9 research outputs found
Hagedorn's Hadron Mass Spectrum and the Onset of Deconfinement
A brief history of the observation of the onset of deconfinement - the
beginning of the creation of quark gluon plasma in nucleus-nucleus collisions
with increasing collision energy - is presented. It starts with the measurement
of hadron mass spectrum and the Hagedorn's hypothesis of the limiting
temperature of hadronic matter (the Hagedorn temperature). Then the conjecture
that the Hagedorn temperature is the phase transition temperature was
formulated with the crucial Hagedorn participation. It was confirmed by the
observation of the onset of deconfinement in lead-lead collisions at the CERN
SPS energies.Comment: arXiv admin note: substantial text overlap with arXiv:1201.048
Radiative corrections to neutral pion-pair production
We calculate the one-photon loop radiative corrections to the neutral
pion-pair photoproduction process . At leading
order this reaction is governed by the chiral pion-pion interaction. Since the
chiral contact-vertex depends only on the final-state
invariant-mass it factors out of all photon-loop diagrams. We give analytical
expressions for the multiplicative correction factor
arising from eight classes of contributing one-photon loop diagrams. An
electromagnetic counterterm has to be included in order to cancel the
ultraviolet divergences generated by the photon-loops. Infrared finiteness of
the virtual radiative corrections is achieved (in the standard way) by
including soft photon radiation below an energy cut-off . The
radiative corrections to the total cross section vary between and
for center-of-mass energies from threshold up to . The finite part of
the electromagnetic counterterm gives an additional constant contribution of
about , however with a large uncertainty.Comment: 10 pages, 6 figures, submitted to Eur. Phys. J.
Electromagnetic Dissociation of Nuclei in Heavy-Ion Collisions
Large discrepancies have been observed between measured Electromagnetic
Dissociation(ED) cross sections and the predictions of the semiclassical
Weiz\"acker-Williams-Fermi(WWF) method. In this paper, the validity of the
semiclassical approximation is examined. The total cross section for
electromagnetic excitation of a nuclear target by a spinless projectile is
calculated in first Born approximation, neglecting recoil. The final result is
expressed in terms of correlation functions and convoluted densities in
configuration space. The result agrees with the WWF approximation to leading
order(unretarded electric dipole approximation), but the method allows an
analytic evaluation of the cutoff, which is determined by the details of the
electric dipole transition charge density. Using the Goldhaber-Teller model of
that density, and uniform charge densities for both projectile and target, the
cutoff is determined for the total cross section in the nonrelativistic limit,
and found to be smaller than values currently used for ED calculations. In
addition, cross sections are calculated using a phenomenological momentum space
cutoff designed to model final state interactions. For moderate projectile
energies, the calculated ED cross section is found to be smaller than the
semiclassical result, in qualitative agreement with experiment.Comment: 28 page
Transverse spin dynamics in a spin-polarized Fermi liquid
The linear equations for transverse spin dynamics in weakly polarised
degenerate Fermi liquid with arbitrary relationship between temperature and
polarization are derived from Landau-Silin phenomenological kinetic equation
with general form of two-particle collision integral. The temperature and
polarization dependence of the spin current relaxation time is established. It
is found in particular that at finite polarization transverse spin wave damping
has a finite value at T=0. The analogy between temperature dependences of spin
waves attenuation and ultrasound absorption in degenerate Fermi liquid at
arbitrary temperature is presented. We also discuss spin-polarized Fermi liquid
in the general context of the Fermi-liquid theory and compare it with "Fermi
liquid" with spontaneous magnetization.Comment: 10 page
A Quantum-Mechanical Equivalent-Photon Spectrum for Heavy-Ion Physics
In a previous paper, we calculated the fully quantum-mechanical cross section
for electromagnetic excitation during peripheral heavy-ion collisions. Here, we
examine the sensitivity of that cross section to the detailed structure of the
projectile and target nuclei. At the transition energies relevant to nuclear
physics, we find the cross section to be weakly dependent on the projectile
charge radius, and to be sensitive to only the leading momentum-transfer
dependence of the target transition form factors. We exploit these facts to
derive a quantum-mechanical ``equivalent-photon spectrum'' valid in the
long-wavelength limit. This improved spectrum includes the effects of
projectile size, the finite longitudinal momentum transfer required by
kinematics, and the response of the target nucleus to the off-shell photon.Comment: 19 pages, 5 figure