6,287 research outputs found
Fluxes of atmospheric muons underwater depending on the small-x gluon density
The prompt muon contribution to the deep-sea atmospheric muon flux can serve
as a tool for probing into the small-x feature of the gluon density inside of a
nucleon, if the muon energy threshold could be lifted to 100 TeV. The prompt
muon flux underwater is calculated taking into consideration predictions of
recent charm production models in which the small-x behaviour of the gluon
distribution is probed. We discuss the possibility of distinguishing the PQCD
models of the charm production differing in the small-x exponent of the gluon
distribution, in measurements of the muon flux at energies 10-100 TeV with
neutrino telescopes.Comment: 9 pages, 4 eps figures, uses iopart.st
Enabling Technologies for Silicon Microstrip Tracking Detectors at the HL-LHC
While the tracking detectors of the ATLAS and CMS experiments have shown
excellent performance in Run 1 of LHC data taking, and are expected to continue
to do so during LHC operation at design luminosity, both experiments will have
to exchange their tracking systems when the LHC is upgraded to the
high-luminosity LHC (HL-LHC) around the year 2024. The new tracking systems
need to operate in an environment in which both the hit densities and the
radiation damage will be about an order of magnitude higher than today. In
addition, the new trackers need to contribute to the first level trigger in
order to maintain a high data-taking efficiency for the interesting processes.
Novel detector technologies have to be developed to meet these very challenging
goals. The German groups active in the upgrades of the ATLAS and CMS tracking
systems have formed a collaborative "Project on Enabling Technologies for
Silicon Microstrip Tracking Detectors at the HL-LHC" (PETTL), which was
supported by the Helmholtz Alliance "Physics at the Terascale" during the years
2013 and 2014. The aim of the project was to share experience and to work
together on key areas of mutual interest during the R&D phase of these
upgrades. The project concentrated on five areas, namely exchange of
experience, radiation hardness of silicon sensors, low mass system design,
automated precision assembly procedures, and irradiations. This report
summarizes the main achievements
O govoru mržnje
European SulfoSYS-project [SysMo P–N-01-09-23] and grant [9P23000 and P25369] by the Austrian Research fund (to C.S.) and by grant [BB/K000314/1] from the Biotechnology and Biological Sciences Research Council (to M.F.W.). Funding for open access charge: Austrian Science Fund.The recently discovered clustered regularly interspaced short palindromic repeat (CRISPR)-mediated virus defense represents an adaptive immune system in many bacteria and archaea. Small CRISPR RNAs cause cleavage of complementary invading nucleic acids in conjunction with an associated protein or a protein complex. Here, we show CRISPR-mediated cleavage of mRNA from an invading virus in the hyperthermophilic archaeon Sulfolobus solfataricus. More than 40% of the targeted mRNA could be cleaved, as demonstrated by quantitative polymerase chain reaction. Cleavage of the mRNA was visualized by northern analyses and cleavage sites were mapped. In vitro, the same substrates were cleaved by the purified CRISPR-associated CMR complex from Sulfolobus solfataricus. The in vivo system was also re-programmed to knock down mRNA of a selected chromosomal gene (β-galactosidase) using an artificial miniCRISPR locus. With a single complementary spacer, ∼50% reduction of the targeted mRNA and of corresponding intracellular protein activity was achieved. Our results demonstrate in vivo cleavage of mRNA in a prokaryote mediated by small RNAs (i.e. analogous to RNA interference in eukaryotes) and the re-programming of the system to silence specific genes of interest.Publisher PDFPeer reviewe
An NLO QCD analysis of inclusive cross-section and jet-production data from the ZEUS experiment
The ZEUS inclusive differential cross-section data from HERA, for charged and
neutral current processes taken with e+ and e- beams, together with
differential cross-section data on inclusive jet production in e+ p scattering
and dijet production in \gamma p scattering, have been used in a new NLO QCD
analysis to extract the parton distribution functions of the proton. The input
of jet data constrains the gluon and allows an accurate extraction of
\alpha_s(M_Z) at NLO;
\alpha_s(M_Z) = 0.1183 \pm 0.0028(exp.) \pm 0.0008(model)
An additional uncertainty from the choice of scales is estimated as \pm
0.005. This is the first extraction of \alpha_s(M_Z) from HERA data alone.Comment: 37 pages, 14 figures, to be submitted to EPJC. PDFs available at
http://durpdg.dur.ac.uk/hepdata in LHAPDFv
High-E_T dijet photoproduction at HERA
The cross section for high-E_T dijet production in photoproduction has been
measured with the ZEUS detector at HERA using an integrated luminosity of 81.8
pb-1. The events were required to have a virtuality of the incoming photon,
Q^2, of less than 1 GeV^2 and a photon-proton centre-of-mass energy in the
range 142 < W < 293 GeV. Events were selected if at least two jets satisfied
the transverse-energy requirements of E_T(jet1) > 20 GeV and E_T(jet2) > 15 GeV
and pseudorapidity requirements of -1 < eta(jet1,2) < 3, with at least one of
the jets satisfying -1 < eta(jet) < 2.5. The measurements show sensitivity to
the parton distributions in the photon and proton and effects beyond
next-to-leading order in QCD. Hence these data can be used to constrain further
the parton densities in the proton and photon.Comment: 36 pages, 13 figures, 20 tables, including minor revisions from
referees. Accepted by Phys. Rev.
Inclusive jet cross sections and dijet correlations in photoproduction at HERA
Inclusive jet cross sections in photoproduction for events containing a
meson have been measured with the ZEUS detector at HERA using an integrated
luminosity of . The events were required to have a
virtuality of the incoming photon, , of less than 1 GeV, and a
photon-proton centre-of-mass energy in the range . The measurements are compared with next-to-leading-order (NLO) QCD
calculations. Good agreement is found with the NLO calculations over most of
the measured kinematic region. Requiring a second jet in the event allowed a
more detailed comparison with QCD calculations. The measured dijet cross
sections are also compared to Monte Carlo (MC) models which incorporate
leading-order matrix elements followed by parton showers and hadronisation. The
NLO QCD predictions are in general agreement with the data although differences
have been isolated to regions where contributions from higher orders are
expected to be significant. The MC models give a better description than the
NLO predictions of the shape of the measured cross sections.Comment: 43 pages, 12 figures, charm jets ZEU
Dissociation of virtual photons in events with a leading proton at HERA
The ZEUS detector has been used to study dissociation of virtual photons in
events with a leading proton, gamma^* p -> X p, in e^+p collisions at HERA. The
data cover photon virtualities in two ranges, 0.03<Q^2<0.60 GeV^2 and 2<Q^2<100
GeV^2, with M_X>1.5 GeV, where M_X is the mass of the hadronic final state, X.
Events were required to have a leading proton, detected in the ZEUS leading
proton spectrometer, carrying at least 90% of the incoming proton energy. The
cross section is presented as a function of t, the squared four-momentum
transfer at the proton vertex, Phi, the azimuthal angle between the positron
scattering plane and the proton scattering plane, and Q^2. The data are
presented in terms of the diffractive structure function, F_2^D(3). A
next-to-leading-order QCD fit to the higher-Q^2 data set and to previously
published diffractive charm production data is presented
Search for lepton-flavor violation at HERA
A search for lepton-flavor-violating interactions and has been performed with the ZEUS detector using the entire HERA I
data sample, corresponding to an integrated luminosity of 130 pb^{-1}. The data
were taken at center-of-mass energies, , of 300 and 318 GeV. No
evidence of lepton-flavor violation was found, and constraints were derived on
leptoquarks (LQs) that could mediate such interactions. For LQ masses below
, limits were set on , where
is the coupling of the LQ to an electron and a
first-generation quark , and is the branching ratio of
the LQ to the final-state lepton ( or ) and a quark . For
LQ masses much larger than , limits were set on the four-fermion
interaction term for LQs that couple to an electron and a quark
and to a lepton and a quark , where and are
quark generation indices. Some of the limits are also applicable to
lepton-flavor-violating processes mediated by squarks in -Parity-violating
supersymmetric models. In some cases, especially when a higher-generation quark
is involved and for the process , the ZEUS limits are the most
stringent to date.Comment: 37 pages, 10 figures, Accepted by EPJC. References and 1 figure (Fig.
6) adde
The dependence of dijet production on photon virtuality in ep collisions at HERA
The dependence of dijet production on the virtuality of the exchanged photon,
Q^2, has been studied by measuring dijet cross sections in the range 0 < Q^2 <
2000 GeV^2 with the ZEUS detector at HERA using an integrated luminosity of
38.6 pb^-1.
Dijet cross sections were measured for jets with transverse energy E_T^jet >
7.5 and 6.5 GeV and pseudorapidities in the photon-proton centre-of-mass frame
in the range -3 < eta^jet <0. The variable xg^obs, a measure of the photon
momentum entering the hard process, was used to enhance the sensitivity of the
measurement to the photon structure. The Q^2 dependence of the ratio of low- to
high-xg^obs events was measured.
Next-to-leading-order QCD predictions were found to generally underestimate
the low-xg^obs contribution relative to that at high xg^obs. Monte Carlo models
based on leading-logarithmic parton-showers, using a partonic structure for the
photon which falls smoothly with increasing Q^2, provide a qualitative
description of the data.Comment: 35 pages, 6 eps figures, submitted to Eur.Phys.J.
Beauty photoproduction measured using decays into muons in dijet events in ep collisions at =318 GeV
The photoproduction of beauty quarks in events with two jets and a muon has
been measured with the ZEUS detector at HERA using an integrated luminosity of
110 pb. The fraction of jets containing b quarks was extracted from the
transverse momentum distribution of the muon relative to the closest jet.
Differential cross sections for beauty production as a function of the
transverse momentum and pseudorapidity of the muon, of the associated jet and
of , the fraction of the photon's momentum participating in
the hard process, are compared with MC models and QCD predictions made at
next-to-leading order. The latter give a good description of the data.Comment: 32 pages, 6 tables, 7 figures Table 6 and Figure 7 revised September
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