4,439 research outputs found
ATLAS RPC offline monitoring and data quality assessment
In this work several aspects of ATLAS RPC offline monitoring and data quality
assessment are illustrated with cosmics data selected by RPC trigger. These
correspond to trigger selection, front-end mapping, detection efficiency and
occupancy, which are studied in terms of low level quantities such as: RPC
off-line hits and standalone tracks. The tools and techniques presented are
also extended to the forthcoming LHC p-p beam collisions.Comment: Poster section at ICHEP08, Philadelphia, USA, July 2008. 3 pages,
LaTeX, 3 eps figure
SnO<sub>2</sub> nanoparticles in silica: nanosized tools for femtosecond-laser machining of refractive index patterns
We show that SnO2 nanoclusters in silica interact with ultrashort infrared laser pulses focused inside the material generating a hydrostatic compression and photoelastic response of the surrounding glass. This effect, together with the laser-induced nanocluster amorphization, gives rise to positive or negative refractive-index changes, up to 10â2, depending on the beam-power density. This result points out a wide tuning of the refractive index patterns obtainable in silica-based optical technology
Inherent bacterial DNA contamination of extraction and sequencing reagents may affect interpretation of microbiota in low bacterial biomass samples
Additional file 1: Table S1. Taxonomic listing of all bacterial genera and species detected as contaminants of DNA extraction and processing kits in the present study and previously reported
Search for new phenomena in high-mass diphoton final states using 37 fb(-1) of proton-proton collisions collected at root(s) = 13 TeV with the ATLAS detector
Searches for new phenomena in high-mass diphoton final states with the
ATLAS experiment at the LHC are presented. The analysis is based on pp
collision data corresponding to an integrated luminosity of 36.7 fb(-1)
at a centre-of-mass energy root s = 13 TeV recorded in 2015 and 2016.
Searches are performed for resonances with spin 0, as predicted by
theories with an extended Higgs sector, and for resonances with spin 2,
using a warped extra-dimension model as a benchmark model, as well as
for non-resonant signals, assuming a large extra-dimension scenario. No
significant deviation from the Standard Model is observed. Upper limits
are placed on the production cross section times branching ratio to two
photons as a function of the resonance mass. In addition, lower limits
are set on the ultraviolet cutoff scale in the large extra-dimensions
model. (C) 2017 The Author(s). Published by Elsevier B.V
Search for new phenomena in events containing a same-flavour opposite-sign dilepton pair, jets, and large missing transverse momentum in root s=13 TeV pp collisions with the ATLAS detector
Two searches for new phenomena in final states containing a same-flavour
opposite-sign lepton (electron or muon) pair, jets, and large missing
transverse momentum are presented. These searches make use of
proton-proton collision data, collected during 2015 and 2016 at a
centre-of-mass energy root s = 13 TeV by the ATLAS detector at the large
hadron collider, which correspond to an integrated luminosity of 14.7
fb(-1). Both searches target the pair production of supersymmetric
particles, squarks or gluinos, which decay to final states containing a
same-flavour opposite-sign lepton pair via one of two mechanisms: a
leptonically decaying Z boson in the final state, leading to a peak in
the dilepton invariant-mass distribution around the Z boson mass; and
decays of neutralinos (e.g.. (chi) over tilde (0)(2) -> l(+)l(-1)(chi)
over tilde (0)(1)), yielding a kinematic endpoint in the dilepton
invariant-mass spectrum. The data are found to be consistent with the
Standard Model expectation. Results are interpreted in simplified models
of gluino-pair (squark-pair) production, and provide sensitivity to
gluinos (squarks) with masses as large as 1.70 TeV (980 GeV)
Reconstruction of primary vertices at the ATLAS experiment in Run 1 proton-proton collisions at the LHC
This paper presents the method and performance of primary vertex
reconstruction in proton-proton collision data recorded by the ATLAS
experiment during Run 1 of the LHC. The studies presented focus on data
taken during 2012 at a centre-of-mass energy of root s = 8 TeV. The
performance has been measured as a function of the number of
interactions per bunch crossing over a wide range, from one to seventy.
The measurement of the position and size of the luminous region and its
use as a constraint to improve the primary vertex resolution are
discussed. A longitudinal vertex position resolution of about 30 mu m is
achieved for events with high multiplicity of reconstructed tracks. The
transverse position resolution is better than 20 mu m and is dominated
by the precision on the size of the luminous region. An analytical model
is proposed to describe the primary vertex reconstruction efficiency as
a function of the number of interactions per bunch crossing and of the
longitudinal size of the luminous region. Agreement between the data and
the predictions of this model is better than 3\% up to seventy
interactions per bunch crossing
Measurements of top-quark pair differential cross-sections in the lepton+jets channel in pp collisions at sqrt(s) = 8 TeV using the ATLAS detector
Measurements of normalized differential cross-sections of top-quark pair production are presented as a function of the top-quark, ttÂŻ system and event-level kinematic observables in proton-proton collisions at a centre-of-mass energy of sâ=8 TeV. The observables have been chosen to emphasize the ttÂŻ production process and to be sensitive to effects of initial- and final-state radiation, to the different parton distribution functions, and to non-resonant processes and higher-order corrections. The dataset corresponds to an integrated luminosity of 20.3 fbâ1, recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider. Events are selected in the lepton+jets channel, requiring exactly one charged lepton and at least four jets with at least two of the jets tagged as originating from a b-quark. The measured spectra are corrected for detector effects and are compared to several Monte Carlo simulations. The results are in fair agreement with the predictions over a wide kinematic range. Nevertheless, most generators predict a harder top-quark transverse momentum distribution at high values than what is observed in the data. The agreement for this observable improves when next-to-next-to-leading order corrections are taken into account. Using the current settings and parton distribution functions, the rapidity distributions are not well modelled by any generator under consideration. However, the level of agreement is improved when more recent sets of parton distribution functions are used
Measurements of top quark spin observables in tt events using dilepton final states in root s=8 TeV pp collisions with the ATLAS detector
Measurements of top quark spin observables in tt events are presented
based on 20.2 fb(-1) of root s = 8TeV proton-proton collisions recorded
with the ATLAS detector at the LHC. The analysis is performed in the
dilepton final state, characterised by the presence of two isolated
leptons ( electrons or muons). There are 15 observables, each sensitive
to a different coefficient of the spin density matrix of tt production,
which are measured independently. Ten of these observables are measured
for the first time. All of them are corrected for detector resolution
and acceptance effects back to the parton and stable-particle levels.
The measured values of the observables at parton level are compared to
Standard Model predictions at next-to-leading order in QCD. The
corrected distributions at stable-particle level are presented and the
means of the distributions are compared to Monte Carlo predictions. No
significant deviation from the Standard Model is observed for any
observable
ATLAS RPC Quality Assurance results at INFN Lecce
The main results of the quality assurance tests performed on the Resistive
Plate Chamber used by the ATLAS experiment at LHC as muon trigger chambers are
reported and discussed.
Since July 2004, about 270 RPC units has been certified at INFN Lecce site
and delivered to CERN, for being integrated in the final muon station of the
ATLAS barrel region.
We show the key RPC characteristics which qualify the performance of this
detector technology as muon trigger chamber in the harsh LHC enviroments.
These are dark current, chamber efficiency, noise rate, gas volume
tomography, and gas leakage.Comment: Comments: 6 pages, 1 table, 9 figures Proceedings of XXV Physics in
Collision-Prague, Czech Republic, 6-9 July 200
Measurement of jet activity produced in top-quark events with an electron, a muon and two b-tagged jets in the final state in pp collisions root s=13TeV with the ATLAS detector
Measurements of jet activity in top-quark pair events produced in
proton-proton collisions are presented, using 3.2 fb of pp collision
data at a centre-of-mass energy of 13 TeV collected by the ATLAS
experiment at the Large Hadron Collider. Events are chosen by requiring
an opposite-charge pair and two b-tagged jets in the final state. The
normalised differential cross-sections of top-quark pair production are
presented as functions of additional-jet multiplicity and transverse
momentum, . The fraction of signal events that do not contain additional
jet activity in a given rapidity region, the gap fraction, is measured
as a function of the threshold for additional jets, and is also
presented for different invariant mass regions of the system. All
measurements are corrected for detector effects and presented as
particle-level distributions compared to predictions with different
theoretical approaches for QCD radiation. While the kinematics of the
jets from top-quark decays are described well, the generators show
differing levels of agreement with the measurements of observables that
depend on the production of additional jets
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