Data collected at centre-of-mass energies from 189 GeV to 202 GeV by the ALEPH detector at LEP, corresponding to an integrated luminosity of 411 pb-1, are analysed in a search for the scalar top in ...the decay channels 'stop -> c/u neutralino' for small mass differences between the stop and the lightest neutralino. No evidence for deviations from the Standard Model expectation is found and a lower limit of 59 GeV/c**2 is set for the stop mass, independent of the stop to neutralino mass difference and of the stop lifetime.
Searches for topologies characteristic of Gauge Mediated SUSY Breaking models (GMSB) are performed by analysing 173.6 pb^-1 of data collected at Ecm = 188.6~GeV with the ALEPH detector.These ...topologies include acoplanar photons, non-pointing single photon, acoplanar leptons, large impact parameter leptons, detached slepton decay vertices, heavy stable charged sleptons and four leptons plus missing energy final states.No evidence for these new phenomena is observed and limits on production cross sections and sparticle masses are derived. A scan of a minimal GMSB parameter space is performed and model dependent lower limits of about 45 GeV/c^2 on the next-to-lightest supersymmetric particle (NLSP) mass and of about 9 TeV on the mass scale parameter Lambda are derived, independently of the NLSP lifetime.
The production rates and the inclusive cross sections of the isovector meson $\pi^0$, the isoscalar mesons $\eta$ and $\eta^\prime(958)$, the strange meson $\mathrm{K^0_S}$ 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 $\sqrt{s}=91.2$~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 $\mathrm{K^0_S}$ spectra in gluon-enriched jets and the $\Lambda$ spectra in quark jets.
Searches for charginos and neutralinos are performed with the data collected by the ALEPH detector at LEP at centre-of-mass energies near 183 GeV. In these searches, it is assumed that R-parity is ...conserved and that the lightest neutralino is the LSP. No evidence of a signal is observed in the 57 pb\(^{-1}\) accumulated, which excludes chargino and associated neutralino production up to the kinematic limit over large regions of the MSSM parameter space. Under the assumptions of common gaugino and common sfermion masses at the unification scale, the interplay between the chargino, neutralino and slepton exclusion limits allows a lower bound of 27 GeV/\(c^2\) to be set on the mass of the lightest neutralino. Tighter constraints on the MSSM parameter space are obtained using in addition exclusions in the Higgs sector. Finally, the results are interpreted within the framework of minimal supergravity.
All ALEPH measurements of branching ratios of tau decays involving kaons are summarized including a combination of results obtained with K^0_S and K^0_L detection. The decay dynamics are studied, ...leading to the determination of contributions from vector K^*(892) and K^{*}(1410), and axial-vector K_1(1270) and K_1(1400) resonances. Agreement with isospin symmetry is observed among the different final states. Under the hypothesis of the conserved vector current, the spectral function for the K\bar{K}\pi mode is compared with the corresponding cross section for low energy e^+e^- annihilation, yielding an axial-vector fraction of (94^{+6}_{-8})% for this mode. The branching ratio for tau decay into all strange final states is determined to be B(\tau^-\to X^-(S=-1)\nu_\tau)=(28.7\pm1.2)\times 10^{-3}. The measured mass spectra of the strange tau decay modes are exploited to derive the S=-1 spectral function. A combination of strange and nonstrange spectral functions is used to determine the strange quark mass and nonperturbative contributions to the strange hadronic width. A method is developed to avoid the bad convergence of the spin zero hadronic component, with the result m_s(M_\tau^2)=(176^{\,+46}_{\, -57}) MeV/c^2. The evolution down to 1~GeV gives m_s(1~{\rm GeV}^2) = (234^{\,+61}_{\,-76})~{\rm MeV}/c^2.
Data collected at centre-of-mass energies of 181-184 GeV by ALEPH at LEP, corresponding to an integrated luminosity of 56.9 pb^-1, are analysed in a search for pair-produced charged Higgs bosons H+-. ...Three analyses are employed to select the tau nu tau nu, tau nu c s and c s c s final states. No evidence for a signal is found. Mass limits are set as a function of the branching fraction B( H+ -> tau+ nu ). Under the assumption that the decay modes considered cover the totality of the possible final states, charged Higgs bosons with masses below 59 GeV/c^2 are excluded at 95% C.L. independently of B( H+ -> tau+ nu ).
The inclusive charm production rate in W decays is measured from a study of the properties of final state particles. The sample of W pairs is selected from 67.7 pb-1 collected by ALEPH in 1996 and ...1997 at centre-of-mass energies near 172 and 183 GeV in the channels W+W- -->4q and W+W- -->lvqq. The branching fraction of hadronic W decays to a final state containing a c quark, R^W_c=Gamma(W-->cX)/Gamma(W-->hadrons), is measured to be 0.51 +- 0.05_stat +- 0.03_syst. This allows a direct determination of the CKM matrix element |V_cs| = 1.00 +- 0.11_stat +- 0.07_syst.
The e+e- -> ZZ cross section at sqrt(s)=182.7 and 188.6 GeV has been measured using the ALEPH detector. The analysis covers all of the visible ZZ final states and yields cross section measurements of ...sigma_ZZ(182.7 GeV) = 0.11 +- (0.16,0.11) (stat.) +- 0.04 (syst.) pb and sigma_ZZ(188.6 GeV) = 0.67 +- 0.13 (stat.) +- 0.04 (syst.) pb consistent with the Standard Model expectations.
Single W production is studied in the data recorded with the ALEPH detector at LEP at centre-of-mass energies between 161 and 183 GeV. The cross section is measured to be sigma_W=0.41+-0.17 (stat) ...+-0.04 (syst) pb at 183 GeV, consistent with the Standard Model expectation. Limits on non-standard WWgamma couplings are deduced as -1.6 < kg < 1.5 (lg=0) and -1.6 < lg < 1.6 (kg=1) at 95% C.L. A search for effectively invisible decays of the W boson in W pair production is performed, leading to an upper limit on the branching ratio of 1.3% (\Gamma_inv= 27 MeV) at 95% C.L.
Inclusive gamma^*gamma interactions to hadronic final states where one scattered electron or positron is detected in the electromagnetic calorimeters have been studied in the LEP 1 data taken by ...ALEPH from 1991 to 1995. The event sample has been used to measure the hadronic structure function of the photon F_2^gamma in three bins with Q^2 of 9.9, 20.7 and 284 GeV^2.
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