This letter describes the first observation of W boson pair production at a centre-of-mass energy s =161 GeV in the OPAL detector at LEP. The analysis is sensitive to all expected W + W − decay channels. A total of 28 events have been selected for an integrated luminosity of 9.89±0.06 pb −1 . This is consistent with the Standard Model expectation, including signal and background contributions. The W pair production cross-section is measured to be σ WW = 3.62 −0.82 +0.93 ±0.16 pb. An analysis of the predicted M W dependence of the accepted cross-section, taking into account interference in the four-fermion production processes, yields M W = 80.40 −0.41−0.10 +0.44+0.09 ±0.10 GeV, where the first and second uncertainties are statistical and systematic, respectively, and the third arises form the beam energy uncertainty.
No description provided.
We have measured the proton and deuteron spin structure functions g_1^p and g_1^d in the region of the nucleon resonances for W^2 < 5 GeV^2 and $Q^2\simeq 0.5$ and $Q^2\simeq 1.2$ GeV^2 by inelastically scattering 9.7 GeV polarized electrons off polarized $^{15}NH_3$ and $^{15}ND_3$ targets. We observe significant structure in g_1^p in the resonance region. We have used the present results, together with the deep-inelastic data at higher W^2, to extract $\Gamma(Q^2)\equiv\int_0^1 g_1(x,Q^2) dx$. This is the first information on the low-Q^2 evolution of Gamma toward the Gerasimov-Drell-Hearn limit at Q^2 = 0.
The integral of the structure functions g1 for the resonance region W**2 < 4 GeV**2.
The integral of the structure functions g1 for the resonance region W**2 < 4 GeV**2.
The integral of the structure functions g1 for the full W region including the deep-inelastic region as given by fits to the world's data.
Inclusive charged particle and event shape distributions are measured using 321 hadronic events collected with the DELPHI experiment at LEP at effective centre of mass energies of 130 to 136 GeV. These distributions are presented and compared to data at lower energies, in particular to the precise Z data. Fragmentation models describe the observed changes of the distributions well. The energy dependence of the means of the event shape variables can also be described using second order QCD plus power terms. A method independent of fragmentation model corrections is used to determine αs from the energy dependence of the mean thrust and heavy jet mass. It is measured to be: $$←pha _s(133 {⤪ GeV})={0.116}pm {0.007}_{exp-0.004theo}^{+0.005}$$ from the high energy data.
mean values for event shape variables.
Integral of event shape distribution over the specified interval.
Integral of event shape distribution over the specified interval.
Using data recorded by the CLEO-II detector at CESR, we report evidence of a pair of excited charmed baryons, one decaying into Λc+π+ and the other into Λc+π−. The doubly charged state has a measured mass difference M(Λc+π+)−M(Λc+) of 234.5±1.1±0.8 MeV/c2 and a width of 17.9−3.2+3.8±4.0MeV/c2, and the neutral state has a measured mass difference M(Λc+π−)−M(Λc+) of 232.6±1.0±0.8 MeV/c2 and a width of 13.0−3.0+3.7±4.0MeV/c2. We interpret these data as evidence of the Σc*++ and Σc*0, the spin 32+ excitations of the Σc baryons.
CONST(NAME=EPS) is the parameter of the Peterson fragmentation function (C.Peterson et al., PR D27, 105 (1983)) D(N)/D(Z) = FD(Z) = const * (1/Z)*1/(1- (1/Z)-CONST(NAME=EPS)/(1-Z))**2.
We present results of a search for W+W− production through the leptonic decay channel W+W−→l+l−νν¯ in p¯p collisions at s=1.8TeV. In a 108pb−1 data sample recorded with the Collider Detector at Fermilab, five W+W− candidates are found with an expected standard model background of 1.2±0.3 events. The W+W− production cross section is measured to be σ(p¯p→W+W−)=10.2−5.1+6.3(stat)±1.6(syst)pb, in agreement with the standard model prediction. Limits on WWγ and WWZ anomalous couplings are presented.
No description provided.
The inclusive one- and two-jet production cross-sections are measured in collisions of quasi-real photons radiated from the LEP beams at e+e− centre-of-mass energies \(\sqrt{s}_{\rm ee}=130\) and 136 GeV using the OPAL detector at LEP. Hard jets are reconstructed using a cone jet finding algorithm. The differential jet cross-sections \({\rm d}\sigma /{\rm d}E_{T}^{\rm jet}\) are compared to next-to-leading order perturbative QCD calculations. Transverse energy flows in jets are studied separately for direct and resolved two-photon events.
Inclusive one-jet cross section.
One-jet rapidity distribution.
Inclusive two-jet cross section.
We report on a measurement of the branching fraction of the Cabibbo-suppressed decay Bu+→J/ψπ+, where J/ψ→μ+μ−. The data were collected by the Collider Detector at Fermilab during 1992–1995 and correspond to an integrated luminosity of 110pb−1 in p¯p collisions at s=1.8TeV. A signal of 28−9+10 events is observed and we determine the ratio of branching fractions B(Bu+→J/ψπ+)/B(Bu+→J/ψK+) to be [5.0−1.7+1.9(stat)±0.1(syst)]%. Using the world average value for B(Bu+→J/ψK+), we calculate the branching fraction B(Bu+→J/ψπ+) to be (5.0−1.9+2.1)×10−5. We also search for the decay Bc+→J/ψπ+ and report a 95% confidence level limit on σ(Bc+)B(Bc+→J/ψπ+)/σ(Bu+)B(Bu+→J/ψK+) as a function of the Bc+ lifetime.
The ratio of the cross sections times the branching fraction.
We have used 106 pb~-1 of data collected in proton-antiproton collisions at sqrt(s)=1.8 TeV by the Collider Detector at Fermilab to measure jet angular distributions in events with two jets in the final state. The angular distributions agree with next to leading order (NLO) predictions of Quantum Chromodynamics (QCD) in all dijet invariant mass regions. The data exclude at 95% confidence level (CL) a model of quark substructure in which only up and down quarks are composite and the contact interaction scale is Lambda_ud(+) < 1.6 TeV or Lambda_ud(-) < 1.4 TeV. For a model in which all quarks are composite the excluded regions are Lambda(+) < 1.8 TeV and Lambda(-) < 1. 6 TeV.
No description provided.
Di-jet angular ratio, defined as the number with CHI < 2.5 divided by the number with CHI between 2.5 and 5.
Event shape and charged particle inclusive distributions are measured using 750000 decays of the Z to hadrons from the DELPHI detector at LEP. These precise data allow a decisive confrontation with models of the hadronization process. Improved tunings of the JETSET, ARIADNE and HERWIG parton shower models and the JETSET matrix element model are obtained by fitting the models to these DELPHI data as well as to identified particle distributions from all LEP experiments. The description of the data distributions by the models is critically reviewed with special importance attributed to identified particles.
Transverse momentum PTIN w.r.t. the Thrust axis. For the first table Thrust axis definition is from seen charged particles corrected to final state particles. For the second table Thrust axis definition is from seen charged plus neutral particles corrected to final state charged plus neutral particles.
Transverse momentum PTOUT w.r.t. the Thrust axis. For the first table Thrust axis definition is from seen charged particles corrected to final state particles. For the second table Thrust axis definition is from seen charged plus neutral particles corrected to final state charged plus neutral particles.
Transverse momentum PTIN w.r.t. the Sphericity axis. For the first table Sphericity axis definition is from seen charged particles corrected to final state particles. For the second table Sphericity axis definition is from seen charged plus neutral particles corrected to final state charged plus neutral particles.
The decay Λb0→J/ψ Λ is observed in 110 pb−1 of pp¯ collisions taken at s=1.8 TeV. These data are used to measure a Λb0 mass of 5621±4(stat)±3(syst) MeV/c2, and a mass difference between the Λb0 and the B0 of 340±5(stat)±1(syst) MeV/c2. The production cross-section times branching fraction for the decay Λb0→J/ψ Λ relative to that for the decay B0→J/ψ KS0 has been measured to be 0.27±0.12(stat)±0.05(syst).
No description provided.
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