4,279 research outputs found
Fermion Determinants
The current status of bounds on and limits of fermion determinants in two,
three and four dimensions in QED and QCD is reviewed. A new lower bound on the
two-dimensional QED determinant is derived. An outline of the demonstration of
the continuity of this determinant at zero mass when the background magnetic
field flux is zero is also given.Comment: 10 page
Scalar Quarkonium Masses and Mixing with the Lightest Scalar Glueball
We evaluate the continuum limit of the valence (quenched) approximation to
the mass of the lightest scalar quarkonium state, for a range of different
quark masses, and to the mixing energy between these states and the lightest
scalar glueball. Our results support the interpretation of as
composed mainly of the lightest scalar glueball.Comment: 14 pages of Latex, 5 PostScript figure
Characterization of new hybrid pixel module concepts for the ATLAS Insertable B-Layer upgrade
The ATLAS Insertable B-Layer (IBL) collaboration plans to insert a fourth
pixel layer inside the present Pixel Detector to recover from eventual failures
in the current pixel system, especially the b-layer. Additionally the IBL will
ensure excellent tracking, vertexing and b-tagging performance during the LHC
phase I and add robustness in tracking with high luminosity pile-up. The
expected peak luminosity for IBL is 2 to 3centerdot1034 cm-2s-1 and IBL is
designed for an integrated luminosity of 700 fb-1. This corresponds to an
expected fluence of 5centerdot1015 1 MeV neqcm-2 and a total ionizing dose of
250 MRad. In order to cope with these requirements, two new module concepts are
under investigation, both based on a new front end IC, called FE-I4. This IC
was designed as readout chip for future ATLAS Pixel Detectors and its first
application will be the IBL. The planar pixel sensor (PPS) based module concept
benefits from its well understood design, which is kept as similar as possible
to the design of the current ATLAS Pixel Detector sensor. The second approach
of the new three dimensional (3D) silicon sensor technology benefits from the
shorter charge carrier drift distance to the electrodes, which completely
penetrate the sensor bulk. Prototype modules of both sensor concepts have been
build and tested in laboratory and test beam environment before and after
irradiation. Both concepts show very high performance even after irradiation to
5centerdot1015 1 MeV neqcm-2 and meet the IBL specifications in terms of hit
efficiency being larger than 97%. Lowest operational threshold studies have
been effected and prove independent of the used sensor concept the excellent
performance of FE-I4 based module concepts in terms of noise hit occupancy at
low thresholds.Comment: Part of 9th International Conference on Position Sensitive Detectors
(PSD9
Light Hadron Spectroscopy: Theory and Experiment
Rapporteur talk at the Lepton-Photon Conference, Rome, July 2001: reviewing
the evidence and strategies for understanding scalar mesons, glueballs and
hybrids, the gluonic Pomeron and the interplay of heavy flavours and light
hadron dynamics. Dedicated to the memory of Nathan Isgur, long-time
collaborator and friend, whose original ideas in hadron spectroscopy formed the
basis for much of the talk.Comment: to be published in "Lepton Photon 2001 Conference Proceedings" (World
Scientific Publishing), 19 pages with 6 figure
Analysis and results of the industrial production of the superconducting Nb/Cu cavities for the LEP2 project
For the energy upgrade of the Large Electron Positron Collider at CERN 216 RF superconducting cavities were ordered from three European industrial firms (Ansaldo, Cerca, Siemens/Accel) at the beginning of 1991. These cavities are made of copper (Cu), internally coated with niobium (Nb) according to a procedure developed at CERN. Up to now about 147 of these cavities fulfilling the specifications have been produced. The large-scale statistics available and the use of dedicated analytical and optical inspection techniques shed new light on the relationship between production procedures, niobium film properties and cavity performance. An overview of this subject is presented, together with some significant trends and results
Complex Probabilities on R^N as Real Probabilities on C^N and an Application to Path Integrals
We establish a necessary and sufficient condition for averages over complex
valued weight functions on R^N to be represented as statistical averages over
real, non-negative probability weights on C^N. Using this result, we show that
many path-integrals for time-ordered expectation values of bosonic degrees of
freedom in real-valued time can be expressed as statistical averages over
ensembles of paths with complex-valued coordinates, and then speculate on
possible consequences of this result for the relation between quantum and
classical mechanics.Comment: 4 pages, 0 figure
Chiral Symmetry Breaking without Bilinear Condensates, Unbroken Axial Z_N Symmetry, and Exact QCD Inequalities
An alternative pattern of the chiral symmetry breaking, suggested recently by
Stern, is investigated. It could be self-consistent provided that the chiral
symmetry is broken spontaneously down to rather than to . The discrete axial then
would play a custodial role preventing the quark bilinears from condensation.
It is shown that this pattern of the chiral symmetry breaking is ruled out in
QCD by exact inequalities. It is not ruled out, however, in other gauge
theories with scalar quarks and/or Yukawa couplings.Comment: 9 pages, Latex, clarifying comments and several references adde
pion scattering amplitude with Wilson fermions
We present an exploratory calculation of the scattering
amplitude at threshold using Wilson fermions in the quenched approximation,
including all the required contractions. We find good agreement with the
predictions of chiral perturbation theory even for pions of mass 560-700 MeV.
Within the 10\% errors, we do not see the onset of the bad chiral behavior
expected for Wilson fermions. We also derive rigorous inequalities that apply
to 2-particle correlators and as a consequence show that the interaction in the
antisymmetric state of two pions has to be attractive.Comment: This PS file includes 4 tables and figures 1-8 on 25 pages. Los
Alamos Preprint Number LAUR-92-364
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