We have measured the dijet angular distribution in $\sqrt{s}$=1.8 TeV $p\bar{p}$ collisions using the D0 detector. Order $\alpha^{3}_{s}$ QCD predictions are in good agreement with the data. At 95% confidence the data exclude models of quark compositeness in which the contact interaction scale is below 2 TeV.
No description provided.
A sample of Lambda's produced in 2 A*GeV Ni + Cu collisions has been obtained with the EOS Time Projection Chamber at the Bevalac. Low background in the invariant mass distribution allows for the unambiguous demonstration of Lambda directed flow. The transverse mass spectrum at mid-rapidity has the characteristic shoulder-arm shape of particles undergoing radial transverse expansion. A linear dependence of Lambda multiplicity on impact parameter is observed, from which a total Lambda + Sigma^0 production cross section of $112 +/- 24 mb is deduced. Detailed comparisons with the ARC and RVUU models are made.
No description provided.
A small electromagnetic sampling calorimeter, installed in the ZEUS experiment in 1995, significantly enhanced the acceptance for very low x and low Q^2 inelastic neutral current scattering, e^{+}p \to e^{+}X, at HERA. A measurement of the proton structure function F_2 and the total virtual photon-proton (\gamma^*p) cross-section is presented for 0.11 \le Q^{2} \le 0.65 GeV^2 and 2 \times 10^{-6} \le x \le 6 \times 10^{-5}, corresponding to a range in the \gamma^{*}p c.m. energy of 100 \le W \le 230 GeV. Comparisons with various models are also presented.
Measured F2 values with the assumption FL=0. The second systematic error isthe change in F2 assuming a value for FL given by VDM.
Measured F2 values with the assumption FL=0. The second systematic error isthe change in F2 assuming a value for FL given by VDM.
Measured F2 values with the assumption FL=0. The second systematic error isthe change in F2 assuming a value for FL given by VDM.
Deep inelastic electron-photon scattering is studied using e+e- data collected by the OPAL detector at centre-of-mass energies sqrt{s_ee} ~ M_{Z^0}. The photon structure function F_2^gamma(x,Q^2) is explored in a Q^2 range of 1.1 to 6.6 GeV/c^2 at lower x values than ever before. To probe this kinematic region events are selected with a beam electron scattered into one of the OPAL luminosity calorimeters at scattering angles between 27 and 55 mrad. A measurement is presented of the photon structure function F_2^gamma(x,Q^2) at
Measurement of the hadron photon structure function. Systematic errors do not contain any effects caused by the four momentum of the quasi-real photon being non zero.
Measurement of the hadron photon structure function. Systematic errors do not contain any effects caused by the four momentum of the quasi-real photon being non zero.
Using the CLEO~II detector, we have measured the differential cross sections for exclusive two-photon production of light pseudoscalar mesons $\pi^0$, $\eta$, and $\eta^{\prime}$. From our measurements we have obtained the form factors associated with the electromagnetic transitions $\gamma^*\gamma$ $\to$ meson. We have measured these form factors in the momentum transfer ranges from 1.5 to 9, 20, and 30 GeV$^2$ for $\pi^0$, $\eta$, and $\eta^{\prime}$, respectively, and have made comparisons to various theoretical predictions.
The results of PI0 --> GAMMA GAMMA analysis assuming Br(PI0-->2GAMMA)=0.99.
The results of ETA --> GAMMA GAMMA analysis assuming Br(ETA-->2GAMMA)=0.39.
The results of ETA --> 3PI0 analysis assuming Br(ETA-->3PI0)*Br(PI0-->2GAM MA)**3 = 0.31.
K+ production far below the free nucleon-nucleon threshold has been investigated in collisions of 36Ar on 12C, natTi, and 181Ta targets at an incident energy of 92 MeV per nucleon. The cross sections for K+ production have been inferred from the observed muon decays of positive kaons. The results are discussed in the framework of a participant-spectator model and are compared to proton induced K+ production and to subthreshold pion production experiments.
Three different production modes are assumed: (C=ISOTROPIC) isotropic emmision inthe lab frame with a kinetic energy EKIN(K) = 35 MeV, (C=SPECTRUM) isotropic emmision inthe lab frame with a kinetic energy spectrum from S. Gosh, PR C45,R518, (C=FIREBALL) isotropic emmision in the fireball frame with a kinetic ener gy EKIN(K) = 35 MeV.
Using the CLEO detector at the Cornell Electron Storage Ring, we have made a measurement of R=sigma(e+e- ->hadrons)/sigma(e+e- ->mu+mu-) =3.56+/-0.01+/-0.07 at ECM=10.52 GeV. This implies a value for the strong coupling constant of alpha_s(10.52 GeV)=0.20+/-0.01+/-0.06, or alpha_s(M_Z)=0.13+/-0.005+/-0.03.
Corrected for background and radiactive effects.
Value of ALPHAS, the strong coupling constant, from the measurement of R. CT,= ALPHAS also given evolved to the Z0 mass.
A search for single and multi-photon events with missing energy is performed using data collected at centre-of-mass energies between 161 GeV and 172 GeV for a total of 20.9 pb −1 of integrated luminosity. The results obtained are used to derive the value for the ν ν γ(γ) cross section as well as upper limits on new physics processes.
SIG(C=TOTAL) means the total cross section deduced from measured one.
Production of events with hadronic and leptonic final states has been measured in e^+e^- collisions at centre-of-mass energies of 130-172 GeV, using the OPAL detector at LEP. Cross-sections and leptonic forward-backward asymmetries are presented, both including and excluding the dominant production of radiative Z \gamma events, and compared to Standard Model expectations. The ratio R_b of the cross-section for bb(bar) production to the hadronic cross-section has been measured. In a model-independent fit to the Z lineshape, the data have been used to obtain an improved precision on the measurement of \gamma-Z interference. The energy dependence of \alpha_em has been investigated. The measurements have also been used to obtain limits on extensions of the Standard Model described by effective four-fermion contact interactions, to search for t-channel contributions from new massive particles and to place limits on chargino pair production with subsequent decay of the chargino into a light gluino and a quark pair.
SIG(C=MEAS) and SIG(C=CORR) stand for measured values without (C=MEAS) and with (C=CORR) correction for interference between initial- and final-state radiation.
The angular distribution of the thrust axis. Errors include statistical and systematic effects combined, with the former dominant.
The measured values include the effect of interference between initial- andfinal-state radiation.
Results are presented of an analysis of the reactions pp -> pf(k0k+pi-)ps and pp -> pf(K0K0pi0)ps at 450 GeV/c. Clear f1(1285) and f1(1420) signals are seen and a spin parity analysis shows that both have IG JPC=0+ 1++. The f1(1285) decays to a0(980)pi and the f1(1420) decays to K* Kbar. Both states have a similar dependence as a function of dPT consistent with what has been observed for other qqbar states. Evidence is also presented for a K*Kbar decay mode of the eta2(1620).
SIG(C=TOT) denotes the total cross section for each resonance.
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