9,491 research outputs found
KLOE results at the Frascati -factory DANE
The KLOE experiment at the Frascati -factory DANE has collected
about 0.5 fb of data till the end of the year 2002. These data allow to
perform a wide physics program, ranging from the physics of charged and neutral
kaons to radiative -decays. Results are presented for the lifetime
and the semileptonic processes . From the light meson
spectroscopy program, results on the decays as well as are presented.Comment: 5 pages, 3 figures, Proceedings contribution to the 10th Int.
Symposium on "Meson-Nucleon Physics and the Structure of the Nucleon"
(MENU04), Beijing, China, Aug. 30 - Sept. 4, 200
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
Eco-friendly gas mixtures for Resistive Plate Chambers based on Tetrafluoropropene and Helium
Due to the recent restrictions deriving from the application of the Kyoto
protocol, the main components of the gas mixtures presently used in the
Resistive Plate Chambers systems of the LHC experiments will be most probably
phased out of production in the coming years. Identifying possible replacements
with the adequate characteristics requires an intense R&D, which was recently
started, also in collaborations across the various experiments. Possible
candidates have been proposed and are thoroughly investigated. Some tests on
one of the most promising candidate - HFO-1234ze, an allotropic form of
tetrafluoropropane- have already been reported. Here an innovative approach,
based on the use of Helium, to solve the problems related to the too elevate
operating voltage of HFO-1234ze based gas mixtures, is discussed and the
relative first results are shown.Comment: 9 pages, 6 figures, 1 tabl
Development of laminar flow control wing surface porous structure
It was concluded that the chordwise air collection method, which actually combines chordwise and spanwise air collection, is the best of the designs conceived up to this time for full chord laminar flow control (LFC). Its shallower ducting improved structural efficiency of the main wing box resulting in a reduction in wing weight, and it provided continuous support of the chordwise panel joints, better matching of suction and clearing airflow requirements, and simplified duct to suction source minifolding. Laminar flow control on both the upper and lower surfaces was previously reduced to LFC suction on the upper surface only, back to 85 percent chord. The study concludes that, in addition to reduced wing area and other practical advantages, this system would be lighter because of the increase in effective structural wing thickness
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 dijet events using 37 fb(-1) of pp collision data collected at root s=13 TeV with the ATLAS detector
Dijet events are studied in the proton-proton collision dataset recorded
at root s = 13 TeV with the ATLAS detector at the Large Hadron Collider
in 2015 and 2016, corresponding to integrated luminosities of 3.5 fb(-1)
and 33.5 fb(-1) respectively. Invariant mass and angular distributions
are compared to background predictions and no significant deviation is
observed. For resonance searches, a new method for fitting the
background component of the invariant mass distribution is employed. The
dataset is then used to set upper limits at a 95\% confidence level on a
range of new physics scenarios. Excited quarks with masses below 6.0 TeV
are excluded, and limits are set on quantum black holes, heavy W'
bosons, W* bosons, and a range of masses and couplings in a Z' dark
matter mediator model. Model-independent limits on signals with a
Gaussian shape are also set, using a new approach allowing factorization
of physics and detector effects. From the angular distributions, a scale
of new physics in contact interaction models is excluded for scenarios
with either constructive or destructive interference. These results
represent a substantial improvement over those obtained previously with
lower integrated luminosity
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
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, tt¯ system and event-level kinematic observables in proton-proton collisions at a centre-of-mass energy of s√=8 TeV. The observables have been chosen to emphasize the tt¯ 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 fb−1, 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
- …