共查询到20条相似文献,搜索用时 15 毫秒
1.
M. Klasen 《The European Physical Journal C - Particles and Fields》1999,7(2):225-232
We calculate three jet cross sections in photoproduction using exact matrix elements for the direct and resolved contributions.
Numerical distributions are presented in a generic, irreducible set of variables that allows to disentangle the dynamics of
partonic QCD subprocesses from each other and from pure phase space distributions. The results are compared to preliminary
data from the ZEUS collaboration at HERA. It is found that the largest contribution comes from photon-gluon fusion in the
mass range 36 GeV 80 GeV. The measured leading jet scattering angle distribution is consistent with the -channel exchange of a massless fermion in scattering, where the third parton is assumed to arise from soft bremsstrahlung. The data are inconsistent with pure phase
space and Rutherford scattering distributions.
Received: 5 August 1998 / Published online: 19 October 1998 相似文献
2.
Inclusive jet differential cross sections for the reaction with quasi-real photons have been measured with the ZEUS detector at HERA. These cross sections are given for the photon-proton
centre-of-mass energy interval 134 277 GeV and jet pseudorapidity in the range in the laboratory frame. The results are presented for three cone radii in the plane, . Measurements of above various jet-transverse-energy thresholds up to 25 GeV and in three ranges of W are presented and compared to next-to-leading order (NLO) QCD calculations. For jets defined with differences between data and NLO calculations are seen at high and low . The measured cross sections for jets defined with are well described by the calculations in the entire measured range of and . The inclusive jet cross section for GeV is consistent with an approximately linear variation with the cone radius R in the range between 0.5 and 1.0, and with NLO calculations.
Received: 11 February 1998 / Published online: 2 July 1998 相似文献
3.
The H Collaboration 《The European Physical Journal C - Particles and Fields》2003,29(4):497-513
Inclusive jet cross sections are measured in photoproduction at HERA using the H1 detector. The data sample of
events in the kinematic range of photon virtualities
and photon-proton centre-of-mass energies
represents an integrated luminosity of
. Jets are defined using the inclusive
algorithm. Single- and multi-differential cross sections are measured as functions of jet transverse energy ET jet and pseudorapidity
in the domain
and
. The cross sections are found to be in good agreement with next-to-leading order perturbative QCD calculations corrected for fragmentation and underlying event effects. The cross section differential in ET jet, which varies by six orders of magnitude over the measured range, is compared with similar distributions from
colliders at equal and higher energies.Received: 24 February 2003, Revised: 26 May 2003, Published online: 11 July 2003 相似文献
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6.
The ZEUS Collaboration J. Breitweg et al. 《The European Physical Journal C - Particles and Fields》1998,5(1):41-56
Differential dijet cross sections have been measured with the ZEUS detector for photoproduction events in which the hadronic
final state containing the jets is separated with respect to the outgoing proton direction by a large rapidity gap. The cross
section has been measured as a function of the fraction of the photon () and pomeron () momentum participating in the production of the dijet system. The observed dependence shows evidence for the presence of a resolved- as well as a direct-photon component. The measured cross section
increases as increases indicating that there is a sizeable contribution to dijet production from those events in which a large fraction
of the pomeron momentum participates in the hard scattering. These cross sections and the ZEUS measurements of the diffractive
structure function can be described by calculations based on parton densities in the pomeron which evolve according to the
QCD evolution equations and include a substantial hard momentum component of gluons in the pomeron.
Received: 20 April 1998 / Published online: 2 July 1998 相似文献
7.
J. J. Engelen S. J. de Jong M. Poletiek J. A. M. Vermaseren 《Zeitschrift fur Physik C Particles and Fields》1988,41(1):173-177
We present cross sections for heavy flavour production through photon gluon fusion in electron proton collisions at HERA energy. The electron photon vertex is taken into account explicitly, and theQ 2 of the exchanged photon ranges from nearly zero (almost real photon) to the kinematically allowed maximum. In our approach the scale is set by the mass of the produced quarks. Our formalism is also applicable to the production of light quarks as long as the invariant mass of the pair is sufficiently high, so we also give cross sections for \(u\bar u,d\bar d\) and \(s\bar s\) production. 相似文献
8.
The H Collaboration C.?Adloff et al. 《The European Physical Journal C - Particles and Fields》2002,25(1):13-23
Dijet cross sections as functions of several jet observables are measured in photoproduction using the H1 detector at HERA.
The data sample comprises data with an integrated luminosity of 34.9 pb. Jets are selected using the inclusive algorithm with a minimum transverse energy of 25 GeV for the leading jet. The phase space covers longitudinal proton momentum
fraction and photon longitudinal momentum fraction in the ranges and . The predictions of next-to-leading order perturbative QCD, including recent photon and proton parton densities, are found
to be compatible with the data in a wide kinematical range.
Received: 4 January 2002 / Published online: 12 July 2002 相似文献
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10.
The H Collaboration 《The European Physical Journal C - Particles and Fields》2005,38(4):437-445
Results are presented on the photoproduction of isolated prompt photons, inclusively and associated with jets, in the
center of mass energy range 142 < W < 266 GeV. The cross sections are measured for the transverse momentum range of the photons
GeV and for associated jets with E
T
jet > 4.5 GeV. They are measured differentially as a function of
, the pseudorapidities
and
and estimators of the momentum fractions
and x
p
of the incident photon and proton carried by the constituents participating in the hard process. In order to further investigate the underlying dynamics, the angular correlation between the prompt photon and the jet in the transverse plane is studied. Predictions by perturbative QCD calculations in next to leading order are about
below the inclusive prompt photon data after corrections for hadronisation and multiple interactions, but are in reasonable agreement with the results for prompt photons associated with jets. Comparisons with the predictions of the event generators PYTHIA and HERWIG are also presented.Received: 13 July 2004, Revised: 15 November 2004, Published online: 17 December 2004 相似文献
11.
The inclusive e+p single and double differential cross sections for neutral and charged current processes are measured with the H1 detector at HERA. The data were taken in 1999 and 2000 at a centre-of-mass energy of
and correspond to an integrated luminosity of 65.2 pb-1. The cross sections are measured in the range of four-momentum transfer squared Q2 between 100 and
and Bjorken x between 0.0013 and 0.65. The neutral current analysis for the new e+p data and the earlier e-p data taken in 1998 and 1999 is extended to small energies of the scattered electron and therefore to higher values of inelasticity y, allowing a determination of the longitudinal structure function FL at high Q2 (
). A new measurement of the structure function
is obtained using
the new e+p and previously published
neutral current cross section data at high Q2. These data together with H1 low Q2 precision data are further used to perform new next-to-leading order QCD analyses in the framework of the Standard Model to extract flavour separated parton distributions in the proton.Arrival of the final proofs: 11 July 2003 相似文献
12.
I. A. Korzhavina 《Physics of Atomic Nuclei》2002,65(2):249-254
The first measurement of the cross sections for D*±-meson diffractive photoproduction was performed with the ZEUS detector at the HERA ep collider by using an integrated luminosity of 38 pb?1. The measurement was performed for photon-proton c.m. energies in the range 130<W<280 GeV and photon virtualities in the region Q 2<1 GeV2. The product D*± mesons were reconstructed for p T D* >2 GeV and ?1.5<η D*<1.5 from the decay channel D*+ → D 0 π s + with D 0 → K ? π + (+ c.c.). The diffractive component was selected for 0.001 <x P<0.018. The measured cross section in this kinematical range is $\sigma _{ep \to e'D^ * X_{p'} }^{diff} = 0.74 \pm 0.21(stat.)_{ - 0.18}^{ + 0.27} (syst.) \pm 0.16(p.diss.)$ nb (ZEUS preliminary). The measured integrated and differential cross sections are compared with theoretical expectations. 相似文献
13.
《Nuclear Physics B》1996,474(1):183-213
We treat hadron-hadron collisions where the final state is kinematically of the kind associated with double-pomeron-exchange (DPE) and has large transverse momentum jets. We show that in addition to the conventional factorized (FDPE) contribution, there is a nonfactorized (NDPE) contribution which has no pomeron beam jet. Within a simple model we compute DPE-two-jet total and differential cross sections at Tevatron energy scales, and show that the NDPE contribution is dominant. 相似文献
14.
H. Holtmann N. N. Nikolaev A. Szczurek J. Speth B. G. Zakharov 《Zeitschrift fur Physik C Particles and Fields》1995,69(1):297-303
The excitation of the proton into undetected multiparticle states (double diffraction dissociation) is an important background
to single diffractive deep-inelastic processesep→e′p′ρ
0,e′p′J/ψ,e′p′X at HERA. We present estimates of the admixture of the double diffraction dissociation events in all diffractive events. We
find that in theJ/ψ photoproduction, electroproduction of theρ
0 at largeQ
2 and diffraction dissociation of real and virtual photons into high mass statesX the contamination of the double diffraction dissociation can be as large as ∼30%, thus affecting substantially the experimental
tests of the pomeron exchange in deep inelastic scattering at HERA. We discuss a possibility of tagging the double diffraction
dissociation by neutrons observed in the forward neutron calorimeter. We present evaluations of the spectra of neutrons and
efficiency of neutron tagging based on the experimental data for diffractive processes in the protonproton collisions. 相似文献
15.
H. Holtmann N. N. Nikolaev A. Szczurek J. Speth B. G. Zakharov 《Zeitschrift fur Physik C Particles and Fields》1996,69(2):297-303
The excitation of the proton into undetected multiparticle states (double diffraction dissociation) is an important background to single diffractive deep-inelastic processes epMe'p'A0,r e'p'J/O,r e'p'X at HERA. We present estimates of the admixture of the double diffraction dissociation events in all diffractive events. We find that in the J/O photoproduction, electroproduction of the A0 at large Q2 and diffraction dissociation of real and virtual photons into high mass states X the contamination of the double diffraction dissociation can be as large as ~30%, thus affecting substantially the experimental tests of the pomeron exchange in deep inelastic scattering at HERA. We discuss a possibility of tagging the double diffraction dissociation by neutrons observed in the forward neutron calorimeter. We present evaluations of the spectra of neutrons and efficiency of neutron tagging based on the experimental data for diffractive processes in the proton-proton collisions. 相似文献
16.
《The European Physical Journal C - Particles and Fields》2007,49(2):523-544
A new method is employed to measure the neutral current cross section up to Bjorken-x values of one with the ZEUS detector
at HERA using an integrated luminosity of 65.1 pb-1 for e+p collisions and 16.7 pb-1 for e-p collisions at and 38.6 pb-1 for e+p collisions at . Cross sections have been extracted for Q2≥648 GeV2 and are compared to predictions using different parton density functions. For the highest x bins, the data have a tendency
to lie above the expectations using recent parton density function parametrizations. 相似文献
17.
We discuss jet reconstruction methods with respect to their suitability forep collisions at HERA and study the expected properties of such jets. The results are based on complete event simulation using current models of jet evolution and hadronization in combination with experimentally tested jet algorithms. The effects of calorimeter resolution are illustrated by explicit simulation of the energy profile and fluctuations in a simplified, but realistic detector. 相似文献
18.
We have calculated inclusive two-jet cross sections in next-to-leading order QCD for low Q 2 ep collisions superimposing direct and resolved contributions. Infrared and collinear singularities in the virtual and real contributions are cancelled with the phase space slicing method. Various inclusive two-jet distributions have been computed. The results are compared with recent data from the ZEUS collaboration at HERA. 相似文献
19.
We have calculated inclusive two-jet cross sections in next-to-leading order QCD for direct photo-production in lowQ 2 ep collisions at HERA. Infrared and collinear singularities in real and virtual contributions are cancelled with the phase space slicing method. Analytical formulas for the different contributions giving the dependence on the slicing parameter are presented. Various one and two-jet distributions have been computed demonstrating the flexibility of the method. 相似文献