Searches for the production of supersymmetric particles under the assumption that R-parity is violated via a single dominant \(LL{\bar E}, LQ{\bar D}\) or \({\bar U}{\bar D}{\bar D}\) coupling were ...performed. These use the data collected by the ALEPH detector at LEP at centre-of-mass energies from 188.6 to 201.6 GeV. The numbers of candidate events observed in the data are consistent with Standard Model expectations. Upper limits on the production cross sections and lower limits on the masses of charginos, sleptons, squarks and sneutrinos are derived.
From a study of the kinematic properties of the final state produced in the semileptonic decays \({\rm b\to X\ell\nu_{\ell}}\), the inclusive charmless semileptonic branching ratio of b hadrons is ...measured. With a sample of 3.6 million hadronic Z decays recorded between 1992 and 1995 with the ALEPH detector at LEP, the value \({\rm Br(b\to X_u\ell\nu_{\ell})}\) is determined to be \((1.73\pm 0.55_{{\rm stat}}\pm 0.55_{{\rm syst}})\times 10^{-3}\), where \({\rm X_u}\) represents any charmless hadronic state and b is a mixture of b hadrons weighted by their production rates. This measurement yields the result where the last error comes from the conversion of the branching ratio to the CKM matrix element squared.
A search for CP violating effects in the mixing of neutral B mesons is performed using a sample of 4.1 million hadronic Z decays collected with the ALEPH detector from 1991 to 1995. By studying ...time-dependent asymmetries in flavour-tagged samples of semileptonic and fully inclusive b-hadron decays, two measurements of the semileptonic asymmetry \(a_{\rm CP}\) are extracted. No evidence for CP violation is observed, and the combined value \(a_{\rm CP}= -0.013 \pm 0.026\) is obtained.
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.
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.
A search for oscillations is performed using approximately 4 million events collected by the ALEPH experiment during 1991–1995. candidates are partially reconstructed by combining tracks with fully ...reconstructed candidates. The production flavour is estimated from the sign of the opposite hemisphere charge, a fragmentation kaon in the same hemisphere, or a lepton in the opposite hemisphere. From a total sample of 1620 candidates, with a purity estimated to be 22%, all values of below 3.9 ps and between 6.5 and 8.8 ps are excluded at 95% CL. From the same sample, the lifetime is measured to be ps. This analysis selects mainly hadronic decays and is statistically independent of a previous ALEPH analysis selecting candidates. Combining these two analyses yields ps at 95% CL and ps.
Inclusive branching ratios involving b \(\to \tau\) transitions are measured in approximately four million hadronic Z decays collected by the ALEPH detector at LEP. The fully-inclusive branching ...ratio BR(b \(\to \tau^- \bar{\nu}_{\tau}\) X) and the semi-inclusive branching ratio BR(b \(\to \tau^- \bar{\nu}_{\tau} {\rm D}^{\ast\pm}\)X) are measured to be \((2.43 \pm 0.20 \pm 0.25)%\) and \((0.88\pm 0.31\pm 0.28)%\), in agreement with the standard model predictions. Upper limits on the branching fractions BR(B\(^- \to \tau^- \bar{\nu}_{\tau})\) and BR(b \(\to{\mathrm s} \nu \bar{\nu})\) are set to \(8.3 \times 10^{-4}\) and \(6.4 \times 10^{-4}\) at the 90% C.L. These results allow a 90% C.L. lower limit of 0.40 GeV/\(c^2)^{-1}\) to be set on the \(\tan\beta/m_{{\mathrm H}^\pm}\) ratio, in the framework of type-II two-Higgs-doublet models.
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 188.6 GeV by the ALEPH experiment at LEP, with an integrated luminosity ...of 176 \({\rm pb}^{-1}\). No evidence for a signal is found. A lower limit of 92.9 \({\mathrm{GeV}/c^2}\) at 95% confidence level is set on the mass of the Standard Model Higgs boson, with an expected sensitivity of 95.9 \({\mathrm{GeV}/c^2}\). In the MSSM, for \(\tan\beta \ge 0.7\) and for benchmark parameter choices, observed (expected) lower limits of 82.5 (83.1) \({\mathrm{GeV}/c^2}\) and 82.6 (83.2) \({\mathrm{GeV}/c^2}\) are derived for the masses of the neutral Higgs bosons \({\mathrm{h}}\) and \({\mathrm{A}}\), respectively. An update of the general MSSM parameter scan is also presented.
The production rates and the inclusive cross sections of the isovector meson \({\rm \pi^0}\), the isoscalar mesons \(\eta\) and \({\rm \eta^{\prime}(958)}\), the strange meson \({\rm K^0_{\rm S}}\) ...and the \({\rm \Lambda}\) 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 \({\rm \Lambda}\) spectra in quark jets.
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