358 research outputs found
On the electromagnetic form factors of the proton from generalized Skyrme models
We compare the prediction of Skyrme-like effective Lagrangians with data for
electromagnetic form factors of proton and consider the possibility of fixing
the parameters of these higher-order Lagrangians. Our results indicate that one
or two-parameter models can lead to better agreement with the data but more
accurate determination of the effective Lagragian faces theoretical
uncertainties.Comment: 8 pages, 2 figures, revte
High- Elastic -scattering and QCD predictions
In the framework of pertubative QCD it is argued that in the elastic
-scattering at few the light-cone-frame
helicity-flip amplitudes could not be omitted. The obtained ratio
of Rosenbluth structure functions is shown to be in a good agreement with
experimental data. The high behavior of tensor analysing power
is discussed.Comment: 6 pages + 2 ps figures not included, LaTeX, ITP-93-33
Light-cone QCD predictions for elastic ed-scattering in the intermediate energy region
The contributions of helicity-flip matrix elements to the deuteron form
factors are discussed in the light-cone frame. Normalized , ,
and are obtained in a simple QCD-inspired model. We find
that plays an important role in . Our numerical results
are consistent with the data in the intermediate energy region.Comment: 9 pages, REVTeX file, 5 figure
New pixelized Micromegas detector for the COMPASS experiment
New Micromegas (Micro-mesh gaseous detectors) are being developed in view of
the future physics projects planned by the COMPASS collaboration at CERN.
Several major upgrades compared to present detectors are being studied:
detectors standing five times higher luminosity with hadron beams, detection of
beam particles (flux up to a few hundred of kHz/mm^2, 10 times larger than for
the present detectors) with pixelized read-out in the central part, light and
integrated electronics, and improved robustness. Studies were done with the
present detectors moved in the beam, and two first pixelized prototypes are
being tested with muon and hadron beams in real conditions at COMPASS. We
present here this new project and report on two series of tests, with old
detectors moved into the beam and with pixelized prototypes operated in real
data taking condition with both muon and hadron beams.Comment: 11 pages, 5 figures, proceedings to the Micro-Pattern Gaseous
Detectors conference (MPGD2009), 12-15 June 2009, Kolympari, Crete, Greece
Minor details added and language corrections don
Deuteron Electromagnetic Form Factors in the Intermediate Energy Region
Based on a Perturbative QCD analysis of the deuteron form factor, a model for
the reduced form factor is suggested. The numerical result is consistent with
the data in the intermediate energy region.Comment: 9 pages, to appear in Phys.Rev.
Effects of the Neutron Spin-Orbit Density on Nuclear Charge Density in Relativistic Models
The neutron spin-orbit density contributes to the nuclear charge density as a
relativistic effect. The contribution is enhanced by the effective mass
stemming from the Lorentz-scalar potential in relativistic models. This
enhancement explains well the difference between the cross sections of elastic
electron scattering off Ca and Ca which was not reproduced in
non-relativistic models. The spin-orbit density will be examined in more detail
in electron scattering off unstable nuclei which would be available in the
future.Comment: 4 pages with 3 eps figures, revte
New pixelized Micromegas detector with low discharge rate for the COMPASS experiment
New Micromegas (Micro-mesh gaseous detectors) are being developed in view of
the future physics projects planned by the COMPASS collaboration at CERN.
Several major upgrades compared to present detectors are being studied:
detectors standing five times higher luminosity with hadron beams, detection of
beam particles (flux up to a few hundred of kHz/mm^{2}, 10 times larger than
for the present Micromegas detectors) with pixelized read-out in the central
part, light and integrated electronics, and improved robustness. Two solutions
of reduction of discharge impact have been studied, with Micromegas detectors
using resistive layers and using an additional GEM foil. Performance of such
detectors has also been measured. A large size prototypes with nominal active
area and pixelized read-out has been produced and installed at COMPASS in 2010.
In 2011 prototypes featuring an additional GEM foil, as well as an resistive
prototype, are installed at COMPASS and preliminary results from those
detectors presented very good performance. We present here the project and
report on its status, in particular the performance of large size prototypes
with an additional GEM foil.Comment: 11 pages, 5 figures, proceedings to the Micro-Pattern Gaseous
Detectors conference (MPGD2011), 29-31 August 2011, Kobe, Japa
Electromagnetic Form Factors of the Nucleon in a Relativistic Quark Pair Creation Model
We study the effects of the | qqq q\bar{q} > component of the hadronic wave
function on the description of the electromagnetic structure of the nucleon.
Starting with a qqq baryonic wave function which describes the baryonic and
mesonic low energy spectrum, the extra q\bar{q} pair is generated through a
relativistic version of the 3P_0 model. It is shown that this model leads to a
renormalization of the quark mass that allows one to construct a conserved
electromagnetic current. We conclude that these dynamical relativistic
corrections play an important role in reproducing the Q2 dependence of the
electromagnetic form factors at low Q^2.Comment: 15 pages, 3 figures. Minor change
Nucleon form factors and a nonpointlike diquark
Nucleon form factors are calculated on q^2 in [0,3] GeV^2 using an Ansatz for
the nucleon's Fadde'ev amplitude motivated by quark-diquark solutions of the
relativistic Fadde'ev equation. Only the scalar diquark is retained, and it and
the quark are confined. A good description of the data requires a nonpointlike
diquark correlation with an electromagnetic radius of 0.8 r_pi. The composite,
nonpointlike nature of the diquark is crucial. It provides for diquark-breakup
terms that are of greater importance than the diquark photon absorption
contribution.Comment: 5 pages, REVTEX, epsfig, 3 figure
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