THE GAIN MONITORING-SYSTEM OF THE ALEPH-HADRON CALORIMETER

The gas gain monitoring system of the Aleph hadron calorimeter is described. The dependence of the charge response to a) the ratio between the pressure to temperature and b) the gas mixture parameters (Ar/CO2 ratio and isobutane percentage) have been determined. The total gain variation is measured with a precision of about 0.4%

Simultaneous Observation Of Extensive Air Showers And Deep Underground Muons At The Gran Sasso Laboratory

none118siCombined measurements of extensive air showers at the surface and high-energy muons deep underground have been initiated at the Gran Sasso Laboratory. The underground detector is the first supermodule of MACRO (area = 140 m2, depth = 3100 m of water equivalent, E>1.3 TeV) and the surface detector is the EAS-TOP array (altitude 2000 m above sea level, total enclosed area A105 m2). We discuss the correlation technique, the comparison between the shower parameters as determined by the two detectors, and some of the characteristics of the reconstructed events. © 1990 The American Physical Society.openBellotti R.; Cafagna F.; Caliccio M.; De Cataldo G.; De Marzo C.; Erriquez O.; Favuzzi C.; Giglietto N.; Nappi E.; Spinelli P.; Cecchini S.; Fabbri M.; Giacomelli G.; Mandrioli G.; Matteuzzi P.; Pal B.; Patrizii L.; Predieri F.; Sanzani G.L.; Serra P.; Spurio M.; Ahlen S.; Ficenec D.; Hazen E.; Klein S.; Levin D.; Marin A.; Stone J.L.; Sulak L.R.; Worstell W.; Barish B.; Coutu S.; Hong J.; Liu G.; Peck C.; Solie D.; Steele J.; Lane C.; Steinberg R.; Battistoni G.; Bilokon H.; Bloise C.; Campana P.; Chiarella V.; Forti C.; Grillo A.; Iarocci E.; Marini A.; Patera V.; Reynoldson J.; Ronga F.; Satta L.; Spinetti M.; Valente V.; Bower C.; Heinz R.; Mufson S.; Petrakis J.; Monacelli P.; Bernardini P.; Mancarella G.; Palamara O.; Pistilli P.; Surdo A.; Longo M.; Musser J.; Smith C.; Tarle G.; Ambrosio M.; Barbarino G.C.; Guarino F.; Baldini A.; Bemporad C.; Flaminio V.; Giannini G.; Grassi M.; Pazzi R.; Auriemma G.; Chrysicopoulou P.; De Vincenzi M.; Iori M.; Lamanna E.; Lipari P.; Martellotti G.; Petrera S.; Petrillo L.; Rosa G.; Sciubba A.; Severi M.; Green P.; Webb R.; Bisi V.; Giubellino P.; Chiesa A.M.; Masera M.; Monteno M.; Ramello L.; Aglietta M.; Alessandro B.; Badino G.; Bergamasco L.; Castagnoli C.; Castellina A.; Cini G.; D'Ettorre-Piazzoli B.; Fulgione W.; Ghia P.; Galeotti P.; Mannocchi G.; Morello C.; Navarra G.; Periale L.; Picchi P.; Riccati L.; Saavedra O.; Trinchero G.; Vallania P.; Vernetto S.Bellotti R.; Cafagna F.; Caliccio M.; De Cataldo G.; De Marzo C.; Erriquez O.; Favuzzi C.; Giglietto N.; Nappi E.; Spinelli P.; Cecchini S.; Fabbri M.; Giacomelli G.; Mandrioli G.; Matteuzzi P.; Pal B.; Patrizii L.; Predieri F.; Sanzani G.L.; Serra P.; Spurio M.; Ahlen S.; Ficenec D.; Hazen E.; Klein S.; Levin D.; Marin A.; Stone J.L.; Sulak L.R.; Worstell W.; Barish B.; Coutu S.; Hong J.; Liu G.; Peck C.; Solie D.; Steele J.; Lane C.; Steinberg R.; Battistoni G.; Bilokon H.; Bloise C.; Campana P.; Chiarella V.; Forti C.; Grillo A.; Iarocci E.; Marini A.; Patera V.; Reynoldson J.; Ronga F.; Satta L.; Spinetti M.; Valente V.; Bower C.; Heinz R.; Mufson S.; Petrakis J.; Monacelli P.; Bernardini P.; Mancarella G.; Palamara O.; Pistilli P.; Surdo A.; Longo M.; Musser J.; Smith C.; Tarle G.; Ambrosio M.; Barbarino G.C.; Guarino F.; Baldini A.; Bemporad C.; Flaminio V.; Giannini G.; Grassi M.; Pazzi R.; Auriemma G.; Chrysicopoulou P.; De Vincenzi M.; Iori M.; Lamanna E.; Lipari P.; Martellotti G.; Petrera S.; Petrillo L.; Rosa G.; Sciubba A.; Severi M.; Green P.; Webb R.; Bisi V.; Giubellino P.; Chiesa A.M.; Masera M.; Monteno M.; Ramello L.; Aglietta M.; Alessandro B.; Badino G.; Bergamasco L.; Castagnoli C.; Castellina A.; Cini G.; D'Ettorre-Piazzoli B.; Fulgione W.; Ghia P.; Galeotti P.; Mannocchi G.; Morello C.; Navarra G.; Periale L.; Picchi P.; Riccati L.; Saavedra O.; Trinchero G.; Vallania P.; Vernetto S

A search for new quarks and leptons from Z0 decay at LEP

A search for Z0 decays into pairs of possible new heavy quarks (t and b′), new heavy charged leptons (L±), stable heavy neutral leptons (νL) and unstable heavy neutral leptons (L0) is performed on data collected by the ALEPH detector corresponding to 11 550 events of Z0→hadrons. The limits on the masses of the heavy quarks are Mt > 45.8 GeV and Mb′ > 46.0 GeV, allowing for both charged-current and flavor-changing neutral-current decays of the b′. If an L± decays into a stable νL, then for MνL MνL. Finally, while the mass of the stable νL is excluded up to 42.7 GeV, the mass of the unstable L0 is excluded up to 45.7 GeV with the mixing parameters |UℓL0|2 down to 10−13 at this mass. For 25.0 GeV < ML0 < 42.7 GeV, all values of |UℓL0|2 are excluded. All limits are given at 95% CL

A STUDY OF BOSE-EINSTEIN CORRELATIONS IN E+E- ANNIHILATION AT 91 GEV

This paper describes a study of Bose-Einstein correlations made using the ALEPH detector at LEP. The correlations are found to enhance the two particle differential cross section for pairs of identical pions by a factor which can be roughly parametrized by R(Q) = 1 + lambda exp(-Q2-sigma(2)), where Q is the difference in the 3-momenta of the two pions in their centre of mass frame, lambda = 0.51 +/- 0.04 +/- 0.11 and sigma = 3.3 +/- 0.2 +/- 0.8 GeV-1, which corresponds to a source size of 0.65 +/- 0.04 +/- 0.16 fm. The large systematic errors on these results reflect their strong dependence on the choice of the reference sample used in the analysis. This problem is believed to occur primarily because of uncertainties in the rates of resonance production and a lack of knowledge about the pion-pion strong interaction. No significant correlations are seen amongst like-charged pion-kaon pairs

Observation of the semileptonic decays of B(s) and LAMBDA(b) hadrons at LEP

In 450 000 hadronic Z decays recorded with the ALEPH detector at LEP, the yields of Ds−ℓ+ and Λc+ℓ− combinations have been measured. 16.0 ± 4.3 Ds−ℓ+ combinations were observed in the Ds− → ππ− channel and 17.0 ± 4.5 combinations were observed in the channel. 21.0 ± 5.0 Λc+ℓ− combinations were observed, with the Λc+ reconstructed in the decay mode Λc+ → pK−π+. These events provide evidence for the decays . Assuming that the Bs and Λb semileptonic decays are dominantly three-body, these observed yields, after background subtraction, translate into the following product branching ratios: ,

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

SEARCHES FOR NEW PARTICLES IN Z-DECAYS USING THE ALEPH DETECTOR

During 1989 and 1990 over 200 000 hadronic and leptonic events, corresponding to about 8.5 pb-1 of data, were collected in a scan of the Z peak using the ALEPH detector at the e+ e- collider, LEP. These data, at the highest centre-of-mass energy available to date in e+ e- collisions, have allowed a broad range of searches for new particles and new phenomena to be performed in a mass range significantly higher than previously attainable. The searches performed by ALEPH for Higgs bosons, supersymmetric particles and leptoquarks, and for evidence of compositeness are reviewed. No positive signals have been observed but a comprehensive set of mass and coupling limits is presented. Branching ratio limits are given for a number of "rare" Z decays

MEASUREMENT OF PROMPT PHOTON PRODUCTION IN HADRONIC-Z DECAYS

The production of isolated photons in hadronic Z decays is measured with the ALEPH detector at LEP using a sample of 450 000 hadronic events. The corrected rate is given for several values of the minimum invariant mass squared cut between the photon and the jets. This measurement of final state radiation from the quarks is compared with the predictions of parton shower models JETSET, ARIADNE and HERWIG as well as with the predictions of QCD matrix element calculations

MEASUREMENT OF THE ABSOLUTE LUMINOSITY WITH THE ALEPH DETECTOR

We report on the absolute luminosity measurement performed with the ALEPH detector at LEP. The systematic errors of the measurements in 1990 are estimated to be 0.6% (experimental) and 0.3% (theoretical)