LHCb

Abstract:

We present a search for B decays to charmless final states involving charged or neutral a0 mesons. The data sample corresponds to 89 × 10⁶ BB̄ pairs collected with the BABAR detector operating at the PEP-II asymmetric-energy B Factory at Stanford Linear Accelerator Center. We find no significant signals and determine the following 90% C.L. upper limits: B(B⁰ → a0 ^-π⁺) < 5.1 × 10^-6, B(B⁰ → a0^-K⁺) < 2.1 × 10^-6, B(B^- → a0^-K̄⁰) < 3.9 × 10^-6, B(B⁺ → a0 ⁰π⁺) < 5.8 × 10^-6, B(B⁺ → a0⁰K⁺) < 2.5 × 10^-6, and B(B⁰ → a0⁰K⁰) < 7.8 × 10^-6, where in all cases B indicates the product of branching fractions for B → a0X and a0 ηπ, where X indicates K or π.

Abstract:

Based on an 87-fb^-1 data set collected by the BABAR detector at the PEP-II asymmetric-energy B Factory, a search for D⁰- D̄⁰ mixing has been made using the semileptonic decay modes D*⁺ → π⁺D⁰, D⁰ → K^(*)eν (+c.c.). The use of these modes allows unambiguous flavor tagging and a combined fit of the D⁰ decay time and D*⁺-D⁰ mass difference (ΔM) distributions. The high-statistics sample of unmixed semileptonic D⁰ decays is used to model the ΔM distribution and time dependence of mixed events directly from the data Neural networks are used to select events and reconstruct the D⁰. A result consistent with no charm mixing has been obtained, Rmix = 0.0023 ± 0.0012 ± 0.0004. This corresponds to an upper limit of Rmix < 0.0042 (90% C.L.).

Abstract:

Oscillations in the Bs⁰-Bs⁰ system were studied in events selected from about 4.3 million hadronic Z ⁰ decays registered by DELPHI between 1992 and 2000. This paper presents updates of two published analyses ([11,12]). The first analysis, which utilizes leptons emitted with large momentum transverse to a jet, was improved by means of a better algorithm for the vertex reconstuction and a new algorithm for flavour-tagging at production time. The second analysis, which utilizes Ds-lepton events, was improved by optimizing the treatment of proper time resolution. No signal of B⁰ oscillations was observed and limits on the mass difference between the physical B⁰ states were obtained to be: δms > 8.0ps^-1 at the 95% C.L. with a sensitivity of δms = 9.1 ps^-1 in the high pt lepton analysis and δms < 4.9 ps-1 at the 95% C.L. with a sensitivity of δms = 8.6 ps^-1 in the D s-lepton analysis. Previously published results on these analyses are superseded. The combination of these results with those obtained in other independent analyses previously performed in DELPHI (Ds-hadron, exclusive Bs⁰, inclusive vertex) gives: δm, > 8.5 ps^-1 at the 95% C.L. with a sensitivity of δms = 12.0 ps-1.

Abstract:

The process e+ e- → π+ π- π0 γ has been studied at a center-of-mass energy near the Y(4S) resonance using a 89.3 fb-1 data sample collected with the BABAR detector at the PEP-II collider. From the measured 3π mass spectrum we have obtained the products of branching fractions for the ω and φ mesons, B(ω → e+ e-) B(ω → 3π) = (6.70 ± 0.06 ± 0.27) × 10 -5 and B(φ → e+e-)B(φ → 3π) = (4.30 ± 0.08 ± 0.21) × 10-5 and evaluated the e+ e- → π+ π- π0 cross section for the e+ e - center-of-mass energy range 1.05 to 3.00 GeV. About 900 e + e- → J/ψγ → π+ π- π0 γ events have been selected and the branching fraction B(J/ψ → π+ π- π0) = (2.18 ± 0.19)% has been measured.

Abstract:

The standard method used for tagging b-hadrons in the DELPHI experiment at the CERN LEP Collider is discussed in detail. The main ingredient of b-tagging is the impact parameters of tracks, which relies mostly on the vertex detector. Additional information, such as the mass of particles associated to a secondary vertex, significantly improves the selection efficiency and the background suppression. The paper describes various discriminating variables used for the tagging and the procedure of their combination. In addition, applications of b-tagging to some physics analyses, which depend crucially on the performance and reliability of b-tagging, are described briefly.