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V. G. Serbo

Publications and source records attributed to V. G. Serbo.

At least 37 records · Page 2Linked to original sources
arXiv2009

Emission of Low-Energy Photons by Electrons at Electron-Positron and Electron-Ion Colliders with Dense Bunches

Usually, the emission of low-energy photons in electron-positron (or electron-ion) bunch collisions is calculated with the same approach as for synchrotron radiation (beamstrahlung). However, for soft photons (E_gamma < E_c where E_c is a critical photon energy), when the coherence length of the radiation becomes comparable to the bunch length, the beamstrahlung approximation becomes invalid. In this paper, we present results of our calculation for this region based on approximation of classical currents. We consider several colliders with dense bunches. The number of low-energy photons dN_gamma emitted by N_e electrons per bunch crossing in the energy interval dE_gamma is dN_gamma = alpha g N_e dE_gamma/E_gamma, where alpha is the fine-structure constant, and the function g, which depends on the bunch parameters, typically is of order unity for modern colliders. In particular, for the ILC, we find that E_c = 83 keV and g=5.5 at a vanishing beam axis displacement, and g=0.88, E_c=0.24 keV for KEKB. We also calculate the specific dependence of dN_gamma on the impact parameter between the two beam axes. In principle, the latter aspect allows for online monitoring of the beam axis displacement.

physics.acc-ph↗
arXiv2008

Revisiting unitarity corrections for electromagnetic processes in collisions of relativistic nuclei

Unitarity corrections to several electromagnetic processes in collisions of relativistic heavy nuclei are considered. They are due to the unitarity requirement for the S-matrix and correspond to the exchange of light-by-light scattering block between colliding nuclei. We obtain improved results for the corrections to e+e- and mu+mu- pair production, as well as new results for unitarity corrections to the production of photons via virtual Compton and virtual Delbruck scattering. These corrections can be numerically large; e.g., the mu+mu- pair production cross section is reduced by about 50% and the nuclear bremsstrahlung by about 15 to 20%.

hep-ph↗
arXiv2007

Large contribution of virtual Delbrueck scattering to the emission of photons by relativistic nuclei in nucleus-nucleus and electron-nucleus collisions

Delbrueck scattering is an elastic scattering of a photon in the Coulomb field of a nucleus via a virtual electron loop. The contribution of this virtual subprocess to the emission of a photon in the collision of ultra-relativistic nuclei Z_1 Z_2 -> Z_1 Z_2 gamma is considered. We identify the incoming virtual photon as being generated by one of the relativistic nuclei involved in the binary collision and the scattered photon as being emitted in the process. The energy and angular distributions of the photons are calculated. The discussed process has no infrared divergence. The total cross section obtained is 14 barn for Au-Au collisions at the RHIC collider and 50 barn for Pb-Pb collisions at the LHC collider. These cross sections are considerably larger than those for ordinary tree-level nuclear bremsstrahlung in the considered photon energy range m_e << E_γ<< m_e gamma, where gamma is the Lorentz factor of the nucleus. Finally, photon emission in electron-nucleus collisions e Z -> e Z gamma is discussed in the context of the eRHIC option.

hep-ph↗
arXiv2005

Muon pair production in relativistic nuclear collisions

The exclusive production of one $μ^+μ^-$ pair in collisions of two ultra-relativistic nuclei is considered. We present the simple method for calculation of the Born cross section for this process. Then we found that the Coulomb corrections to this cross section (which correspond to multi-photon exchange of the produced $μ^{\pm}$ with nuclei) are small while the unitarity corrections are large. This is in sharp contrast to the exclusive $e^+e^-$ pair production where the Coulomb corrections to the Born cross section are large while the unitarity corrections are small. We calculated also the cross section for the production of one $μ^+μ^-$ pair and several $e^+e^-$ pairs in the leading logarithmic approximation. Using this cross section we found that the inclusive production of $μ^+μ^-$ pair coincides in this approximation with its Born value.

hep-ph↗
arXiv2005

Polarization effects in the non-linear Compton scattering

We consider emission of a photon by an electron in the field of a strong laser wave. A probability of this process for circularly or linearly polarized laser photons and for arbitrary polarization of all other particles is calculated. We obtain the complete set of functions which describe such a probability in a compact invariant form. Besides, we discuss in some detail the polarization effects in the kinematics relevant to the problem of electron to photon conversion at photon-photon and electron-photon colliders.

hep-ph↗
arXiv2004

Complete description of polarization effects in e^+e^- pair production by a photon in the field of a strong laser wave

We consider production of a e^+e^- pair by a high-energy photon in the field of a strong laser wave. A probability of this process for circularly or linearly polarized laser photons and for arbitrary polarization of all other particles is calculated. We obtain the complete set of functions which describe such a probability in a compact invariant form. Besides, we discuss in some detail the polarization effects in the kinematics relevant to the problem of electron-photon conversion at photon-photon and electron-photon colliders.

hep-ph↗
arXiv2003

Complete description of polarization effects in the nonlinear Compton scattering. II. Linearly polarized laser photons

We consider emission of a photon by an electron in the field of a strong laser wave. Polarization effects in this process are important for a number of physical problems. We discuss a probability of this process for linearly polarized laser photons and for arbitrary polarization of all other particles. We obtain the complete set of functions which describe such a probability in a compact form.

hep-ph↗
arXiv2003

Muon Colliders, Monte Carlo and Gauge Invariance

If calculated in the standard way, the cross section for the collision of two unstable particles turns out to diverge. This is because this cross section is actually proportional to the size of the colliding beams. The effect is called the "linear beam size effect". We present a way of including this linear beam size effect in the usual Monte Carlo integration procedure. Furthermore we discuss the gauge breaking that this may cause.

hep-ph↗
arXiv2003

Complete description of polarization effects in the nonlinear Compton scattering. I. Circularly polarized laser photons

We consider emission of a photon by an electron in the field of a strong laser wave. Polarization effects in this process are important for a number of physical problems. We discuss a probability of this process for circularly polarized laser photons and for arbitrary polarization of all other particles. We obtain the complete set of functions which describe such a probability in a compact covariant form. Besides, we discuss an application of the obtained formulas to the problem of electron -> photon conversion at photon-photon and photon-electron colliders.

hep-ph↗
arXiv2003

Beam-size or MD-effect at colliders and correlations of particles in a beam

For several processes at colliding beams, macroscopically large impact parameters give an essential contribution to the standard cross section. These impact parameters may be much larger than the transverse sizes of the colliding bunches. In that case, the standard calculations have to be essentially modify. The corresponding formulae for such a beam-size effect were given twenty years ago without taking into account correlations of particle coordinates in the beams. In the present paper we derive formulae which necessary to take into account quantitatively the effect of particle correlations in the spectrum of bremsstrahlung as well as in pair production. Besides, we consider critically recent papers of Baier and Katkov [Phys. Rev. D {\bf 66}, 053009 (2002) and hep-ph/0305304] in which it was calculated a new additional ``subtraction term'' related to the coherent contribution into beam-size effect. We show that this result is groundless and point out the origin of the mistake.

hep-ph↗
arXiv2003

A new method for calculating jet-like QED processes

We consider inelastic QED processes, the cross sections of which do not drop with increasing energy. Such reactions have the form of two-jet processes with the exchange of a virtual photon in the t-channel. We consider them in the region of small scattering angles m/E <= theta << 1, which yield the dominant contribution to their cross sections. A new effective method is presented to calculate the corresponding helicity amplitudes. Its basic idea consists in replacing spinor structures for real and weakly virtual intermediate leptons by simple transition vertices for real leptons. The obtained compact amplitudes are particularly suitable for numerical calculations in jet-like kinematics.

hep-ph↗
arXiv2003

New method for calculating helicity amplitudes of jet-like QED processes for high-energy colliders II. Processes with lepton pair production

As continuation of our previous paper we further develop our new method for calculating helicity amplitudes of jet-like QED processes described by tree diagrams, applying it to lepton pair production. This method consists in replacing spinor structures for real and weakly virtual intermediate leptons by simple transition vertices. New vertices are introduced for the pair production case, and previous bremsstrahlung vertices are generalized to include virtual photons inside the considered jet. We present a diagrammatic approach that allows to write down in an efficient way the leading helicity amplitudes, at tree level. The obtained compact amplitudes are particularly suitable for numerical calculations in jet-like kinematics. Several examples with up to four particles in a jet are discussed in detail.

hep-ph↗
arXiv2002

Influence of the beam-size or MD-effect on particle losses at B-factories PEP-II and KEKB

For the $e^+ e^- \to e^+ e^- γ$ process at colliding beams, macroscopically large impact parameters give an essential contribution to the standard cross section. These impact parameters may be much larger than the transverse sizes of the colliding bunches. It means that the standard calculations have to be essentially modify. In the present paper such a beam-size or MD-effect is calculated for bremsstrahlung at B-factories PEP-II and KEKB using the list of nominal parameters from Review of Particle Physics (2002). We find out that this effect reduces beam losses due to bremsstrahlung by about 20%.

hep-ph↗
arXiv2002

Once Again about Beam-Size or MD-Effect at Colliding Beams

For several processes at colliding beams, macroscopically large impact parameters give an essential contribution to the standard cross section. These impact parameters may be much larger than the transverse sizes of the colliding bunches. In that case, the standard calculations have to be essentially modify. The corresponding formulae were given twenty years ago. In recent paper of Baier and Katkov [17] it was claimed that the previous results about bremsstrahlung spectrum have to be revised and an additional subtraction related to the coherent contribution has to be done. This additional term has been calculated with the result that it may be essential for the performed and future experiments. In the present paper we analyze in detail the coherent and incoherent contributions in the conditions, considered in paper [17]. In contract to above claims, we found out that under these conditions the coherent contribution is completely negligible and, therefore, there is no need to revise the previous results.

hep-ph↗
arXiv2001

New method for calculating helicity amplitudes of jet--like QED processes for high--energy colliders I. Bremsstrahlung processes

Inelastic QED processes, the cross sections of which do not drop with increasing energy, play an important role at high-energy colliders. Such reactions have the form of two-jet processes with the exchange of a virtual photon in the t-channel. We consider them in the region of small scattering angles $m/E \lesssim θ\ll 1$, which yields the dominant contribution to their total cross sections. A new effective method is presented and applied to QED processes with emission of real photons to calculate the helicity amplitudes of these processes. Its basic idea is similar to the well-known equivalent-lepton method. Compact analytical expressions for those amplitudes up to $e^8$ are derived omitting only terms of the order of $m^2/E^2, θ^2$, $θm/E$ and higher order. The helicity amplitudes are presented in a compact form in which large compensating terms are already cancelled. Some common properties for all jet-like processes are found and we discuss their origin.

hep-ph↗
arXiv2001

Structure of the Coulomb and unitarity corrections to the cross section of $e^+e^-$ pair production in ultra-relativistic nuclear collisions

We analyze the structure of the Coulomb and unitarity corrections to the single pair production as well as the cross section for the multiple pair production. In the external field approximation we consider the probability of $e^+e^-$ pair production at fixed impact parameter $ρ$ between colliding ultra-relativistic heavy nuclei. We obtain the analytical result for this probability at large $ρ$ as compared to the electron Compton wavelength. We estimate also the unitary corrections to the total cross section of the process.

hep-ph↗
arXiv2000

Charge asymmetry of pions in the process $e^-e^+\to e^-e^+π^+π^-$

The study of the charge asymmetry of produced particles allows to investigate the interference of different production mechanisms and to determine new features of the corresponding amplitudes. In the process $e^- e^+ \to e^- e^+ π^+ π^-$ the two-pion system is produced via two mechanisms: two-photon (C-even state) and bremsstrahlung (C-odd state) production. We study the charge asymmetry of pions in a differential in the pion momenta cross section originating from an interference between these two mechanisms. At low effective mass of dipions this asymmetry is directly related to the s- and p-phases of elastic $ππ$ scattering. At higher energies it can give new information about the $f_0$ meson family, $f_2(1270)$ meson, etc. The asymmetry is expressed via the pion form factor $F_π$ and helicity amplitudes $M_{ab}$ for the subprocess $γ^*γ\to π^+π^-$ as $\sum G_{ab}{\rm Re}(F_π^*M_{ab})$ where we have calculated analytically the coefficients $G_{ab}$ for the region giving the main contribution to the effect. Several distributions of pions are presented performing a numerical analysis in a model with point-like pions. In the region near the dipion threshold the asymmetry is of the order of 1%. We show that with suitable cuts the signal to background ratio can be increased up to about 10%.

hep-ph↗