LHCb

Abstract:

Using the ZEUS detector at the HERA electron-proton collider, we have searched for lepton flavor violation in ep collisions at a center-of-mass energy (√s) of 300 GeV. Events of the type e + p → ℓ + X with a final-state lepton of high transverse momentum, ℓ = μ or τ, were sought. No evidence was found for lepton flavor violation in the combined 1993 and 1994 data samples, for which the integrated luminosities were 0.84 pb-1 for e-p collisions and 2.94 pb-1 for e+p collisions. Limits on coupling vs. mass are provided for leptoquarks and R-parity violating squarks. For flavor violating couplings of electromagnetic strength, we set 95% confidence level lower limits on leptoquark masses between 207 GeV and 272 GeV, depending on the leptoquark species and final-state lepton. For leptoquark masses larger than 300 GeV, limits on flavor-changing couplings are determined, many of which supersede prior limits from rare decay processes. © Springer-Verlag 1997.

Abstract:

A search with the DELPHI detector at LEP for excited leptons (e*, μ*, τ* and v*) decaying through γ, W or Z transitions is reported. The data used correspond to an integrated luminosity of 10 pb^-1 at an e⁺e^- centre-of-mass energy of 161 GeV. The search for pair produced excited leptons established the limits me* > 79.6 GeV/c², mμ* > 79.6 GeV/c², mτ* > 79.4 GeV/c² and mv* > 56.4 GeV/c² at 95% confidence level, assuming that the SU(2) and U(1) couplings of excited leptons are in the same ratio as for normal leptons and considering both left and right-handed components. Limits corresponding to other assumptions are also given. The search for single excited lepton production established upper limits on the ratio λ/mℓ* of the coupling of the excited lepton to its mass.

Abstract:

From data recorded by DELPHI between 1991 and 1994, which corresponds to 3.2 million hadronic Z0 decays, a measurement of the Bd0 meson lifetime, based on the inclusive reconstruction of 3520 ± 150 semileptonic decays of the type Bd0 → D*+ X ℓ νℓ, has been performed. The result is: τ(Bd0) = 1.532 ± 0.041(stat.) ± 0.040(syst.)ps. The contribution to the systematic uncertainty which depends on external errors is ±0.015. © Springer-Verlag 1997.

Abstract:

A study of the channel e+e- → μ+μ-γISR, where γISR is an initial state radiation photon, is presented using data collected by the DELPHI experiment from 1991 to 1994. The total cross-section at effective annihilation energies (√s′) below the Z0 peak is obtained by using the events with relatively hard initial state radiative photon(s) (Eγ > 1 GeV). The differential cross-section as a function of the muon polar production angle is also determined in order to extract the forward-backward asymmetries for the reaction e+e- → μ+μ- at energies √s′ between 20 and 87 GeV. The ratio of the helicity cross-sections σLL+σRR/σRL+σ LR, where the two subscripts stand for the helicities of the incoming e- and outgoing μ- respectively, is extracted from the differential cross-sections in order to test the Standard Model and to look for new physics near 80 GeV. No deviations from the Standard Model were found. © Springer-Verlag 1997.

Abstract:

Bd0meson oscillations are measured in hadronic Z0decays using the charge of a lepton or the mean charge of an event hemisphere to sign the presence of a b or a b quark when it is produced, and using the charge of a lepton emitted at large ptor of a D∗±to sign the presence of a B or a B meson when it decays. With 3.2 million hadronic Z0decays registered by DELPHI between 1991 and 1994, the mass difference Δmdbetween the two physical Bd0states is measured in four channels: Δmd= 0.523 ± 0.072 ± 0.043 ps-1(D∗±- Qhem) Δmd= 0.493 ± 0.042 ± 0.027 ps-1(ℓ - Qhem) Δmd= 0.499 ± 0.053 ± 0.015 ps-1((π∗- ℓ) - Qhem) Δmd= 0.480 ± 0.040 ± 0.051 ps-1(ℓ - ℓ). Taking into account the statistical overlap between these measurements and the common systematic uncertainties, the combined result is: Δmd= 0.497 ± 0.035 ps-1.