7 research outputs found
Measurement of D* Meson Cross Sections at HERA and Determination of the Gluon Density in the Proton using NLO QCD
With the H1 detector at the ep collider HERA, D* meson production cross
sections have been measured in deep inelastic scattering with four-momentum
transfers Q^2>2 GeV2 and in photoproduction at energies around W(gamma p)~ 88
GeV and 194 GeV. Next-to-Leading Order QCD calculations are found to describe
the differential cross sections within theoretical and experimental
uncertainties. Using these calculations, the NLO gluon momentum distribution in
the proton, x_g g(x_g), has been extracted in the momentum fraction range
7.5x10^{-4}< x_g <4x10^{-2} at average scales mu^2 =25 to 50 GeV2. The gluon
momentum fraction x_g has been obtained from the measured kinematics of the
scattered electron and the D* meson in the final state. The results compare
well with the gluon distribution obtained from the analysis of scaling
violations of the proton structure function F_2.Comment: 27 pages, 9 figures, 2 tables, submitted to Nucl. Phys.
Measurement of open beauty production at HERA
The first observation of open b production in ep collisions is reported. An
event sample containing muons and jets has been selected which is enriched in
semileptonic b quark decays. The visible cross section \sigma(ep -> b \bar{b}X
-> \mu X') for Q^2 < 1 GeV^2, 0.1 < y < 0.8 is measured to be
0.176+-0.016(stat.)+0.026-0.017(syst.) nb for the muons to be detected in the
range 35 deg 2.0 GeV in the laboratory
frame. The expected visible cross section based on a NLO QCD calculation is
0.104+-0.017 nb. The cross sections for electroproduction with Q^2<1 GeV^2 and
photoproduction are derived from the data and found to be \sigma(ep-> e
b\bar{b}X) = 7.1+-0.6(stat.)+1.5-1.3(syst.) nb and \sigma(\gamma p-> b\bar{b}
X) = 111+-10(stat.)+23-20(syst.) at an average \sim 180 GeV,
respectively.Comment: 11 pages, 4 figures, 0 tables, submitted to Physics Letters
Measurement of dijet cross-sections in photoproduction and photon structure
The production of hard di-jet events in photoproduction at HERA is dominated
by resolved photon processes in which a parton in the photon with momentum
fraction x_gamma is scattered from a parton in the proton. These processes are
sensitive to the quark and gluon content of the photon. The differential di-jet
cross-section dsigma/dlog(x_gamma) is presented here, measured in tagged
photoproduction at HERA using data taken with the H1 detector, corresponding to
an integrated luminosity of 7.2 pb^(-1). Using a restricted data sample at high
transverse jet energy, E_(T,jet)>6 GeV, the effective parton density
f_gamma,eff(x_gamma) = [q(x_gamma) + bar(q)(x_gamma) +9/4g(x_gamma)] in the
photon in leading order QCD is measured down to x_gamma=0.05 from which the
gluon density in the photon is derived.Comment: 19 pages, 5 figures and 2 table
Measurement of internal jet structure in dijet production in deep inelastic scattering at HERA
Internal jet structure in dijet production in deep-inelastic scattering is
measured with the H1 detector at HERA. Jets with transverse energies ET,Breit >
5 GeV are selected in the Breit frame employing k_perp and cone jet algorithms.
In the kinematic region of squared momentum transfers 10 < Q2 <~ 120 GeV2 and
x-Bjorken values 2.10^-4 <~ xBj <~ 8.10^-3, jet shapes and subjet
multiplicities are measured as a function of a resolution parameter.
Distributions of both observables are corrected for detector effects and
presented as functions of the transverse jet energy and jet pseudo-rapidity.
Dependences of the jet shape and the average number of subjets on the
transverse energy and the pseudo-rapidity of the jet are observed. With
increasing transverse jet energies and decreasing pseudo-rapidities,
i.e.towards the photon hemisphere, the jets are more collimated. QCD models
give a fair description of the data.Comment: 18 pages, 6 figures, submitted to Nucl. Phys.
Search for compositeness, leptoquarks and large extra dimensions in e q contact interactions at HERA
The reaction e+p --> e+X is studied with the H1 detector at Hera. The data
cover momentum transfers Q^2 between 200 GeV^2 and 30,000 GeV^2 and correspond
to an integrated luminosity of 35.6 pb^(-1). The differential cross section
dsigma/dQ^2 is compared to the Standard Model expectation for neutral current
scattering and analysed to search for bar(e)e bar(q)q contact interactions. No
evidence for new phenomena is observed. The results are used to set limits on
scales within models of electron--quark compositeness, quark form factors and
the exchange of virtual heavy leptoquarks. A search for gravitational effects
mediated through the exchange of virtual gravitons which propagate into large
extra dimensions is presented.Comment: 21 pages, 6 figures, 2 tables, Update to reference
Photoproduction with a leading proton at HERA
The total cross section for the photoproduction process with a leading proton in the final state has been measured at γp centre-of-mass energies W of 91, 181 and 231GeV. The measured cross sections apply to the kinematic range with the transverse momentum of the scattered proton restricted to pT≤0.2GeV and 0.68≤z≤0.88, where z=Ep′/Ep is the scattered proton energy normalised to the beam energy. The cross section dσγp→Xp′(W,z)/dz is observed to be independent of W and z within the measurement errors and amounts to (8.05±0.06(stat)±0.89(syst)) μb on average. The data are well described by a Triple Regge model in which the process is mediated by a mixture of exchanges with an effective Regge trajectory of intercept αi(0)=0.33±0.04(stat)±0.04(syst). The total cross section for the interaction of the photon with this mixture (γαi→X) can be described by an effective trajectory of intercept αk(0)=0.99±0.01(stat)±0.05(syst). Predictions based on previous triple Regge analyses of pp→pX data assuming vertex factorisation are broadly consistent with the γp data. The measured cross sections are compared with deep inelastic scattering leading proton data in the same region of z and pT for photon virtuality Q2 > 2.5GeV2. The ratio of the cross section for leading proton production to the total cross section is found to rise with Q2. © 2001 Elsevier Science B.V.0H1 Collaboration.info:eu-repo/semantics/publishe
Three Jet production in deep inelastic scattering at HERA
Three-jet production is studied for the first time in deep-inelastic
positron-proton scattering. The measurement carried out with the H1 detector at
HERA covers a large range of four-momentum transfer squared 5 < Q^2 < 5000
GeV^2 and invariant three-jet masses 25 < M_(3jet) < 140 GeV. Jets are defined
by the inclusive k_T algorithm in the Breit frame. The size of the three-jet
cross section and the ratio of the three-jet to the dijet cross section R_(3/2)
are described over the whole phase space by the predictions of perturbative QCD
in next-to-leading order. The shapes of angular jet distributions deviate
significantly from a uniform population of the available phase space but are
well described by the QCD calculation.Comment: 17 pages, 5 figures, 1 tabl