853 research outputs found
High Efficiency Detection of Argon Scintillation Light of 128nm Using LAAPDs
The possibility of efficient collection and detection of vacuum ultraviolet
light as emitted by argon, krypton, and xenon gas is studied. Absolute quantum
efficiencies of large area avalanche photodiodes (LAAPDs) are derived at these
wavelengths. VUV light of wavelengths down to the 128nm of Ar emission is shown
to be detectable with silicon avalanche photodiodes at quantum efficiencies
above 42%. Flexible Mylar foil overcoated with Al+MgF is measured to have a
specular reflectivity of 91% at argon emission wavelength. Low-pressure
argon gas is shown to emit significant amounts of non-UV radiation. The average
energy expenditure for the creation of non-UV photons in argon gas at this
pressure is measured to be below 378 eV.Comment: 5 pages, 4 figures, Talk given at IEEE 2005 Nuclear Science Symposium
and Medical Imaging Conference, Puerto Ric
Kosterlitz-Thouless Universality in a Fermionic System
A new extension of the attractive Hubbard model is constructed to study the
critical behavior near a finite temperature superconducting phase transition in
two dimensions using the recently developed meron-cluster algorithm. Unlike
previous calculations in the attractive Hubbard model which were limited to
small lattices, the new algorithm is used to study the critical behavior on
lattices as large as . These precise results for the first time
show that a fermionic system can undergo a finite temperature phase transition
whose critical behavior is well described by the predictions of Kosterlitz and
Thouless almost three decades ago. In particular it is confirmed that the
spatial winding number susceptibility obeys the well known predictions of
finite size scaling for and up to logarithmic corrections the pair
susceptibility scales as at large volumes with for .Comment: Revtex format; 4 pages, 2 figure
Topological Phases in Neuberger-Dirac operator
The response of the Neuberger-Dirac fermion operator D=\Id + V in the
topologically nontrivial background gauge field depends on the negative mass
parameter in the Wilson-Dirac fermion operator which enters
through the unitary operator . We classify
the topological phases of by comparing its index to the topological charge
of the smooth background gauge field. An exact discrete symmetry in the
topological phase diagram is proved for any gauge configurations. A formula for
the index of D in each topological phase is derived by obtaining the total
chiral charge of the zero modes in the exact solution of the free fermion
propagator.Comment: 27 pages, Latex, 3 figures, appendix A has been revise
Luminescence quenching of the triplet excimer state by air traces in gaseous argon
While developing a liquid argon detector for dark matter searches we
investigate the influence of air contamination on the VUV scintillation yield
in gaseous argon at atmospheric pressure. We determine with a radioactive
alpha-source the photon yield for various partial air pressures and different
reflectors and wavelength shifters. We find for the fast scintillation
component a time constant tau1= 11.3 +- 2.8 ns, independent of gas purity.
However, the decay time of the slow component depends on gas purity and is a
good indicator for the total VUV light yield. This dependence is attributed to
impurities destroying the long-lived argon excimer states. The population ratio
between the slowly and the fast decaying excimer states is determined for
alpha-particles to be 5.5 +-0.6 in argon gas at 1100 mbar and room temperature.
The measured mean life of the slow component is tau2 = 3.140 +- 0.067 microsec
at a partial air pressure of 2 x 10-6 mbar.Comment: 7 pages submitted to NIM
Landau-Ginsberg Theory of Quark Confinement
We describe the SU(3) deconfinement transition using Landau-Ginsberg theory.
Drawing on perturbation theory and symmetry principles, we construct the free
energy as a function of temperature and the Polyakov loop. Once the two
adjustable parameters of the model are fixed, the pressure p, energy epsilon
and Polyakov loop expectation value P_F are calculable functions of
temperature. An excellent fit to the continuum extrapolation of lattice
thermodynamics data can be achieved. In an extended form of the model, the
glueball potential is responsible for breaking scale invariance at low
temperatures. Three parameters are required, but the glueball mass and the
gluon condensate are calculable functions of temperature, along with p, epsilon
and P_F.Comment: Lattice99(Finite Temperature and Density) <= added keywords only
change in revised version, sorry; 3 pages, LaTeX with espcrc2.sty and
epsf.tex. Talk presented at Lattice99, Pisa, 29 June - 3 July 1999, to appear
in Nucl. Phys. B (Proc.Suppl.
Anomaly Cancellation in 2+1 dimensions in the presence of a domainwall mass
A Fermion in 2+1 dimensions, with a mass function which depends on one
spatial coordinate and passes through a zero ( a domain wall mass), is
considered. In this model, originally proposed by Callan and Harvey, the gauge
variation of the effective gauge action mainly consists of two terms. One comes
from the induced Chern-Simons term and the other from the chiral fermions,
bound to the 1+1 dimensional wall, and they are expected to cancel each other.
Though there exist arguments in favour of this, based on the possible forms of
the effective action valid far from the wall and some facts about theories of
chiral fermions in 1+1 dimensions, a complete calculation is lacking. In this
paper we present an explicit calculation of this cancellation at one loop valid
even close to the wall. We show that, integrating out the ``massive'' modes of
the theory does produce the Chern-Simons term, as appreciated previously. In
addition we show that it generates a term that softens the high energy
behaviour of the 1+1 dimensional effective chiral theory thereby resolving an
ambiguity present in a general 1+1 dimensional theory.Comment: 17 pages, LaTex file, CU-TP-61
Characterization of the Hamamatsu S8664 Avalanche Photodiode for X-Ray and VUV-light detection
We present the first operation of the Avalanche Photodiode (APD) from
Hamamatsu to xenon scintillation light and to direct X-rays of 22.1 keV and 5.9
keV. A large non-linear response was observed for the direct X-ray detection.
At 415 V APD bias voltage it was of about 30 % for 22.1 keV and about 45 % for
5.9 keV. The quantum efficiency for 172 nm photons has been measured to be 69
+/- 15 %.Comment: 11 pages, 3 figures, submitted to Elsevie
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