9,377 research outputs found
Recent Heavy Ion Results with the ATLAS Detector at the LHC
Results are presented from the ATLAS collaboration from the 2010 LHC heavy
ion run, during which nearly 10 inverse microbarns of luminosity were
delivered. Soft physics results include charged particle multiplicities and
collective flow. The charged particle multiplicity, which tracks initial state
entropy production, increases by a factor of two relative to the top RHIC
energy, with a centrality dependence very similar to that already measured at
RHIC. Measurements of elliptic flow out to large transverse momentum also show
similar results to what was measured at RHIC, but no significant pseudorapidity
dependence. Extensions of these measurements to higher harmonics have also been
made, and can be used to explain structures in the two-particle correlation
functions that had long been attributed to jet-medium interactions. New hard
probe measurements include single muons, jets and high hadrons. Single
muons at high momentum are used to extract the yield of bosons and
are found to be consistent within statistical uncertainties with binary
collision scaling. Conversely, jets are found to be suppressed in central
events by a factor of two relative to peripheral events, with no significant
dependence on the jet energy. Fragmentation functions are also found to be the
same in central and peripheral events. Finally, charged hadrons have been
measured out to 30 GeV, and their centrality dependence relative to peripheral
events is similar to that found for jets.Comment: 9 pages, 9 figures, proceedings for Quark Matter 2011, Annecy,
France, May 23-28, 201
Atmospheric response to variations in sea surface temperature
An extended range prediction experiment was performed with the GISS atmospheric model on a global data to test the sensitivity of the model to sea surface temperature (SST) variation over a two-week forecast period. The use of an initial observed SST field in place of the climatological monthly mean sea temperatures for surface flux calculations in the model was found to have a significant effect on the predicted precipitation over the ocean, with enhanced convection computed over areas where moderately large warm SST anomalies are found. However, there was no detectable positive effect of the SST anomaly field on forecast quality. The influence of the SST anomalies on the daily predicted fields of pressure and geopotential is relatively insignificant up to about one week compared with the growth of prediction error, and is no greater over a two-week period than that resulting from random errors in the initial meteorological state. The 14-day average fields of sea level pressure and 500-mb height predicted by the model, appear to be similarly insensitive to anomalies of sea surface temperature
Measurement of elliptic and higher order flow harmonics at TeV Pb+Pb collisions with the ATLAS Detector
The measurements of flow harmonics - using the event plane and two
particle correlations methods in broad , and centrality ranges
using the ATLAS detector at LHC are presented. ATLAS recorded about 9 of lead-lead collision data in the 2010 heavy ion run. The
full azimuthal acceptance of the ATLAS detector in units of
pseudorapidity for charged hadrons and the large amount of data allows for a
detailed study of the flow harmonics. The , centrality and ranges
where the two methods give consistent and where they disagree are
discussed. It is shown that the ridge as well as the so called "mach-cone" seen
in two particle correlations are largely accounted for by the collective flow.
Some scaling relations in the dependence of the are also discussed
ATLAS silicon module assembly and qualification tests at IFIC Valencia
ATLAS experiment, designed to probe the interactions of particles emerging
out of proton proton collisions at energies of up to 14 TeV, will assume
operation at the Large Hadron Collider (LHC) at CERN in 2007. This paper
discusses the assembly and the quality control tests of forward detector
modules for the ATLAS silicon microstrip detector assembled at the Instituto de
Fisica Corpuscular (IFIC) in Valencia. The construction and testing procedures
are outlined and the laboratory equipment is briefly described. Emphasis is
given on the module quality achieved in terms of mechanical and electrical
stability.Comment: 23 pages, 38 EPS figures, uses JINST LaTeX clas
Measurement of Jets and Jet Suppression in sqrt(s_NN)=2.76 TeV Lead-Lead Collisions with the ATLAS detector at the LHC
The first results of single jet observables in Pb+Pb collisions at
sqrt(s_NN)=2.76 TeV measured with the ATLAS detector at the LHC are presented.
Full jets are reconstructed with the anti-kt algorithm with R= 0.2 and 0.4,
using an event-by-event subtraction procedure to correct for the effects of the
underlying event including elliptic flow. The geometrically-scaled ratio of jet
yields in central and peripheral events,Rcp, indicates a clear suppression of
jets with ET >100 GeV. The transverse and longitudinal distributions of jet
fragments is also presented. We find little no substantial change to the
fragmentation properties and no significant change in the level of suppression
when moving to the larger jet definition.Comment: 5 pages, 6 figures, proceedings for Quark Matter 2011, Annecy,
France, May 23-28, 201
Upgrade of the ATLAS Muon Trigger for the SLHC
The outer shell of the ATLAS experiment at the LHC consists of a system of
toroidal air-core magnets in order to allow for the precise measurement of the
transverse momentum p of muons, which in many physics channels are a
signature of interesting physics processes. For the precise determination of
the muon momentum Monitored Drift Tube chambers (MDT) with high position
accuracy are used, while for the fast identification of muon tracks chambers
with high time resolution are used, able to select muons above a predefined
p threshold for use in the first Level of the ATLAS triggering system
(Level-1 trigger). When the luminosity of the LHC will be upgraded to 4-5 times
the present nominal value (SLHC) in about a decade from now, an improvement of
the selectivity of the ATLAS Level-1 triggering system will be mandatory in
order to cope with the maximum allowed trigger rate of 100 kHz. For the Level-1
trigger of the ATLAS muon spectrometer this means an increase of the p
threshold for single muons. Due to the limited spatial resolution of the
trigger chambers, however, the selectivity for tracks above ~20 GeV/c is
insufficient for an effective reduction of the Level-1 rate. We describe how
the track coordinates measured in the MDT precision chambers can be used to
decisively improve the selectivity for high momentum tracks. The resulting
increase in latency will also be discussed.Comment: These are the proceedings of a presentation given at the Topical
Workshop of Electronics for Particle Physics 2010 in Aachen, Germany (sept.,
20-24, 2010
Determination of rain rate from a spaceborne radar using measurements of total attenuation
Studies shows that path-integrated rain rates can be determined by means of a direct measurement of attenuation. For ground based radars this is done by measuring the backscattering cross section of a fixed target in the presence and absence of rain along the radar beam. A ratio of the two measurements yields a factor proportional to the attenuation from which the average rain rate is deduced. The technique is extended to spaceborne radars by choosing the ground as reference target. The technique is also generalized so that both the average and range-profiled rain rates are determined. The accuracies of the resulting estimates are evaluated for a narrow beam radar located on a low earth orbiting satellite
LHC Coverage of RPV MSSM with Light Stops
We examine the sensitivity of recent LHC searches to signatures of
supersymmetry with R-parity violation (RPV). Motivated by naturalness of the
Higgs potential, which would favor light third-generation squarks, and the
stringent LHC bounds on spectra in which the gluino or first and second
generation squarks are light, we focus on scenarios dominated by the pair
production of light stops. We consider the various possible direct and cascade
decays of the stop that involve the trilinear RPV operators. We find that in
many cases, the existing searches exclude stops in the natural mass range and
beyond. However, typically there is little or no sensitivity to cases dominated
by UDD operators or LQD operators involving taus. We propose several ideas for
searches which could address the existing gaps in experimental coverage of
these signals.Comment: 41 pages, 12 figures; v2: included new searches (see footnote 10),
minor corrections and improvement
Searches for phenomena beyond the Standard Model at the LHC with the ATLAS and CMS detectors
The LHC has delivered several fb-1 of data in spring and summer 2011, opening
new windows of opportunity for discovering phenomena beyond the Standard Model.
A summary of the searches conducted by the ATLAS and CMS experiments based on
about 1 fb-1 of data is presented.Comment: Presented at Lepton-Photon 2011, Mumbai, India; 10 pages, 11 figure
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