Measurement of the W mass by direct reconstruction in e+e−e^+ e^- collisions at 172 GeV

The mass of the W boson is obtained from reconstructed invariant mass distributions in W-pair events. The sample of W pairs is selected from 10.65~pb$^{-1}$ collected with the ALEPH detector at a mean centre-of-mass energy of 172.09 \GEV. The invariant mass distribution of simulated events are fitted to the experimental distributions and the following W masses are obtained: $WW \to q\overline{q}q\overline{q } m_W = 81.30 +- 0.47(stat.) +- 0.11(syst.) GeV/c^2$, $WW \to l\nu q\overline{q}(l=e,\mu) m_W = 80.54 +- 0.47(stat.) +- 0.11(syst.) GeV/c^2$, $WW \to \tau\nu q\overline{q} m_W = 79.56 +- 1.08(stat.) +- 0.23(syst.) GeV/C62$. The statistical errors are the expected errors for Monte Carlo samples of the same integrated luminosity as the data. The combination of these measurements gives: $m_W = 80.80 +- 0.11(syst.) +- 0.03(LEP energy) GeV/^2$

Inclusive production of pi(0), eta, eta '(958), K-S(0) and Lambda in two- and three-jet events from hadronic Z decays

The production rates and the inclusive cross sections of the isovector meson pi(0), the isoscalar mesons eta and eta'(958), the strange meson K-S(0) and the Lambda baryon have been measured as functions of scaled energy in hadronic events, two-jet events and each jet of three-jet events from hadronic Z decays and compared to Monte Carlo models. The analysis is based on 3.7 million hadronic events collected with the ALEPH detector at LEP at a centre-of-mass energy of root s = 91.2 GeV. The JETSET modelling of the gluon fragmentation into isoscalar mesons is found to be in agreement with the experimental results. HERWIG fails to describe the K-S(0) spectra in gluon-enriched jets and the A spectra in quark jets

Fermi-Dirac Correlations in lambda pairs in hadronic Z decays

Two-particle correlations of Lambda Lambda and Anti-Lambda Anti-Lambda pairshave been studied in multihadronic Z decays recorded with the ALEPH detector at LEP in the years from 1992 to 1995. The correlations were measured as a function of the four-momentum difference Q of the pair. A depletion of events is observed in the region Q 2 GeV the fraction of pairs with spin one is consistent with the value of 0.75 expected for a statistical spin mixture, whilst for Q < 2 GeV this fraction is found to be lower. For Lambda Anti-Lambda pairs, where no Fermi-Dirac correlations are expected, the spin one fraction is measured to be consistent with 0.75 over the entire analysed Q range

Search for R-parity violating decays of supersymmetric particles in e+e−e^+ e^- collisions at center-of-mass energies near 183-GeV

Searches for pair-production of supersymmetric particles under the assumption that R-parity is violated via a single dominant LLE¯ , LQD¯ or U¯D¯D¯ coupling are performed using the data collected by the ALEPH collaboration at centre-of-mass energies of 181–184 GeV. The observed candidate events in the data are in agreement with the Standard Model expectations. Upper limits on the production cross-sections and lower limits on the masses of charginos, sleptons, squarks and sneutrinos are derived

Search for the neutral Higgs bosons of the Standard Model and the MSSM in e(+)e(-) collisions at root s=189 GeV

Neutral Higgs bosons of the Standard Model and of the MSSM are searched for in the data collected at a centre-of-mass energy of 188.6GeV by the ALEPH experiment at LEP, with an integrated luminosity of 176 pb(-1). No evidence for a signal is found. A lower limit of 92.9GeV/c(2) at 95% confidence level is set on the mass of the Standard Model Higgs boson, with an expected sensitivity of 95.9 GeV/c(2). In the MSSM, for tan beta greater than or equal to 0.7 and for benchmark parameter choices, observed (expected) lower limits of 82.5 (83.1) GeV/c(2) and 82.6 (83.2) GeV/c(2) are derived for the masses of the neutral Higgs bosons h and A, respectively. An update of the general MSSM parameter scan is also presented

Search for the standard model Higgs boson at the LEP2 collider near root s=183 GeV (vol 440, pg 403, 1998)

During 1997 the ALEPH experiment at LEP gathered 57 pb(-1) of data at centre-of-mass energies near 183 GeV. These data are used to look for possible signals from the production of the Standard Model Higgs boson in the reaction e(+)e(-) --&gt; HZ. No evidence of a signal is found in the data; seven events are selected, in agreement with the expectation of 7.2 events from background processes. This observation results in an improved lower limit on the mass of the Higgs boson: m(H) greater-than 87.9 GeV/c(2) at 95% confidence level. (C) 1999 Elsevier Science B.V. All rights reserved

Search for supersymmetry with a dominant R-parity violating LQ anti-D coupling in e+ e- collisions at center-of-mass energies of 130-GeV to 172-GeV

A search for pair-production of supersymmetric particles under the assumption that R-parity is violated via a dominant LQ (D) over bar coupling has been performed using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV. The observed candidate events in the data are in agreement with the Standard Model expectation. This result is translated into lower limits on the masses of charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, for m(o) = 500 GeV/c(2) and tan beta = root 2 charginos with masses smaller than 81 GeV/c(2) and neutralinos with masses smaller than 29 GeV/c(2) are excluded at the 95% confidence level for any generation structure of the LQ (D) over bar coupling

Measurement of the axial-vector ? spectral functions and determination of ?s(M2?) from hadronic ? decays

An analysis based on 124 000 selected τ pairs recorded by the ALEPH detector at LEP provides the vector (V) and axial-vector (A) spectral functions of hadronic τ decays together with their total widths. This allows the evaluation of finite energy chiral sum rules that are weighted integrals over the (V−A) spectral functions. In addition, a precise measurement of αs along with a determination of nonperturbative contributions at the τ mass scale is performed. The experimentally and theoretically most robust determination of αs(M2τ) is obtained from the (V+A) fit that yields αs(M2τ)=0.334±0.022 giving αs(M2Z)=0.1202±0.0027 after the extrapolation to the mass of the Z boson. The approach of the Operator Product Expansion (OPE) is tested experimentally studying the evolution of the τ hadronic widths to masses smaller than the τ mass

Search for supersymmetry with a dominant R-parity violating L L anti-E coupling in e+ e- collisions at center-of-mass energies of 130-GeV to 172-GeV

A search for pair-production of supersymmetric particles under the assumption that R-parity is violated via a dominant LLE coupling has been performed using the data collected by ALEPH at centre-of-mass energies of 130-172 GeV. The observed candidate events in the data are in agreement with the Standard Model expectation. This is translated into lower limits on the mass of charginos, neutralinos, sleptons, sneutrinos and squarks. For instance, charginos with masses less than 73 GeV and neutralinos with masses less than 23 GeV are excluded at 95% confidence level for any generation structure of the LLE coupling, and for neutralino, slepton or sneutrino LSPs.Comment: 31 pages, 12 figures, 6 tables; submitted to Zeitschrift fuer Physik