INCLUSIVE PI(+/-), K+/- AND (P,(P)OVER-BAR) DIFFERENTIAL CROSS-SECTIONS AT THE Z-RESONANCE

Inclusive pi(+/-), K-+/- and (p, (p) over bar) differential cross-sections in hadronic decays of the Z have been measured as a function of z = p(hadron)/p(beam), the scaled momentum. The results are based on approximately 520 000 events measured by the ALEPH detector at LEP during 1992. Charged particles are identified bp their rate of ionization energy loss in the ALEPH Time Projection Chamber. The position, xi*, of the peak in the ln(1/z) distribution is determined, and the evolution of the peak position with centre-of-mass energy is compared with the prediction of QCD

Improved measurements of electroweak parameters from Z decays into fermion pairs

The properties of the Z resonance are measured on the basis of 190000 Z decays into fermion pairs collected with the ALEPH detector at LEP. Assuming lepton universality, M(Z) = (91.182 +/- 0.009exp +/- 0.020L;P) GeV, GAMMA(Z) = (2484 +/- 17) MeV, sigma(had)0 = (41.44 +/- 0.36) nb, and GAMMA(had)/GAMMA(ll) = 21.00 +/- 0.20. The corresponding number of light neutrino species is 2.97 +/- 0.07. The forward-backward asymmetry in leptonic decays is used to determine the ratio of vector to axial-vector coupling constants of leptons: g(V)2(M(Z)2)/g(A)2(M(Z)2) = 0.0072 +/- 0.0027. Combining these results with ALEPH results on quark charge and bbBAR asymmetries, and tau-polarization, sin2 theta(W)(M(Z)2) = 0.2312 +/- 0.0018. In the context of the Minimal Standard Model, limits are placed on the top-quark mass

MEASUREMENT OF TAU BRANCHING RATIOS

Using the data accumulated at LEP in 1989 and 1990 with the ALEPH detector, the inclusive and exclusive branching ratios of the tau-lepton have been measured assuming lepton universality in Z0 decays. The inclusive branching fractions for the tau-decay into one, three, and five charged particles have been determined to be (85.45 +/- 0.97)%, (14.35 +/- 0.48)%, and (0.10 +/- 0.05)%, respectively, in agreement with the world averages. New undetected decay modes are determined to have a branching fraction of less than 2.1% at 95% CL. The measured branching ratios for quasi-exclusive channels are slightly larger than, but consistent with the world averages, except for the modes tau --> 3 hadrons + nu(tau) and tau --> hadron + 2-pi(0)nu(tau), which are significantly larger. These latter branching ratios have been found to be (9.5 +/- 0.7)% and (10.2 +/- 1.1)%, respectively. The sum of all the measured quasi-exclusive branching ratios is (100.4 +/- 1.8)%. A fully exclusive analysis of modes with neutral pions shows no evidence for new photonic decay modes with a branching fraction limit of 3.4% at 95% CL

PRODUCTION OF CHARMED MESONS IN Z DECAYS

The production of charmed mesons D0(-), D+/-, and D*+/- is studied in a sample of 478,000 hadronic Z decays. The production rates are measured to be GAMMA(Z --> D*+/- X)/GAMMA(had) = 0.187 +/- 0.015 (exp.) +/- 0.013 (BR), GAMMA(Z --> D+/- X) = 0.251 +/- 0.026 (exp.) +/- 0.025 (BR), GAMMA(Z --> D0(-) X)/GAMMA(had) = 0.518 +/- 0.052 (exp.) +/- 0.035 (BR), where the errors from this analysis are separated from those coming from the D branching ratios (BR). The D *+/momentum distribution is extracted separately for Z --> cc and Z --> bbBAR events with the help of event shape variables. It is consistent with the prediction of the JETSET Monte Carlo program after adjustment of the charm fragmentation function. Constraining the shape of the Z --> bbBAR contribution, the average fraction of the beam energy taken by a D* meson produced in the fragmentation of a charm quark is extracted by a parametric fit to be [X(E)]c = 0.495 +/- 0.011 +/- 0.007. Evidence for D**0 (D1(2420)0 and/or D2*(2460)0) production is found in the D*+/-pi-/+ channel, accounting for a fraction (18 +/- 5 +/- 2)% of all D*+/- production. The relative production of vector and pseudoscalar mesons is dicussed, together with the possible effects of D** production. The c-quark forward-backward Z-pole asymmetry is determined from that of high momentum D*+/- to be A(FB)0,c = (7.7 +/- 4.4)%

Measurement of the Z resonance parameters at LEP

The properties of the Z resonance are measured from the analysis of 4.5 million Z decays into fermion pairs collected with the ALEPII detector at LEP. The data are consistent with lepton universality. The resonance parameters are measured to be M(Z) = (91.1885 +/- 0.0031) GeV/c(2), Gamma(Z) = (2.4941 +/- 0.0043) GeV, sigma(had)(0) = (41.559 +/- 0.058) nb and, combining the three lepton flavours, R(l) = 20.725 +/- 0.039. The corresponding number of light neutrino species is N(v) = 2.983 +/- 0.013 and the strong coupling constant is alpha(s)(M(Z)) = 0.114 +/- 0.004 +/- 0.002(QCD) + 0.005 log(10) [M(H)/150 GeV/c(2)]. The lepton pair forward-backward asymmetry is measured to be A(FB)(0,l) = 0.0173 +/- 0.0016 from which the effective weak mixing angle is described: sin(2) theta(eff)(lept) = 0.23089 +/- 0.00089. The measurement of the leptonic width Gamma(ll) = 84.02 +/- 0.15 MeV leads to a determination of the effective rho parameter rho(eff)(lept) = 1.0064 +/- 0.0018. The data support the Standard Model and favour a light Higgs

PRODUCTION OF K(0) AND LAMBDA IN HADRONIC Z-DECAYS

Measurements of the inclusive cross-sections for K0 and LAMBDA production in hadronic decays of the Z are presented together with measurements of two-particle correlations within pairs of LAMBDA and K0. The results are compared with predictions from the hadronization models Jetset, based on string fragmentation, and Herwig, based on cluster decays. The K0 spectrum is found to be harder than predicted by both models, while the LAMBDA spectrum is softer than predicted. The correlation measurements are all reproduced well by Jetset, while Herwig misses some of the qualitative features and overestimates the size of the LAMBDALAMBDABAR correlation. Finally, the possibility of Bose-Einstein correlation in the K(S)0K(S)0 system is discussed

K0 production in one prong tau decays

From a sample of about 75000 τ decays identified with the ALEPH detector, K0 production in 1-prong hadronic decays is investigated by tagging the KL0 component in a hadronic calorimeter. Results are given for the final states ντh−K0 and ντh−π0K0 where the h− is separated into π and K contributions by means of the dE/dx measurement in in the central detector. The resulting branching ratios are: (Bτ → ντπ−K0) = (0.88±0.14±0.09)%, (Bτ → ντK−K0) = (0.29±0.12±0.03)%, (Bτ → ντπ−π0K0) = (0.33±0.14±0.07)% aand (Bτ → ντK−π0K0) = (0.05±0.05±0.01)%. The K∗ decay rate in the K0π channel agrees with that in the Kπ0 mode: the combined value for the branching ratio is

Measurement of the B(s)0 lifetime

The lifetime of the Bs0 has been measured in a data sample of 8890000 hadronic events recorded with the ALEPH detector at LEP. After background subtraction 30.8 ± 6.9 events are attributed to the semileptonic decay of the Bs0 to a Ds− and an opposite-sign lepton. A maximum-likelihood fit to the distribution of the proper times of these events yields a Bs0 lifetime of τBs = 1.92−0.35+0.45 ± 0.04 ps