383 research outputs found
Perspectives for the radiative return at meson factories
The measurement of the pion form factor and, more generally, of the cross
section for electron-positron annihilation into hadrons through the radiative
return has become an important task for high luminosity colliders such as the
Phi- or B-meson factories. This quantity is crucial for predictions of the
hadronic contributions to the anomalous magnetic moment of the muon, and to the
running of the electromagnetic coupling. But the radiative return opens the
possibility of many other physical applications. The physics potential of this
method at high luminosity meson factories is discussed, the last upgraded
version of the event generator PHOKHARA is presented, and future developments
are highlighted.Comment: Presented at SIGHAD03: Worskhop on Hadronic Cross Section at Low
Energy, Pisa,Italy, October 8th-10th, 200
Measuring an entropy in heavy ion collisions
We propose to use the coincidence method of Ma to measure an entropy of the
system created in heavy ion collisions. Moreover we estimate, in a simple
model, the values of parameters for which the thermodynamical behaviour sets
in.Comment: LATTICE98(hightemp), 3 pages, LaTeX with two eps figure
Studying thermodynamics in heavy ion collisions
We discuss the possibility to measure entropy of the system created in heavy ion collisions using the Ma coincidence method
Effects of physics beyond the standard model on the neutrino charge radius: an effective Lagrangian approach
In this work, we look for possible new physics effects on the electromagnetic
charge and anapole form factors, and , for a massless
Dirac neutrino, when these quantities are calculated in the context of an
effective electroweak Yang-Mills theory, which induces the most general
--invariant Lorentz tensor structure of nonrenormalizable type for the
vertex. It is found that in this context, besides the standard model
contribution, the additional contribution to and
( and , respectively) are gauge independent
and finite functions of after adopting a renormalization scheme. These
form factors, and , get contribution at
the one loop level only from the proper neutrino electromagnetic vertex.
Besides, the relation
(,
) is still fulfilled and
hence the relation (, )is gotten, just as in the SM. Using the experimental
constraint on the anomalous vertex, a value for the additional
contribution to the charge radius of |^{O_W}| \lsim 10^{-34}
cm^2 is obtained, which is one order of magnitude lower than the SM value.Comment: 9 pages, 3 figure
Improved Term of the Electron Anomalous Magnetic Moment
We report a new value of electron , or , from 891 Feynman diagrams
of order . The FORTRAN codes of 373 diagrams containing closed
electron loops have been verified by at least two independent formulations. For
the remaining 518 diagrams, which have no closed lepton loop, verification by a
second formulation is not yet attempted because of the enormous amount of
additional work required. However, these integrals have structures that allow
extensive cross-checking as well as detailed comparison with lower-order
diagrams through the renormalization procedure. No algebraic error has been
uncovered for them. The numerical evaluation of the entire term by
the integration routine VEGAS gives , where the
uncertainty is obtained by careful examination of error estimates by VEGAS.
This leads to ,
where the uncertainties come from the term, the estimated
uncertainty of term, and the inverse fine structure constant,
, measured by atom interferometry combined
with a frequency comb technique, respectively. The inverse fine structure
constant derived from the theory and the Seattle
measurement of is .Comment: 64 pages and 10 figures. Eq.(16) is corrected. Comments are added
after Eq.(40
Special case of sunset: reduction and epsilon-expansion
We consider two loop sunset diagrams with two mass scales m and M at the
threshold and pseudotreshold that cannot be treated by earlier published
formula. The complete reduction to master integrals is given. The master
integrals are evaluated as series in ratio m/M and in epsilon with the help of
differential equation method. The rules of asymptotic expansion in the case
when q^2 is at the (pseudo)threshold are given.Comment: LaTeX, 13 pages, 1 figur
Interpretation of y-scaling of the nuclear response
The behavior of the nuclear matter response in the region of large momentum
transfer, in which plane wave impulse approximation predicts the onset of
y-scaling, is discussed. The theoretical analysis shows that scaling violations
produced by final state interactions are driven by the momentum dependence of
the nucleon-nucleon scattering cross section.
Their study may provide valuable information on possible modifications of
nucleon-nucleon scattering in the nuclear medium.Comment: 4 pages with 3 figures. To appear in Physical Review Letter
High Energy Hadron-Nucleus Cross Sections and Their Extrapolation to Cosmic Ray Energies
Old models of the scattering of composite systems based on the Glauber model
of multiple diffraction are applied to hadron-nucleus scattering. We obtain an
excellent fit with only two free parameters to the highest energy
hadron-nucleus data available. Because of the quality of the fit and the
simplicity of the model it is argued that it should continue to be reliable up
to the highest cosmic ray energies. Logarithmic extrapolations of proton-proton
and proton-antiproton data are used to calculate the proton-air cross sections
at very high energy. Finally, it is observed that if the exponential behavior
of the proton-antiproton diffraction peak continues into the few TeV energy
range it will violate partial wave unitarity. We propose a simple modification
that will guarantee unitarity throughout the cosmic ray energy region.Comment: 8 pages, 9 postscript figures. This manuscript replaces a partial
manuscript incorrectly submitte
Nuclear Physics with Electroweak Probes
In recent years, the italian theoretical Nuclear Physics community has played
a leading role in the development of a unified approach, allowing for a
consistent and fully quantitative description of the nuclear response to
electromagnetic and weak probes. In this paper I review the main achievements
in both fields, point out some of the open problems, and outline the most
promising prospects.Comment: Invited Talk at the XII Workshop on Theoretical Nuclear Physics in
Italy, Cortona, October 8-10, 200
Event by Event Analysis and Entropy of Multiparticle Systems
The coincidence method of measuring the entropy of a system, proposed some
time ago by Ma, is generalized to include systems out of equilibrium. It is
suggested that the method can be adapted to analyze multiparticle states
produced in high-energy collisions.Comment: 13 pages, 2 figure
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