Constraints on anomalous QGC's in e+e−e^{+}e^{-} interactions from 183 to 209 GeV

The acoplanar photon pairs produced in the reaction e(+) e(-) - → vvyy are analysed in the 700 pb(-1) of data collected by the ALEPH detector at centre-of-mass energies between 183 and 209 GeV. No deviation from the Standard Model predictions is seen in any of the distributions examined. The resulting 95% C.L. limits set on anomalous QGCs, a(0)(Z), a(c)(Z), a(0)(W) and a(c)(W), are -0.012 lt a(0)(Z)/Lambda(2) lt +0.019 GeV-2, -0.041 lt a(c)(Z)/Lambda(2) lt +0.044 GeV-2, -0.060 lt a(0)(W)/Lambda(2) lt +0.055 GeV-2, -0.099 lt a(c)(W)/Lambda(2) lt +0.093 GeV-2, where Lambda is the energy scale of the new physics responsible for the anomalous couplings

Electroweak measurements in electron–positron collisions at w-boson-pair energies at lep

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Search for neutral MSSM Higgs bosons at LEP

The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by the Minimal Supersymmetric standard model (MSSM). The data of the four collaborations are statistically combined and examined for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number of "benchmark" models, including CP-conserving and CP-violating scenarios. These interpretations lead in all cases to large exclusions in the MSSM parameter space. Absolute limits are set on the parameter tan β and, in some scenarios, on the masses of neutral Higgs bosons

Electroweak measurements in electron-positron collisions at W-boson-pair energies at LEP

Electroweak measurements performed with data taken at the electron-positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3fb-1 collected by the four LEP experiments ALEPH, DELPHI, L3 and OPAL, at centre-of-mass energies ranging from 130GeV to 209GeV. Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant W W and Z Z production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron-positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose-Einstein correlations between the two W decay systems arising in W W production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, mW and ΓW, the branching fraction of W decays to hadrons, B (W → had), and the trilinear gauge-boson self-couplings g1 Z, κγ and λγ are determined to be: mW=80.376±0.033GeV ΓW=2.195±0.083GeV B(W→had)=67.41±0.27% g1 Z=0.9840+0.018 -0.020 κγ=0.982±0.042λγ=-0.022±0.019. © 2013 Elsevier B.V

Exclusive production of pion and kaon meson pairs in two photon collisions at LEP.

Exclusive production of π and K meson pairs in two photon collisions is measured with ALEPH data collected between 1992 and 2000. Cross-sections are presented as a function of cosθ* and invariant mass, for |cosθ*|<0.6 and invariant masses between 2.0 and 6.0 GeV/c2 (2.25 and 4.0 GeV/c2) for pions (kaons). The shape of the distributions are found to be well described by QCD predictions but the data have a significantly higher normalization

Study of hadronic final states from double tagged gammagammagammagamma events at LEP

The interaction of virtual photons is investigated using double tagged gammagamma events with hadronic final states recorded by the ALEPH experiment at e^+e^- centre-of-mass energies between 188 and 209 GeV. The measured cross section is compared to Monte Carlo models, and to next-to-leading-order QCD and BFKL calculations.The interaction of virtual photons is investigated using double tagged gammagamma events with hadronic final states recorded by the ALEPH experiment at e^+e^- centre-of-mass energies between 188 and 209 GeV. The measured cross section is compared to Monte Carlo models, and to next-to-leading-order QCD and BFKL calculations

Bose-Einstein correlations in W-pair decays with an event-mixing technique

Bose–Einstein correlations in W-pair decays are studied using data collected by the ALEPH detector at LEP at e+e− centre-of-mass energies from 183 to 209 GeV. The analysis is based on the comparison of events to “mixed” events constructed with the hadronic part of events. The data are in agreement with the hypothesis that Bose–Einstein correlations are present only for pions from the same W decay. The JETSET model with Bose–Einstein correlations between pions from different W bosons is disfavoured

Single- and multi-photon production in ee collisions at s√ up to 209 GeV

Events containing only energetic photons are analysed in a sample of 628pb−1 of data recorded from e+e− collisions at centre-of-mass energies between 189 and 209 GeV by the ALEPH detector at LEP. The e+e−→νν¯γ(γ) and e+e−→γγ(γ) cross sections are measured and found to be in agreement with the standard model predictions. The number of light neutrino generations is determined to be Nν=2.86±0.09 . Upper limits are derived on the cross sections for photon production in the context of several supersymmetric models. Limits are also set on the parameters of models with extra spatial dimensions, with contact interactions and with excited electrons

Search for R-parity violating production of single sneutrinos in e+ e- collisions at s**(1/2) = 189-GeV to 209-GeV

A search for single sneutrino production under the assumption that R-parity is violated via a single dominant $LL\bar{E}$ coupling is presented. This search considers the process ${\rm e} \gamma {\smash{\mathop{\to}}} \tilde{\nu}\ell$ and is performed using the data collected by the ALEPH detector at centre-of-mass energies from 189 GeV up to 209 GeV corresponding to an integrated luminosity of 637.1 $\mathrm{pb}^{-1}$. The numbers of observed candidate events are in agreement with Standard Model expectations and 95% confidence level upper limits on five of the $LL\bar{E}$ couplings are given as a function of the assumed sneutrino mass.Comment: 22 pages, 14 figure

A flavour-independent Higgs boson search in e+e− collisions at√s up to 209 GeV

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