We have studied hadronic events produced at LEP at a centre-of-mass energy of 161 GeV. We present distributions of event shape variables, jet rates, charged particle momentum spectra and multiplicities. We determine the strong coupling strength to be αs(161 GeV) = 0.101±0.005(stat.)±0.007(syst.), the mean charged particle multiplicity to be 〈nch〉(161 GeV) = 24.46 ± 0.45(stat.) ± 0.44(syst.) and the position of the peak in the ξp = ln(1/xp) distribution to be ξ0(161 GeV) = 4.00 ±0.03(stat.)±0.04(syst.). These results are compared to data taken at lower centre-of-mass energies and to analytic QCD or Monte Carlo predictions. Our measured value of αs(161 GeV) is consistent with other measurements of αs. Within the current statistical and systematic uncertainties, the PYTHIA, HERWIG and ARIADNE QCD Monte Carlo models and analytic calculations are in overall agreement with our measurements. The COJETS QCD Monte Carlo is in general agreement with the data for momentum weighted distributions like Thrust, but predicts a significantly larger charged particle multiplicity than is observed experimentally.
Determination of alpha_s.
Multiplicity and higher moments.
Thrust distribution.
We report on the measurement of W-boson pair-production with the L3 detector at LEP at a centre-of-mass energy of 161.34 GeV. In a data sample corresponding to a total luminosity of 11 pb −1 , we select four-fermion events with high invariant masses of pairs of hadronic jets or leptons. Combining all final states, the measured total cross section for W-pair production is: sigma WW = 2.89 −0.70 +0.81 (stat.) ± 0.14 (syst.) pb. Within the Standard Model, this corresponds to a mass of the W boson of: M W = 80.80 −0.42 +0.48 (exp.) ± 0.03 (LEP) GeV. Limits on anomalous triple-vector-boson couplings are derived.
No description provided.
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We have measured the spin-dependent structure function $g_1~p$ in inclusive deep-inelastic scattering of polarized muons off polarized protons, in the kinematic range $0.003 < x < 0.7$ and $1 GeV~2 < Q~2 < 60 GeV~2$. A next-to-leading order QCD analysis is used to evolve the measured $g_1~p(x,Q~2)$ to a fixed $Q~2_0$. The first moment of $g_1~p$ at $Q~2_0 = 10 GeV~2$ is $\Gamma~p = 0.136\pm 0.013(stat.) \pm 0.009(syst.)\pm 0.005(evol.)$. This result is below the prediction of the Ellis-Jaffe sum rule by more than two standard deviations. The singlet axial charge $a_0$ is found to be $0.28 \pm 0.16$. In the Adler-Bardeen factorization scheme, $\Delta g \simeq 2$ is required to bring $\Delta \Sigma$ in agreement with the Quark-Parton Model. A combined analysis of all available proton and deuteron data confirms the Bjorken sum rule.
Data for Q**2 > 1 GeV**2.
Data for Q**2 > 0.2 GeV**2.
Statistical errors only.
We report the first observation of diffractively produced W bosons. In a sample of W -> e nu events produced in p-barp collisions at sqrt{s}=1.8 TeV, we find an excess of events with a forward rapidity gap, which is attributed to diffraction. The probability that this excess is consistent with non-diffractive production is 1.1 10^{-4} (3.8 sigma). The relatively low fraction of W+Jet events observed within this excess implies that mainly quarks from the pomeron, which mediates diffraction, participate in W production. The diffractive to non-diffractive W production ratio is found to be R_W=(1.15 +/- 0.55)%.
No description provided.
We present an improved determination of the proton structure functions $F_{2}$ and $xF_{3}$ from the CCFR $\nu $-Fe deep inelastic scattering (DIS) experiment. Comparisons to high-statistics charged-lepton scattering results for $F_{2}$ from the NMC, E665, SLAC, and BCDMS experiments, after correcting for quark-charge and heavy-target effects, indicate good agreement for $x>0.1$ but some discrepancy at lower x. The $Q^{2}$ evolution of the structure functions yields the quantum chromodynamics (QCD) scale parameter $\Lambda_{\bar{MS}}^{NLO,(4)}=337 \pm 28$(exp.) MeV. This corresponds to a value of the strong coupling constant at the scale of mass of the Z-boson of $\alpha _{S}(M_{Z}^{2})=0.119 \pm 0.002 (exp.) \pm 0.004 (theory)$ and is one of the most precise measurements of this quantity.
No description provided.
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We measured the in flight annihilation frequencies and cross sections of reactions n p → π + π 0 ,π + η and K + K S in the antineutron momentum range between 50 and 400 MeV/c. The annihilation frequencies of these channels from the different allowed initial states were calculated and some information about the n p annihilation dynamics were obtained. The first determination of the D-wave contribution in this momentum range was also obtained.
No description provided.
Using data collected from 1992 to 1995 with the ALEPH detector at LEP, a measurement of the colour factor ratios CA/CF and TF /CF and the strong coupling constant αs = CFαs(MZ)/(2π) has been performed by fitting theoretical predictions simultaneously to the measured differential two-jet rate and angular distributions in four-jet events. The result is found to be in excellent agreement with QCD, {fx4-1} Fixing CA/CF and TF/CF to the QCD values permits a determination of αs(MZ) and ηf, the number of active flavours. With this measurement the existence of a gluino with mass below 6.3 GeV/c2 is excluded at 95% confidence level.
Fit A: using all kinematical distributions. NC, CF, and TF are the color factors for SU(3) group, NF is the number of the active flavors.
Fit B: using all kinematical distributions, but QCD magnitudes for color factors are used: FA(DEF=NC/CF)) = 2.25 and TF/CF = 0.375. NC, CF, and TF are the color factors for SU(3) group, NF is the number of the active flavors.
Fit C: the QCD magnitudes for color factors and NF = 5 are used.
The Drell-Yan and J ψ cross-sections measured in PbPb collisions are compared with the values extrapolated from the results obtained in proton and light ion induced reactions. While the Drell-Yan production exhibits the normal expected behaviour, the yield of J ψ in PbPb interactions is abnormally low, as it lies 9 standard deviations below the expected value. Moreover, the departure from the expected behaviour increases significantly from peripheral to central collisions.
The results from other experiments are also presented.
Different data are rescaled at 200 GeV.
A partial wave analysis of p̄p → π 0 π 0 η ′ has been performed using the η′ → π 0 π 0 η and η ′ → γγ decay modes. The data are dominated by an η ′ recoiling against the ( ππ ) S-wave. In addition, α 2 (1320) → η′π 0 is needed. There is evidence for contributions from α 0 (1450) → η′π 0 . The branching ratio of α 0 (1450) → η′π 0 with respect to ηπ 0 is consistent with the prediction of SU(3).
No description provided.
First results are reported on J ψ and Drell-Yan cross-sections in PbPb reactions at 158 GeV/ c per nucleon. The ratio of cross-sections σ J/ψ /σ DY is studied as a function of the impact parameter of the collision estimated from the measured transverse energy.
No description provided.
No description provided.
The Drell-Yan cross sections are taken in the mass interval 2.9 to 4.5 GeV. SIG/SIG ratio are free from most systematic errors.
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