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The cross section for the production of Z gamma in proton-proton collisions at 8 TeV is measured based on data collected by the CMS experiment at the LHC corresponding to an integrated luminosity of 19.5 inverse femtobarns. Events with an oppositely-charged pair of muons or electrons together with an isolated photon are selected. The differential cross section as a function of the photon transverse momentum is measured inclusively and exclusively, where the exclusive selection applies a veto on central jets. The observed cross sections are compatible with the expectations of next-to-next-to-leading-order quantum chromodynamics. Limits on anomalous triple gauge couplings of Z Z gamma and Z gamma gamma are set that improve on previous experimental results obtained with the charged lepton decay modes of the Z boson.
Inclusive fiducial cross sections in bins of pT(gamma) with statistical, systematic, and luminosity uncertainties, respectivley. Results are not divided by bin-widths. The last bin is the cross section for pT(gamma) > 120 GeV. Combined result of electron and muon channels.
Fiducial cross sections with jet-veto in bins of pT(gamma) with statistical, systematic, and luminosity uncertainties, respectivley. Results are not divided by bin-widths. The last bin is the cross section for pT(gamma) > 120 GeV. Combined result of electron and muon channels.
Ratio of fiducial cross section with jet-veto and the inclusive cross section in bins of pT(gamma). The last bin is the cross section for pT(gamma) > 120 GeV. Combined result of electron and muon channels.
We describe a search for the pair production of first-generation scalar and vector leptoquarks in the eejj and enujj channels by the D0 Collaboration. The data are from the 1992--1996 ppbar run at sqrt{s} = 1.8 TeV at the Fermilab Tevatron collider. We find no evidence for leptoquark production; in addition, no kinematically interesting events are observed using relaxed selection criteria. The results from the eejj and enujj channels are combined with those from a previous D0 analysis of the nunujj channel to obtain 95% confidence level (C.L.) upper limits on the leptoquark pair-production cross section as a function of mass and of beta, the branching fraction to a charged lepton. These limits are compared to next-to-leading-order theory to set 95% C.L. lower limits on the mass of a first-generation scalar leptoquark of 225, 204, and 79 GeV/c^2 for beta=1, 1/2, and 0, respectively. For vector leptoquarks with gauge (Yang-Mills) couplings, 95% C.L. lower limits of 345, 337, and 206 GeV/c^2 are set on the mass for beta=1, 1/2, and 0, respectively. Mass limits for vector leptoquarks are also set for anomalous vector couplings.
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The interaction of virtual photons is investigated using the reaction e+e- -> e+e- hadrons based on data taken by the OPAL experiment at e+e- centre-of-mass energies sqrt(s_ee)=189-209 GeV, for W>5 GeV and at an average Q^2 of 17.9 GeV^2. The measured cross-sections are compared to predictions of the Quark Parton Model (QPM), to the Leading Order QCD Monte Carlo model PHOJET to the NLO prediction for the reaction e+e- -> e+e-qqbar, and to BFKL calculations. PHOJET, NLO e+e- -> e+e-qqbar, and QPM describe the data reasonably well, whereas the cross-section predicted by a Leading Order BFKL calculation is too large.
Total cross section in the given phase space and assuming ALPHA = 1/137.
Differential cross section as a function of X where X is the maximum value of X1 or X2, the upper and lower vertex values.
Differential cross section as a function of Q**2 where Q**2 is the maximum value of Q1**2 or Q2**2, the upper and lower vertex values.
Using 13.5-GeV beams at Stanford Linear Accelerator Center, we have compared electron and positron inelastic scattering over the range 1.2<|q2|<3.3 (GeV/c)2, 2<ν<9.5 GeV for the four-momentum and energy transfers, respectively. We find the ratio of the cross sections to be e+e−=1.0027±0.0035 (including statistical and systematic effects), with no significant dependence on q2 or ν. This result has appreciably smaller errors than previous attempts to find two-photon-exchange effects in electron or muon scattering.
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Using 20.5 GeV electrons on protons, we measured inclusive π 0 's (of transverse momentum, p T , from 0 to 1.4 GeV/ c ) produced by virtual photons of energy, ν, from 4 to 16.5 GeV and four-momentum squared, q 2 , from −1.8 to −8.5 (GeV/ c ) 2 . Comparing with charged pion data, we find σ π 0 = 1 2 (σ π + + σ π − ) , supporting the quark model. Photon knockout of a quark is favored as the interpretation of these data because of scaling in z = E π / ν and similarity in z -dependence of other pion production data. Consistent with this interpretation are the dependence of 〈 p T 〉 on q 2 , the azimuthal dependence, and fits to the constituent interchange model. We also observe a possible p T −4 dependence at large | q 2 | over a limited p T range.
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Inclusive e+e− production in 17-GeV/c π−p collisions has been measured. An excess of e+e− pairs over those from known sources for 0.1<~mee<~0.6 GeV and x<0.5 was found. No evidence is found for enhancements in specific final states involving electrons and photons or charged particles. The photon multiplicity associated with these pairs is measured.
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