233 research outputs found
Bulk matter physics and its future at the Large Hadron Collider
Measurements at low transverse momentum will be performed at the LHC for
studying particle production mechanisms in and heavy-ion collisions. Some
of the experimental capabilities for bulk matter physics are presented,
focusing on tracking elements and particle identification. In order to
anticipate the study of baryon production for both colliding systems at
multi-TeV energies, measurements for identified species and recent model
extrapolations are discussed. Several mechanisms are expected to compete for
hadro-production in the low momentum region. For this reason, experimental
observables that could be used for investigating multi-parton interactions and
help understanding the "underlying event" content in the first collisions
at the LHC are also mentioned.Comment: 6 pages, 7 figures. To appear in the proceedings of Hot Quarks 2008,
Estes Park, Colorado, 18-23 August 200
Top Quark Physics at the LHC: A Review of the First Two Years
This review summarizes the highlights in the area of top quark physics
obtained with the two general purpose detectors ATLAS and CMS during the first
two years of operation of the Large Hadron Collider LHC. It covers the 2010 and
2011 data taking periods, where the LHC provided pp collisions at a
center-of-mass energy of sqrt(s)=7 TeV. Measurements are presented of the total
and differential top quark pair production cross section in many different
channels, the top quark mass and various other properties of the top quark and
its interactions, for instance the charge asymmetry. Measurements of single top
quark production and various searches for new physics involving top quarks are
also discussed. The already very precise experimental data are in good
agreement with the standard model.Comment: 107 pages, invited review for Int. J. Mod. Phys. A, v2 is identical
to v1 except for the addition of the table of content
Heavy Ions: Results from the Large Hadron Collider
On November 8, 2010 the Large Hadron Collider (LHC) at CERN collided first
stable beams of heavy ions (Pb on Pb) at center-of-mass energy of 2.76
TeV/nucleon. The LHC worked exceedingly well during its one month of operation
with heavy ions, delivering about 10 microbarn-inverse of data, with peak
luminosity reaching to
towards the end of the run. Three experiments, ALICE, ATLAS and CMS, recorded
their first heavy ion data, which were analyzed in a record time. The results
of the multiplicity, flow, fluctuations, and Bose-Einstein correlations
indicate that the fireball formed in nuclear collisions at the LHC is hotter,
lives longer, and expands to a larger size at freeze-out as compared to lower
energies. We give an overview of these as well as new results on quarkonia and
heavy flavour suppression, and jet energy loss.Comment: Proceedings of Lepton-Photon 2011 Conference, to be published in
Pramana, Journal of Physics. 15 page
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
Measurements of the Production, Decay and Properties of the Top Quark: A Review
With the full Tevatron Run II and early LHC data samples, the opportunity for
furthering our understanding of the properties of the top quark has never been
more promising. Although the current knowledge of the top quark comes largely
from Tevatron measurements, the experiments at the LHC are poised to probe
top-quark production and decay in unprecedented regimes. Although no current
top quark measurements conclusively contradict predictions from the standard
model, the precision of most measurements remains statistically limited.
Additionally, some measurements, most notably the forward-backward asymmetry in
top quark pair production, show tantalizing hints of beyond-the-Standard-Model
dynamics. The top quark sample is growing rapidly at the LHC, with initial
results now public. This review examines the current status of top quark
measurements in the particular light of searching for evidence of new physics,
either through direct searches for beyond the standard model phenomena or
indirectly via precise measurements of standard model top quark properties
Performance of the CMS Cathode Strip Chambers with Cosmic Rays
The Cathode Strip Chambers (CSCs) constitute the primary muon tracking device
in the CMS endcaps. Their performance has been evaluated using data taken
during a cosmic ray run in fall 2008. Measured noise levels are low, with the
number of noisy channels well below 1%. Coordinate resolution was measured for
all types of chambers, and fall in the range 47 microns to 243 microns. The
efficiencies for local charged track triggers, for hit and for segments
reconstruction were measured, and are above 99%. The timing resolution per
layer is approximately 5 ns
Heavy quarkonium: progress, puzzles, and opportunities
A golden age for heavy quarkonium physics dawned a decade ago, initiated by
the confluence of exciting advances in quantum chromodynamics (QCD) and an
explosion of related experimental activity. The early years of this period were
chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in
2004, which presented a comprehensive review of the status of the field at that
time and provided specific recommendations for further progress. However, the
broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles
could only be partially anticipated. Since the release of the YR, the BESII
program concluded only to give birth to BESIII; the -factories and CLEO-c
flourished; quarkonium production and polarization measurements at HERA and the
Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the
deconfinement regime. All these experiments leave legacies of quality,
precision, and unsolved mysteries for quarkonium physics, and therefore beg for
continuing investigations. The plethora of newly-found quarkonium-like states
unleashed a flood of theoretical investigations into new forms of matter such
as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the
spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b},
and b\bar{c} bound states have been shown to validate some theoretical
approaches to QCD and highlight lack of quantitative success for others. The
intriguing details of quarkonium suppression in heavy-ion collisions that have
emerged from RHIC have elevated the importance of separating hot- and
cold-nuclear-matter effects in quark-gluon plasma studies. This review
systematically addresses all these matters and concludes by prioritizing
directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K.
Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D.
Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A.
Petrov, P. Robbe, A. Vair
Neutrino Masses at LHC: Minimal Lepton Flavour Violation in Type-III See-saw
We study the signatures of minimal lepton flavour violation in a simple
Type-III see - saw model in which the flavour scale is given by the new fermion
triplet mass and it can be naturally light enough to be produced at the LHC. In
this model the flavour structure of the lepton number conserving couplings of
the triplet fermions to the Standard Model leptons can be reconstructed from
the neutrino mass matrix and the smallness of the neutrino mass is associated
with a tiny violation of total lepton number. Characteristic signatures of this
model include suppressed lepton number violation decays of the triplet
fermions, absence of displaced vertices in their decays and predictable lepton
flavour composition of the states produced in their decays. We study the
observability of these signals in the processes pp\rightarrow 3\ell + 2j
+\Sla{E_T} and with or taking into
account the present low energy data on neutrino physics and the corresponding
Standard Model backgrounds. Our results indicate that the new fermionic states
can be observed for masses up to 500 GeV depending on the CP violating Majorana
phase for an integrated luminosity of 30 fb. Moreover, the flavour of
the final state leptons in the above processes can shed light on the neutrino
mass ordering.Comment: 31 pages, 11 Figures, matches published versio
Performance and Operation of the CMS Electromagnetic Calorimeter
The operation and general performance of the CMS electromagnetic calorimeter
using cosmic-ray muons are described. These muons were recorded after the
closure of the CMS detector in late 2008. The calorimeter is made of lead
tungstate crystals and the overall status of the 75848 channels corresponding
to the barrel and endcap detectors is reported. The stability of crucial
operational parameters, such as high voltage, temperature and electronic noise,
is summarised and the performance of the light monitoring system is presented
Precise date for the Laacher See eruption synchronizes the Younger Dryas
The Laacher See eruption (LSE) in Germany ranks among Europeâs largest volcanic events of the Upper Pleistocene. Although tephra deposits of the LSE represent an
important isochron for the synchronization of proxy archives at the Late Glacial to Early Holocene transition, uncertainty in the age of the eruption has prevailed. Here we present dendrochronological and radiocarbon measurements of subfossil trees that were buried by pyroclastic deposits that frmly date the LSE to 13,006 Âą 9 calibrated years before present (bp; taken as ad 1950), which is more than a century earlier than previously accepted. The revised age of the LSE necessarily shifts the chronology of European varved lakes relative to the Greenland ice core record, thereby dating the onset of the Younger Dryas to 12,807 Âą 12 calibrated years bp, which is around 130 years earlier than thought. Our results synchronize the onset of the Younger Dryas across the North AtlanticâEuropean sector, preclude a direct link between the LSE and Greenland Stadial-1 cooling, and suggest a large-scale common mechanism of a weakened Atlantic Meridional Overturning Circulation under warming condition
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