We present a search for electroweak production of single top quarks in $\approx 90$ $pb^{-1}$ of data collected with the DZero detector at the Fermilab Tevatron collider. Using arrays of neural networks to separate signals from backgrounds, we set upper limits on the cross sections of 17 pb for the s-channel process $p\bar{p} \to tb + X$, and 22 pb for the t-channel process $p\bar{p} \to tqb + X$, both at the 95% confidence level.
No description provided.
The magnitude of the CKM matrix element Vub is determined by measuring the inclusive charmless semileptonic branching fraction of beauty hadrons at OPAL based on b -> Xu l nu event topology and kinematics. This analysis uses OPAL data collected between 1991 and 1995, which correspond to about four million hadronic Z decays. We measure Br(b -> Xu l) to be (1.63 +/- 0.53 +0.55/-0.62) x 10^(-3). The first uncertainty is the statistical error and the second is the systematic error. From this analysis, Vub is determined to be: |Vub| = (4.00 +/- 0.65(stat) +0.67/-0.76(sys) +/- 0.19(HQE)) x 10^(-3). The last error represents the theoretical uncertainties related to the extraction of |Vub| from Br(b -> Xu l) using the Heavy Quark Expansion.
CKM is Cabibbo-Kobayashi-Maskawa (CKM) matrix element. The last DSYS error comes from the theoretical uncertainty.
The inclusive cross section for production of isolated photons has been measured in \pbarp collisions at $\sqrt{s} = 630$ GeV with the \D0 detector at the Fermilab Tevatron Collider. The photons span a transverse energy ($E_T$) range from 7-49 GeV and have pseudorapidity $|\eta| < 2.5$. This measurement is combined with to previous \D0 result at $\sqrt{s} = 1800$ GeV to form a ratio of the cross sections. Comparison of next-to-leading order QCD with the measured cross section at 630 GeV and ratio of cross sections show satisfactory agreement in most of the $E_T$ range.
No description provided.
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The minimum bias multiplicity distribution and the transverse momentum and pseudorapidity distributions for central collisions have been measured for negative hadrons (h-) in Au+Au interactions at sqrt(s_nn) = 130 GeV. The multiplicity density at midrapidity for the 5% most central interactions is dNh-/deta|_{eta = 0} = 280 +- 1(stat)+- 20(syst), an increase per participant of 38% relative to ppbar collisions at the same energy. The mean transverse momentum is 0.508 +- 0.012 GeV/c and is larger than in central Pb+Pb collisions at lower energies. The scaling of the h- yield per participant is a strong function of pt. The pseudorapidity distribution is almost constant within |eta|<1.
Normalized multiplicity distribution of $h^{−}$ with $p_{T} > 100$ MeV/$c$ at $|\eta| < 0.5$ in Au+Au collisions at $\sqrt{s_{NN}} = 130$ GeV. Systematic error on the vertical scale is estimated to be $10\%$. The systematic error on the horizontal scale is $6\%$ for the entire range of multiplicity. The shaded area is $5\%$ most central collisions, selected by ZDC coincidence. The solid curve is the prediction from the HIJING model.
$h^{−}$ $p_{T}$-spectra for the $5\%$ most central Au+Au collisions at midrapidity ($|\eta| < 0.1$) for several systems. The correlated systematical error is estimated to be below $6\%$. The curves are power-law fits to the data.
ratio of STAR and scaled UA1 $p_{T}$-distributions. The errors given are the errors of the STAR data only and do not include the systematic errors from the scaling of the UA1 data to $130$ GeV (i.e., the shaded region in Fig.2 lower panel). The STAR data is for the $5\%$ most central collisions.
K+ meson production in pA (A = C, Cu, Au) collisions has been studied using the ANKE spectrometer at an internal target position of the COSY-Juelich accelerator. The complete momentum spectrum of kaons emitted at forward angles, theta < 12 degrees, has been measured for a beam energy of T(p)=1.0 GeV, far below the free NN threshold of 1.58 GeV. The spectrum does not follow a thermal distribution at low kaon momenta and the larger momenta reflect a high degree of collectivity in the target nucleus.
Double differential K+ production cross section for forward K+ angles < 12 degs. Statistical errors only.
The invariant cross section for K+ production. Statistical errors only.
Ratio of K+ production cross sections for CU/C and AU/C.
The cross section and the proton structure function F2 for neutral current deep inelastic e+p scattering have been measured with the ZEUS detector at HERA using an integrated luminosity of 30 pb-1. The data were collected in 1996 and 1997 at a centre-of-mass energy of 300 GeV. They cover the kinematic range 2.7 < Q^2 < 30000 GeV2 and 6.10^-5 < x < 0.65. The variation of F2 with x and Q2 is well described by next-to-leading-order perturbative QCD as implemented in the DGLAP evolution equations.
The electromagnetic structure function, F2(C=EM), in NC DIS scattering at Q**2 from 2.7 to 30000 GeV**2.
The corrections to the structure function, F2(C=EM), in NC DIS scattering at Q**2 from 2.7 to 30000 GeV**2.
The relative uncertainties in the reduced cross section. See text of paper for more details. There is an additional 2 PCT overall normalization error not included, andan addtional uncertainty of 1 PCT at low Q**2.. DUNC - Uncorrelated systematic error. Correlated Systematic Errors:. D1 - positron finding and efficiency. D2 - positron scattering angle - A. D3 - positron scattering angle - B. D4 - positron energy scale. D5 - hadronic energy measurment - FCAL. D6 - hadronic energy measurment - BCAL. D7 - hadronic energy measurment - RCAL. D8 - hadronic energy flow - A. D9 - background subtractions. D10 - hadronic energy flow - B.
We present the first measurement of the form factor ratios g1/f1 (direct axial-vector to vector), g2/f1 (second class current) and f2/f1 (weak magnetism) for the decay Xi0 -> Sigma+ e- anti-nu/e using the KTeV (E799) beam line and detector at Fermilab. From the Sigma+ polarization measured with the decay Sigma+ -> p pi0 and the e- - anti-nu/e correlation, we measure g1/f1 to be 1.32 +0.21-0.17(stat.) +/- 0.05(syst.), assuming the SU(3)f (flavor) values for g2/f1 and f2/f1. Our results are all consistent with exact SU(3)f symmetry.
Vector(F1) to axial(G1) formfactor ratio. Total systematic error is 0.054.
A direct measurement of the helicity dependence of the total photoabsorption cross section on the proton was carried out at MAMI (Mainz) in the energy range 200 < E_gamma < 800 MeV. The experiment used a 4$\pi$ detection system, a circularly polarized tagged photon beam and a frozen spin target. The contributions to the Gerasimov-Drell-Hearn sum rule and to the forward spin polarizability $\gamma_0$ determined from the data are 226 \pm 5 (stat)\pm 12(sys) \mu b and -187 \pm 8 (stat)\pm 10(sys)10^{-6} fm^4, respectively, for 200 < E_\gamma < 800 MeV.
Two absorption cross sections, SIG(C=3/2) and SIG(C=1/2), are determined bytwo relative spin configurations, namely parallel and antiparallel. N=RE.
Charged Current reactions of $\nu_e$ on $^{12}C$ have been studied using a $\mu^+$ decay-at-rest $\nu_e$ beam at the Los Alamos Neutron Science Center. The cross section for the exclusive reaction $^{12}C(\nu_e,e^-)^{12}N_{g.s.}$ was measured to be $(8.9\pm0.3\pm0.9)\times10^{-42}$ cm$^2$. The observed energy dependence of the cross section and angular distribution of the outgoing electron agree well with theoretical expectations. Measurements are also presented for inclusive transitions to $^{12}N$ excited states, $^{12}C(\nu_e,e^-)^{12}N^*$ and compared with theoretical expectations. The measured cross section, $(4.3\pm0.4\pm0.6)\times10^{-42}$ cm$^2$, is somewhat lower than previous measurements and than a continuum random phase approximation calculation. It is in better agreement with a recent shell model calculation.
No description provided.
We present results from a measurement of double diffraction dissociation in $\bar pp$ collisions at the Fermilab Tevatron collider. The production cross section for events with a central pseudorapidity gap of width $\Delta\eta^0>3$ (overlapping $\eta=0$) is found to be $4.43\pm 0.02{(stat)}{\pm 1.18}{(syst) mb}$ [$3.42\pm 0.01{(stat)}{\pm 1.09}{(syst) mb}$] at $\sqrt{s}=1800$ [630] GeV. Our results are compared with previous measurements and with predictions based on Regge theory and factorization.
Cross sections for double diffractive production.
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