A measurement of elastic deeply virtual Compton scattering γ∗p→γp using e+p and e−p collision data recorded with the H1 detector at HERA is presented. The analysed data sample corresponds to an ...integrated luminosity of 306 pb−1, almost equally shared between both beam charges. The cross section is measured as a function of the virtuality Q2 of the exchanged photon and the centre-of-mass energy W of the γ∗p system in the kinematic domain 6.5<Q2<80 GeV2, 30<W<140 GeV and |t|<1 GeV2, where t denotes the squared momentum transfer at the proton vertex. The cross section is determined differentially in t for different Q2 and W values and exponential t-slope parameters are derived. Using e+p and e−p data samples, a beam charge asymmetry is extracted for the first time in the low Bjorken x kinematic domain. The observed asymmetry is attributed to the interference between Bethe–Heitler and deeply virtual Compton scattering processes. Experimental results are discussed in the context of two different models, one based on generalised parton distributions and one based on the dipole approach.
A first measurement is reported of the longitudinal proton structure function FL(X, Q(2)) at the ep collider HERA. It is based on inclusive deep inelastic e(+)p scattering cross section measurements ...with a positron beam energy of 27.5 GeV and proton beam energies of 920, 575 and 460 GeV. Employing the energy dependence of the cross section, FL is measured in a range of squared four-momentum transfers 12 <= Q2 <=, 90 GeV2 and low Bjorken x 0.00024 <= x <= 0.0036. The F-L values agree with higher order QCD calculations based on parton densities obtained using cross section data previously measured at HERA. (C) 2008 Elsevier B.V. All rights reserved.
A measurement of elastic deeply virtual Compton scattering γ∗p→γp using e−p collision data recorded with the H1 detector at HERA is presented. The analysed data sample corresponds to an integrated ...luminosity of 145 pb−1. The cross section is measured as a function of the virtuality Q2 of the exchanged photon and the centre-of-mass energy W of the γ∗p system in the kinematic domain 6.5<Q2<80 GeV2, 30<W<140 GeV and |t|<1 GeV2, where t denotes the squared momentum transfer at the proton vertex. The cross section is determined differentially in t for different Q2 and W values and exponential t-slope parameters are derived. The measurements are compared to a NLO QCD calculation based on generalised parton distributions. In the context of the dipole approach, the geometric scaling property of the DVCS cross section is studied for different values of t.
The diffractive process
ep
→
eXY
, where
Y
denotes a proton or its low mass excitation with
M
Y
<1.6 GeV, is studied with the H1 experiment at HERA. The analysis is restricted to the phase space ...region of the photon virtuality 3 ≤
Q
2
≤ 1600 GeV
2
, the square of the four-momentum transfer at the proton vertex |
t
|< 1.0 GeV
2
and the longitudinal momentum fraction of the incident proton carried by the colourless exchange
x
ℙ
<0.05.
\printthanks
Triple differential cross sections are measured as a function of
x
ℙ
,
Q
2
and
β
=
x
/
x
ℙ
where
x
is the Bjorken scaling variable. These measurements are made after selecting diffractive events by demanding a large empty rapidity interval separating the final state hadronic systems
X
and
Y
. High statistics measurements covering the data taking periods 1999–2000 and 2004–2007 are combined with previously published results in order to provide a single set of diffractive cross sections from the H1 experiment using the large rapidity gap selection method. The combined data represent a factor between three and thirty increase in statistics with respect to the previously published results. The measurements are compared with predictions from NLO QCD calculations based on diffractive parton densities and from a dipole model. The proton vertex factorisation hypothesis is tested.
The Level-1 Calorimeter Trigger is a major part of the first stage of event selection for the ATLAS experiment at the LHC. It is a digital, pipelined system with several stages of processing, largely ...based on FPGAs, which perform programmable algorithms in parallel with a fixed latency to process about 300 Gbyte/s of input data. The real-time output consists of counts of different types of trigger objects and energy sums. Prototypes of all module types have been undergoing intensive testing before final production during 2005. Verification of their correct operation has been performed stand-alone and in the ATLAS test-beam at CERN. Results from these investigations will be presented, along with a description of the methodology used to perform the tests.
The cross section of diffractive deep-inelastic scattering
ep
→
eXp
is measured, where the system
X
contains at least two jets and the leading final state proton is detected in the H1 Forward Proton ...Spectrometer. The measurement is performed for fractional proton longitudinal momentum loss
x
ℙ
<0.1 and covers the range 0.1<|
t
|<0.7 GeV
2
in squared four-momentum transfer at the proton vertex and 4<
Q
2
<110 GeV
2
in photon virtuality. The differential cross sections extrapolated to |
t
|<1 GeV
2
are in agreement with next-to-leading order QCD predictions based on diffractive parton distribution functions extracted from measurements of inclusive and dijet cross sections in diffractive deep-inelastic scattering. The data are also compared with leading order Monte Carlo models.
The cross section for the diffractive deep-inelastic scattering process
ep
→
eXp
is measured, with the leading final state proton detected in the H1 Forward Proton Spectrometer. The data sample ...covers the range
x
ℙ
<0.1 in fractional proton longitudinal momentum loss, 0.1<|
t
|<0.7 GeV
2
in squared four-momentum transfer at the proton vertex and 4<
Q
2
<700 GeV
2
in photon virtuality. The cross section is measured four-fold differentially in
t
,
x
ℙ
,
Q
2
and
β
=
x
/
x
ℙ
, where
x
is the Bjorken scaling variable. The
t
and
x
ℙ
dependences are interpreted in terms of an effective pomeron trajectory and a sub-leading exchange. The data are compared with perturbative QCD predictions at next-to-leading order based on diffractive parton distribution functions previously extracted from complementary measurements of inclusive diffractive deep-inelastic scattering. The ratio of the diffractive to the inclusive
ep
cross section is studied as a function of
Q
2
,
β
and
x
ℙ
.
A search for first generation scalar and vector leptoquarks produced in ep collisions is performed by the H1 experiment at HERA. The full H1 data sample is used in the analysis, corresponding to an ...integrated luminosity of 446 pb−1. No evidence for the production of leptoquarks is observed in final states with a large transverse momentum electron or with large missing transverse momentum, and constraints on leptoquark models are derived. For leptoquark couplings of electromagnetic strength λ=0.3, first generation leptoquarks with masses up to 800 GeV are excluded at 95% confidence level.
A
bstract
A measurement is presented of single- and double-differential dijet cross sections in diffractive deep-inelastic
ep
scattering at HERA using data collected by the H1 experiment ...corresponding to an integrated luminosity of 290 pb
−1
. The investigated phase space is spanned by the photon virtuality in the range of 4
< Q
2
<
100 GeV
2
and by the fractional proton longitudinal momentum loss
x
ℙ
<
0
.
03. The resulting cross sections are compared with next-to-leading order QCD predictions based on diffractive parton distribution functions and the value of the strong coupling constant is extracted.
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