arXiv subjects

V. G. Serbo

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

54 records · Page 3Linked to original sources

arXiv2000

Production of bound triplet $μ^{+} μ^{-}$ system in collisions of electrons with atoms

This paper deals with the production of orthodimuonium (OM) ($μ^{+} μ^{-}$ atom in triplet state) in collisions of high-energy electrons with nuclei or atoms. This reaction was previously studied by Holvik and Olsen [Phys. Rev. D 35, 2124 (1987)] on the basis of a bremsstrahlung mechanism where OM is produced by only one virtual photon. In the present paper we consider a competing three-photon mechanism where the production of OM results from the collision of a photon generated by the electron with two photons emitted by the nucleus. We derive the corresponding spectrum and production rate of OM and show that the three-photon mechanism is the dominant one for heavy atom target.

hep-ph↗

arXiv1998

Large Coulomb corrections to the $e^+e^-$ pair production at relativistic heavy ion colliders

We consider the Coulomb correction (CC) to the $e^+e^-$ pair production related to multiphoton exchange of the produced $e^{\pm}$ with nuclei. The contribution of CC to the energy distribution of $e^+$ and $e^-$ as well as to the total pair production cross section are calculated with an accuracy of the order of 1%. The found correction to the total Born cross section is negative and equal to -25% at the RHIC for Au--Au and -14% at the LHC for Pb--Pb collisions.

hep-ph↗

arXiv1998

Production of para-- and orthopositronium at relativistic heavy ion colliders

We consider the ortho-- and parapositronium production in the process $AA \to AA+$ Ps where A is a nucleus with the charge number Z. The inclusive cross section and the energy distribution of the relativistic Ps are calculated which are of primary interest from the experimental point of view. The accuracy of the corresponding cross sections is given by omitting terms $\sim (Zα)^2/L^2$ for the para--Ps and $\sim (Zα)^2/L$ for the ortho--Ps production where $L=\ln{γ^2} \approx 9$ and 16 for the RHIC and the LHC. Within this accuracy the multiphoton (Coulomb) corrections are taken into account. We show that the RHIC and the LHC will be Ps factories with a productions rate of about $10^5 ÷10^8$ relativistic Ps per day. The fraction of the ortho--Ps is expected to be of the same order as that of the para--Ps for Au--Au and Pb--Pb collisions.

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↗

arXiv1998

Comment on the absence of Coulomb effects on $e^+e^-$ pair production in ultrarelativistic heavy-ion collisions

In recent works [Segev,Wells; Baltz, McLerran; Eichmann, Reinhardt, Schramm, Greiner] it was claimed that the Coulomb correction to the $e^+e^-$ production cross section in relativistic heavy-ion collisions is absent. We point out that this statement is in obvious contradiction to some well known results. We obtain large Coulomb corrections in the pair production cross section for the RHIC and LHC heavy-ion colliders.

hep-ph↗

arXiv1998

Production of $e^+e^-$ pairs to all orders in $Zα$ for collisions of high-energy muons with heavy nuclei

The $e^+e^-$ pair production in collisions of muon with atoms is considered to all orders in the parameter $Zα$. We obtain energy distribution of $e^+$ and $e^-$ as well as energy loss of muon passing through matter with heavy atoms. The found corrections to the Born contribution do not depend on the details of the target properties except of a simple factor. For the considered example of Pb target the muon energy loss corrections vary from -65 % to -10 % depending on the pair energy.

hep-ph↗

arXiv1998

Coherent bremsstrahlung at the BEPC collider

Coherent bremsstrahlung (CBS) is a sopecific type of radiation at colliders with short bunches. In the present paper we calculate the main characteristic of CBS for the BEPC collider. At this collider $d N_γ\sim 3\cdot 10^8 dE_γ/E_γ$ photons of CBS will be emitted for a single collision of the beams in the energy range $E_γ$ smaller than 240 eV. It seems that CBS can be a potential tool for optimazing collisions and for measuring beam parameters. Indeed, the bunch length $σ_z$ can be found from the CBS spectrum because critical energy $E_c \propto 1/σ_z$; the horizontal transverse bunch size $σ_x $ is related to $dN_γ\propto 1/σ_x^2$. Besides, CBS may be very useful for a fast control over an impact parameter $R$ between the colliding bunch axex because a dependence of $dN_γ$ on $R$ has a very specific behavior. It seems quite interesting to investigate this type of radiation on the BEPC collider (for example, in the range of a visible light with the rate about $3 \cdot 10^{14} $ photons per second) and apply it for the fast beam control.

hep-ph↗

arXiv1998

Production of bound {$μ^{+}μ^{-}$}-systems in relativistic heavy ion collisions

Dimuonium (the bound system of two muons, $μ^+μ^-$-atom) has not been observed yet. In this paper we discuss the electromagnetic production of dimuonium at RHIC and LHC in relativistic heavy ion collisions. The production of parastates is analyzed in the equivalent photon approximation. For the treatment of orthostates, we develop a three photon formalism. We determine the production rates at RHIC and LHC with an accuracy of a few percent and discuss problems related to the observation of dimuonium.

hep-ph↗

arXiv1997

Helicity amplitudes for the small angle lepton pair production in e^+e^- or μ^+ μ^- collisions

The lepton pair production $e^- e^+ \to e^- e^+ l^- l^+ $ or $μ^- μ^+ \to μ^- μ^+ l^- l^+ $ is studied in the dominant cross section region of scattering angles ${m_j}/{E_j} \stackrel{<}{\sim} θ_j \ll 1 $. An analytical expression is found for all 64 helicity amplitudes of these processes. The accuracy of the obtained formulae is given omitting only terms of the order of ${m_j^2}/{E_j^2}$, $θ_j^2$ and $ θ_j {m_j}/{E_j}$. The result has a compact form convenient both for analytical and numerical calculations of various cross sections in this dominating scattering regime.

hep-ph↗

arXiv1997

Polarization of high-energy electrons traversing a laser beam

When polarized electrons traverse a region where the laser light is focused their polarization varies even if their energy and direction of motion are not changed. This effect is due to interference of the incoming electron wave and an electron wave scattered at zero angle. Equations are obtained which determine the variation of the electron density matrix, and their solutions are given. The change in the electron polarization depends not only on the Compton cross section but on the real part of the forward Compton amplitude as well. It should be taken into account, for example, in simulations of the $e \to γ$ conversion for future $γγ$ colliders.

hep-ph↗

arXiv1996

Variation in polarization of high-energy $γ$-quanta traversing a bunch of polarized laser photons

The elastic light-light scattering below the threshold of the $e^+e^-$ pair production leads to a variation in polarization of hard $γ$-quanta traversing without loss a region where the laser light is focused. Equations are obtained which determine the variation of Stokes parameters of $γ$-quanta in this case, and their solutions are given. It is pointed out that this effect can be observed in the experiment E-144 at SLAC. It should be taken into account (and, perhaps, it can be used) in experiments at future $γγ$ colliders.

hep-ph↗

arXiv1996

Physical mechanism of the linear beam-size effect at colliders

We present qualitative but precise description of the linear beam-size effect predicted for the processes in which unstable but long--living particles collide with each other. We derive physically pronounced equation for the events rate which proves that the linear beam-size effect corresponds to the scattering of one beam of particles on the decay products of the other. We compare this linear beam-size effect with the known logarithmic beam-size effect measured in the experiments on a single bremsstrahlung at VEPP-4 and HERA.

hep-ph↗

arXiv1996

Quantum effects in radiation on short bunches

The radiation caused by particles of one bunch in the collective electromagnetic field of the short oncoming bunch is studied. Quantum effects are calculated for the spectrum of radiated photons. Using this spectrum, the dependence of the relative energy loss delta on a quantum parameter kappa is dicussed. It is shown that the behaviour of delta changes considerably with the increase of that parameter. In the classical regime (kappa << 1) the energy loss is proportional to the incoming particle energy, while in the extreme quantum regime (kappa >> 1) the energy loss becomes a constant. The coherent e+e- pair production for gamma-e colliders as cross-channel to CBS is considered.

hep-ph↗

arXiv1996

Processes with the $t$-channel singularity in the physical region: finite beam sizes make cross sections finite

It is known that some high-energy processes have a $t$-channel singularity in the physical region. In this paper we show that this singularity is regularized if one takes into account the finite sizes of the colliding beams, i.e. the realistic situation which takes place at high--energy colliders. On this way we obtain the finite cross section which is linear proportional to the transverse sizes of the colliding beams. As an application of the above result we study the production of the single $W$ boson at $μ^+μ^-$ colliders in the reaction $μ^- μ^+ \to e \bar ν_e W^+ $. For the total energy $\sqrt {s}\approx 95$ GeV and reasonable parameters of the muon beams the ``beam--size '' dependent part of the cross section for this reaction is of the order of the standard cross section of the $μ^- μ^+ \to μ^- \bar ν_μ W^+ $ process.

hep-ph↗

arXiv1996

New type of beam size effect and the $W$-boson production at $μ^+μ^-$ colliders

The cross section for the reactions of the type $μ^-μ^+ \to e\barν_e X$ can not be calculated by the standard methods due to the $t$--channel singularity in the physical region. In this letter we show that accounting for the finite sizes of the colliding beams results in the regularization of this singularity. The finite cross section, which is obtained in this way, turns out to be linear proportional to the transverse sizes of the colliding beams. As an application of the above result, we calculate the cross section of the $W$ boson production at $μ^+μ^-$ colliders in the reaction $μ^- μ^+ \to e\barν_e W^+$.

hep-ph↗

arXiv1995

A new possibility to monitor collisions of relativistic heavy ions at LHC and RHIC

We consider the radiation of particles of one bunch in the collective field of the oncoming bunch, called coherent bremsstrahlung (CBS). The main characteristics of CBS for LHC (in the Pb-Pb mode) and for RHIC are calculated. At LHC about $3.9 10^8 dE_γ/E_γ$ photons per second are expected for photon energies $E_γ\stackrel{<} {\sim} E_c= 93 $ eV. It seems that CBS can be a potential tool for optimizing collisions and for measuring beam parameters. The bunch length can be found from the critical energy of the CBS spectrum; the transverse bunch size is related to the photon rate. A specific dependence of photon rate on the impact parameter between the beams allows for a fast control over the beam displacement.

hep-ph↗

arXiv1995

The equivalent photon approximation for coherent processes at colliders

We consider coherent electromagnetic processes for colliders with short bunches, in particular the coherent bremsstrahlung (CBS). CBS is the radiation of one bunch particles in the collective field of the oncoming bunch. It can be a potential tool for optimizing collisions and for measuring beam parameters. A new simple and transparent method to calculate CBS is presented based on the equivalent photon approximation for this collective field. The results are applied to the $ϕ$--factory $DAΦNE$. For this collider about $ 5 \cdot 10^{14} d E_γ/ E_γ$ photons per second are expected in the photon energy $E_γ$ range from the visible light up to 25 eV.

hep-ph↗

arXiv1995

Semihard diffractive production of neutral mesons by off shell photons and the range of pQCD validity

We study the dependence on photon virtuality $Q^2$ for the semihard quasi--elastic photoproduction of neutral vector mesons on a quark, gluon or real photon (at $s\gg p_{\bot}^2, Q^2; p_{\bot}^2 \gg μ^2 \approx (0.3$ GeV)$^2$). To this end we calculate the corresponding amplitudes (in an analytical form) in the lowest nontrivial approximation of the perturbative QCD. The amplitudes for the production of mesons consisting of light quarks vary very rapidly with the photon virtuality near $Q^2=0$. We estimate the bound of the pQCD validity region for such processes. For the process with mass shell photon the obtained bound is very high, and this region seems beyond opportunities of real experiment. This bound decreases fast with the increase of $Q^2$, and we expect that the virtual photoproduction at HERA provides the opportunity to test the pQCD results. The signature of this region is discussed.

hep-ph↗