Event shapes in e+e- annihilation and deep inelastic scattering

This article reviews the status of event-shape studies in e+e- annihilation and DIS. It includes discussions of perturbative calculations, of various approaches to modelling hadronisation and of comparisons to data.Comment: Invited topical review for J.Phys.G; 40 pages; revised version corrects some nomenclatur

Slepton Discovery in Electroweak Cascade Decay

The LHC studies on the MSSM slepton sector have mostly been focused on direct slepton Drell-Yan pair production. In this paper, we analyze the case when the sleptons are lighter than heavy neutralinos and can appear in the on-shell decay of neutralino states. In particular, we have studied the \chi_1^\pm \chi_2^0 associated production, with the consequent decays of \chi_1^\pm and \chi_2^0 via on-shell sleptons. The invariant mass of the lepton pairs, m_{\ell\ell}, from the neutralino decay has a distinctive triangle shape with a sharp kinematic cutoff. We discuss the utilization of this triangle shape in m_{\ell\ell} distribution to identify the slepton signal. We studied the trilepton plus missing E_T signal and obtained the effective cross section, \sigma \times BR \times acceptance, that is needed for a 5\sigma discovery as a function of the cutoff mass for the LHC with center of mass energy 14 TeV and 100 fb^{-1} integrated luminosity. Our results are model independent such that they could be applied to other models with similar decay topology. When applied to the MSSM under simple assumptions, it is found that with 100 fb^{-1} integrated luminosity, a discovery reach in the left-handed slepton mass of about 600 GeV could be reached, which extends far beyond the slepton mass reach in the usual Drell-Yan studies.Comment: 20 pages, 5 figure

Search for Single Top Production in e+e- Collisions at sqrt(s) up to 209GeV

Single top production via the flavour changing neutral current reactions e+e- -> \bar{t}c, \bar{t}u is searched for within the 214 pb-1 of data collected by ALEPH at centre-of-mass energies between 204 and 209 GeV. No deviation from the Standard Model expectation is observed and upper limits on the single top production cross sections are derived. The combination with data collected at lower centre-of-mass energies yields an upper limit on the branching ratio BR(t -> Zc)+BR(t -> Zu) 14%, for BR(t -> \gamma c)+BR(t -> \gamma u)= 0 and mt=174 GeV/c2

Search for the Standard Model Higgs Boson at LEP

The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have collected a total of 2461 pb-1 of e+e- collision data at centre-of-mass energies between 189 and 209 GeV. The data are used to search for the Standard Model Higgs boson. The search results of the four collaborations are combined and examined in a likelihood test for their consistency with two hypotheses: the background hypothesis and the signal plus background hypothesis. The corresponding confidences have been computed as functions of the hypothetical Higgs boson mass. A lower bound of 114.4 GeV/c2 is established, at the 95% confidence level, on the mass of the Standard Model Higgs boson. The LEP data are also used to set upper bounds on the HZZ coupling for various assumptions concerning the decay of the Higgs boson

Search for the Standard Model Higgs Boson at LEP

The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have collected a total of 2461 pb-1 of e+e- collision data at centre-of-mass energies between 189 and 209 GeV. The data are used to search for the Standard Model Higgs boson. The search results of the four collaborations are combined and examined in a likelihood test for their consistency with two hypotheses: the background hypothesis and the signal plus background hypothesis. The corresponding confidences have been computed as functions of the hypothetical Higgs boson mass. A lower bound of 114.4 GeV/c2 is established, at the 95% confidence level, on the mass of the Standard Model Higgs boson. The LEP data are also used to set upper bounds on the HZZ coupling for various assumptions concerning the decay of the Higgs boson

Search for scalar quarks in e(+)e(-) collisions at root s up to 209 GeV

Searches for scalar top, scalar bottom and mass-degenerate scalar quarks are performed in the data collected by the ALEPH detector at LEP. at centre-of-mass energies up to 209 GeV, corresponding to an integrated luminosity of 675 pb(-1). No evidence for the production of such particles is found in the decay channels (t) over tilde -->C/uchi, (t) over tilde -->bl (nu) over tilde, (q) over tilde -->bchi, ($) over tilde -->qchi or in the stop four-body decay channel (t) over tilde -->bchif (f) over bar' studied for the first time at LEP. The results of these searches yield improved mass lower limits. In particular, an absolute lower limit of 63 GeV/c(2) is obtained for the stop mass, at 95% confidence level, irrespective of the stop lifetime and decay branching ratios. (C) 2002 Elsevier Science B.V All rights reserved

Production of D-s(**) mesons in hadronic Z decays

The production rates of the orbitally excited D-s** mesons, D-s1(+/-) and D-s2(*+/-), are measured with the 4.1 million hadronic Z decays recorded by the ALEPH detector during 1991-1995. The D-s** mesons are reconstructed in the decay modes D-s1(+) --> (D*+K0), D-s1(+) --> (DK+)-K-*0 and D-s2(*+) --> (DK+)-K-0. The production rate of the D-s1(+/-) is measured to be f (Z --> D-s1(+/-)) = (0.52 +/- 0.09 +/- 0.06)%, under the assumption that the two considered decay modes of the D-s1(+/-) saturate the branching ratio. The production rate of the D-s2(*+/-) is determined to be f (Z --> D-s2(*+/-)) = (0.83 +/- 0.29(-0.13)(+0.17))%, assuming that the branching fraction of the decay D-s2(*+) --> (DK+)-K-0 is 45%. The production rates in Z --> c (c) over bar and Z --> b (b) over bar decays are measured separately. (C) 2002 Elsevier Science B.V. All rights reserved

Search for gamma gamma -> eta(b) in e(+)e(-) collisions at LEP 2

A search for the pseudoscalar meson eta(b) is performed in two-photon interactions at LEP 2 with an integrated luminosity of 699 pb(-1) collected at e(+)e(-) centre-of-mass energies from 181 GeV to 209 GeV. One candidate event is found in the six-charged-particle final state and none in the four-charged-particle final state, in agreement with the total expected background of about one event. Upper limits of Gamma(gammagamma)(eta(b)) x BR(eta(b) --> 4 charged particles) < 48 eV, Gamma(gammagamma) (eta(b)) x BR(eta(b) --> 6 charged particles) < 132 eV are obtained at 95% confidence level, which correspond to upper limits of 9.0% and 25% on these branching ratios. (C) 2002 Elsevier Science B.V. All rights reserved

Search for single top production in e(+)e(-) collisions at root s up to 209 GeV

Single top production via the flavour changing neutral current reactions e(+)e(-) --> (t) over barc, (t) over baru is searched for within the 214 pb(-1) of data collected by ALEPH at centre-of-mass energies between 204 and 209 GeV No deviation from the Standard Model expectation is observed and upper limits on the single top production cross sections are derived. The combination with data collected at lower centre-of-mass energies yields an upper limit on the branching ratio BR(t --> Zc) + BR(t --> Zu) < 14%, for BR(t --> gammac) + BR(t --> gammau) = 0 and m(t) = 174 GeV/c(2). (C) 2002 Elsevier Science B.V All rights reserved

Improved search for B(0)S anti-B(0)S oscillations

An improved search for B s 0 oscillations is performed in the ALEPH data sample collected during the first phase of LEP, and reprocessed in 1998. Three analyses based on complementary event selections are presented. First, decays of B s 0 mesons into hadronic flavour eigenstates are fully reconstructed. This selection yields a small sample of candidates with excellent decay length and momentum resolution and hi gh average B s 0 purity. Semileptonic decays with a reconstructed D s - meson provide a second sample with larger statistics, high average B s 0 purity, but a poorer momentum and decay length resolution due to the partial decay reconstruction. Finally, semileptonic b-hadron decays are inclusively selected and yield the data sample with the highest sensitivity to B s 0 oscillations, as the much higher statistics compensate for the low average B s 0 purity and poorer time resolution. A lower limit is set at Δms>10.9 ps-1 at 95% C.L., significantly lower than the expected limit of 15.2 ps-1