16,269 research outputs found
Parity-violating longitudinal response
The longitudinal quasielastic parity-violating electron scattering response
is explored within the context of a model that builds antisymmetrized RPA-HF
correlations on a relativistic Fermi gas basis. The large sensitivity to
nuclear dynamics of this observable, found in previous studies where only
pionic correlations were included, is shown to survive in the present model
where the effects from pion, rho, sigma and omega exchange in a version of the
Bonn potential are incorporated. Through an intricate diagrammatic
cancellation/filtration mechanism the longitudinal parity-violating response
turns out to be close to the one obtained in first-order perturbation theory
with the pion alone. Finally, in accord with our previous work, the
parity-violating response is seen to display appreciable sensitivity to the
electric strangeness content of the nucleon, especially at high momentum
transfer.Comment: 13 pages, uses REVTeX and epsfig, 10 postscript figures; a postscript
version of the paper is available by anonymous ftp at
ftp://carmen.to.infn.it/pub/barbaro/papers/951
Gauge and Lorentz invariant pionic correlations in quasi-elastic electron scattering
The role of the pion in the parity-conserving and parity-violating
quasi-elastic nuclear response functions is analyzed within a relativistic
model which fulfills gauge invariance.Comment: 14 pages, 4 figures, Proceedings of the Varenna School "From Nuclei
and Thier Constituents to Stars", August 200
Relativistic effects in quasielastic electron scattering
The impact of pionic correlations and meson-exchange currents on the
quasi-elastic electromagnetic response functions is studied in a fully
relativistic framework.Comment: 6 pages, 5 figures, to appear in the Proceedings of "The Nuclear Many
Body Problem 2001", NATO Science Series II - Mathematics, Physics and
Chemistry, Kluwer Academic Publisher
Relativistic Effects in Electroweak Nuclear Responses
The electroweak response functions for inclusive electron scattering are
calculated in the Relativistic Fermi Gas model, both in the quasi-elastic and
in the peak regions. The impact of relativistic kinematics at high
momentum transfer is investigated through an expansion in the initial nucleonic
momentum, which is however exact in the four-momentum of the exchanged boson.
The same expansion is applied to the meson exchange currents in the
particle-hole sector: it is shown that the non-relativistic currents can be
corrected by simple kinematical factors to account for relativity. The
left-right asymmetry measured via polarized electron scattering is finally
evaluated in the quasi-elastic and peaks.Comment: 9 pages, 3 figures, to appear in "Proceedings of the VIII Convegno su
Problemi di Fisica Nucleare Teorica, 18-20 October 2000", World Scientifi
Single Top Production and Top Properties at the Tevatron
We summarize recent measurements made at the Tevatron Collider using top
event candidates. Cross section and mass measurements are discussed in a
separate contribution to these Proceedings. Here we report on studies of the
top P distribution in \ttbar production and studies of single top
production. Properties of top decays examined are:
BF(t \into Wb)/BF(t \into Wq), helicity amplitudes of W's from top decays
and correlations of \ttbar decay products. Searches for new physics in rare
top decays and a search for a state X \into \ttbar are also reported.Comment: 19 pages including 9 figures. Proceedings of the 1999 Lathuile
Conferenc
The distributional impact of subsidies to higher education: empirical evidence from Germany
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The multilevel pairing Hamiltonian versus the degenerate case
We study the pairing Hamiltonian in a set of non degenerate levels. First, we
review in the path integral framework the spontaneous breaking of the U(1)
symmetry occurring in such a system for the degenerate situation. Then the
behaviors with the coupling constant of the ground state energy in the
multilevel and in the degenerate case are compared. Next we discuss, in the
multilevel case, an exact strong coupling expansion for the ground state energy
which introduces the moments of the single particle level distribution. The
domain of validity of the expansion, which is known in the macroscopic limit,
is explored for finite systems and its implications for the energy of the
latter is discussed. Finally the seniority and Gaudin excitations of the
pairing Hamiltonian are addressed and shown to display the same gap in leading
order.Comment: 20 pages, 4 figure
CMS Central Hadron Calorimeter
We present a description of the CMS central hadron calorimeter. We describe
the production of the 1996 CMS hadron testbeam module. We show the results of
the quality control tests of the testbeam module. We present some results of
the 1995 CMS hadron testbeam.Comment: 7 pages, 11 Figures, corresponding author: H. Budd, [email protected]
Influence of nucleonic motion in Relativistic Fermi Gas inclusive responses
Impulsive hadronic descriptions of electroweak processes in nuclei involve
two distinctly different elements: one stems from the nuclear many-body physics
--- the medium --- which is rather similar for the various inclusive response
functions, and the other embodies the responses of the hadrons themselves to
the electroweak probe and varies with the channel selected. In this letter we
investigate within the context of the relativistic Fermi gas in both the
quasi-elastic and regimes the interplay between these two
elements. Specifically, we focus on expansions in the one small parameter in
the problem, namely, the momentum of a nucleon in the initial wave function
compared with the hadronic scale, the nucleon mass. Both parity-conserving and
-violating inclusive responses are studied and the interplay between
longitudinal () and transverse ( and ) contributions is highlighted.Comment: 11 pages, 1 figur
The many levels pairing Hamiltonian for two pairs
We address the problem of two pairs of fermions living on an arbitrary number
of single particle levels of a potential well (mean field) and interacting
through a pairing force. The associated solutions of the Richardson's equations
are classified in terms of a number , which reduces to the seniority
in the limit of large values of the pairing strength and yields the number
of pairs not developing a collective behaviour, their energy remaining finite
in the limit. We express analytically, through the moments of the
single particle levels distribution, the collective mode energy and the two
critical values and of the coupling which can
exist on a single particle level with no pair degeneracy. Notably and merge when the number of single particle levels
goes to infinity, where they coincide with the (when it exists) of
a one pair system, not envisioned by the Richardson theory. In correspondence
of the system undergoes a transition from a mean field to a
pairing dominated regime. We finally explore the behaviour of the excitation
energies, wave functions and pair transfer amplitudes finding out that the
former, for , come close to the BCS predictions, whereas the
latter display a divergence at , signaling the onset of a long
range off-diagonal order in the system.Comment: 35 pages, 6 figures, 2 tables, to be published in EPJ
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