Cross sections for elastic photoproduction of
J/
ψ and
ϒ mesons are presented. For
J/
ψ mesons the dependence on the photon-proton centre-of-mass energy
W
γp
is analysed in an extended range with ...respect to previous measurements of
26≤W
γp≤285
GeV
. The measured energy dependence is parameterized as
σ
γp
∝
W
γp
δ
with
δ=0.83±0.07. The differential cross section
dσ/
dt for
J/
ψ mesons is derived, its dependence on
W
γp
and on
t is analysed and the effective trajectory (in terms of Regge theory) is determined to be
α(
t)=(1.27±0.05)+(0.08±0.17)·
t/GeV
2. Models based on perturbative QCD and on pomeron exchange are compared to the data.
The inclusive production of D*+/-(2010) mesons in deep-inelastic scattering is studied with the HI detector at HERA. In the kinematic region 1 < Q(2) < 100 GeV2 and 0.05 < y < 0.7 an e(+) p cross ...section for inclusive D*+/- meson production of 8.50 +/- 0.42(stat.)(-100)(+1.21)(syst.) nb is measured in the visible range p(tD*) > 1.5 GeV and eta(D*) < 1.5. Single and double differential inclusive D*+/- meson cross sections are compared to perturbative QCD calculations in two different evolution schemes, The charm contribution to the proton structure, F-c(2)(x, Q(2)), is determined by extrapolating the visible charm cross section to the full phase space. This contribution is found to rise from about 10% at Q(2) = 1.5 GeV2 to more than 25% at Q(2) = 60 GeV2 corresponding to x values ranging from 5 x 10(-5) to 3 x 10(-3). (C) 2002 Elsevier Science B.V. All rights reserved.
A measurement of the derivative (d ln F_2 / d lnx)_(Q^2)= -lambda(x,Q^2) of the proton structure function F_2 is presented in the low x domain of deeply inelastic positron-proton scattering. For ...5*10^(-5)<=x<=0.01 and Q^2>=1.5 GeV^2, lambda(x,Q^2) is found to be independent of x and to increase linearly with ln(Q^2).
The inclusive single and double differential cross-sections for neutral and charged current processes with four-momentum transfer squared \(Q^2\) between 150 and 30 000 GeV\(^2\) and with Bjorken x ...between 0.0032 and 0.65 are measured in \(e^+ p\) collisions. The data were taken with the H1 detector at HERA between 1994 and 1997, and they correspond to an integrated luminosity of \(35.6\,{\rm pb}^{-1}\). The \(Q^2\) evolution of the parton densities of the proton is tested, yielding no significant deviation from the prediction of perturbative QCD. The proton structure function \(F_2(x,Q^2)\) is determined. An extraction of the u and d quark distributions at high x is presented. At high \(Q^2\) electroweak effects of the heavy bosons \(Z^\circ\) and \(W\) are observed and found to be consistent with Standard Model expectation.
The elastic electroproduction of rho mesons is studied at HERA with the H1 detector for a photon virtuality in the range 1 Q^2 60 GeV^2 and for a hadronic centre of mass energy in the range 30 W 140 ...GeV. The shape of the pipi mass distribution in the rho resonance region is measured as a function of Q^2. The full set of rho spin density matrix elements is determined, and evidence is found for a helicity flip amplitude at the level of 8 +- 3 % of the non-flip amplitudes. Measurements are presented of the dependence of the cross section on Q^2, W and t (the four-momentum transfer squared to the proton). They suggest that, especially at large Q^2, the gamma^*p cross section develops a stronger W dependence than that expected from the behaviour of elastic and total hadron-hadron cross sections.
We present measurements of the differential cross section dσ/dργτ for the inclusive production of a photon in association with a b -quark jet for photons with rapidities |yγ| < 1.0 and 30 < ργτ < 300 ...GeV , as well as for photons with 1.5 <|yγ| < 2.5 and 30 < ργτ < 200 GeV, where ργτ is the photon transverse momentum. The b -quark jets are required to have pT > 15 GeV and rapidity |yjet| < 1.5. The results are based on data corresponding to an integrated luminosity of 8.7 fb-1, recorded with the D0 detector at the Fermilab Tevatron $p\bar{p}$ Collider at $\sqrt{s}$ =1.96 TeV. The measured cross sections are compared with next-to-leading order perturbative QCD calculations using different sets of parton distribution functions as well as to predictions based on the kT-factorization QCD approach, and those from the SHERPA and PYTHIA Monte Carlo event generators.
We present new direct constraints on a general Wtb interaction using data corresponding to an integrated luminosity of 5.4 fb-1 collected by the D0 detector at the Tevatron p p macr collider. The ...standard model provides a purely left-handed vector coupling at the Wtb vertex, while the most general, lowest dimension Lagrangian allows right-handed vector and left- or right-handed tensor couplings as well. We obtain precise limits on these anomalous couplings by comparing the data to the expectations from different assumptions on the Wtb coupling.
We present a search for the production of neutral Higgs bosons decaying into tau + tau - pairs in p p macr collisions at a center-of-mass energy of 1.96 TeV. The data, corresponding to an integrated ...luminosity of 5.4 fb-1, were collected by the D0 experiment at the Fermilab Tevatron Collider. We set upper limits at the 95% C.L. on the product of production cross section and branching ratio for a scalar resonance decaying into tau + tau - pairs, and we interpret these limits as limits on the production of Higgs bosons in the minimal supersymmetric standard model (MSSM) and as constraints in the MSSM parameter space.
We measure the correlation between the spin of the top quark and the spin of the anti-top quark in inline imageinline image final states produced in inline imageinline image collisions at a center of ...mass energy inline imageinline image, where l is an electron or muon. The data correspond to an integrated luminosity of 5.4 fb super(-1) and were collected with the D0 detector at the Fermilab Tevatron collider. The correlation is extracted from the angles of the two leptons in the t and inline imageinline image rest frames, yielding a correlation strength inline imageinline image, in agreement with the NLO QCD prediction within two standard deviations, but also in agreement with the no correlation hypothesis.
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