3,642 research outputs found
Precision Drift Chambers for the Atlas Muon Spectrometer
ATLAS is a detector under construction to explore the physics at the Large
Hadron Collider at CERN. It has a muon spectrometer with an excellent momentum
resolution of 3-10%, provided by three layers of precision monitored-drift-tube
chambers in a toroidal magnetic field. A single drift tube measures a track
point with a mean resolution close to 100 micron, even at the expected high
neutron and gamma background rates. The tubes are positioned within the chamber
with an accuracy of 20 microns, achieved by elaborate construction and assembly
monitoring procedures.Comment: 3 pages, 2 eps figures, Proceedings for poster at Physics in
Collisions Conference (PIC03), Zeuthen, Germany, June 2003. FRAP1
Echo of the Quantum Phase Transition of CeCuAu in XPS: Breakdown of Kondo Screening
We present an X-ray photoemission study of the heavy-fermion system
CeCuAu across the magnetic quantum phase transition of this
compound at temperatures above the single-ion Kondo temperature . In
dependence of the Au concentration we observe a sudden change of the
-occupation number and the core-hole potential at the
critical concentration . We interpret these findings in the framework
of the single-impurity Anderson model. Our results are in excellent agreement
with findings from earlier UPS measurements %\cite{klein08qpt} and provide
further information about the precursors of quantum criticality at elevated
temperatures.Comment: 5 pages, 3 figures; published version, references updated, minor
changes in wordin
High-temperature signatures of quantum criticality in heavy fermion systems
We propose a new criterion for distinguishing the Hertz-Millis (HM) and the
local quantum critical (LQC) mechanism in heavy fermion systems with a magnetic
quantum phase transition (QPT). The criterion is based on our finding that the
spin screening of Kondo ions can be completely suppressed by the RKKY coupling
to the surrounding magnetic ions even without magnetic ordering and that,
consequently, the signature of this suppression can be observed in
spectroscopic measurements above the magnetic ordering temperature. We apply
the criterion to high-resolution photoemission (UPS) measurements on
CeCuAu and conclude that the QPT in this system is dominated by
the LQC scenario.Comment: Inveted paper, International Conference on Magnetism, ICM 2009,
Karlsruhe. Published version, added discussions of the relevance of
Fermi-surface fluctuations and of a structural transition near the QC
Estimation of Top Background to SUSY Searches from Data
The Standard Model process of ttbar production is one of the most important backgrounds to searches for Supersymmetry (SUSY) at the Large Hadron Collider (LHC) at CERN. We describe the methods to estimate the contributions of ttbar decay with one and two leptons in SUSY searches with zero, one or two isolated leptons, multi-jets and large missing transverse energy with the first data of the ATLAS experiment. The performance has been evaluated with simulated data
Large-Scale Production of Monitored Drift Tube Chambers for the ATLAS Muon Spectrometer
Precision drift tube chambers with a sense wire positioning accuracy of
better than 20 microns are under construction for the ATLAS muon spectrometer.
70% of the 88 large chambers for the outermost layer of the central part of the
spectrometer have been assembled. Measurements during chamber construction of
the positions of the sense wires and of the sensors for the optical alignment
monitoring system demonstrate that the requirements for the mechanical
precision of the chambers are fulfilled
Switchable lasing in coupled multimode microcavities
We propose the new concept of a switchable multimode microlaser. As a
generic, realistic model of a multimode microresonator a system of two coupled
defects in a two-dimensional photonic crystal is considered. We demonstrate
theoretically that lasing of the cavity into one selected resonator mode can be
caused by injecting an appropriate optical pulse at the onset of laser action
(injection seeding). Temporal mode-to-mode switching by re-seeding the cavity
after a short cool-down period is demonstrated by direct numerical solution. A
qualitative analytical explanation of the mode switching in terms of the laser
bistability is presented.Comment: Accepted for publication in Physical Review Letters. Published,
somewhat shortened versio
Signature of quantum criticality in photoemission spectroscopy at elevated temperature
A quantum phase transition (QPT) in a heavy-fermion (HF) compound may destroy
the Fermi liquid groundstate. However, the conditions for this breakdown have
remained obscure. We report the first direct investigation of heavy
quasiparticle formation and breakdown in the canonical system
CeCuAu by ultraviolet photoemission spectroscopy at elevated
temperatures without the complications of lattice coherence. Surprisingly, the
single-ion Kondo energy scale exhibits an abrupt step near the quantum
critical Au concentration of . We show theoretically that this step is
expected from a highly non-linear renormalization of the local spin coupling at
each Ce site, induced by spin fluctuations on neighboring sites. It provides a
general high-temperature indicator for HF quasiparticle breakdown at a QPT.Comment: Published version, PRL, minor changes in wordin
Scattering of Be and B and the astrophysical S factor
Measurements of scattering of Be at 87 MeV on a melamine (CNH) target and of B at 95 MeV on C were performed. For Be
the angular range was extended over previous measurements and monitoring of the
intensity of the radioactive beam was improved. The measurements allowed us to
check and improve the optical model potentials used in the incoming and
outgoing channels for the analysis of existing data on the proton transfer
reaction N(Be,B)C. The resultslead to an updated
determination of the asymptotic normalization coefficient for the virtual decay
B Be + . We find a slightly larger value,
fm, for the melamine target. This
implies an astrophysical factor, eVb, for the
solar neutrino generating reaction Be(,)B.Comment: 7 pages, 4 figure
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