Cross-sections and angular distributions for hadronic and lepton pair final states in e+e- collisions at a centre-of-mass energy near 189 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the Standard Model. The results are used to measure the energy dependence of the electromagnetic coupling constant alpha_em, and to place limits on new physics as described by four-fermion contact interactions or by the exchange of a new heavy particle such as a sneutrino in supersymmetric theories with R-parity violation. A search for the indirect effects of the gravitational interaction in extra dimensions on the mu+mu- and tau+tau- final states is also presented.
The forward-backward asymmetry in muon- and tau-pair production in the two sprime/s regions.
The forward-backward asymmetry in electron-pair production for cos(theta_e) <0.7.
During the LEP running periods in 1990 and 1991 DELPHI has accumulated approximately 450 000 Z 0 decays into hadrons and charged leptons. The increased event statistics coupled with improved analysis techniques and improved knowledge of the LEP beam energies permit significantly better measurements of the mass and width of the Z 0 resonance. Model independent fits to the cross sections and leptonic forward- backward asymmetries yield the following Z 0 parameters: the mass and total width M Z = 91.187 ± 0.009 GeV, Γ Z = 2.486 ± 0.012 GeV, the hadronicf and leptonic partials widths Γ had = 1.725 ± 0.012 GeV, Γ ℓ = 83.01 ± 0.52 MeV, the invisible width Γ inv = 512 ± 10 MeV, the ratio of hadronic to leptonic partial widths R ℓ = 20.78 ± 0.15, and the Born level hadronic peak cross section σ 0 = 40.90 ± 0.28 nb. Using these results and the value of α s determined from DELPHI data, the number of light neutrino species is determined to be 3.08 ± 0.05. The individual leptonic widths are found to be: Γ e = 82.93 ± 0.70 MeV, Γ μ = 83.20 ± 1.11 MeV and Γ τ = 82.89 ± 1.31 MeV. Using the measured leptonic forward-backward asymmetries and assuming lepton universality, the squared vector and axial-vector couplings of the Z 0 to charged leptons are found to be g V ℓ 2 = (1.47 ± 0.51) × 10 −3 and g A ℓ 2 = 0.2483 ± 0.0016. A full Standard Model fit to the data yields a value of the top mass m t = 115 −82 +52 (expt.) −24 +52 (Higgs) GeV, corresponding to a value of the weak mixing angle sin 2 θ eff lept = 0.2339±0.0015 (expt.) −0.0004 +0.0001 (Higgs). Values are obtained for the variables S and T , or ϵ 1 and ϵ 3 which parameterize electroweak loop effects.
E+ E- forward-backward asymmetries from the 1990 data set for both final state fermions in the polar angle range 44 to 136 degrees and accollinearity < 10 degrees (the s + t data).
E+ E- forward-backward asymmetries from the 1991 data set for both final state fermions in the polar angle range 44 to 136 degrees and accollinearity < 10 degrees (the s + t data). Additional systematic error, excluding luminosity, is 0.002.
E+ E- forward-backward asymmetries from the 1990 data set after t-channel subtraction with only the E- constraint by polar angle 44 to 136 degrees and accollinearity < 10 degrees. Additional systematic error, excluding luminosity, is 0.003 at the peak.
Cross-sections for hadronic, b-bbar and lepton pair final states in e+e- collisions at sqrt(s) = 183 GeV, measured with the OPAL detector at LEP, are presented and compared with the predictions of the Standard Model. Forward-backward asymmetries for the leptonic final states have also been measured. Cross-sections and asymmetries are also presented for data recorded in 1997 at sqrt(s) = 130 and 136 GeV. The results are used to measure the energy dependence of the electromagnetic coupling constant alpha_em, and to place limits on new physics as described by four-fermion contact interactions or by the exchange of a new heavy particle such as a leptoquark, or of a squark or sneutrino in supersymmetric theories with R-parity violation.
The asymmetries have been corrected for interference between initial- and final-state radiation. The errors shown are the combined statistical and systematic errors.
The asymmetries have been corrected for interference between initial- and final-state radiation. The errors shown are the combined statistical and systematic errors.
The asymmetries have been corrected for interference between initial- and final-state radiation. The errors shown are the combined statistical and systematic errors.
We present a measurement of the cross section and transverse single-spin asymmetry ($A_N$) for $\eta$ mesons at large pseudorapidity from $\sqrt{s}=200$~GeV $p^{\uparrow}+p$ collisions. The measured cross section for $0.5<p_T<5.0$~GeV/$c$ and $3.0<|\eta|<3.8$ is well described by a next-to-leading-order perturbative-quantum-chromodynamics calculation. The asymmetries $A_N$ have been measured as a function of Feynman-$x$ ($x_F$) from $0.2<|x_{F}|<0.7$, as well as transverse momentum ($p_T$) from $1.0<p_T<4.5$~GeV/$c$. The asymmetry averaged over positive $x_F$ is $\langle{A_{N}}\rangle=0.061{\pm}0.014$. The results are consistent with prior transverse single-spin measurements of forward $\eta$ and $\pi^{0}$ mesons at various energies in overlapping $x_F$ ranges. Comparison of different particle species can help to determine the origin of the large observed asymmetries in $p^{\uparrow}+p$ collisions.
ASYM(PEAK) and ASYM(BG) for ETA mesons measured as a function of XF in the range 0.3 < ABS(XF) < 0.7 from the 4X4B triggered dataset. The values represented are the weighted mean of the South and North MPC (Muon Piston Calorimeter). The uncertainties listed are statistical only.
ASYM for ETA mesons measured as a function of XF in the range 0.2 < ABS(XF) < 0.7. Uncertainties listed are those due to the statistics, the XF uncorrelated uncertainties due to extracting the yields, and the correlated relative luminosity uncertainty.
ASYM for ETA mesons measured as a function of PT for ABS(XF) > 0.2. Uncertainties listed are those due to the statistics, the PT uncorrelated uncertainties due to extracting ASYM, and the correlated relative luminosity uncertainty.
We report on the properties of theZ resonance from 62 500Z decays into fermion pairs collected with the ALEPH detector at LEP, the Large Electron-Positron storage ring at CERN. We findMZ=(91.193±0.016exp±0.030LEP) GeV, ΓZ=(2497±31) MeV, σhad0=(41.86±0.66)nb, and for the partial widths Γinv=(489±24) MeV, Γhad(1754±27) MeV, Γee=(85.0±1.6)MeV, Γμμ=(80.0±2.5) MeV, and Γττ=(81.3±2.5) MeV, all in good agreement with the Standard Model. Assuming lepton universality and using a lepton sample without distinction of the final state we measure Γu=(84.3±1.3) MeV. The forward-backward asymmetry in leptonic decays is used to determine the vector and axial-vector weak coupling constants of leptors,gv2(MZ2)=(0.12±0.12)×10−2 andgA2(MZ2)=0.2528±0.0040. The number of light neutrino species isNν=2.91±0.13; the electroweak mixing angle is sin2θW(MZ2)=0.2291±0.0040.
No description provided.
No description provided.
No description provided.
We report on a study of inclusive production ofD*± mesons ine+e− annihilation at c.m. energies between 28 and 46.8 GeV using the TASSO detector at the PETRA storage ring. A hardD*± energy spectrum is measured with a maximum nearED*±≃0.6Ebeam. The measured cross section ratio\((\sigma _{D^{* + } }+ \sigma _{D^{* - } } )/\sigma _{\mu \mu }= 1.28 \pm 0.09 \pm 0.18\) indicates thatD* production accounts for a large fraction of the observed charm production. Two complementary methods have been used to determine the forward-backward asymmetry of charm pair production due to electroweak interference. Combining both measurements the product of the axial vector couplings of the electron and the charm quark to the weak neutral current was determined to begAegAc=−(0.276±0.073), in agreement with the standard model prediction of −0.25. Using a sample of reconstructedD*± mesons, the relative strength of the strong interaction coupling of thec quark compared to that of an average of all flavours is measured as αs(c)/αs(all)=0.91±0.38±0.15, consistent with the coupling constant being flavour independent. An update of ourD0 lifetime measurement is presented, based on a considerable increase in statistics, the final result being\(\tau _{D^0= } (4.8 \pm _{0.9 - 0.7}^{1.0 + 0.5} )10^{ - 13} s\).
Measurement of the charm quark production asymmetry using reconstructed D* mesons.
Measurement of the charm quark production asymmetry using an independent method based on the measurement of the direction of low PT pions.
We report on the measurement of the leptonic and hadronic cross sections and leptonic forward-backward asymmetries at theZ peak with the L3 detector at LEP. The total luminosity of 40.8 pb−1 collected
Results from 1990 data. Additional systematic uncertainty of 0.005.. Acollinearity required to be <15 degrees.
Results from 1991 data. Additional systematic uncertainty of 0.002.. Acollinearity required to be <15 degrees.
Results from 1992 data. Additional systematic uncertainty of 0.002.. Acollinearity required to be <15 degrees.
A measurement of elastic deeply virtual Compton scattering gamma* p -> gamma p using e^+ p and e^- p collision data recorded with the H1 detector at HERA is presented. The analysed data sample corresponds to an integrated luminosity of 306 pb^-1, almost equally shared between both beam charges. The cross section is measured as a function of the virtuality Q^2 of the exchanged photon and the centre-of-mass energy W of the gamma* p system in the kinematic domain 6.5 < Q^2 < 80 GeV^2, 30 < W < 140 GeV and |t| < 1 GeV^2, where t denotes the squared momentum transfer at the proton vertex. The cross section is determined differentially in t for different Q^2 and W values and exponential t-slope parameters are derived. Using e^+ p and e^- p data samples, a beam charge asymmetry is extracted for the first time in the low Bjorken x kinematic domain. The observed asymmetry is attributed to the interference between Bethe-Heitler and deeply virtual Compton scattering processes. Experimental results are discussed in the context of two different models, one based on generalised parton distributions and one based on the dipole approach.
The measured beam charge asymmetry defined as the difference in the DSIG/DPHI distributions between E+ P and E- P collisions.
We report the first measurement of the longitudinal double-spin asymmetry $A_{LL}$ for mid-rapidity di-jet production in polarized $pp$ collisions at a center-of-mass energy of $\sqrt{s} = 200$ GeV. The di-jet cross section was measured and is shown to be consistent with next-to-leading order (NLO) perturbative QCD predictions. $A_{LL}$ results are presented for two distinct topologies, defined by the jet pseudorapidities, and are compared to predictions from several recent NLO global analyses. The measured asymmetries, the first such correlation measurements, support those analyses that find positive gluon polarization at the level of roughly 0.2 over the region of Bjorken-$x > 0.05$.
Di-jet A_LL asymmetry vs parton-level invariant mass for the same-sign di-jet topology. The systematic uncertainty on the mass includes contributions from jet energy scale, the correction to parton-level, and the difference between NLO and PYTHIA cross sections. The systematic uncertainty on the asymmetry includes contributions from trigger and reconstruction bias and residual transverse beam polarization components. A 6.5% uncertainty common to all points due to uncertainty on the measured beam polarizations is also present, but not included in the uncertainties quoted below.
Theoretical predictions for the di-jet A_LL asymmetry for the same-sign topology using the DSSV14 and NNPDFpol1.1 polarized PDF sets. The DSSV14 prediction is presented without uncertainty while the systematic uncertainty on the NNPDFpol1.1 prediction contains contributions from factorization and renormalization scale uncertainties and PDF uncertainties.
Di-jet A_LL asymmetry vs parton-level invariant mass for the opposite-sign di-jet topology. The systematic uncertainty on the mass includes contributions from jet energy scale, the correction to parton-level, and the difference between NLO and PYTHIA cross sections. The systematic uncertainty on the asymmetry includes contributions from trigger and reconstruction bias and residual transverse beam polarization components. A 6.5% uncertainty common to all points due to uncertainty on the measured beam polarizations is also present, but not included in the uncertainties quoted below.
By combining results from the MARK-J at PETRA on Bhabha scattering, μ + μ - and τ + τ - production with recent world data from neutrino-electron scattering experiments, we determine unique values for the leptonic weak neutral current coupling constants g V and g A in the framework of electroweak models containing a single Z 0 . In contrast to previous analyses, we only use data from purely leptonic interactions, and therefore avoid the inherent uncertainties resulting from the use of hadronic targets. From the MARK-J data alone in the context of the standard SU(2) ⊗ U (1) model of Glashow, Weinberg and Salam, we find sin 2 θ W =0.24±0.11.
No description provided.
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