Four-fermion production in e+e−e^+e^- collisions at centre-of-mass energies of 130 and 136 GeV

Four-fermion events have been selected in a data sample of 5.8 pb−1 collected with the aleph detector at centre-of-mass energies of 130 and 136 GeV. The final states , ℓ+ℓ−ℓ+ℓ−, , and have been examined. Five events are observed in the data, in agreement with the Standard Model predictions of 6.67±0.38 events from four-fermion processes and 0.14−0.05+0.19 from background processes

Observation of charmless hadronic B decays

Four candidates for charmless hadronic B decay are observed in a data sample of four million hadronic Z decays recorded by the ALEPH detector at LEP. The probability that these events come from background sources is estimated to be less than 10(-6). The average branching of weakly decaying B hadrons (a mixture of B-d(0), B-s(0) and Lambda(b) weighted by their production The average branching ratio of weakly decaying B hadrons (a mixture of B-d(0) cross sections and lifetimes, here denoted B) into two long-lived charged hadrons (pions, kaons or protons) is measured to be Br(B-->h(+)h(-))=(1.7(-0.7)(+1.0)+/-0.2)x10(-5). The relative branching fraction Br(B-d(s)(0)-->pi(+)pi(-)(K-))/Br(B-d(s)(0)-->h(+)h(-)) is measured to be 1.0(-0.3-0.1)(+0.0+0.0). In addition, branching ratio upper limits are obtained for a variety of exclusive charmless hadronic two-body decays of B hadrons

Search for supersymmetry in the photon(s) plus missing energy channels at s\sqrt{s}=161 GeV and 172 GeV

Searches for supersymmetric particles in channels with one or more photons and missing energy have been performed with data collected by the ALEPH detector at LEP. The data consist of 11.1 \pb\ at $\sqrt{s} = 161 ~\, \rm GeV$, 1.1 \pb\ at 170 \gev\ and 9.5 \pb\ at 172 GeV. The \eenunu\ cross se ction is measured. The data are in good agreement with predictions based on the Standard Model, and are used to set upper limits on the cross sections for anomalous photon production. These limits are compared to two different SUSY models and used to set limits on the neutralino mass. A limit of 71 \gevsq\ at 95\% C.L. is set on the mass of the lightest neutralin o ($\tau_{\chi_{1}^{0}} \leq$ 3 ns) for the gauge-mediated supersymmetry breaking and LNZ models

Characterization of MOS transistors integrated on high resistivity silicon with a DSSD process

We have fabricated MOS transistors with a commercial double-sided silicon detector (DSSD) process, on the same wafer as the detector. These devices have been simulated and measured in the lab both in the DC characteristics and in the noise figures

Results on double-sided ac-coupled silicon strip detectors

We have designed and fabricated double-sided a.c.-coupled silicon strip detectors on high-resistivity substrates. We discuss the first electrical measurements on a 16 cm(2) strip detector. These detectors are biased via polysilicon resistors on both sides and the decoupling capacitors are integrated on the strip themselves. For a large fraction of the fabricated detectors, the current densities are about 15 nA/cm(2) and the yield of the integrated capacitor is about 99%, without any sign of breakdown up to 100 V (the maximum voltage we have applied)

Beam test results for single-and double-sided silicon detector prototypes of the CMS central detector

We report the results of two beam tests performed in July and September 1995 at CERN using silicon microstrip detectors of various types: single sided, double sided with small-angle stereo strips, double sided with orthogonal strips, double sided with pads. For the read-out electronics, use was made of Preshape32 Premux128 and VA1 chips. The signal-to-noise ratio and the resolution of the detectors was studied at different incident angles of the incoming particles and for different values of the detector bias voltage. The goal of these tests was to check and improve the performances of the prototypes for the CMS Central Detector

Search for the standard model Higgs boson in e+e−e^+ e^- collisions at s\sqrt{s}=161, 170 and 172 GeV

The reaction e+e- -> HZ is used to search for the Standard Model Higgs boson. The data sample consists of integrated luminosities of 10.9pb-1 1.1pb-1 and 9.5pb-1 collected by the ALEPH experiment at LEP during 1996, at centre-of-mass energies of 161, 170 and 172GeV, respectively. No candidate events were found, in agreement with the expected background of 0.84 events from all Standard Model processes. This search results in a 95%C.L. lower limit on the Higgs boson mass of 69.4GeV. When combined with earlier ALEPH searches performed at energies at and around the Z peak, this limit increases to 70.7Ge

Inclusive production of neutral pions in hadronic Z decays

A measurement of the inclusive production of pi0 mesons in hadronic Z decays is presented and compared to Monte Carlo model predictions. The analysis is based on approximately 2 million hadronic events recorded with the ALEPH detector at LEP at a centre-of-mass energy of sqrt(s) = 91.2 GeV. Neutral pions are reconstructed using photons from conversion pairs and photons measured in the electromagnetic calorimeter. The inclusive pi0 momentum spectrum is measured in the range from 0.025 < x(p) = p/p(beam) < 1 to be 4.80 +/- 0.07(stat) +/- 0.31(sys). The differential inclusive pi0 cross section has also been measured as a function of transverse momentum with respect to the event plane (p_T^in and p_T^out_T)

Determination of sin**2 theta(w)(eff) 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 forbb ¯ andcc ¯ events in subsamples selected by their long lifetimes or using fastD*’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 andΛ’s. The separations are used to measure the electroweak mixing angle precisely as sin2ϑweff=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