A measurement is presented of the inclusive neutral current e±p scattering cross section using data collected by the H1 experiment at HERA during the years 2003 to 2007 with proton beam energies Ep ...of 920, 575, and 460 GeV. The kinematic range of the measurement covers low absolute four-momentum transfers squared, 1.5 GeV2<Q2<120 GeV2, small values of Bjorken x, 2.9⋅10−5<x<0.01, and extends to high inelasticity up to y=0.85. The structure function FL is measured by combining the new results with previously published H1 data at Ep=920 GeV and Ep=820 GeV. The new measurements are used to test several phenomenological and QCD models applicable in this low Q2 and low x kinematic domain.
Inclusive charm and beauty cross sections are measured in
e
−
p
and
e
+
p
neutral current collisions at HERA in the kinematic region of photon virtuality 5≤
Q
2
≤2000 GeV
2
and Bjorken scaling ...variable 0.0002≤
x
≤0.05. The data were collected with the H1 detector in the years 2006 and 2007 corresponding to an integrated luminosity of 189 pb
−1
. The numbers of charm and beauty events are determined using variables reconstructed by the H1 vertex detector including the impact parameter of tracks to the primary vertex and the position of the secondary vertex. The measurements are combined with previous data and compared to QCD predictions.
Diffractive electroproduction of ρ and ϕ mesons is measured at HERA with the H1 detector in the elastic and proton dissociative channels. The data correspond to an integrated luminosity of 51 pb
−1
. ...About 10500 ρ and 2000 φ events are analysed in the kinematic range of squared photon virtuality 2.5 ≤
Q
2
≤ 60 GeV
2
, photon-proton centre of mass energy 35 ≤
W
≤ 180 GeV and squared four-momentum transfer to the proton |
t
| ≤ 3 GeV
2
. The total, longitudinal and transverse cross sections are measured as a function of
Q
2
,
W
and |
t
|. The measurements show a transition to a dominantly “hard” behaviour, typical of high gluon densities and small
dipoles, for
Q
2
larger than 10 to 20 GeV
2
. They support flavour independence of the diffractive exchange, expressed in terms of the scaling variable (
Q
2
+
M
2
V
)/4, and proton vertex factorisation. The spin density matrix elements are measured as a function of kinematic variables. The ratio of the longitudinal to transverse cross sections, the ratio of the helicity amplitudes and their relative phases are extracted. Several of these measurements have not been performed before and bring new information on the dynamics of diffraction in a QCD framework. The measurements are discussed in the context of models using generalised parton distributions or universal dipole cross sections.
Microplastics are found in marine and freshwater environments; however, their specific sources are not yet well understood. Understanding sources will be of key importance in efforts to reduce ...emissions into the environment. We examined the emissions of microfibers from domestic washing of a new microfiber polyester fleece textile. Analyzing released fibers collected with a 200 μm filter during 10 mild, successive washing cycles showed that emission initially decreased and then stabilized at approx. 0.0012 wt%. This value is our estimation for the long-term release of fibers during each washing. Use of detergent and softener did not significantly influence emission. Release of fibers during tumble drying was approx. 3.5 times higher than during washing.
Thin-film dye-sensitized solar cells (DSCs) based on mesoporous semiconductor electrodes are low-cost alternatives to conventional silicon devices. High-efficiency DSCs typically operate as ...photoanodes (n-DSCs), where photocurrents result from dye-sensitized electron injection into n-type semiconductors. Dye-sensitized photocathodes (p-DSCs) operate in an inverse mode, where dye-excitation is followed by rapid electron transfer from a p-type semiconductor to the dye (dye-sensitized hole injection). Such p-DSCs and n-DSCs can be combined to construct tandem solar cells (pn-DSCs) with a theoretical efficiency limitation well beyond that of single-junction DSCs (ref. 4). Nevertheless, the efficiencies of such tandem pn-DSCs have so far been hampered by the poor performance of the available p-DSCs (refs 3, 5-15). Here we show for the first time that p-DSCs can convert absorbed photons to electrons with yields of up to 96%, resulting in a sevenfold increase in energy conversion efficiency compared with previously reported photocathodes. The donor-acceptor dyes, studied as photocathodic sensitizers, comprise a variable-length oligothiophene bridge, which provides control over the spatial separation of the photogenerated charge carriers. As a result, charge recombination is decelerated by several orders of magnitude and tandem pn-DSCs can be constructed that exceed the efficiency of their individual components.
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 measurement is presented of inelastic photo- and electroproduction of
J
/
ψ
mesons in
ep
scattering at HERA. The data were recorded with the H1 detector in the period from 2004 to 2007. Single and ...double differential cross sections are determined and the helicity distributions of the
J
/
ψ
mesons are analysed. The results are compared to theoretical predictions in the colour singlet model and in the framework of non-relativistic QCD. Calculations in the colour singlet model using a
k
T
factorisation ansatz are able to give a good description of the data, while colour singlet model calculations to next-to-leading order in collinear factorisation underestimate the data.
Measurements are presented of single and double-differential dijet cross sections in diffractive photoproduction based on a data sample with an integrated luminosity of 47 pb
−1
. The events are of ...the type
ep
→
eXY
, where the hadronic system
X
contains at least two jets and is separated by a large rapidity gap from the system
Y
, which consists of a leading proton or low-mass proton excitation. The dijet cross sections are compared with QCD calculations at next-to-leading order and with a Monte Carlo model based on leading order matrix elements with parton showers. The measured cross sections are smaller than those obtained from the next-to-leading order calculations by a factor of about 0.6. This suppression factor has no significant dependence on the fraction
x
γ
of the photon four-momentum entering the hard subprocess. Ratios of the diffractive to the inclusive dijet cross sections are measured for the first time and are compared with Monte Carlo models.
QCD factorization in diffraction Mozer, M U
Journal of physics. Conference series,
05/2008, Letnik:
110, Številka:
2
Journal Article
Recenzirano
Odprti dostop
I present measurements of dijet and open charm cross-sections in diffractive DIS and photoproduction taken with the H1 and ZEUS detectors at the HERA accelerator. Diffractive events were identified ...by a rapidity gap selection. The resulting differential cross sections are compared to QCD calculations in NLO, based on parton densities extracted from inclusive diffraction. Additionally a fit of diffractive parton densities to the combined data sets of the inclusive F2D measurement and the dijet data was performed. This leads to reduced uncertainties for the gluon density.
First Results from the THEMIS Mission Angelopoulos, V.; Sibeck, D.; Carlson, C. W. ...
Space science reviews,
12/2008, Letnik:
141, Številka:
1-4
Journal Article
Recenzirano
Odprti dostop
THEMIS was launched on February 17, 2007 to determine the trigger and large-scale evolution of substorms. During the first seven months of the mission the five satellites coasted near their injection ...orbit to avoid differential precession in anticipation of orbit placement, which started in September 2007 and led to a commencement of the baseline mission in December 2007. During the coast phase the probes were put into a string-of-pearls configuration at 100 s of km to 2 R
E
along-track separations, which provided a unique view of the magnetosphere and enabled an unprecedented dataset in anticipation of the first tail season. In this paper we describe the first THEMIS substorm observations, captured during instrument commissioning on March 23, 2007. THEMIS measured the rapid expansion of the plasma sheet at a speed that is commensurate with the simultaneous expansion of the auroras on the ground. These are the first unequivocal observations of the rapid westward expansion process in space and on the ground. Aided by the remote sensing technique at energetic particle boundaries and combined with ancillary measurements and MHD simulations, they allow determination and mapping of space currents. These measurements show the power of the THEMIS instrumentation in the tail and the radiation belts. We also present THEMIS Flux Transfer Events (FTE) observations at the magnetopause, which demonstrate the importance of multi-point observations there and the quality of the THEMIS instrumentation in that region of space.
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