5,992 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
Dark matter searches at LHC
Besides Standard Model measurements and other Beyond Standard Model studies,
the ATLAS and CMS experiments at the LHC will search for Supersymmetry, one of
the most attractive explanation for dark matter. The SUSY discovery potential
with early data is presented here together with some first results obtained
with 2010 collision data at 7 TeV. Emphasis is placed on measurements and
parameter determination that can be performed to disentangle the possible SUSY
models and SUSY look-alike and the interpretation of a possible positive
supersymmetric signal as an explanation of dark matter.Comment: 15 pages, 14 figures, Invited plenary talk given at DISCRETE 2010:
Symposium On Prospects In The Physics Of Discrete Symmetries, 6-11 Dec 2010,
Rome, Ital
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
Macroscopic Strings and "Quirks" at Colliders
We consider extensions of the standard model containing additional heavy
particles ("quirks") charged under a new unbroken non-abelian gauge group as
well as the standard model. We assume that the quirk mass m is in the
phenomenologically interesting range 100 GeV--TeV, and that the new gauge group
gets strong at a scale Lambda < m. In this case breaking of strings is
exponentially suppressed, and quirk production results in strings that are long
compared to 1/Lambda. The existence of these long stable strings leads to
highly exotic events at colliders. For 100 eV < Lambda < keV the strings are
macroscopic, giving rise to events with two separated quirk tracks with
measurable curvature toward each other due to the string interaction. For keV <
Lambda < MeV the typical strings are mesoscopic: too small to resolve in the
detector, but large compared to atomic scales. In this case, the bound state
appears as a single particle, but its mass is the invariant mass of a quirk
pair, which has an event-by-event distribution. For MeV < Lambda < m the
strings are microscopic, and the quirks annihilate promptly within the
detector. For colored quirks, this can lead to hadronic fireball events with
10^3 hadrons with energy of order GeV emitted in conjunction with hard decay
products from the final annihilation.Comment: Added discussion of photon-jet decay, fixed minor typo
Forward production of beauty baryons in pp collisions at LHC
The production of charmed and beauty baryons in proton-proton collisions at
high energies is analyzed within the modified quark-gluon string model. We
present some predictions for the experiments on the forward beauty baryon
production in pp collisions at LHC energies. This analysis allows us to find
useful information on the Regge trajectories of the heavy (b barb) mesons and
the sea beauty quark distributions in the proton.Comment: 14 pages, 12 figure
Constraining SUSY Dark Matter with the ATLAS Detector at the LHC
In the event that R-Parity conserving supersymmetry (SUSY) is discovered at
the LHC, a key issue which will need to be addressed will be the consistency of
that signal with astrophysical and non-accelerator constraints on SUSY Dark
Matter. This issue is studied for the SPS1a mSUGRA benchmark model by using
measurements of end-points and thresholds in the invariant mass spectra of
various combinations of leptons and jets in ATLAS to constrain the model
parameters. These constraints are then used to assess the statistical accuracy
with which quantities such as the Dark Matter relic density and direct
detection cross-section can be measured. Systematic effects arising from the
use of different mSUGRA RGE codes are also estimated. Results indicate that for
SPS1a a statistical(systematic) precision on the relic abundance ~ 2.8% (3 %)
can be obtained given 300 fb-1 of data.Comment: 11 pages, 10 encapsulated postscript figures. Minor modification to
ref
Neural NILM: Deep Neural Networks Applied to Energy Disaggregation
Energy disaggregation estimates appliance-by-appliance electricity
consumption from a single meter that measures the whole home's electricity
demand. Recently, deep neural networks have driven remarkable improvements in
classification performance in neighbouring machine learning fields such as
image classification and automatic speech recognition. In this paper, we adapt
three deep neural network architectures to energy disaggregation: 1) a form of
recurrent neural network called `long short-term memory' (LSTM); 2) denoising
autoencoders; and 3) a network which regresses the start time, end time and
average power demand of each appliance activation. We use seven metrics to test
the performance of these algorithms on real aggregate power data from five
appliances. Tests are performed against a house not seen during training and
against houses seen during training. We find that all three neural nets achieve
better F1 scores (averaged over all five appliances) than either combinatorial
optimisation or factorial hidden Markov models and that our neural net
algorithms generalise well to an unseen house.Comment: To appear in ACM BuildSys'15, November 4--5, 2015, Seou
A mobile data acquisition system
A mobile data aquisition (MobiDAQ) was developed for the ATLAS central hadronic
calorimeter (TileCal). MobiDAQ has been designed in order to test the functionalities of the TileCal
front-end electronics and to acquire calibration data before the final back-end electronics were built
and tested. MobiDAQ was also used to record the first cosmic ray events acquired by an ATLAS
subdetector in the underground experimental area
High-Temperature Superconducting Level Meter for Liquid Argon Detectors
Capacitive devices are customarily used as probes to measure the level of
noble liquids in detectors operated for neutrino studies and dark matter
searches. In this work we describe the use of a high-temperature
superconducting material as an alternative to control the level of a cryogenic
noble liquid. Lab measurements indicate that the superconductor shows a linear
behaviour, a high degree of stability and offers a very accurate determination
of the liquid volume. This device is therefore a competitive instrument and
shows several advantages over conventional level meters.Comment: 13 pages, 11 figures. Accepted for publication in JINS
Absorbing systematic effects to obtain a better background model in a search for new physics
This paper presents a novel approach to estimate the Standard Model
backgrounds based on modifying Monte Carlo predictions within their systematic
uncertainties. The improved background model is obtained by altering the
original predictions with successively more complex correction functions in
signal-free control selections. Statistical tests indicate when sufficient
compatibility with data is reached. In this way, systematic effects are
absorbed into the new background model. The same correction is then applied on
the Monte Carlo prediction in the signal region. Comparing this method to other
background estimation techniques shows improvements with respect to statistical
and systematical uncertainties. The proposed method can also be applied in
other fields beyond high energy physics
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