The dissociation of virtual photons, $\gamma^{\star} p \to X p$, in events with a large rapidity gap between $X$ and the outgoing proton, as well as in events in which the leading proton was directly measured, has been studied with the ZEUS detector at HERA. The data cover photon virtualities $Q^2>2$ GeV$^2$ and $\gamma^{\star} p$ centre-of-mass energies $40<W<240$ GeV, with $M_X>2$ GeV, where $M_X$ is the mass of the hadronic final state, $X$. Leading protons were detected in the ZEUS leading proton spectrometer. The cross section is presented as a function of $t$, the squared four-momentum transfer at the proton vertex and $\Phi$, the azimuthal angle between the positron scattering plane and the proton scattering plane. It is also shown as a function of $Q^2$ and $\xpom$, the fraction of the proton's momentum carried by the diffractive exchange, as well as $\beta$, the Bjorken variable defined with respect to the diffractive exchange.
The differential cross section DSIG/DT for the LRG and the LPS data samples.
The fitted exponential slope of the T distribution as a function of X(NAME=POMERON).
The fitted exponential slope of the T distribution as a function of X(NAME=POMERON).
We present a measurement of the forward-backward charge asymmetry ($A_{FB}$) in $p\bar{p} \to Z/\gamma^{*}+X \to e^+e^-+X$ events at a center-of-mass energy of 1.96 TeV using 1.1 fb$^{-1}$ of data collected with the D0 detector at the Fermilab Tevatron collider. $A_{FB}$ is measured as a function of the invariant mass of the electron-positron pair, and found to be consistent with the standard model prediction. We use the $A_{FB}$ measurement to extract the effective weak mixing angle sin$^2\Theta^{eff}_W = 0.2327 \pm 0.0018 (stat.) \pm 0.0006 (syst.)$.
Unfolded forward-backward asymmetry as a function of the di-electron mass.
The production of the neutral strange hadrons $K^{0}_{S}$, $\Lambda$ and $\bar{\Lambda}$ has been measured in $ep$ collisions at HERA using the ZEUS detector. Cross sections, baryon-to-meson ratios, relative yields of strange and charged light hadrons, $\Lambda$ ($\bar{\Lambda}$) asymmetry and polarization have been measured in three kinematic regions: $Q^2 > 25 \gev^2$: $5 < Q^2 < 25 \gev^2$: and in photoproduction ($Q^2 \simeq 0$). In photoproduction the presence of two hadronic jets, each with at least $5 \gev$ transverse energy, was required. The measurements agree in general with Monte Carlo models and are consistent with measurements made at $e^+ e^-$ colliders, except for an enhancement of baryon relative to meson production in photoproduction.
Differential K0S cross section in DIS events as a function of transverse momentum (lab). for Q**2 from 5 to 25 GeV**2.
Differential K0S cross section in DIS events as a function of transverse momentum (lab). for Q**2 > 25 GeV**2.
Differential K0S cross section in DIS events as a function of pseudorapidity (lab). for Q**2 from 5 to 25 GeV**2.
Hadron production and lepton-pair production in e+e- collisions are studied with data collected with the L3 detector at LEP at centre-of-mass energies sqrt{s}=192-208GeV. Using a total integrated luminosity of 453/pb, 36057 hadronic events and 12863 lepton-pair events are selected. The cross sections for hadron production and lepton-pair production are measured for the full sample and for events where no high-energy initial-state-radiation photon is emitted prior to the collisions. Lepton-pair events are further investigated and forward-backward asymmetries are measured. Finally, the differential cross sections for electron-positron pair-production is determined as a function of the scattering angle. An overall good agreement is found with Standard Model predictions.
Measured hadron cross section for the inclusive data sample.
Measured hadron cross section for the high-energy data sample.
Measured MU+ MU- cross section for the inclusive data sample.
Cross-section and angular distributions for hadronic and lepton-pair final states in e+e- collisions at centre-of-mass energies between 189 GeV and 209 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the Standard Model. The measurements are used to determine the electromagnetic coupling constant alphaem at LEP2 energies. In addition, the results are used together with OPAL measurements at 91-183 GeV within the S-matrix formalism to determine the gamma-Z interference term and to make an almost model-independent measurement of the Z mass. Limits on extensions to the Standard Model described by effective four-fermion contact interactions or the addition of a heavy Z boson are also presented.
CM energy values.
Measured cross section for QUARK QUARKBAR (HADRON) production. The data are corrected to no interference between initial and final state radiation.
Measured cross section for MU+ MU- production. The data are corrected to no interference between initial and final state radiation.
This final analysis of hadronic and leptonic cross-sections and of leptonic forward-backward asymmetries in e+e- collisions with the OPAL detector makes use of the full LEP1 data sample comprising 161 pb^-1 of integrated luminosity and 4.5 x 10^6 selected Z decays. An interpretation of the data in terms of contributions from pure Z exchange and from Z-gamma interference allows the parameters of the Z resonance to be determined in a model-independent way. Our results are in good agreement with lepton universality and consistent with the vector and axial-vector couplings predicted in the Standard Model. A fit to the complete dataset yields the fundamental Z resonance parameters: mZ = 91.1852 +- 0.0030 GeV, GZ = 2.4948 +- 0.0041 GeV, s0h = 41.501 +- 0.055 nb, Rl = 20.823 +- 0.044, and Afb0l = 0.0145 +- 0.0017. Transforming these parameters gives a measurement of the ratio between the decay width into invisible particles and the width to a single species of charged lepton, Ginv/Gl = 5.942 +- 0.027. Attributing the entire invisible width to neutrino decays and assuming the Standard Model couplings for neutrinos, this translates into a measurement of the effective number of light neutrino species, N_nu = 2.984 +- 0.013. Interpreting the data within the context of the Standard Model allows the mass of the top quark, mt = 162 +29-16 GeV, to be determined through its influence on radiative corrections. Alternatively, utilising the direct external measurement of mt as an additional constraint leads to a measurement of the strong coupling constant and the mass of the Higgs boson: alfa_s(mZ) = 0.127 +- 0.005 and mH = 390 +750-280 GeV.
The cross section for hadron production corrected to the simple kinematic acceptance region defined by SPRIME/S > 0.01. Statistical errors only are shown. Also given is the cross section value corrected for the beam energy spread to correspond to the physical cross section at the central value of SQRT(S).
The cross section for E+ E- production corrected to the simple kinematic acceptance region defined by ABS(COS(THETA(C=E-))) < 0.7 and THETA(C=ACOL) < 10 degrees. Statistical errors only are shown. Also given is the cross section value corrected for the beam energy spread to correspond to the physical cross sectionat the central value of SQRT(S).
The cross section for mu+ mu- production corrected to the simple kinematic acceptance region defined by N = M(P=3_4)**2/S > 0.01. Statistical errors only are shown. Also given is the cross section value corrected for the beam energy spread to correspond to the physical cross section at the central value of SQRT(S).
We present the first measurement of the electron angular distribution parameter alpha_2 in W to e nu events produced in proton-antiproton collisions as a function of the W boson transverse momentum. Our analysis is based on data collected using the D0 detector during the 1994--1995 Fermilab Tevatron run. We compare our results with next-to-leading order perturbative QCD, which predicts an angular distribution of (1 +/- alpha_1 cos theta* + alpha_2 cos^2 theta*), where theta* is the polar angle of the electron in the Collins-Soper frame. In the presence of QCD corrections, the parameters alpha_1 and alpha_2 become functions of p_T^W, the W boson transverse momentum. This measurement provides a test of next-to-leading order QCD corrections which are a non-negligible contribution to the W boson mass measurement.
Angular distributions of the emitted charged lepton is fitted to the formula d(sig)/d(pt**2)/dy/d(cos(theta*)) = const*(1 +- alpha_1*cos(theta*) + alpha_2*(cos(theta*))**2). The angle theta* is measured in the Collins-Soper frame. alpha_1 velues are calculated based on the measured PT(W) of each event. Possible variations of alpha_1 are treated as a source of systematic uncertainty.
We report on measurements of hadronic and leptonic cross sections and leptonic forward-backward asymmetries performed with the L3 detector in the years 1993-95. A total luminosity of 103 pb^-1 was collected at centre-of-mass energies \sqrt{s} ~ m_Z and \sqrt{s} ~ m_Z +/- 1.8 GeV which corresponds to 2.5 million hadronic and 245 thousand leptonic events selected. These data lead to a significantly improved determination of Z parameters. From the total cross sections, combined with our measurements in 1990-92, we obtain the final results: m_Z = 91189.8 +/- 3.1 MeV, Gamma_Z = 2502.4 +/- 4.2 MeV, Gamma_had = 1741.1 +/- 3.8 MeV, Gamma_l = 84.14 +/- 0.17 MeV. An invisible width of Gamma_inv = 499.1 +/- 2.9 MeV is derived which in the Standard Model yields for the number of light neutrino species N_nu = 2.978 +/- 0.014. Adding our results on the leptonic forward-backward asymmetries and the tau polarisation, the effective vector and axial-vector coupling constants of the neutral weak current to charged leptons are determined to be \bar{g}_V^l = -0.0397 +/- 0.0017 and \bar{g}_A^l = -0.50153 +/- 0.00053.Including our measurements of the Z -> b \bar{b} forward-backward and quark charge asymmetries a value for the effective electroweak mixing angle of sin^2\bar{\theta}_W = 0.23093 +/- 0.00066 is derived. All these measurements are in good agreement with the Standard Model of electroweak interactions. Using all our measurements of electroweak observables an upper limit on the mass of the Standard Model Higgs boson of m_H < 133 GeV is set at 95% confidence level.
Updated values of coupling constants and electroweak mixing angle.
Cross sections for hadron production from the 1993 data. The first DSYS error is the uncorrelated part of the systematic error. The second DSYS error is from the statistical error on the absolute luminosity. In addition there is a fully correlated multiplicative contribution to the systematic error of 0.039 PCT plus an absolute uncertainty of 3.2pb together with an additional error from the absolute luminosity of 0.105 PCT.
Cross sections for hadron production from the 1994 data. The first DSYS error is the uncorrelated part of the systematic error. The second DSYS error is from the statistical error on the absolute luminosity. In addition there is a fully correlated multiplicative contribution to the systematic error of 0.039 PCT plus an absolute uncertainty of 3.2pb together with an additional error from the absolute luminosity of 0.088 PCT.
The D0 collaboration has performed a study of spin correlation in tt-bar production for the process tt-bar to bb-bar W^+W^-, where the W bosons decay to e-nu or mu-nu. A sample of six events was collected during an exposure of the D0 detector to an integrated luminosity of approximately 125 pb^-1 of sqrt{s}=1.8 TeV pp-bar collisions. The standard model (SM) predicts that the short lifetime of the top quark ensures the transmission of any spin information at production to the tt-bar decay products. The degree of spin correlation is characterized by a correlation coefficient k. We find that k>-0.25 at the 68% confidence level, in agreement with the SM prediction of k=0.88.
No description provided.
We report on measurements of e+e- annihilation into hadrons and lepton pairs. The data have been collected with the L3 detector at LEP at centre-of-mass energies between 130 and 189 GeV. Using a total integrated luminosity of 243.7 pb^-1, 25864 hadronic and 8573 lepton-pair events are selected for the measurement of cross sections and leptonic forward-backward asymmetries. The results are in good agreement with Standard Model predictions.
Measured cross sections for the hadronic events.
Measured cross sections for the muon-pair events.
Measured cross sections for the tau-pair events.
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