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.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Production of exclusive dijets in diffractive deep inelastic Formula omitted scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 372 pb Formula omitted. The ...measurement was performed for Formula omitted-p centre-of-mass energies in the range Formula omitted and for photon virtualities Formula omitted. Energy flows around the jet axis are presented. The cross section is presented as a function of Formula omitted and Formula omitted, where Formula omitted, x is the Bjorken variable and Formula omitted is the proton fractional longitudinal momentum loss. The angle Formula omitted is defined by the Formula omitted-dijet plane and the Formula omitted- Formula omitted plane in the rest frame of the diffractive final state. The Formula omitted cross section is measured in bins of Formula omitted. The results are compared to predictions from models based on different assumptions about the nature of the diffractive exchange.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Charm production in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 120 pb
−1
. The hadronic decay channels
D
+
→
K
S
0
π
+
, Λ
c
+
→
pK
S
...0
and Λ
c
+
→ Λ
π
+
, and their charge conjugates, were reconstructed. The presence of a neutral strange hadron in the final state reduces the combinatorial background and extends the measured sensitivity into the low transverse momentum region. The kinematic range is 0
< p
T
(
D
+
, Λ
c
+
) < 10 GeV, |
η
(
D
+
, Λ
c
+
)| < 1
.
6, 1.5 <
Q
2
< 1000 GeV
2
and 0
.
02 <
y
< 0.7. Inclusive and differential cross sections for the production of
D
+
mesons are compared to next-to-leading-order QCD predictions. The fraction of
c
quarks hadronising into Λ
c
+
baryons is extracted.
A
bstract
The photoproduction of
D
∗±
mesons has been measured with the ZEUS detector at HERA at three different
ep
centre-of-mass energies,
s
, of 318, 251 and 225 GeV. For each data set,
D
∗±
...mesons were required to have transverse momentum,
p
T
D
∗
, and pseudo-rapidity,
η
D
∗
, in the ranges 1
.
9
< p
T
D
∗
<
20 GeV and |
η
D
∗
|
<
1
.
6. The events were required to have a virtuality of the incoming photon,
Q
2
, of less than 1 GeV
2
. The dependence on
s
was studied by normalising to the high-statistics measurement at
s
=
318
GeV. This led to the cancellation of a number of systematic effects both in data and theory. Predictions from next-to-leading-order QCD describe the
s
dependence of the data well.
The proton-dissociative diffractive photoproduction of
J
/
ψ
mesons has been studied in ep collisions with the ZEUS detector at HERA using an integrated luminosity of 112 pb
−1
. The cross section is ...presented as a function of the photon-proton centre-of-mass energy and of the squared four-momentum transfer at the proton vertex. The results are compared to perturbative QCD calculations.
A search for events containing an isolated electron or muon and missing transverse momentum produced in
e
±
p
collisions is performed with the H1 and ZEUS detectors at HERA. The data were taken in ...the period 1994–2007 and correspond to an integrated luminosity of 0.98 fb
−1
. The observed event yields are in good overall agreement with the Standard Model prediction, which is dominated by single W production. In the
e
+
p
data, at large hadronic transverse momentum
P
T
X
> 25GeV, a total of 23 events are observed compared to a prediction of 14.0 ± 1.9. The total single
W
boson production cross section is measured as 1.06 ± 0.16 (stat.) ± 0.07 (sys.) pb, in agreement with an Standard Model (SM) expectation of 1.26 ± 0.19 pb.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Charged particle production has been studied in neutral current deep inelastic
ep
scattering with the ZEUS detector at HERA using an integrated luminosity of 0.44 fb
−1
. Distributions of scaled ...momenta in the Breit frame are presented for particles in the current fragmentation region. The evolution of these spectra with the photon virtuality,
Q
2
, is described in the kinematic region 10 <
Q
2
< 41000Ge V
2
. Next-to-leading-order and modified leading-log-approximation QCD calculations as well as predictions from Monte Carlo models are compared to the data. The results are also compared to
e
+
e
−
annihilation data. The dependences of the pseudorapidity distribution of the particles on
Q
2
and on the energy in the γ
p
system,
W
, are presented and interpreted in the context of the hypothesis of limiting fragmentation.
Study of taupair production at HERA Aggarwal, R.; Antonelli, S.; Antonov, A. ...
The journal of high energy physics,
02/2011, Volume:
2011, Issue:
2
Journal Article
Peer reviewed
Open access
A study of events containing two tau leptons with high transverse momentum has been performed with the ZEUS detector at HERA, using a data sample corresponding to an integrated luminosity of 0.33 fb
...−1
. The tau candidates were identified from their decays into electrons, muons or hadronic jets. The number of tau-pair candidates has been compared with the prediction from the Standard Model, where the largest contribution is expected from Bethe-Heitler processes. The total visible cross section was extracted. Standard Model expectations agree well with the measured distributions, also at high invariant mass of the tau pair.
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