Search for CP Violation in the Decay Z -> b (b bar) g

About three million hadronic decays of the Z collected by ALEPH in the years 1991-1994 are used to search for anomalous CP violation beyond the Standard Model in the decay Z -> b \bar{b} g. The study is performed by analyzing angular correlations between the two quarks and the gluon in three-jet events and by measuring the differential two-jet rate. No signal of CP violation is found. For the combinations of anomalous CP violating couplings, ${\hat{h}}_b = {\hat{h}}_{Ab}g_{Vb}-{\hat{h}}_{Vb}g_{Ab}$ and $h^{\ast}_b = \sqrt{\hat{h}_{Vb}^{2}+\hat{h}_{Ab}^{2}}$, limits of \hat{h}_b < 0.59$and$h^{\ast}_{b} < 3.02$ are given at 95\% CL.Comment: 8 pages, 1 postscript figure, uses here.sty, epsfig.st

Decomposing Service Definition in Predicate/Transition-Nets for Designing Distributed Systems

In this paper, we propose a new algorithm for the derivation of a protocol specification in Pr/T-nets, which is the specification of communicating N entities (N can be given), from a given service specification in Pr/T-nets and an allocation of the places of the service specification to the N entities. Our algorithm decomposes each transition of the service specification into a set of communicating Pr/T-subnets running on the N entities. Moreover, for the efficient control of conflict of shared resources, we present a timestamp-based mutual exclusion algorithm and incorporate it into the derivation algorithm

Measurement of the tau lepton lifetime with the three-dimensional impact parameter method.

A new method is presented for the measurement of the mean $\tau$ lepton lifetime using events in which $\tau$'s are pair-produced and both $\tau$'s decay to hadrons and $\nu_\tau$. Based on the correlation between the two $\tau$'s produced at a symmetric $e^+ e^-$ collider, the 3DIP method relies on the three-dimensional information from a double-sided vertex detector and on kinematic constraints for the precise measurement of the $\tau$ decay angles. Using the data collected from 1992 to 1994 with the ALEPH detector at LEP, a $\tau$ lifetime of $288.0 \pm 3.1 \pm 1.3$\fs is obtained from the sample in which both $\tau$'s decay to one charged track, and $292.8 \pm 5.6 \pm 3.0$\fs from the sample in which one $\tau$ decays to one prong and the other to three prongs. The results show small statistical correlations with those derived from other methods. When combined with the previously published ALEPH measurements, the resulting $\tau$ lifetime is $291.2 \pm 2.0 \pm 1.2$\fs

Measurement of the tau lepton lifetime with the three-dimensional impact parameter method.

A new method is presented for the measurement of the mean $\tau$ lepton lifetime using events in which $\tau$'s are pair-produced and both $\tau$'s decay to hadrons and $\nu_\tau$. Based on the correlation between the two $\tau$'s produced at a symmetric $e^+ e^-$ collider, the 3DIP method relies on the three-dimensional information from a double-sided vertex detector and on kinematic constraints for the precise measurement of the $\tau$ decay angles. Using the data collected from 1992 to 1994 with the ALEPH detector at LEP, a $\tau$ lifetime of $288.0 \pm 3.1 \pm 1.3$\fs is obtained from the sample in which both $\tau$'s decay to one charged track, and $292.8 \pm 5.6 \pm 3.0$\fs from the sample in which one $\tau$ decays to one prong and the other to three prongs. The results show small statistical correlations with those derived from other methods. When combined with the previously published ALEPH measurements, the resulting $\tau$ lifetime is $291.2 \pm 2.0 \pm 1.2$\fs

Measurement of the tau lepton lifetime with the three-dimensional impact parameter method.

A new method is presented for the measurement of the mean $\tau$ lepton lifetime using events in which $\tau$'s are pair-produced and both $\tau$'s decay to hadrons and $\nu_\tau$. Based on the correlation between the two $\tau$'s produced at a symmetric $e^+ e^-$ collider, the 3DIP method relies on the three-dimensional information from a double-sided vertex detector and on kinematic constraints for the precise measurement of the $\tau$ decay angles. Using the data collected from 1992 to 1994 with the ALEPH detector at LEP, a $\tau$ lifetime of $288.0 \pm 3.1 \pm 1.3$\fs is obtained from the sample in which both $\tau$'s decay to one charged track, and $292.8 \pm 5.6 \pm 3.0$\fs from the sample in which one $\tau$ decays to one prong and the other to three prongs. The results show small statistical correlations with those derived from other methods. When combined with the previously published ALEPH measurements, the resulting $\tau$ lifetime is $291.2 \pm 2.0 \pm 1.2$\fs

Search for the bcb_c meson in hadronic Z decays

A search for the Bc meson decaying into the channels J/psi pi+ and J/psi l nu (l = e or mu) is performed in a sample of 3.9 million hadronic Z decays collected by the ALEPH detector. This search results in the observation of 0 and 2 candidates in each of these channels, respectively, while 0.44 and 0.81 background events are expected. The following 90\% confidence level upper limits are derived: Br(Z->Bc X)/Br(Z->q q )*Br(Bc->J/psi pi+) 3.6 10^-5 Br(Z->Bc X)/Br(Z->q q )*Br(Bc->J/psi l nu) 5.2 10^-5 An additional Bc->J/psi(e+e-) mu nu candidate with very low background probability, found in an independent analysis, is also described in detail

Production of excited beauty states in Z decays

A data sample of about 3.0 million hadronic Z decays collected by the ALEPH experiment at LEP in the years 1991 through 1994, is used to make an inclusive selection of B~hadron events. In this event sample 4227 \pm 140 \pm 252 B^* mesons in the decay B^* \to B \gamma and 1944 \pm 108 \pm 161 B^{**} mesons decaying into a B~meson and a charged pion are reconstructed. For the well established B^* meson the following quantities areobtained: \Delta M = M_{B^*} - M_{B} = (45.30\pm 0.35\pm 0.87)~\mathrm{MeV}/c^2 and N_{B^*}/(N_B+N_{B^*}) = (77.1 \pm 2.6 \pm 7.0)\%. The angular distribution of the photons in the B^* rest frame is used to measure the relative contribution of longitudinal B^* polarization states to be \sigma_L/(\sigma_L + \sigma_T)= (33 \pm 6 \pm 5)\%. \\ Resonance structure in the M(B\pi)-M(B) mass difference is observed at (424 \pm 4 \pm 10)~\mathrm{MeV}/c^2. Its shape and position is in agreement with the expectation for B^{**}_{u,d} states decaying into B_{u,d}^{(*)} \pi^\pm. The signal is therefore interpreted as arising from them. The relative production rate is determined to be \frac{BR(Z \to b \to B_{u,d}^{**})}{BR(Z \to b \to B_{u,d})} = [27.9 \pm 1.6(stat) \pm 5.9(syst) \phantom{a}^{+3.9}_{-5.6}(model)]\%. where the third error reflects the uncertainty due to different production and decay models for the broad B_{u,d}^{**} states

Measurement of the W mass in e+e−e^+e^- collisions at production threshold

In June 1996, the LEP centre-of-mass energy was raised to 161 GeV. Pair production of W bosons in e+e- collisions was observed for the first time by the LEP experiments. An integrated luminosity of 11 pb-1 was recorded in the ALEPH detector, in which WW candidate events were observed. In 6 events both Ws decay leptonically. In 16 events, one W decays leptonically, the other into hadrons. In the channel where both Ws decay into hadrons, a signal was separated from the large background by means of several multi-variate analyses. The W pair cross-section is measured to be sigma_WW = 4.23 +-0.73 (stat.) +- 0.19 (syst.) pb From this cross-section, the W mass is derived within the framework of the Standard Model: MW = 80.14 +- 0.34 (stat.) +- 0.09 (syst.) +- 0.03 (LEP~energy) GeV/c2