Determination of sin2 θeff w using jet charge measurements in hadronic Z decays

The electroweak mixing angle is determined with high precision from measurements of the mean difference between forward and backward hemisphere charges in hadronic decays of the Z. A data sample of 2.5 million hadronic Z decays recorded over the period 1990 to 1994 in the ALEPH detector at LEP is used. The mean charge separation between event hemispheres containing the original quark and antiquark is measured for bb̄ and cc̄ events in subsamples selected by their long lifetimes or using fast D*'s. The corresponding average charge separation for light quarks is measured in an inclusive sample from the anticorrelation between charges of opposite hemispheres and agrees with predictions of hadronisation models with a precision of 2%. It is shown that differences between light quark charge separations and the measured average can be determined using hadronisation models, with systematic uncertainties constrained by measurements of inclusive production of kaons, protons and A's. The separations are used to measure the electroweak mixing angle precisely as sin2 θeff w = 0.2322 ± 0.0008(exp. stat.) ±0.0007(exp. syst.) ± 0.0008(sep.). The first two errors are due to purely experimental sources whereas the third stems from uncertainties in the quark charge separations

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

Four-jet final state production in e(+)e(-) collisions at centre-of-mass energies of 130 and 136 GeV

The four-jet final state is analyzed to search for hadronic decays of pair-produced heavy particles. The analysis uses the ALEPH data collected at LEP in November 1995 at centre-of-mass energies of 130 and 136 GeV, corresponding to a total integrated luminosity of 5.7 pb(-1). An excess of four-jet events is observed with respect to the standard model predictions. In addition, these events exhibit an enhancement in the sum of the two di-jet masses around 105 GeV/c(2). The properties of these events are studied and compared to the expectations from standard processes and to pair production hypotheses. RI ANTONELLI, ANTONELLA/C-6238-2011; Passalacqua, Luca/F-5127-2011; Murtas, Fabrizio/B-5729-2012; St.Denis, Richard/C-8997-2012; Sanchez, Federico/F-5809-2012; Ferrante, Isidoro/F-1017-201

Measurement of D(s)+ meson production in Z decays and of the anti-B(s)0 lifetime

D-s(+) mesons produced in Z(0) --> b (b) over bar events were separated from the Z(0) --> c (c) over bar component using a lifetime tag. Using a sample of 1.5 million hadronic Z decays collected with the ALEPH detector the (B) over bar(s)(0) and D-s(+) yields have been measured: [GRAPHICS] The (B) over bar(2)(0) lifetime was measured in a (B) over bar(s)(0) enriched sample reconstructing the decay length from the vertex of the D-s(+) with a hadron from the (B) over bar(0)(s) decay, The result obtained is: [GRAPHICS

Determination of sin(2) theta(eff)(w) using jet charge measurements in hadronic Z decays

The electroweak mixing angle is determined with high precision from measurements of the mean difference between forward and backward hemisphere charges in hadronic decays of the Z. A data sample of 2.5 million hadronic Z decays recorded over the period 1990 to 1994 in the ALEPH detector at LEP is used. The mean charge separation between event hemispheres containing the original quark and antiquark is measured for b (b) over bar and c (c) over bar events in subsamples selected by their long lifetimes or using fast D*'s. The corresponding average charge separation for light quarks is measured in an inclusive sample from the anticorrelation between charges of opposite hemispheres and agrees with predictions of hadronisation models with a precision of 2%. It is shown that differences between light quark charge separations and the measured average can be determined using hadronisation models, with systematic uncertainties con strained by measurements of inclusive production of kaons, protons and Lambda's. The separations are used to measure the electroweak mixing angle precisely as sin(2) theta(w)(eff) = 0.2322 +/- 0.0008(exp. stat.) +/-0.0007(exp. syst.) +/- 0.0008(sep.). The first two errors are due to purely experimental sources whereas the third stems from uncertainties in the quark charge separations