V. G. Serbo

COLLIDING ge AND gg BEAMS BASED ON THE SINGLE-PASS e ~ e COLLIDERS (VLEPP TYPE)

Abstract We discuss in detail our proposed [1,2] method of obtaining colliding γe and γγ beams with high energies and luminosities using the designed linear accelerators VLEPP and SLC with colliding e + e − beams at the energies 2 E ≳ 100 GeV. The intense γ beams are obtained by backward Compton scattering of laser light which is focused on the electron beams of these accelerators. This paper contains the scheme for conversion of an electron beam into a γ beam, a calculation of the conversion coefficient and of the total and spectral γe and γγ luminosities. To get the luminosity L γ e , L γγ ∼ L ee , one needs a laser flash with energy ∼ 15J, and a pulse duration ∼ 30 ps at a repetition rate of 10 or 180 Hz. Such parameters seem to be achievable on the basis of current technology. The luminosity distribution over the γe or γγ invariant mass is broad. A method of monochromatization is described. It demands an increase of the laser flash energy (with a possible increase of pulse duration) and leads to a decrease of luminosity. We also describe a method for calibrating the total and spectral luminosities. Problems concerning the background are shown to be easier than in e + e − collisions. Some examples of interesting physical problems for γe and γγ collisions are enumerated.

Colliding γe and γγ beams based on single-pass e+e− accelerators II. Polarization effects, monochromatization improvement

Polarization effects are considered in colliding γe and γγ beams, which are proposed to be obtained on the basis of linear e+e− colliders (by backward Compton scattering of laser light on electron beams). It is shown that using electrons and laser photons with helicities λ and Pc, such that λPc<0, essentially improves the monochromatization. The characteristic laser flash energy, A0, which is necessary to obtain a conversion coefficient k ≈ 1 with a definite degree of monochromatization, is considerably less (sometimes by one order of magnitude) in the case 2λPc = −1 in contrast to the case λPc=0. Simultaneously the luminosities Lγe and Lggγ essentially increase. Formulae are obtained which allow one to extract the polarization information about γe → X and γγ → X reactions. Perculiarities connected with the specific scheme of the γ beam preparation are discussed. Problems of the calibration of the γe and γγ collisions for the polarized beams are discussed.

W± boson production at the e+e−, γe and γγ colliding beams

Abstract W ± boson production in e + e − → W + W − , γ e → W + W ν , γγ → W + W − reactions at the e + e − , γe and γγ colliding beams is considered. What physical information can be extracted from such experiments, including those with polarized beams, is discussed. Conditions of observation, are considered together with the background problems.

Semihard γγ → V1V2, γγ → V + X processes (V = ϱ0,ω,ϕ,γ).: The possibility of the experimental investigation of the QCD pomeron

Abstract We consider both the semiexclusive reactions γγ → A + X and the exclusive ones γγ → AB with the production of neutral vector mesons and photons at s ⪢ | t | ⪢ (0.3 GeV) 2 . (Here A,B = ϱ 0 , ω , ϕ , γ and X is a hadron system with the invariant mass m X ⪷ √|t| .) In this region one can use perturbative QCD and the cross sections are given by the t -channel gluon exchange with the vacuum quantum numbers, i.e. QCD pomeron. We have calculated these cross sections in the low non-trivial order of perturbative QCD (two-gluon exchange). We found impact factors of the γ → vector meson and γ → X transitions. We used them to obtain amplitudes by means of a simple impact-representation method well known in QED. The cross sections obtained are s -independent and at t = −3 GeV 2 they vary from 3 × 10 −34 cm 2 for γγ → ϱ 0 + X to 10 −38 cm 2 for γγ → γγ . Taking into account the high-order QCD corrections leads to an essential increase of the cross sections with the growth of s . Therefore, an experimental study of these processes allows one to check not only the low order but the whole series of perturbative QCD.

Possibility of the Experimental Investigation of the {QCD} Pomeron in Semihard Processes at the

Abstract We consider both the semiexclusive reactions γγ → A + X and the exclusive ones γγ → AB with the production of neutral vector mesons and photons at s ⪢ | t | ⪢ (0.3 GeV) 2 . (Here A,B = ϱ 0 , ω , ϕ , γ and X is a hadron system with the invariant mass m X ⪷ √|t| .) In this region one can use perturbative QCD and the cross sections are given by the t -channel gluon exchange with the vacuum quantum numbers, i.e. QCD pomeron. We have calculated these cross sections in the low non-trivial order of perturbative QCD (two-gluon exchange). We found impact factors of the γ → vector meson and γ → X transitions. We used them to obtain amplitudes by means of a simple impact-representation method well known in QED. The cross sections obtained are s -independent and at t = −3 GeV 2 they vary from 3 × 10 −34 cm 2 for γγ → ϱ 0 + X to 10 −38 cm 2 for γγ → γγ . Taking into account the high-order QCD corrections leads to an essential increase of the cross sections with the growth of s . Therefore, an experimental study of these processes allows one to check not only the low order but the whole series of perturbative QCD.

\gamma \gamma

Abstract We consider the Coulomb correction (CC) to the e + e − pair production related to multiphoton exchange of the produced e ± with nuclei. The contribution of CC to the energy distribution of e + and e − as well as to the total pair production cross section is calculated with an accuracy of the order of 1%. The found correction to the total Born cross section is negative and equals −25% at the RHIC for Au-Au and −14% at the LHC for Pb–Pb collisions.

Collisions

Abstract The cross sections for Ψ -production in the semihard collisions are calculated at s ⪢ | t |, m Ψ 2 and at not too large a jet effective mass m X 2 ≲ m Ψ 2 + | t | for the process γγ → Ψ X. We found these cross sections in the lowest nontrivial QCD order (two-gluon exchange in the t -channel): σ ( γγ → Ψ X) ≈ 10 35 cm 2 , σ ( γγ → ΨΨ )=2×10 −36 cm 2 . The polarization of Ψ in these processes is transversal (contrary to the longitudinal one of light mesons ϱ 0 , ω, ϕ in similar processes).

Large Coulomb corrections to the e+e− pair production at relativistic heavy ion colliders

The exclusive production of one

The semihard processes γγ→ΨX, γγ→ΨΨ, γγ→ϱΨ

{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}

Exclusive and inclusive muon pair production in collisions of relativistic nuclei

pair in collisions of two ultrarelativistic nuclei is considered. We present a simple method for the calculation of the Born cross section for this process based on an improved equivalent photon approximation. We find that the Coulomb corrections to this cross section (corresponding to multiphoton exchange of the produced