The main theoretical activity in RNPL is focused on investigation of
hard processes in the high energy domain:
Scale dependence in hard exclusive quasifree knockout of protons from nuclei.
One of the important
findings of the exclusive A(e,e’p)
and A(p,2p) studies at low energies was an observation of suppression of the
single-particle valence strength as compared to the independent particle model
description. This phenomenon of quenching in the low energy physics is
naturally explained in the nuclear quasiparticle theory[A. B. Migdal. Theory of
Finite Fermi System and Application to Atomic Nuclei (Interscience,
New York, 1967)] as a result of the single particle strength fragmentation over
wide excitation energy range due to the long and short range nucleon-nucleon
correlations. Basing on the joint analysis of the exclusive A(e,e’p) and A(e,e’)X data it is
shown that this strong effect (about 40
%), observed in the low energy domain, practically disappears with increase
of the momentum transfer when a probe resolves the quasiparticle
structure of the nucleon arising due to the long-range correlations inside the
nuclear medium. A strong momentum transfer dependence of quenching comes very naturally in
the Fermi liquid theory[L. D. Landau and E. M. Lifshitz,
Statistical Physics,part 1 (Course of Theoretical
Physics, v. 5) Pergamon Press, 1980; G. E. Brown,
Unified Theory of Nuclear Models and Forces. North-Holland, 316p., 1971] and really represents the generic property of
fermionic systems where the interaction between
fermions is described by a renormalizable theory[K.
G. Wilson, Phys. Rev. B4 (3174), 1971], like QED or QCD, since in this case the
wave functions of constituents depend strongly on the resolution scale.
Momentum
transfer dependence
of the summed single particle strength for 1p and 1s proton knockout in C(e, e'p) up
to excitation energy 80 MeV.
Coherent charmonium photoproduction off nuclei
in the low energy domain.
The
coherent charmonium photoproduction in the photon energy
domain where the coherence and formation lengths exceed the average internucleon distance in nuclei but are comparable to the
nuclear radii has been analysed in the generalized
vector dominance model (GVDM)
adjusted to account for
the physics of bound charmonium states and for the
color screening phenomenon. Significant
oscillations found in the energy dependence of the total and forward
photoproduction cross sections are due to the oscillating behavior of the
longitudinal nuclear form factor. Within the GVDM these oscillations are
strongly modified by the nondiagonal rescatterings of the charmonium. It is shown how to use this pronounced
oscillating behavior to determine the elementary charmonium
photoproduction amplitudes and the genuine charmonium-nucleon
cross sections in the forthcoming SLAC E160 experiment. The precise values of these cross sections
are urgently needed in analysis of the data from the central collisions of the ultrarelativistic heavy ions where the suppression of the charmoium yield is considered as one of the most promising
signal of the Quark Gluon Plasma creation.
The
energy dependence of the integrated over transverse momentum coherent cross sections
calculated in the Gribov-Glauber
Model (dark shaded area) compared to the cross sections in
the Impulse Approximation (dashed
lines). The filled areas depict the variation of results due to
the experimental uncertainties in the J/psi N cross section.
TRANSVERSE
STRUCTURE OF THE STRONG INTERACTIONS AT LHC WAS DISCUSSED IN THE PAPER
Published as preprint
HEP_PH/0412260, 2004
In 2005 the
paper devoted to the universality of hadron interactions at high energies was also
published (abstract is given below)
Study of the coherent vector meson
production in ultraperipheral relativistic heavy ion collisions.
These
investigations are aimed to reveal the small x QCD dynamics phenomena. The ultrarelativistic heavy ions produce the significant flux of
quasireal photons. The photon wave function contains the hadron components as
well as the direct quark-antiquark components with
sizes which are controlled by a quark mass. Hence, coherent photoproduction of
vector mesons off nuclei by quasireal photons in the peripheral ion collisions
presents the unique opportunities. Selecting a particular final state one can postselect the quark-antiquark configurations of
different sizes and study a variety of phenomena ranging from nuclear Color
Transparency to Color Opacity effect and even closing to the regime of the
Black Body Limit. The reliability of
such expectations has recently been proven by comparison of our predictions for
the coherent ρ meson production in kinematics of RHIC with the cross
section measured by STAR.
Recently, cross section
of J/ψ photoproduction in UPC at RHIC was presented by PHENIX.
Experimental measurement confirmed prediction of our calculations for this
cross section in kinematics of RHIC (see figure below, theoretical calculations
M.Strikman et.al. are given in “ NEUTRON TAGGING OF QUASIELASTIC
J/PSI PHOTOPRODUCTION OFF NUCLEUS IN ULTRAPERIPHERAL HEAVY ION COLLISIONS AT
RHIC ENERGIES.
By M. Strikman
(Penn State U.),
M. Tverskoy,
M. Zhalov
(St. Petersburg, INP),.
May
2005. 12pp.
Published in Phys.Lett.B626:72-79,2005 )
.
A
systematic study of the onium production in the UPC at the LHC
energies will be especially interesting and undoubtedly useful to verify many QCD-based
predictions as well as to gain new information about high energy hadron
interactions. One should also emphasize the practical goal of such theoretical
investigations at the LHC energies. It is believed that one of the promising
signals of the QGP formation is anomalous suppression of the quarkonium yield
from the region occupied by QGP. Such suppression can occur due to the Debye screening of the color field within the plasma and
due to the dissolving of already formed quarkonia by hot gluons. However, to
draw unambiguous conclusion about existence of the QGP from observation of
suppression pattern, one should reliably estimate all other possible sources of quarkonium
suppression , for example, the nuclear gluon shadowing, the comover
effects. Basing on the results of
theoretical analysis the yield of heavy quarkonia in ultraperipheral ion
collisions in the kinematics of
Comparison
of the cross sections calculated in the Impulse Approximation(dashed
line) to that in the model which was developed to account the gluon shadowing
in nuclei within the leading twist approximation demonstrated high sensitivity
of the coherent quarkonium photoproduction to the QCD dynamics in the small x
region.
Also
we have calculated the coherent photoproduction of heavy quarkonia in
ultraperipheral proton-nucleus collisions. The results of study are formulated
in the abstract of paper published in Phys. Lett. B.
2005
