A combination is presented of the inclusive deep inelastic cross sections measured by the H1 and ZEUS Collaborations in neutral and charged current unpolarised
e
±
p
scattering at HERA during the ...period 1994-2000. The data span six orders of magnitude in negative four-momentum-transfer squared,
Q
2
, and in Bjorken
x
. The combination method used takes the correlations of systematic uncertainties into account, resulting in an improved accuracy. The combined data are the sole input in a NLO QCD analysis which determines a new set of parton distributions, HERAPDF1.0, with small experimental uncertainties. This set includes an estimate of the model and parametrisation uncertainties of the fit result.
Measurements of open charm production cross sections in deep-inelastic
ep
scattering at HERA from the H1 and ZEUS Collaborations are combined. Reduced cross sections
for charm production are obtained ...in the kinematic range of photon virtuality 2.5≤
Q
2
≤2000 GeV
2
and Bjorken scaling variable 3⋅10
−5
≤
x
≤5⋅10
−2
. The combination method accounts for the correlations of the systematic uncertainties among the different data sets. The combined charm data together with the combined inclusive deep-inelastic scattering cross sections from HERA are used as input for a detailed NLO QCD analysis to study the influence of different heavy flavour schemes on the parton distribution functions. The optimal values of the charm mass as a parameter in these different schemes are obtained. The implications on the NLO predictions for
W
±
and
Z
production cross sections at the LHC are investigated. Using the fixed flavour number scheme, the running mass of the charm quark is determined.
The exclusive photoproduction reaction γp→ϒp has been studied with the ZEUS experiment 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. These results, which represent the analysis of the full ZEUS data sample for this channel, are compared to predictions based on perturbative QCD.
ZEUS inclusive diffractive-cross-section measurements have been used in a DGLAP next-to-leading-order QCD analysis to extract the diffractive parton distribution functions. Data on diffractive dijet ...production in deep inelastic scattering have also been included to constrain the gluon density. Predictions based on the extracted parton densities are compared to diffractive charm and dijet photoproduction data.
A combination of the inclusive diffractive cross section measurements made by the H1 and ZEUS Collaborations at HERA is presented. The analysis uses samples of diffractive deep inelastic
ep
...scattering data at a centre-of-mass energy
where leading protons are detected by dedicated spectrometers. Correlations of systematic uncertainties are taken into account, resulting in an improved precision of the cross section measurement which reaches 6 % for the most precise points. The combined data cover the range 2.5<
Q
2
<200 GeV
2
in photon virtuality,
in proton fractional momentum loss, 0.09<|
t
|<0.55 GeV
2
in squared four-momentum transfer at the proton vertex and 0.0018<
β
<0.816 in
, where
x
is the Bjorken scaling variable.
A
bstract
The production of
D
0
,
D
*
+
,
D
+
,
and
charm hadrons and their antiparticles in
ep
scattering at HERA has been studied with the ZEUS detector, using a total integrated luminosity of 372 ...pb
−1
. The fractions of charm quarks hadronising into a particular charm hadron were derived. In addition, the ratio of neutral to charged
D
-meson production rates, the fraction of charged
D
mesons produced in a vector state, and the stangeness-suppression factor have been determined. The measurements have been performed in the photoproduction regime. The charm hadrons were reconstructed in the range of transverse momentum
p
T
>
3
.
8 GeV and pseudorapidity |
η
|
<
1
.
6. The charm fragmentation fractions are compared to previous results from HERA and from
e
+
e
−
experiments. The data support the hypothesis that fragmentation is independent of the production process.
The dissociation of virtual photons,
γ
⋆
p
→
X
p
, in events with a large rapidity gap between
X and the outgoing proton, as well as in events in which the leading proton was directly measured, has ...been studied with the ZEUS detector at HERA. The data cover photon virtualities
Q
2
>
2
GeV
2
and
γ
⋆
p
centre-of-mass energies
40
<
W
<
240
GeV
, with
M
X
>
2
GeV
, where
M
X
is the mass of the hadronic final state,
X. Leading protons were detected in the ZEUS leading proton spectrometer. The cross section is presented as a function of
t, the squared four-momentum transfer at the proton vertex and
Φ, the azimuthal angle between the positron scattering plane and the proton scattering plane. It is also shown as a function of
Q
2
and
x
P
, the fraction of the proton's momentum carried by the diffractive exchange, as well as
β, the Bjorken variable defined with respect to the diffractive exchange.
Inclusive-jet cross sections have been measured in the reaction ep→e+jet+X for photon virtuality Q2<1 GeV2 and γp centre-of-mass energies in the region 142<Wγp<293 GeV with the ZEUS detector at HERA ...using an integrated luminosity of 300 pb−1. Jets were identified using the kT, anti-kT or SIScone jet algorithms in the laboratory frame. Single-differential cross sections are presented as functions of the jet transverse energy, ETjet, and pseudorapidity, ηjet, for jets with ETjet>17 GeV and −1<ηjet<2.5. In addition, measurements of double-differential inclusive-jet cross sections are presented as functions of ETjet in different regions of ηjet. Next-to-leading-order QCD calculations give a good description of the measurements, except for jets with low ETjet and high ηjet. The influence of non-perturbative effects not related to hadronisation was studied. Measurements of the ratios of cross sections using different jet algorithms are also presented; the measured ratios are well described by calculations including up to O(αs2) terms. Values of αs(MZ) were extracted from the measurements and the energy-scale dependence of the coupling was determined. The value of αs(MZ) extracted from the measurements based on the kT jet algorithm is αs(MZ)=0.1206−0.0022+0.0023(exp.)−0.0035+0.0042(th.); the results from the anti-kT and SIScone algorithms are compatible with this value and have a similar precision.
The reduced cross sections for ep deep inelastic scattering have been measured with the ZEUS detector at HERA at three different centre-of-mass energies, 318, 251 and 225 GeV. From the cross ...sections, measured double differentially in Bjorken x and the virtuality, Q2, the proton structure functions FL and F2 have been extracted in the region 5×10−4<x<0.007 and 20<Q2<130 GeV2.
A search for single-top production, ep→etX, has been performed with the ZEUS detector at HERA using data corresponding to an integrated luminosity of 0.37 fb−1. No evidence for top production was ...found, consistent with the expectation from the Standard Model. Limits were computed for single-top production via flavour changing neutral current transitions involving a neutral electroweak vector boson, γ or Z. The result was combined with a previous ZEUS result yielding a total luminosity of 0.50 fb−1. A 95% credibility level upper limit of 0.13 pb was obtained for the cross section at the centre-of-mass energy of s=315 GeV.
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