LHCb

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.

Abstract:

Inclusive charged particle and event shape distributions are measured using 321 hadronic events collected with the DELPHI experiment at LEP at effective centre of mass energies of 130 to 136 GeV. These distributions are presented and compared to data at lower energies, in particular to the precise Z data. Fragmentation models describe the observed changes of the distributions well. The energy dependence of the means of the event shape variables can also be described using second order QCD plus power terms. A method independent of fragmentation model corrections is used to determine αs from the energy dependence of the mean thrust and heavy jet mass. It is measured to be: αs(133 GeV) = 0.116 ± 0.007exp-0.004theo+0.005 from the high energy data. © Springer-Verlag 1997.