LHCb

Abstract:

The total and the differential cross-sections for the reaction e⁺e^- → γγ(γ) have been measured with the DELPHI detector at LEP at centre-of-mass energies from 130 to 183 GeV for an integrated luminosity of 78.19 pb^-1. The results agree with the QED predictions. The lower limits (obtained including previously published results at the Z⁰ energies) on the QED cutoff parameters are Λ+ > 253 GeV and Λ-> 225 GeV and the lower bound on the mass of an excited electron with an effective coupling constant λγ = 1 is 231 GeV/c². All the limits are at the 95% confidence level. © 1998 Published by Elsevier Science B.V. All rights reserved.

Abstract:

The hadronic structure of the decay of the τ lepton to three charged particles, τ → 3πντ, is studied using data collected by the DELPHI detector at LEP between 1992 and 1995. The invariant mass of the 3π system, m3π, is fitted using the models of Kühn and Santamaria, Isgur Morningstar and Reader, and Feindt. The 3π and π⁺π^- mass spectra are compared with each model. Below m²3π = 2.3 GeV², all are in good qualitative agreement. Above m²3π = 2.3 GeV², anomalous behaviour is observed, consistent with the existence of a hitherto unseen decay mode of the τ through a radial excitation of the a1 meson. © 1998 Published by Elsevier Science B.V. All rights reserved.

Abstract:

The LHCb experiment is based on a single arm forward spectrometer optimized to study CP violation in the B system at the LHC. The experiment includes a dedicated trigger system, particle identification and a precise vertex determination; recent developments in these areas will be summarized. The detector will provide precise measurements of all angles of the unitarity triangle, the length of one of the sides (via B-s(0) - (B) over bar(s)(0) mixing) and the height of the triangle. The physics performance for selected channels will be reviewed. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

Using D *+ mesons exclusively reconstructed in the DELPHI detector at LEP, an excess of 66 ± 14(stat.) events is observed in the D *+π+ π- final state with a mass of 2637 ± 2(stat.) ± 6(syst.) MeV/c2 and a full width smaller than 15 MeV/c2 (95% C.L.). This signal is compatible with the expected decay of a radially excited D *′ (JP = 1-) meson. © 1998 Published by Elsevier Science B.V. All rights reserved.

Abstract:

The DELPHI experiment at LEP has measured the inclusive charmless B hadron decay branching ratio, the B branching ratio into two charmed particles, and the total number of charmed particles per B decay, using the hadronic Z data taken between 1992 and 1995. The results are extracted from a fit to the b-tagging probability distribution based on the precise impact parameter measurements made using the microvertex detector. The inclusive charmless B branching ratio, including B decays into hidden charm (cc̄), is measured to be 0.033 ± 0.021. The B branching ratio into two open charmed particles is 0.136 ± 0.042. The mean number of charmed particles per B decay (including hidden charm) is 1.147 ± 0.041. After subtracting the B decay branching ratio into hidden charm, the charmless B branching ratio is found to be 0.007 ± 0.021, compatible with the Standard Model expectation. Models that predict an additional contribution to the charmless B branching ratio of 0.037 or higher are excluded with at least 95% confidence. © 1998 Elsevier Science B.V. All rights reserved.