Search results for "Pair Production"
showing 10 items of 431 documents
Measurement of W-pair production in $e^+ e^-$ collisions at 189 GeV
2000
The production of W-pairs is analysed in a data sample collected by ALEPH at a mean centre-of-mass energy of 188.6 GeV, corresponding to an integrated luminosity of 174.2 pb^-1. Cross sections are given for different topologies of W decays into leptons or hadrons. Combining all final states and assuming Standard Model branching fractions, the total W-pair cross section is measured to be 15.71 +- 0.34 (stat) +- 0.18 (syst) pb. Using also the W-pair data samples collected by ALEPH at lower centre-of-mass energies, the decay branching fraction of the W boson into hadrons is measured to be BR (W > hadrons) = 66.97 +- 0.65 (stat) +- 0.32 (syst) %, allowing a determination of the CKM matrix el…
Angular distributions in the decay B -> K*l(+)l(-)
2009
We use a sample of 384 million BBbar events collected with the Babar detector at the PEP-II e+e- collider to study angular distributions in the rare decays B -> K* l+l-, where l+l- is either e+e- or mu+mu-. For low dilepton invariant masses, m(l+l-)3.2$ GeV/c^2, we measure AFB=0.76 (+0.52,-0.32) +/- 0.07 FL=0.71 (+0.20,-0.22) +/- 0.04.
Partial wave analysis of ψ(2S)→ppˉη
2013
Using a sample of 1.06 x 10(8) psi(2) events collected with the BESIII detector at BEPCII, the decay psi(2S) -> p (p) over bar eta is studied. A partial wave analysis determines that the intermediate state N(1535) with a mass of 1524 +/- 5(-4)(+10) MeV/c(2) and a width of 130(-24-10)(+27+57) MeV/c(2) is dominant in the decay; the product branching fraction is determined to be B(psi(2S) -> N(1535)(p) over bar x B(N(1535) -> p eta + c.c. = 5.2 +/- 0.3(-1.2)(+3.2)) x 10(-5). Furthermore, the branching fraction of psi(2S) -> p (p) over bar eta is measured to be (6.4 +/- 0.2 +/- 0.6) x 10(-5). Here, the first error is statistical and the second is systematic.
Study of the four-jet anomaly observed at LEP centre-of-mass energies of 130 and 136 GeV
1999
The four-jet events collected by DELPHI during the special LEP run at centre-of-mass energies of 130 and 136 GeV in 1997 with an integrated luminosity of 5.9 pb(-1) are analysed. Their rate and the distributions of their di-jet masses, their smallest jet charges, and their di-jet charge separations all agree well with Standard Model predictions. Thus the hypothesis of pair production of a new particle with a sum of di-jet masses around 105 GeV/c(2) is not supported. The combined result of the four LEP collaborations refuting this hypothesis at over 99% confidence level is also given. (C) 1999 Published by Elsevier Science B.V. All rights reserved.
Search for particles with unexpected mass and charge in Z decays
1993
During 1989 and 1990 over 180 000 hadronic and leptonic events, corresponding to 8 pb-1 of luminosity, were collected by the ALEPH detector in a scan of the Z peak at the e+e- collider LEP. This letter reports the results of a search in these data for particles with unexpected mass and charge by measurement of the ionization energy loss of charged tracks in the ALEPH TPC central tracking detector. The mass limits for the pair production of fractionally charged particles and of heavy, long lived charged particles are extended to 43 GeV/c2 at 90% confidence level. If single production of a heavy particle is considered, the mass limit is extended to more than 70 GeV/c2. RI Perrier, Frederic/A-…
Search for sleptons in e+e− collisions at centre-of-mass energies of 161 GeV and 172 GeV
1997
The data recorded by the ALEPH experiment at LEP at centre-of-mass energies of 161 GeV and 172 GeV were analysed to search for sleptons, the supersymmetric partners of leptons. No evidence for the production of these particles was found. The number of candidates observed is consistent with the background expected from four-fermion processes and gammagamma-interactions. Improved mass limits at 95% C.L. are reported.
Transverse spin effects in hadron-pair production from semi-inclusive deep inelastic scattering
2012
First measurements of azimuthal asymmetries in hadron-pair production in deep-inelastic scattering of muons on transversely polarised ^6LiD (deuteron) and NH_3 (proton) targets are presented. The data were taken in the years 2002-2004 and 2007 with the COMPASS spectrometer using a muon beam of 160 GeV/c at the CERN SPS. The asymmetries provide access to the transversity distribution functions, without involving the Collins effect as in single hadron production. The sizeable asymmetries measured on the NH_ target indicate non-vanishing u-quark transversity and two-hadron interference fragmentation functions. The small asymmetries measured on the ^6LiD target can be interpreted as indication …
Search for dark matter candidates and large extra dimensions in events with a jet and missing transverse momentum with the ATLAS detector
2013
A search for new phenomena in events with a high-energy jet and large missing transverse momentum is performed using data from proton-proton collisions at √s = 7 TeV with the ATLAS experiment at the Large Hadron Collider. Four kinematic regions are explored using a dataset corresponding to an integrated luminosity of 4.7 fb[superscript −1]. No excess of events beyond expectations from Standard Model processes is observed, and limits are set on large extra dimensions and the pair production of dark matter particles.
W pair production cross-section and W branching fractions in $e^{+}e^{-}$ interactions at 189 GeV
2000
The cross-section for the process e+e- -> W+W- has been measured with the data sample collected by DELPHI at an average centre-of-mass energy of 189 GeV and corresponding to an integrated luminosity of 155 pb^{-1}. Based on the 2392 events selected as WW candidates, the cross-section for the doubly resonant process e+e- -> W+W- has been measured to be 15.83 +- 0.38 (stat) +- 0.20 (syst) pb. The branching fractions of the W decay were also measured and found to be in good agreement with the Standard Model expectation. From these a value of the CKM mixing matrix element |V_{cs}| = 1.001 +- 0.040 (stat) +- 0.020 (syst) was derived.
Limits on tau lepton-flavor violating decays into three charged leptons
2010
A search for the neutrinoless, lepton-flavor violating decay of the tau lepton into three charged leptons has been performed using an integrated luminosity of 468 fb(-1) collected with the BABAR detector at the PEP-II collider. In all six decay modes considered, the numbers of events found in data are compatible with the background expectations. Upper limits on the branching fractions are set in the range (1.8-3.3) x 10(-8) at 90% confidence level.