arXiv subjects

S. R. Gevorkyan

Publications and source records attributed to S. R. Gevorkyan.

23 records · Page 2Linked to original sources

arXiv2002

Multiple lepton pair production in relativistic ion collisions

We apply the Sudakov technique to description of the multiple production of lepton pairs in peripheral collisions of ultrarelativistic heavy ions. For heavy ions with $Z_1α\sim Z_2α\ll 1$ one needs a careful treatment of the multiple Coulomb exchange between colliding ions and screening effects, whereas interaction of real or virtual lepton pairs with colliding ions can be neglected. We demonstrate that while the inclusive spectra are modified by multiple Coulomb exchange between the colliding ions, the Coulomb corrections to the momentum integrated multiplicity distributions do vanish. After transformation to the impact parameter representation the probability of $n$ lepton pair production is shown to obey the Poisson distribution. The relevant cross section is obtained.

hep-ph↗

arXiv2002

Process 3 -> 3 and crossing symmetry violation

Using the Sudakov technique we sum the perturbation series for the process $3\to 3$ and obtain the compact analytical expression for the amplitude of this process, which takes into account all possible Coulomb interactions between colliding particles. Compare it with the amplitude of the lepton pair production in heavy ion collision i.e. in the process $ 2\to 4$, we show that crossing symmetry between this processes holds only if one neglects the interaction of produced pair with ions (i.e. in the approximation $Z_{1,2}α\ll 1$).

hep-ph↗

arXiv2002

The lepton pair production in heavy ion collisions in perturbation theory

We derive the first terms in the amplitude of lepton pair production in the Coulomb fields of two relativistic heavy ions. Using the Sudakov technique, which very simplify the calculations in momentum space for the processes at high energies, we get the compact analytical expressions for differential cross section of the process under consideration in the lowest order in fine structure constant (Born approximation) valid for any momentum transfer and in a wide kinematics region for produced particles. Exploiting the same technique we consider the next terms of perturbation series (up to fourth order in fine structure constant) and investigate their energy dependence and limiting cases. It has been shown that taking in account all relevant terms in corresponding order one obtains the expressions which are gauge invariant and finite. We estimate the contribution of the Coulomb corrections to the total cross section and discuss the cancellations of the different terms which holds in the total cross section.

hep-ph↗

arXiv2001

Photoproduction of relativistic positronium atoms on extended targets

It is shown that the yield of relativistic positronium atoms in photoproduction on extended targets is much larger than usually accepted.The cause of such difference is transparent. At high energies, when the positronium atom formation time $τ_f$ becomes greater than the target length L, it is the free $e^+e^-$ pair that propagates through the target and the formation of positronium atoms take place out of the target.In the framework of the light-cone technique we consider the interaction of $e^+e^-$ pair with the screened Coulomb field of atoms in matter and obtain the analytical expressions for relativistic positronium atoms photoproduction cross sections on extended targets.The relations to free pair photoproduction on extended targets are discussed.

hep-ph↗

arXiv1998

Production of relativistic positronium in collisions of photons and electrons with nuclei and atoms

We consider the production of ultrarelativistic positronium (Ps) in $γA \to Ps + A$ and $e A \to Ps + e A$ processes where $A$ is an atom or a nucleus with charge $Ze$. For the photoproduction of para- and ortho-Ps and the electroproduction of para-Ps we obtain the most complete description compared with previous works. It includes high order $Z α$ corrections and polarization effects. The accuracy of the obtained cross sections is determined by omitted terms of the order of the inverse Ps Lorentz factor squared. The studied high order multi-photon electroproduction of ortho-Ps dominates for the collision of electrons with heavy atoms over the bremsstrahlung production from the electron via a virtual photon proposed by Holvik and Olsen. Our results complete and correct the studies of those authors.

hep-ph↗