共查询到20条相似文献,搜索用时 62 毫秒
1.
《The European Physical Journal C - Particles and Fields》2007,51(3):549-568
Measurements are presented of differential dijet cross sections in diffractive photoproduction (Q2<0.01 GeV2) and deep-inelastic scattering processes (DIS, 4<Q2<80 GeV2). The event topology is given by ep→eXY, in which the system X, containing at least two jets, is separated from a leading
low-mass baryonic system Y by a large rapidity gap. The dijet cross sections are compared with NLO QCD predictions based on
diffractive parton densities previously obtained from a QCD analysis of inclusive diffractive DIS cross sections by H1. In
DIS, the dijet data are well described, supporting the validity of QCD factorisation. The diffractive DIS dijet data are more
sensitive to the diffractive gluon density at high fractional parton momentum than the measurements of inclusive diffractive
DIS. In photoproduction, the predicted dijet cross section has to be multiplied by a factor of approximately 0.5 for both
direct and resolved photon interactions to describe the measurements. The ratio of measured dijet cross section to NLO prediction
in photoproduction is a factor 0.5±0.1 smaller than the same ratio in DIS. This suppression is the first clear observation
of QCD hard scattering factorisation breaking at HERA. The measurements are also compared to the two soft colour neutralisation
models SCI and GAL. The SCI model describes diffractive dijet production in DIS but not in photoproduction. The GAL model
fails in both kinematic regions. 相似文献
2.
《Nuclear Physics B》2004,700(1-3):3-50
Jet substructure and differential cross sections for jets produced in the photoproduction and deep inelastic ep scattering regimes have been measured with the ZEUS detector at HERA using an integrated luminosity of 82.2 pb−1. The substructure of jets has been studied in terms of the jet shape and subjet multiplicity for jets with transverse energies . The data are well described by the QCD calculations. The jet shape and subjet multiplicity are used to tag gluon- and quark-initiated jets. Jet cross sections as functions of , jet pseudorapidity, the jet–jet scattering angle, dijet invariant mass and the fraction of the photon energy carried by the dijet system are presented for gluon- and quark-tagged jets. The data exhibit the behaviour expected from the underlying parton dynamics. A value of αs(MZ) of was extracted from the measurements of jet shapes in deep inelastic scattering. 相似文献
3.
《The European Physical Journal C - Particles and Fields》2007,52(4):813-832
The production of dijets in diffractive deep inelastic scattering has been measured with the ZEUS detector at HERA using an
integrated luminosity of 61 pb-1. The dijet cross section has been measured for virtualities of the exchanged virtual photon, 5 < Q2 < 100 GeV2, and γ*p centre-of-mass energies, 100 < W < 250 GeV. The jets, identified using the inclusive kT algorithm in the γ*p frame, were required to have a transverse energy E*
T,jet > 4 GeV and the jet with the highest transverse energy was required to have E*
T,jet > 5 GeV. All jets were required to be in the pseudorapidity range -3.5<η*
jet<0. The differential cross sections are compared to leading-order predictions and next-to-leading-order QCD calculations based
on recent diffractive parton densities extracted from inclusive diffractive deep inelastic scattering data. 相似文献
4.
J. Breitweg et al. 《The European Physical Journal C - Particles and Fields》2001,18(4):625-637
The production and semi-leptonic decay of heavy quarks have been studied in the photoproduction process with the ZEUS detector at HERA using an integrated luminosity of 38.5 pb. Events with photon-proton centre-of-mass energies, , between 134 and 269 GeV and a photon virtuality, , less than 1 GeV were selected requiring at least two jets of transverse energy GeV and an electron in the final state. The electrons were identified by employing the ionisation energy loss measurement.
The contribution of beauty quarks was determined using the transverse momentum of the electron relative to the axis of the
closest jet, . The data, after background subtraction, were fit with a Monte Carlo simulation including beauty and charm decays. The measured
beauty cross section was extrapolated to the parton level with the b quark restricted to the region of transverse momentum 5 GeV and pseudorapidity 2. The extrapolated cross section is . The result is compared to a perturbative QCD calculation performed to next-to-leading order.
Received: 22 November 2000 / Published online: 5 February 2001 相似文献
5.
M. Klasen G. Kramer B. Pötter 《The European Physical Journal C - Particles and Fields》1998,1(1-2):261-270
We present a next-to-leading order calculation for the virtual photoproduction of one and two jets inep collisions. Soft and collinear singularities are extracted using the phase space slicing method. The collinear photon initial state singularity depends logarithmically on the mass of the virtual photon and is absorbed into the virtual photon structure function. An $\overline {MS} $ factorization scheme is defined similarly to the real photon case. Numerical results are presented for HERA conditions using the Snowmass jet definition for inclusive single jet and dijet cross sections. We study the dependence of these cross sections on the transverse energies and rapidities of the jets. Finally, we compare the ratio of the experimentally defined resolved and direct cross sections with recent ZEUS data as a function of the photon virtualityP 2. 相似文献
6.
《The European Physical Journal C - Particles and Fields》2007,49(2):511-522
The photoproduction of prompt photons, together with an accompanying jet, has been studied in ep collisions at a centre-of-mass
energy of 318 GeV with the ZEUS detector at HERA using an integrated luminosity of 77 pb-1. Cross sections were measured for the transverse energy of the photon and the jet larger than 5 and 6 GeV, respectively.
The differential γ+jet cross sections were reconstructed as functions of the transverse energy, pseudorapidity and xγ
obs, the fraction of the incoming photon momentum taken by the photon-jet system. Predictions based on leading-logarithm parton-shower
Monte Carlo models and next-to-leading-order (NLO) QCD generally underestimate the cross sections for the transverse energies
of prompt photons below 7 GeV, while the kT-factorisation QCD calculation agrees with the data better. When the minimum transverse energy of prompt photons is increased
to 7 GeV, both NLO QCD and the kT-factorisation calculations are in good agreement with the data. 相似文献
7.
Inclusive photoproduction of mesons has been measured for photon-proton centre-of-mass energies in the range GeV and photon virtuality 1 GeV. The data sample used corresponds to an integrated luminosity of 37 pb. Total and differential cross sections as functions of the transverse momentum and pseudorapidity are presented in restricted kinematical regions and the data are compared with next-to-leading
order (NLO) perturbative QCD calculations using the “massive charm” and “massless charm” schemes. The measured cross sections
are generally above the NLO calculations, in particular in the forward (proton) direction. The large data sample also allows
the study of dijet production associated with charm. A significant resolved as well as a direct photon component contribute
to the cross section. Leading order QCD Monte Carlo calculations indicate that the resolved contribution arises from a significant
charm component in the photon. A massive charm NLO parton level calculation yields lower cross sections compared to the measured
results in a kinematic region where the resolved photon contribution is significant.
Received: 9 July 1998 / Published online: 22 October 1998 相似文献
8.
《The European Physical Journal C - Particles and Fields》2007,50(2):251-267
Differential photoproduction cross sections are measured for events containing D*± mesons. The data were taken with the H1 detector at the ep collider HERA and correspond to an integrated luminosity of 51.1 pb-1. The kinematic region covers small photon virtualities Q2 < 0.01 GeV2 and photon–proton centre-of-mass energies of 171 < Wγ p < 256 GeV. The details of the heavy quark production process are further investigated in events with one or two jets in addition
to the D*± meson. Differential cross sections for D*+jet production are determined and the correlations between the D*± meson and the jet(s) are studied. The results are compared with perturbative QCD predictions applying collinear- or kt-factorisation. 相似文献
9.
《Physics letters. [Part B]》1999,459(4):644-648
We study the properties of dijet production in deep inelastic scattering using a unified BFKL/DGLAP framework, which includes important subleading ln(1/x) contributions. We calculate the azimuthal decorrelation between the jets. We compute the cross section for dijet production as a function of Q2 and the jet transverse momentum, as well as calculate the total dijet rate. We compare the predictions with HERA data. 相似文献
10.
The cross section for dijet photoproduction at high transverse energies is presented as a function of the transverse energies
and the pseudorapidities of the jets. The measurement is performed using a sample of ep-interactions corresponding to an integrated luminosity of 6.3 pb, recorded by the ZEUS detector. Jets are defined by applying a -clustering algorithm to the hadrons observed in the final state. The measured cross sections are compared to next-to-leading
order QCD calculations. In a kinematic regime where theoretical uncertainties are expected to be small, the measured cross
sections are higher than these calculations.
Received: 18 May 1999 / Published online: 14 October 1999 相似文献
11.
《The European Physical Journal C - Particles and Fields》2008,58(4):531-541
The production of two high-p
T
jets in the interactions of quasi-real photons in e
+
e
− collisions at
from 189 GeV to 209 GeV is studied with data corresponding to an integrated e
+
e
− luminosity of 550 pb−1. The jets reconstructed by the k
⊥
-cluster algorithm are defined within the pseudo-rapidity range −1<η<1 and with jet transverse momentum, p
T
, above 3 GeV/c. The differential di-jet cross-section is measured as a function of the mean transverse momentum
of the jets and is compared to perturbative QCD calculations.
Deceased 相似文献
12.
《The European Physical Journal C - Particles and Fields》2008,55(2):177-191
Diffractive photoproduction of dijets was measured with the ZEUS detector at the ep collider HERA using an integrated luminosity
of 77.2 pb-1. The measurements were made in the kinematic range Q2 < 1 GeV2, 0.20<y<0.85 and xIP<0.025, where Q2 is the photon virtuality, y is the inelasticity and xIP is the fraction of the proton momentum taken by the diffractive exchange. The two jets with the highest transverse energy,
ET
jet, were required to satisfy ET
jet>7.5 and 6.5 GeV, respectively, and to lie in the pseudorapidity range -1.5<ηjet<1.5. Differential cross sections were compared to perturbative QCD calculations using available parameterisations of diffractive
parton distributions of the proton. 相似文献
13.
《The European Physical Journal C - Particles and Fields》2008,54(3):371-387
The production of isolated photons in deep-inelastic scattering ep→eγX is measured with the H1 detector at HERA. The measurement
is performed in the kinematic range of negative four-momentum transfer squared 4<Q2<150 GeV2 and a mass of the hadronic system WX>50 GeV. The analysis is based on a total integrated luminosity of 227 pb-1. The production cross section of isolated photons with a transverse energy in the range 3<ET
γ<10 GeV and pseudorapidity range -1.2<ηγ<1.8 is measured as a function of ET
γ, ηγ and Q2. Isolated photon cross sections are also measured for events with no jets or at least one hadronic jet. The measurements
are compared with predictions from Monte Carlo generators modelling the photon radiation from the quark and the electron lines,
as well as with calculations at leading and next to leading order in the strong coupling. The predictions significantly underestimate
the measured cross sections. 相似文献
14.
《The European Physical Journal C - Particles and Fields》2007,49(2):395-410
Measurements of inclusive production of the Λ, Ξ- and Ξ*(1530) baryons in two-photon collisions with the L3 detector at LEP are presented. The inclusive differential cross sections
for Λ and Ξ- are measured as a function of the baryon transverse momentum, pt, and pseudo-rapidity, η. The mean number of Λ, Ξ- and Ξ*(1530) baryons per hadronic two-photon event is determined in the kinematic range 0.4 GeV<pt<2.5 GeV, |η|<1.2. Overall agreement with the theoretical models and Monte Carlo predictions is observed. A search for inclusive
production of the pentaquark θ+(1540) in two-photon collisions through the decay θ+→pK0
S is also presented. No evidence for production of this state is found. 相似文献
15.
The production of forward jets has been measured in deep inelastic ep collisions at HERA. The results are presented in terms of single differential cross sections as a function of the Bjorken
scaling variable (xBj) and as triple differential cross sections d3σ/dxBjdQ2
, where Q2 is the four momentum transfer squared and
is the squared transverse momentum of the forward jet. Also cross sections for events with a di-jet system in addition to
the forward jet are measured as a function of the rapidity separation between the forward jet and the two additional jets.
The measurements are compared with next-to-leading order QCD calculations and with the predictions of various QCD-based models. 相似文献
16.
《The European Physical Journal C - Particles and Fields》2007,51(2):301-315
Diffractive photoproduction of D*±(2010) mesons was measured with the ZEUS detector at the ep collider HERA, using an integrated luminosity of 78.6 pb-1. The D* mesons were reconstructed in the kinematic range: transverse momentum pT(D*) > 1.9 GeV and pseudorapidity |η(D*)|<1.6, using the decay D*+→D0π+
s followed by D0→K-π+(+c.c.). Diffractive events were identified by a large gap in pseudorapidity between the produced hadronic state and the outgoing
proton. Cross sections are reported for photon–proton centre-of-mass energies in the range 130 < W < 300 GeV and for photon
virtualities Q2 < 1 GeV2, in two ranges of the Pomeron fractional momentum xIP<0.035 and xIP<0.01. The relative contribution of diffractive events to the inclusive D*±(2010) photoproduction cross section is about 6%. The data are in agreement with perturbative QCD calculations based on various
parameterisations of diffractive parton distribution functions. The results are consistent with diffractive QCD factorisation. 相似文献
17.
The H Collaboration 《The European Physical Journal C - Particles and Fields》2006,46(3):585-603
Cross sections for elastic production of J/ψ mesons in photoproduction and electroproduction are measured in electron proton
collisions at HERA using an integrated luminosity of 55 pb-1. Results are presented for photon virtualities Q2 up to 80 GeV2. The dependence on the photon-proton centre of mass energy Wγp is analysed in the range 40≤Wγp≤305 GeV in photoproduction and 40≤Wγp≤160 GeV in electroproduction. The Wγp dependences of the cross sections do not change significantly with Q2 and can be described by models based on perturbative QCD. Within such models, the data show a high sensitivity to the gluon
density of the proton in the domain of low Bjorken x and low Q2. Differential cross sections dσ/dt, where t is the squared four-momentum transfer at the proton vertex, are measured in the
range |t|<1.2 GeV2 as functions of Wγp and Q2. Effective Pomeron trajectories are determined for photoproduction and electroproduction. The J/ψ production and decay angular
distributions are consistent with s-channel helicity conservation. The ratio of the cross sections for longitudinally and
transversely polarised photons is measured as a function of Q2 and is found to be described by perturbative QCD based models. 相似文献
18.
《The European Physical Journal C - Particles and Fields》2007,51(1):1-23
The production of the neutral strange hadrons K0
S, Λ and Λ̄ has been measured in ep collisions at HERA using the ZEUS detector. Cross sections, baryon-to-meson ratios, relative
yields of strange and charged light hadrons, Λ (Λ̄) asymmetry and polarization have been measured in three kinematic regions:
Q2 > 25 GeV2; 5 < Q2 < 25 GeV2; and in photoproduction (Q2≃0). In photoproduction the presence of two hadronic jets, each with at least 5 GeV transverse energy, was required. The measurements
agree in general with Monte Carlo models and are consistent with measurements made at e+e- colliders, except for an enhancement of baryon relative to meson production in photoproduction. 相似文献
19.
《The European Physical Journal C - Particles and Fields》2007,50(2):283-297
The photoproduction of dijet events, where the two jets with the highest transverse energy are separated by a large gap in
pseudorapidity, have been studied with the ZEUS detector using an integrated luminosity of 39 pb-1. Rapidity-gap events are defined in terms of the energy flow between the jets, such that the total summed transverse energy
in this region is less than some value ET
CUT. The data show a clear excess over the predictions of standard photoproduction models. This is interpreted as evidence for
a strongly interacting exchange of a color-singlet object. Monte Carlo models which include such a color-singlet exchange
are able to describe the data. 相似文献