336 research outputs found
Experimental Tests of Particle Flow Calorimetry
Precision physics at future colliders requires highly granular calorimeters
to support the Particle Flow Approach for event reconstruction. This article
presents a review of about 10 - 15 years of R\&D, mainly conducted within the
CALICE collaboration, for this novel type of detector. The performance of large
scale prototypes in beam tests validate the technical concept of particle flow
calorimeters. The comparison of test beam data with simulation, of e.g.\
hadronic showers, supports full detector studies and gives deeper insight into
the structure of hadronic cascades than was possible previously.Comment: 55 pages, 83 figures, to appear in Reviews of Modern physic
Collaborative yet independent: Information practices in the physical sciences
In many ways, the physical sciences are at the forefront of using digital tools and methods to work with information and data. However, the fields and disciplines that make up the physical sciences are by no means uniform, and physical scientists find, use, and disseminate information in a variety of ways. This report examines information practices in the physical sciences across seven cases, and demonstrates the richly varied ways in which physical scientists work, collaborate, and share information and data.
This report details seven case studies in the physical sciences. For each case, qualitative interviews and focus groups were used to understand the domain. Quantitative data gathered from a survey of participants highlights different information strategies employed across the cases, and identifies important software used for research.
Finally, conclusions from across the cases are drawn, and recommendations are made. This report is the third in a series commissioned by the Research Information Network (RIN), each looking at information practices in a specific domain (life sciences, humanities, and physical sciences). The aim is to understand how researchers within a range of disciplines find and use information, and in particular how that has changed with the introduction of new technologies
Particle Physics and Cosmology
Today, both particle physics and cosmology are described by few parameter
Standard Models, i.e. it is possible to deduce consequence of particle physics
in cosmology and vice verse. The former is examined in this lecture, in light
of the recent systematic exploration of the electroweak scale by the LHC
experiments. The two main results of the first phase of the LHC, the discovery
of a Higgs-like particle and the absence so far of new particles predicted by
"natural" theories beyond the Standard Model (supersymmetry, extra-dimension
and composite Higgs) are put in a historical context to enlighten their
importance and then presented extensively. To be complete, a short review from
the neutrino physics, which can not be probed at LHC, is also given. The
ability of all these results to resolve the 3 fundamental questions of
cosmology about the nature of dark energy and dark matter as well as the origin
of matter-antimatter asymmetry is discussed in each case.Comment: 32 pages, 47 figures, Proceeding from the 100th Les Houches Summer
School on Post-Planck Cosmology, July 8th - Aug 2nd 2013. Update with
recently published ATLAS/CMS 8 TeV result
Distributed computing and farm management with application to the search for heavy gauge bosons using the ATLAS experiment at the LHC (CERN)
The Standard Model of particle physics describes the strong, weak, and electromagnetic forces between the fundamental particles of ordinary matter. However, it presents several problems and some questions remain unanswered so it cannot be considered a complete theory of fundamental interactions. Many extensions have been proposed in order to address these problems. Some important recent extensions are the Extra Dimensions theories. In the context of some models with Extra Dimensions of size about , in particular in the ADD model with only fermions confined to a D-brane, heavy Kaluza-Klein excitations are expected, with the same properties as SM gauge bosons but more massive. In this work, three hadronic decay modes of some of such massive gauge bosons, Z* and W*, are investigated using the ATLAS experiment at the Large Hadron Collider (LHC), presently under construction at CERN. These hadronic modes are more difficult to detect than the leptonic ones, but they should allow a measurement of the couplings between heavy gauge bosons and quarks. The events were generated using the ATLAS fast simulation and reconstruction MC program Atlfast coupled to the Monte Carlo generator PYTHIA. We found that for an integrated luminosity of and a heavy gauge boson mass of 2 TeV, the channels Z*->bb and Z*->tt would be difficult to detect because the signal would be very small compared with the expected backgrou nd, although the significance in the case of Z*->tt is larger. In the channel W*->tb , the decay might yield a signal separable from the background and a significance larger than 5 so we conclude that it would be possible to detect this particular mode at the LHC. The analysis was also performed for masses of 1 TeV and we conclude that the observability decreases with the mass. In particular, a significance higher than 5 may be achieved below approximately 1.4, 1.9 and 2.2 TeV for Z*->bb , Z*->tt and W*->tb respectively. The LHC will start to operate in 2008 and collect data in 2009. It will produce roughly 15 Petabytes of data per year. Access to this experimental data has to be provided for some 5,000 scientists working in 500 research institutes and universities. In addition, all data need to be available over the estimated 15-year lifetime of the LHC. The analysis of the data, including comparison with theoretical simulations, requires an enormous computing power. The computing challenges that scientists have to face are the huge amount of data, calculations to perform and collaborators. The Grid has been proposed as a solution for those challenges. The LHC Computing Grid project (LCG) is the Grid used by ATLAS and the other LHC experiments and it is analised in depth with the aim of studying the possible complementary use of it with another Grid project. That is the Berkeley Open Infrastructure for Network C omputing middle-ware (BOINC) developed for the SETI@home project, a Grid specialised in high CPU requirements and in using volunteer computing resources. Several important packages of physics software used by ATLAS and other LHC experiments have been successfully adapted/ported to be used with this platform with the aim of integrating them into the LHC@home project at CERN: Atlfast, PYTHIA, Geant4 and Garfield. The events used in our physics analysis with Atlfast were reproduced using BOINC obtaining exactly the same results. The LCG software, in particular SEAL, ROOT and the external software, was ported to the Solaris/sparc platform to study it's portability in general as well. A testbed was performed including a big number of heterogeneous hardware and software that involves a farm of 100 computers at CERN's computing center (lxboinc) together with 30 PCs from CIEMAT and 45 from schools from Extremadura (Spain). That required a preliminary study, development and creation of components of the Quattor software and configuration management tool to install and manage the lxboinc farm and it also involved the set up of a collaboration between the Spanish research centers and government and CERN. The testbed was successful and 26,597 Grid jobs were delivered, executed and received successfully. We conclude that BOINC and LCG are complementary and useful kinds of Grid that can be used by ATLAS and the other LHC experiments. LCG has very good data distribution, management and storage capabilities that BOINC does not have. In the other hand, BOINC does not need high bandwidth or Internet speed and it also can provide a huge and inexpensive amount of computing power coming from volunteers. In addition, it is possible to send jobs from LCG to BOINC and vice versa. So, possible complementary cases are to use volunteer BOINC nodes when the LCG nodes have too many jobs to do or to use BOINC for high CPU tasks like event generators or reconstructions while concentrating LCG for data analysis
A Roadmap for HEP Software and Computing R&D for the 2020s
Particle physics has an ambitious and broad experimental programme for the coming decades. This programme requires large investments in detector hardware, either to build new facilities and experiments, or to upgrade existing ones. Similarly, it requires commensurate investment in the R&D of software to acquire, manage, process, and analyse the shear amounts of data to be recorded. In planning for the HL-LHC in particular, it is critical that all of the collaborating stakeholders agree on the software goals and priorities, and that the efforts complement each other. In this spirit, this white paper describes the R&D activities required to prepare for this software upgrade.Peer reviewe
Top-squark pair production at the LHC: a complete analysis at next-to-leading order
We present a complete next-to-leading order study of top-squark pair
production at the LHC, including QCD and EW corrections. The calculation is
performed within the Minimal Supersymmetric Standard Model and numerical
results are presented for parameter regions compatible with the observed Higgs
boson. We employ the most recent parton distribution functions including QED
corrections and we find NLO EW corrections to the inclusive stop-pair
production cross section up to compared to the leading-order
prediction. Besides corrections to inclusive cross sections also important
kinematic distributions are investigated.Comment: 27 pages, 10 figures. Version published in JHEP. The numerical
discussion in Section 3 has been extended. References have been adde
Trigger and Timing Distributions using the TTC-PON and GBT Bridge Connection in ALICE for the LHC Run 3 Upgrade
The ALICE experiment at CERN is preparing for a major upgrade for the third
phase of data taking run (Run 3), when the high luminosity phase of the Large
Hadron Collider (LHC) starts. The increase in the beam luminosity will result
in high interaction rate causing the data acquisition rate to exceed 3 TB/sec.
In order to acquire data for all the events and to handle the increased data
rate, a transition in the readout electronics architecture from the triggered
to the trigger-less acquisition mode is required. In this new architecture, a
dedicated electronics block called the Common Readout Unit (CRU) is defined to
act as a nodal communication point for detector data aggregation and as a
distribution point for timing, trigger and control (TTC) information. TTC
information in the upgraded triggerless readout architecture uses two
asynchronous high-speed serial links connections: the TTC-PON and the GBT. We
have carried out a study to evaluate the quality of the embedded timing signals
forwarded by the CRU to the connected electronics using the TTC-PON and GBT
bridge connection. We have used four performance metrics to characterize the
communication bridge: (a)the latency added by the firmware logic, (b)the jitter
cleaning effect of the PLL on the timing signal, (c)BER analysis for
quantitative measurement of signal quality, and (d)the effect of optical
transceivers parameter settings on the signal strength. Reliability study of
the bridge connection in maintaining the phase consistency of timing signals is
conducted by performing multiple iterations of power on/off cycle, firmware
upgrade and reset assertion/de-assertion cycle (PFR cycle). The test results
are presented and discussed concerning the performance of the TTC-PON and GBT
bridge communication chain using the CRU prototype and its compliance with the
ALICE timing requirements
The Hierarchy Solution to the LHC Inverse Problem
Supersymmetric (SUSY) models, even those described by relatively few
parameters, generically allow many possible SUSY particle (sparticle) mass
hierarchies. As the sparticle mass hierarchy determines, to a great extent, the
collider phenomenology of a model, the enumeration of these hierarchies is of
the utmost importance. We therefore provide a readily generalizable procedure
for determining the number of sparticle mass hierarchies in a given SUSY model.
As an application, we analyze the gravity-mediated SUSY breaking scenario with
various combinations of GUT-scale boundary conditions involving different
levels of universality among the gaugino and scalar masses. For each of the
eight considered models, we provide the complete list of forbidden hierarchies
in a compact form. Our main result is that the complete (typically rather
large) set of forbidden hierarchies among the eight sparticles considered in
this analysis can be fully specified by just a few forbidden relations
involving much smaller subsets of sparticles.Comment: 44 pages, 2 figures. Python code providing lists of allowed and
forbidden hierarchy is included in ancillary file
Search for Supersymmetry in Trilepton Final States with the ATLAS Detector and the Alignment of the ATLAS Silicon Tracker
One of the main goals of the ATLAS detector at the LHC of CERN, a
proton-proton collider with a nominal centre-of-mass energy of 14 TeV, is to
search for New Physics beyond the Standard Model (BSM). A widely favoured BSM
candidate is Supersymmetry (SUSY), which postulates a superpartner for each
Standard Model particle. The first part of this thesis describes a strategy for
an early discovery of SUSY using the trilepton signature, with a focus on
gravity-mediated SUSY breaking, mSUGRA. The discovery potential for SUSY for
the case where strongly interacting supersymmetric particles are very massive
is critically investigated. A possible choice of triggers for L = 10-31cm-2s-1
is suggested by optimising the event yield at intermediate and final selection
stages. A novel method to measure the rate of leptons from heavy flavour decays
passing isolation requirements by isolating tt events in data is outlined.
The task of the ATLAS silicon tracker is to track particles produced in
proton-proton collisions in its centre, measuring their momenta and production
vertices. The precise knowledge of the silicon tracker module positions and
their orientation in space (alignment) down to some microns and fractions of a
miliradian in the critical coordinates is of vital importance for large parts
of the ambitious ATLAS physics program. In the second part of the thesis, the
alignment of the ATLAS silicon tracker using the Robust Alignment algorithm and
particle tracks is described. The algorithm is applied to align end-cap A of
the pixel detector using cosmic ray particle tracks recorded during its
on-surface commissioning in 2006. Finally, about 2M cosmic ray tracks collected
by ATLAS in situ in autumn 2008 are utilised to provide a coherent alignment of
the entire silicon tracker with the Robust Alignment algorithm.Comment: 236 pages, Ph.D. thesis; http://cdsweb.cern.ch/record/123186
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