The production of leading neutrons, where the neutron carries a large fraction
x
L
of the incoming proton’s longitudinal momentum, is studied in deep-inelastic positron-proton scattering at HERA. The ...data were taken with the H1 detector in the years 2006 and 2007 and correspond to an integrated luminosity of 122 pb
−1
. The semi-inclusive cross section is measured in the phase space defined by the photon virtuality 6<
Q
2
<100 GeV
2
, Bjorken scaling variable 1.5⋅10
−4
<
x
<3⋅10
−2
, longitudinal momentum fraction 0.32<
x
L
<0.95 and neutron transverse momentum
p
T
<0.2 GeV. The leading neutron structure function,
, and the fraction of deep-inelastic scattering events containing a leading neutron are studied as a function of
Q
2
,
x
and
x
L
. Assuming that the pion exchange mechanism dominates leading neutron production, the data provide constraints on the shape of the pion structure function.
A measurement of the inclusive ep scattering cross section is presented in the region of low momentum transfers, 0.2 GeV2 a parts per thousand currency signQ (2)a parts per thousand currency sign12 ...GeV2, and low Bjorken x, 5a <...10(-6)a parts per thousand currency signxa parts per thousand currency sign0.02. The result is based on two data sets collected in dedicated runs by the H1 Collaboration at HERA at beam energies of 27.6 GeV and 920 GeV for positrons and protons, respectively. A combination with data previously published by H1 leads to a cross section measurement of a few percent accuracy. A kinematic reconstruction method exploiting radiative ep events extends the measurement to lower Q (2) and larger x. The data are compared with theoretical models which apply to the transition region from photoproduction to deep inelastic scattering.
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 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.
A measurement of the inclusive deep inelastic neutral current
e
+
p
scattering cross section is reported in the region of four-momentum transfer squared, 12 GeV
2
≤
Q
2
≤150 GeV
2
, and Bjorken
x
, ...2×10
−4
≤
x
≤0.1. The results are based on data collected by the H1 Collaboration at the
ep
collider HERA at positron and proton beam energies of
E
e
=27.6 GeV and
E
p
=920 GeV, respectively. The data are combined with previously published data, taken at
E
p
=820 GeV. The accuracy of the combined measurement is typically in the range of 1.3–2%. A QCD analysis at next-to-leading order is performed to determine the parton distributions in the proton based on H1 data.
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 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.
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.
A wide-field space-based imaging telescope is necessary to fully exploit the technique of observing dark matter via weak gravitational lensing. This first paper in a three part series outlines the ...survey strategies and relevant instrumental parameters for such a mission. As a concrete example of hardware design, we consider the proposed
Supernova/Acceleration Probe (SNAP). Using SNAP engineering models, we quantify the major contributions to this telescope’s point spread function (PSF). These PSF contributions are relevant to any similar wide-field space telescope. We further show that the PSF of SNAP or a similar telescope will be smaller than current ground-based PSFs, and more isotropic and stable over time than the PSF of the
Hubble Space Telescope. We outline survey strategies for two different regimes––a “wide” 300 square degree survey and a “deep” 15 square degree survey that will accomplish various weak lensing goals including statistical studies and dark matter mapping.
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