New CKM-related studies on b decays in the DELPHI experiment at LEP

The e-e+ collider LEP, running at sqrt{s} = m(Z0), has been a copious source of b-hadrons produced in decays Z0 -> b \b. We present recent studies using up to 4*10^6 hadronic Z0 decays acquired by the DELPHI detector between 1992 and 2000. They rely on efficient particle identification, precise track and vertex reconstruction and sophisticated data analysis algorithms. Presented are: a new measurement of the CKM matrix element |V_cb| in the semileptonic exclusive decays B0_d -> D*+ l- \nu_l; a new measurement of the B0_d - \B0_d oscillation frequency Delta(m_d); and searches by three methods for B0_s - \B0_s oscillations, yielding new lower limits on Delta(m_s).Comment: Contribution to the XXIII Conf. on Physics in Collision (PIC'03), Zeuthen, Germany, June 26-28, 2003 [3 pages LaTeX + 2 figs EPS, PSN = FRAP19

Statistical analysis of event classification in experimental data

The paper addresses general aspects of experimental data analysis, dealing with the separation of ``signal vs. background''. It consists of two parts. Part I is a tutorial on statistical event classification, Bayesian inference, and test optimization. Aspects of the base data sample if being created by Poisson processes are discussed, and a method for estimating the unknown numbers of signal and background events is presented. Data quality of the selected events sample is assessed by the expected purity and background contamination. Part II contains a rigorous statistical analysis of the methods discussed in Part I. Both Bayesian and frequentist estimators of the unknown signal/background content are investigated. The estimates and their stochastic uncertainties are calculated for various conjugate priors in the Bayesian case, and for three choices of the virtual parent population in the frequentist case.Comment: 26 pages, 6 figure

Implementation and application of kinematic vertex fitting in the software environment of ILD

The vertex reconstruction toolkit RAVE has been extended by an option for the inclusion of kinematic constraints, and embedded into the ILD analysis framework Marlin. The new tools have been tested with an exemplary reconstruction of WW and ZZ decays. The presented results show the improvements achieved in precision of the fitted masses, and demonstrate the usage and functionality of the toolkit.Comment: Proc. 11th Int. Linear Collider Workshop (LCWS'08), UIC, Chicago, USA, 16-20 Nov. 200

An Improved Measurement of Mixing-induced CP Violation in the Neutral B Meson System

We present an improved measurement of the standard model CP violation parameter sin2phi_1 (also known as sin2beta) based on a sample of 85 times 10^6 B Bbar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. One neutral B meson is reconstructed in a J/psi K_S, psi(2S) K_S, chi_{c1} K_S, eta_c K_S, J/psi K^{*0}, or J/psi K_L CP-eigenstate decay channel and the flavor of accompanying B meson is identified from itsdecay products. From the asymmetry in the distribution of the time intervals between the two B meson decay points, we obtain sin2phi_1 = 0.719 +/- 0.074(stat) +/- 0.035(syst). We also report measurements of CP violation parameters for the related B^0 -> J/psi pi^0 decay mode and the penguin-dominated processes B^0 -> eta' K_S, phi K_S and K^+K^- K_S.Comment: 11 pages, 4 figures, 4 tables, contributed to ICHEP200

Measurement of the Tau Lepton Polarisation at LEP2

A first measurement of the average polarisation P_tau of tau leptons produced in e+e- annihilation at energies significantly above the Z resonance is presented. The polarisation is determined from the kinematic spectra of tau hadronic decays. The measured value P_tau = -0.164 +/- 0.125 is consistent with the Standard Model prediction for the mean LEP energy of 197 GeV.A first measurement of the average polarisation Pτ of tau leptons produced in e + e − annihilation at energies significantly above the Z resonance is presented. The polarisation is determined from the kinematic spectra of tau hadronic decays. The measured value Pτ=−0.164±0.125 is consistent with the Standard Model prediction for the mean LEP energy of 197 GeV.A first measurement of the average polarisation P_tau of tau leptons produced in e+e- annihilation at energies significantly above the Z resonance is presented. The polarisation is determined from the kinematic spectra of tau hadronic decays. The measured value P_tau = -0.164 +/- 0.125 is consistent with the Standard Model prediction for the mean LEP energy of 197 GeV

Measurements of the leptonic branching fractions of the τ\tau

Data collected with the DELPHI detector from 1993 to 1995 combined with previous DELPHI results for data from 1991 and 1992 yield the branching fractions B({\tau \rightarrow \mbox{\rm e} \nu \bar{\nu}}) = (17.877 \pm 0.109_{stat} \pm 0.110_{sys} )\% and $B({\tau \rightarrow \mu \nu \bar{\nu}}) = (17.325 \pm 0.095_{stat} \pm 0.077_{sys} )\%$

Measurement of inclusive π0\pi^{0} production in hadronic Z0Z^{0} decays

An analysis is presented of inclusive \pi^0 production in Z^0 decays measured with the DELPHI detector. At low energies, \pi^0 decays are reconstructed by \linebreak using pairs of converted photons and combinations of converted photons and photons reconstructed in the barrel electromagnetic calorimeter (HPC). At high energies (up to x_p = 2 \cdot p_{\pi}/\sqrt{s} = 0.75) the excellent granularity of the HPC is exploited to search for two-photon substructures in single showers. The inclusive differential cross section is measured as a function of energy for {q\overline q} and {b \bar b} events. The number of \pi^0's per hadronic Z^0 event is N(\pi^0)/ Z_{had}^0 = 9.2 \pm 0.2 \mbox{(stat)} \pm 1.0 \mbox{(syst)} and for {b \bar b}~events the number of \pi^0's is {\mathrm N(\pi^0)/ b \overline b} = 10.1 \pm 0.4 \mbox{(stat)} \pm 1.1 \mbox{(syst)} . The ratio of the number of \pi^0's in b \overline b events to hadronic Z^0 events is less affected by the systematic errors and is found to be 1.09 \pm 0.05 \pm 0.01. The measured \pi^0 cross sections are compared with the predictions of different parton shower models. For hadronic events, the peak position in the \mathrm \xi_p = \ln(1/x_p) distribution is \xi_p^{\star} = 3.90^{+0.24}_{-0.14}. The average number of \pi^0's from the decay of primary \mathrm B hadrons is found to be {\mathrm N} (B \rightarrow \pi^0 \, X)/\mbox{B hadron} = 2.78 \pm 0.15 \mbox{(stat)} \pm 0.60 \mbox{(syst)}