LHCb

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.

Abstract:

A search is presented for massive long-lived particles decaying into a muon and two quarks. The dataset consists of proton-proton interactions at centre-of-mass energies of 7 and 8 TeV, corresponding to integrated luminosities of 1 and 2[Formula: see text], respectively. The analysis is performed assuming a set of production mechanisms with simple topologies, including the production of a Higgs-like particle decaying into two long-lived particles. The mass range from 20 to 80 [Formula: see text] and lifetimes from 5 to 100[Formula: see text] are explored. Results are also interpreted in terms of neutralino production in different R-Parity violating supersymmetric models, with masses in the 23-198 GeV/[Formula: see text] range. No excess above the background expectation is observed and upper limits are set on the production cross-section for various points in the parameter space of theoretical models.

Abstract:

Measurements of charm mixing and CP violation parameters from the decay-time-dependent ratio of D⁰ K+π- to D⁰ K-π+ decay rates and the charge-conjugate ratio are reported. The analysis uses &Bmacr; D^*+μ-X, and charge-conjugate decays, where D^*+ D⁰π+, and D⁰ K∓π±. The pp collision data are recorded by the LHCb experiment at center-of-mass energies √_s=7 and 8 TeV, corresponding to an integrated luminosity of 3 fb^-1. The data are analyzed under three hypotheses: (i) mixing assuming CP symmetry, (ii) mixing assuming no direct CP violation in the Cabibbo-favored or doubly Cabibbo-suppressed decay amplitudes, and (iii) mixing allowing either direct CP violation and/or CP violation in the superpositions of flavor eigenstates defining the mass eigenstates. The data are also combined with those from a previous LHCb study of D⁰ Kπ decays from a disjoint set of D^*+ candidates produced directly in pp collisions. In all cases, the data are consistent with the hypothesis of CP symmetry.