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Уважаемые сотрудники ИТФ,<br>
<br>
На заседании Ученого совета ИТФ в пятницу 29 ноября будут заслушаны
доклады:<br>
<br>
1) Baerbel Rethfeld (Technische Universitaet Kaiserslautern,
Germany)<br>
<b>Relaxation dynamics of nonequilibrium electrons in laser-excited
solids</b><br>
<br>
When an ultrashort laser pulse of visible light is absorbed by a
solid, mainly the electrons in the material are excited. In metals,
free electrons in the conduction band can directly absorb photons.
In semiconductors and dielectrics, on the other hand, a band gap has
to be overcome first, as almost no free electrons are present at
room temperature in the unexcited material. Due to this excitation,
the electronic system, or the so-called electron-hole plasma, is in
a nonequilibrium state. A sequence of different relaxation processes
transfers the material into a new equilibrium. Depending on the
interaction associated with the particular relaxation process, it
occurs on a characteristic timescale. On the basis of complete
Boltzmann-type collision integrals, we calculate the transient
distribution functions of electrons and phonons in different
materials. We consider electron-electron interaction, different
ionization processes, as well as electron-phonon coupling. By that
we trace the relaxation cascade of nonequilibrium electrons after
ultrafast heating. Distinct material properties enter through the
density of states of the electrons in the conduction band. We study
in particular noble metals, dielectrics and ferromagnets. In noble
metals and ferromagnets, d-electrons play an important role, whereas
in dielectrics two separated bands govern the dynamics and the
ionization state may differ from. We show, that the electron
distributions deviate from Fermi distributions for timescales up to
a few picoseconds. While the initial thermalization within one band
has an intrinsic timescale of typically only a few tens of
femtoseconds, nonequilibrium occupations of the different bands as
well as continous electron-phonon coupling can drive the conduction
electrons out of equilibrium for much longer times [1, 2]. We
present in detail the mutual influence of different interaction and
relaxation processes.<br>
[1] N. Brouwer and B. Rethfeld, Phys. Rev. B 95, 245139 (2017). [2]
S.T. Weber and B. Rethfeld, Phys. Rev. B 99, 174314 (2019).<br>
<br>
<br>
2) Б.Г. Захаров<br>
<b>Color randomization of fast two-parton states in quark-gluon
plasma in heavy ion collisions</b><br>
<br>
We study the color randomization of two-parton states produced after
splitting of a primary fast parton in the quark-gluon plasma. We
find that the color randomization of the two-parton states in the
quark-gluon plasma produced in heavy ion collisions at RHIC and LHC
energies is rather slow. At jet energies E= 100 and 500 GeV, for
typical jet path length in the plasma in central Pb+Pb collisions,
the SU(3)-multiplet averaged color Casimir of the two-parton states
differs considerably from its value for the fully color randomized
state. We evaluate the energy dependence for generation of the
nearly collinear gluon-gluon pairs in the decuplet color state and
quark-gluon pairs in the anti-sextet color states, that can lead to
an anomalous baryon jet fragmentation, which are forbidden in vacuum
for nucleon-nucleon collisions. Our results show that the baryon
production via the color anomalous two-parton states can be
important in the enhancement of the baryon/meson ratio observed in
heavy ion collisions at RHIC and LHC.<br>
<br>
<br>
3) Б.Г. Захаров<br>
<b>Radiative parton energy loss and baryon stopping in heavy ion
collisions</b> (короткий доклад)<br>
<br>
We study the radiative energy loss contribution to proton stopping
in heavy ion collisions. The radiative parton energy loss is
calculated within the light-cone path integral approach to induced
gluon emission. We have found that the radiative correction can fill
in partly the midrapidity dip in the net proton rapidity
distribution in AA collisions at center of mass energy \sqrt{s}
about 10 GeV. This energy region is of great interest in connection
with the beam energy scan program at RHIC (Brookhaven) and future
experiments at collider NICA (Dubna) motivated by searching for the
QCD critical point. We show that the net proton fluctuations at
midrapidity, that have been proposed to be a good probe of the QCD
critical point, may be dominated by the initial fluctuations of the
proton flow, which, to a good accuracy, should be binomial, even in
the presence of the critical point. <br>
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