The production of isolated high-energy photons accompanied by jets has been measured in deep inelastic ep scattering with the ZEUS detector at HERA, using an integrated luminosity of 326 pb−1. ...Measurements were made for exchanged photon virtualities, Q2, in the range 10 to 350 GeV2. The photons were measured in the transverse-energy and pseudorapidity ranges 4<ETγ<15 GeV and −0.7<ηγ<0.9, and the jets were measured in the transverse-energy and pseudorapidity ranges 2.5<ETjet<35 GeV and −1.5<ηjet<1.8. Differential cross sections are presented as functions of these quantities. Perturbative QCD predictions give a reasonable description of the shape of the measured cross sections over most of the kinematic range, but the absolute normalisation is typically in disagreement by 20–30%.
The ZEUS detector has been used to study dissociation of virtual photons in events with a leading proton, \(\gamma^{*} p \to X p\), in e + p collisions at HERA. The data cover photon virtualities in ...two ranges, 0.03 < Q2 < 0.60 GeV2 and 2 < Q2 < 100 GeV2, with MX > 1.5 GeV, where MX is the mass of the hadronic final state, X. Events were required to have a leading proton, detected in the ZEUS leading proton spectrometer, carrying at least 90% of the incoming proton energy. The cross section is presented as a function of t, the squared four-momentum transfer at the proton vertex, \(\Phi\), the azimuthal angle between the positron scattering plane and the proton scattering plane, and Q2. The data are presented in terms of the diffractive structure function, \(F_2^{\smasht{D(3)}}\). A next-to-leading-order QCD fit to the higher-Q2 data set and to previously published diffractive charm production data is presented.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The exclusive photoproduction reaction γp→ϒ(1S)p has been studied with the ZEUS detector in ep collisions at HERA using an integrated luminosity of 468 pb−1. The measurement covers the kinematic ...range 60<W<220 GeV and Q2<1 GeV2, where W is the photon–proton centre-of-mass energy and Q2 is the photon virtuality. The exponential slope, b, of the t dependence of the cross section, where t is the squared four-momentum transfer at the proton vertex, has been measured, yielding b=4.3−1.3+2.0(stat.)−0.6+0.5(syst.) GeV−2. This constitutes the first measurement of the t dependence of the γp→ϒ(1S)p cross section.
Inclusive-jet and dijet differential cross sections have been measured in neutral current deep inelastic
ep scattering for exchanged boson virtualities
Q
2
>
125
GeV
2
with the ZEUS detector at ...HERA using an integrated luminosity of 82 pb
−1. Jets were identified in the Breit frame using the
k
T
cluster algorithm. Jet cross sections are presented as functions of several kinematic and jet variables. The results are also presented in different regions of
Q
2
. Next-to-leading-order QCD calculations describe the measurements well. Regions of phase space where the theoretical uncertainties are small have been identified. Measurements in these regions have the potential to constrain the gluon density in the proton when used as inputs to global fits of the proton parton distribution functions.
The production of beauty quarks in
ep
interactions has been studied with the ZEUS detector at HERA for exchanged four-momentum squared
Q
2
>10 GeV
2
, using an integrated luminosity of 363 pb
−1
. ...The beauty events were identified using electrons from semileptonic
b
decays with a transverse momentum
GeV and pseudorapidity |
η
e
|<1.5. Cross sections for beauty production were measured and compared with next-to-leading-order QCD calculations. The beauty contribution to the proton structure function
F
2
was extracted from the double-differential cross section as a function of Bjorken-
x
and
Q
2
.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A
bstract
The cross sections for inelastic photoproduction of
J/ψ
and
ψ
′ mesons have been measured in
ep
collisions with the ZEUS detector at HERA, using an integrated luminosity of 468 pb
−1
...collected in the period 1996–2007. The
ψ
′ to
J/
ψ cross section ratio was measured in the range 0
.
55
< z <
0
.
9 and 60
< W <
190 GeV as a function of
W
,
z
and
p
T
. Here
W
denotes the photon-proton centre-of-mass energy,
z
is the fraction of the incident photon energy carried by the meson and
p
T
is the transverse momentum of the meson with respect to the beam axis. The
J/ψ
cross sections were measured for 0
.
1
< z <
0
.
9, 60
< W <
240 GeV and
p
T
>
1 GeV. Theoretical predictions within the non-relativistic QCD framework including NLO colour-singlet and colour-octet contributions were compared to the data, as were predictions based on the
k
T
-factorisation approach.
A search for single-top production, ep→etX, has been made with the ZEUS detector at HERA using an integrated luminosity of 130.1pb−1. Events from both the leptonic and hadronic decay channels of the ...W boson resulting from the decay of the top quark were sought. For the leptonic mode, the search was made for events with isolated high-energy leptons and significant missing transverse momentum. For the hadronic decay mode, three-jet events in which two of the jets had an invariant mass consistent with that of the W were selected. No evidence for top production was found. The results are used to constrain single-top production via flavour-changing neutral current (FCNC) transitions. The ZEUS limit excludes a substantial region in the FCNC tuγ coupling not ruled out by other experiments.
Photoproduction of beauty and charm quarks in events with at least two jets has been measured with the ZEUS detector at HERA using an integrated luminosity of 133 pb
−1
. The fractions of jets ...containing
b
and
c
quarks were extracted using the invariant mass of charged tracks associated with secondary vertices and the decay-length significance of these vertices. Differential cross sections as a function of jet transverse momentum,
, and pseudorapidity,
η
jet
, were measured. The data are compared with previous measurements and are well described by next-to-leading-order QCD predictions.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Differential inclusive-jet cross sections have been measured for different jet radii in neutral current deep inelastic ep scattering for boson virtualities Q2>125 GeV2 with the ZEUS detector at HERA ...using an integrated luminosity of 81.7 pb−1. Jets were identified in the Breit frame using the kT cluster algorithm in the longitudinally inclusive mode for different values of the jet radius R. Differential cross sections are presented as functions of Q2 and the jet transverse energy, ET,Bjet. The dependence on R of the inclusive-jet cross section has been measured for Q2>125 and 500 GeV2 and found to be linear with R in the range studied. Next-to-leading-order QCD calculations give a good description of the measurements for 0.5⩽R⩽1. A value of αs(MZ) has been extracted from the measurements of the inclusive-jet cross section dσ/dQ2 with R=1 for Q2>500 GeV2: αs(MZ)=0.1207±0.0014(stat.)−0.0033+0.0035(exp.)−0.0023+0.0022(th.). The variation of αs with ET,Bjet is in a good agreement with the running of αs as predicted by QCD.
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