+ decays from pp collision data collected by LHCb at centre-of-mass energies of 7 and 8TeV. The tagging power of the new pion algorithm is 60% greater than the previously available one; the algorithm using protons to identify the flavour of a B0 meson is the first of its kind..

Abstract:

A search for time-integrated CP violation in the Cabibbo-suppressed decay D0 → π+π−π+π− is performed using an unbinned, model-independent technique known as the energy test. This is the first application of the energy test in four-body decays. The search is performed for P-even CP asymmetries and, for the first time, is extended to probe the P-odd case. Using proton–proton collision data corresponding to an integrated luminosity of 3.0 fb −1 collected by the LHCb detector at centre-of-mass energies of s=7 TeV and 8 TeV, the world's best sensitivity to CP violation in this decay is obtained. The data are found to be consistent with the hypothesis of CP symmetry with a p-value of (4.6±0.5)% in the P-even case, and marginally consistent with a p-value of (0.6±0.2)% in the P-odd case, corresponding to a significance for CP non-conservation of 2.7 standard deviations.

Abstract:

A search for a long-lived scalar particle χ is performed, looking for the decay B+→K+χ with χ→μ+μ- in pp collision data corresponding to an integrated luminosity of 3 fb-1, collected by the LHCb experiment at center-of-mass energies of s=7 and 8 TeV. This new scalar particle, predicted by hidden sector models, is assumed to have a narrow width. The signal would manifest itself as an excess in the dimuon invariant mass distribution over the Standard Model background. No significant excess is observed in the accessible ranges of mass 250 < m(χ) < 4700 MeV/c2 and lifetime 0.1 < τ(χ) < 1000 ps. Upper limits on the branching fraction B(B+→K+χ(μ+μ-)) at 95% confidence level are set as a function of m(χ) and τ(χ), varying between 2×10-10 and 10-7. These are the most stringent limits to date. The limits are interpreted in the context of a model with a light inflaton particle.