6,317 research outputs found
Spectral function at high missing energies and momenta
The nuclear spectral function at high missing energies and momenta has been
determined from a self-consistent calculation of the Green's function in
nuclear matter using realistic nucleon-nucleon interactions. The results are
compared with recent experimental data derived from () reactions on
. A rather good agreement is obtained if the Green's functions are
calculated in a non-perturbative way.Comment: 10 pages, 3 figure
Quasi-particle functional Renormalisation Group calculations in the two-dimensional half-filled Hubbard model at finite temperatures
We present a highly parallelisable scheme for treating functional
Renormalisation Group equations which incorporates a quasi-particle-based
feedback on the flow and provides direct access to real-frequency self-energy
data. This allows to map out the boundaries of Fermi-liquid regimes and to
study the effect of quasi-particle degradation near Fermi liquid instabilities.
As a first application, selected results for the two-dimensional half-filled
perfectly nested Hubbard model are shown
Renormalized mean-field analysis of antiferromagnetism and d-wave superconductivity in the two-dimensional Hubbard model
We analyze the competition between antiferromagnetism and superconductivity
in the two-dimensional Hubbard model by combining a functional renormalization
group flow with a mean-field theory for spontaneous symmetry breaking.
Effective interactions are computed by integrating out states above a scale
Lambda_{MF} in one-loop approximation, which captures in particular the
generation of an attraction in the d-wave Cooper channel from fluctuations in
the particle-hole channel. These effective interactions are then used as an
input for a mean-field treatment of the remaining low-energy states, with
antiferromagnetism, singlet superconductivity and triplet pi-pairing as the
possible order parameters. Antiferromagnetism and superconductivity suppress
each other, leaving only a small region in parameter space where both orders
can coexist with a sizable order parameter for each. Triplet pi-pairing appears
generically in the coexistence region, but its feedback on the other order
parameters is very small.Comment: 28 pages, 14 figure
Performance of the CMS Pixel Detector at an upgraded LHC
The CMS experiment will include a pixel detector for pattern recognition and
vertexing. It will consist of three barrel layers and two endcaps on each side,
providing three space-points up to a pseudoraditity of 2.1. Taking into account
the expected limitations of its performance in the LHC environment an 8-9 layer
pixel detector for an upgraded LHC is discussed.Comment: Contribution to the 10th European Symposium on Semiconductor
Detectors, June 12 - 16, 2005 in Wildbad Kreuth, Germany. 6 pages, 4 figures,
1 table. Referee's comments implemente
Experiments with polarized 3He at MAMI
Abstract.: Experiments with polarized 3¯He at MAMI have already a long tradition. The A3 Collaboration started in 1993 with the aim to measure the electric form factor of the neutron. At this time MAMI was the second accelerator where experiments with 3¯He were possible. Some years before this pilot experiment the development of the apparatus to polarize 3He in Mainz started. There are two techniques which allow to polarize sufficient large quantities of 3He. Both techniques will be compared and the benefit of 3¯He for nuclear physics will be discussed. A review of the experiments done so far with 3¯He at MAMI will be given and the progress in the target development, the detector setup and the electron beam performance will be pointed ou
Fluence Dependence of Charge Collection of irradiated Pixel Sensors
The barrel region of the CMS pixel detector will be equipped with ``n-in-n''
type silicon sensors. They are processed on DOFZ material, use the moderated
p-spray technique and feature a bias grid. The latter leads to a small fraction
of the pixel area to be less sensitive to particles. In order to quantify this
inefficiency prototype pixel sensors irradiated to particle fluences between
and 2.6\times 10^{15} \Neq have been bump bonded to
un-irradiated readout chips and tested using high energy pions at the H2 beam
line of the CERN SPS. The readout chip allows a non zero suppressed analogue
readout and is therefore well suited to measure the charge collection
properties of the sensors.
In this paper we discuss the fluence dependence of the collected signal and
the particle detection efficiency. Further the position dependence of the
efficiency is investigated.Comment: 11 Pages, Presented at the 5th Int. Conf. on Radiation Effects on
Semiconductor Materials Detectors and Devices, October 10-13, 2004 in
Florence, Italy, v3: more typos corrected, minor changes required by the
refere
First measurement of the spectral function at high energy and momentum in medium-heavy nuclei
The experiment E97-006 was performed at Jefferson Lab to measure the momentum
and energy distribution of protons in the nucleus far from the region of the
(approximate) validity of the mean field description, i.e. at high momentum and
energies. The occurrence of this strength is long known from occupation numbers
less than one. In the experiment reported here this strength was directly
measured for the first time. The results are compared to modern many-body
theories. Further the transparency factor of C12 was determined in the
Q^2-region of 0.6 to 1.8 (GeV/c)^2.Comment: Proceeding for Fourth International Workshop on Neutrino-Nucleus
Interactions in the Few-GeV Region 26.-29. Sept. 2005, Okayam
Pseudogap at hot spots in the two-dimensional Hubbard model at weak coupling
We analyze the interaction-induced renormalization of single-particle
excitations in the two-dimensional Hubbard model at weak coupling using the
Wick-ordered version of the functional renormalization group. The self energy
is computed for real frequencies by integrating a flow equation with
renormalized two-particle interactions. In the vicinity of hot spots, that is
points where the Fermi surface intersects the umklapp surface, self energy
effects beyond the usual quasi-particle renormalizations and damping occur near
instabilities of the normal, metallic phase. Strongly enhanced renormalized
interactions between particles at different hot spots generate a pronounced
low-energy peak in the imaginary part of the self energy, leading to a
pseudogap-like double-peak structure in the spectral function for
single-particle excitations.Comment: 14 pages, 7 figure
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