Probing the photon at γe-colliders

We investigate the feasibility of studying the photon structure function at a e-collider. We show that the deep inelastic probe of the real photon by a highly virtual photon in such a collider will extend significantly thex andQ ² range presently accessible ate ⁺ e ^– colliders. In addition, we study the production of large transverse momentum dijet final states to determine the sensitivity of these cross sections to different parametrisations of the quark and gluon distributions in the photon.     

Production of electron-positron pairs by a photon propagating in a strongly magnetized thermal bath

The production of electron-positron pairs by a photon propagating in a thermal bath in both zero and strong (B ≫ 4.41 × 10¹³ G) magnetic fields has been considered. The mean free path has been calculated for the high-energy photon propagating through a thermodynamically equilibrium photon gas along the magnetic field lines so that the γ → e ⁻ e ⁺ decay is kinematically forbidden. It has been shown that the strong magnetic field suppresses the probability of the γγ′ → e ⁻ e ⁺ process. The analyzed process can be useful for analysis of possible mechanisms of the generation of the e ⁻ e ⁺ plasma in the regions of the polar caps of magnetars.     

Resolved photon processes

We review high-energy scattering processes that are sensitive to the hadronic structure of the photon, describing theoretical predictions as well as recent experimental results. These processes include deep-inelastic electron-photon scattering ate ⁺ e ⁻ colliders; and the production of jets, heavy quarks and isolated photons in the collision of real photons ate ⁺ e ⁻ colliders, as well as in photon-photon collisions atep colliders. We also comment on minijet based calculations of totalγp andγγ cross-sections, and discuss the possibility that future lineare ⁺ e ⁻ colliders might produce very large photon fluxes due to the beamstrahlung phenomenon; in the most extreme cases, we predict more than one hadronicγγ event to occur at every bunch crossing.     

Associated production of light gravitinos in e+e? and e?γ collisions

Light gravitino productions in association with a neutralino (selectron) in e ⁺ e ⁻ (e ⁻ γ) collisions are restudied in a scenario that the lightest supersymmetric particle is a gravitino and the produced neutralino (selectron) promptly decays into a photon (electron) and a gravitino. We explicitly give the helicity amplitudes for the production processes by using the effective goldstino interaction Lagrangian, and present the cross sections with different collision energies and mass spectra. We also examine selection efficiencies by kinematical cuts and beam polarizations for the signal and background processes, and show that the energy and angular distributions of the photon (electron) can explore the mass of the t-channel exchange particle as well as the mass of the decaying particle at a future e ⁺ e ⁻ (e ⁻ γ) collider.     

Ultimate parameters of the photon collider at the international linear collider

At linear colliders, the e ⁺ e ⁻ luminosity is limited by beam-collision effects, which determine the required emittances of beams in damping rings (DRs). In γγ collisions at the photon collider, these effects are absent, and so smaller emittances are desirable. In the present damping ring designs, nominal DR parameters correspond to those required for e ⁺ e ⁻ collisions. In this note, I would like to stress once again that as soon as we plan the photon collider mode of ILC operation, the damping ring emittances are dictated by the photon collider requirements — namely, they should be as small as possible. This can be achieved by adding more wigglers to the DRs; the incremental cost is easily justified by a considerable potential improvement of the γγ luminosity. No expert analysis exists as of now, but it seems realistic to obtain a factor five increase of the γγ luminosity compared to the ‘nominal’ DR design.      

Bremsstrahlung photon polarization for ee ± → ( e γ) e ± and ep → ( e γ) p high-energy collisions

The polarization of a bremsstrahlung photon during the processes ee ^± → (eγ)e ^± and ep → (eγ)p is calculated for peripheral kinematics in the high-energy limit, where the cross section does not decrease with the incident energy. When the initial electron is unpolarized (longitudinally polarized), the final photon can be linearly (circularly) polarized. The Stokes parameters of the photon polarization are calculated as a function of the kinematical variables of the process: the energy of the recoil particle, the energy fraction of the scattered electron, and the polar and azimuthal angles of the photon. The numerical results are given in the form of tables for typical values of the relevant kinematic variables. The text was submitted by the authors in English.     

Recent results on resolved photon processes

During the last 18 months, experiments at bothe ⁺ e ⁻ andep colliders have begun to test earlier predictions for processes that probe the hadronic structure of the photon. All the main qualitative predictions have already been verified; more detailed analyses are now starting to improve our quantitative understanding of photon structure functions. Some comments on minijets and total cross sections are also included.     

Graviton-induced bremsstrahlung at e + e - colliders

We consider graviton-induced bremsstrahlung at future e ⁺ e ^- colliders in both the ADD and RS models, with emphasis on the photon perpendicular momentum and angular distribution. The photon spectrum is shown to be harder than in the standard model, and there is an enhancement for photons making large angles with respect to the beam. In the ADD scenario, the excess at large photon perpendicular momenta should be measurable for values of the cut-off up to about twice times the CM energy. In the RS scenario, radiative return to graviton resonances below the CM energy can lead to large enhancements of the cross section.Received: 28 March 2004, Published online: 3 June 2004     

Detector issues for a photon collider

The photon collider is an option at the ILC. In this note detector issues are discussed that are relevant for the change from the e ⁺ e ⁻ mode of the ILC to the γγ mode.      

Photo-Production of Muons

The total cross-section for the photo-production of muons in the reaction γ + e^? → μ^? + v_e + v_μ is calculated. The dependence of the total cross-section on the incident photon energy is explicitly shown.     

Radiative events as a probe of dark forces at GeV-scale <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> colliders

High-luminosity e ⁺ e ⁻ colliders at the GeV scale (flavor factories) have been recently recognized to be an ideal environment to search for a light weakly coupled vector boson U (dark photon) emerging in several new physics models. At flavor factories a particularly clean channel is the production of the U boson in association with a photon, followed by the decay of the U boson into lepton pairs. Beyond the approximations addressed in previous works, we perform an exact lowest order calculation of the signal and background processes of this channel. We also include the effect of initial- and final-state QED corrections neglected so far, to show how they affect the distributions of experimental interest. We present new results for the expected statistical significance to a dark photon signal at KLOE/KLOE-2 and future super-B factories. The calculation is implemented in a new release of the event generator BabaYaga@NLO, which is available for full event simulations and data analysis.     

Polarization effects accompanying penetration of high-energy electrons,positrons and gamma-quanta through crystals

Abstract

Synchrotron-like processes of radiation and pair production in fields of crystal planes are accompanied by large number of polarization effects. These effects can be used for production and analysis of TeV-energy polarized e ⁺, e ^?, photon and hadron beams for their use in high-energy physics. The process of e ⁺ and e ^? self-polarization accomapnies their radiation in bent crystals, where channeled particles are moving in regions having a preferential direction of the electric field. The results of numerical simulation of self-polarization process with both radiation and multiple scattering taken into account are presented. It is shown that the self-polarization process can be observed using present-day CERN secondary positron beam. At TeV-energy region the efficiency of both e ⁺ and e ^? self-polarization can be considerably risen by making the crystal curvature growing along the crystal.     

Photon splitting in an ultrastrong magnetic field

We analyze the splitting of a photon with energy ω below the e ⁺ e ⁻ pair-production threshold in an ultrastrong magnetic field. We use the amplitudes found by employing the operator diagrammatic technique. In a field considerably above the critical values the process amplitudes become independent of the field strength. A study of the polarization operator of a photon in an external field of arbitrary strength in the energy range considered in the present investigation shows that there is only one set of polarizations of the initial and final photons for which the splitting amplitude is nonzero. Zh. éksp. Teor. Fiz. 111, 52–62 (January 1997)     

Monte-Carlo generator photon jets for the process e+e?→γγ

Monte-Carlo generator with photon jets radiation in collinear regions for the process e ⁺ e ⁻→γγ is described in detail. Radiative corrections in the first order of α are treated exactly. Large leading logarithmic corrections coming from collinear regions are taken into account in all orders of α by applying the Structure Function approach. Theoretical precision of the cross section with radiative corrections is estimated to be 0.2%. This process is considered as an additional tool to measure luminosity in forthcoming experiments with the CMD-3 detector at the e ⁺ e ⁻ collider VEPP-2000.     

Atomic levels in superstrong magnetic fields and <Emphasis Type="Italic">D</Emphasis> = 2 QED of massive electrons: Screening

The photon polarization operator in superstrong magnetic fields induces the dynamical photon “mass” which leads to screening of Coulomb potential at small distances z ≪ 1/m, m is the mass of an electron. We demonstrate that this behavior is qualitatively different from the case of D = 2 QED, where the same formula for a polarization operator leads to screening at large distances as well. Because of screening the ground state energy of the hydrogen atom at the magnetic fields B ≫ m ²/e ³ has the finite value E ⁰ = −me ⁴/2 ln²(1/e ⁶).     

Probing universal extra dimension at the international linear collider

We consider the UED scenario and study the detectability of the first KK electron-positron pair at the ILC. A few hundred GeV KK electron decays into a nearly degenerate KK photon, which carries away missing energy, and the standard electron. The mass splitting between the KK electron and KK photon is controlled by the bulk-and brane-induced radiative corrections. We look for the signal event e ⁺ e ⁻ + large missing energy for √s = 1 TeV and observe that with a few hundred fb⁻¹ luminosity the signal can be deciphered from the standard model background. We briefly outline how the UED signals may be distinguished from the supersymmetric signals. This talk is based on a work the author did with Paramita Dey, Anirban Kundu and Amitava Raychaudhuri [1].     

Formulation and picture of quantum phase

Based on the concept of classical phase, we formulate a new explanation for the quantum phase from the quantum mechanical point of view. The quantum phase is the canonically conjugate variable of an angular momentum operator, which corresponds to the angular position φ in an actual physical space with a classical reference frame, but it takes a complex exponential form e ^iφ≡cosφ+i sinφ in the abstract Hilbert space of a quantum reference frame. This formulation is simply the famous Euler formula in a complex number field. In particular, when φ = π/2, the correlative quantum phase is a unitary pure imaginary number e ^iπ/2≡cos(π/2)+i sin(π/2) ≡ i. By using a photon state-vector function that is the general solution of photon Schr?dinger equation and can completely describe a photon’s behavior, we discuss the relationship between the angular momentum of a photon and the phase of the photon; we also analyze the intrinsic relationship between the macroscopic light wave phase and the microscopic photon phase.     

Associated single photons and doubly-charged scalars at linear <Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> colliders

Doubly-charged scalars, predicted in many models having exotic Higgs rep-resentations, can in general have lepton-number violating (LFV) couplings. We show that by using an associated monoenergetic final state photon seen at a future linear e ⁻ e ⁻ collider, we can have a clear and distinct signature for a doubly-charged resonance. The strength of the ΔL = 2 coupling can also be probed quite effectively as a function of the recoil mass of the doubly-charged scalar.      

Generation of 1015–1017 eV photons by ultrahigh-energy cosmic rays in the Galactic magnetic field

It is shown that the expected dip in the diffuse photon spectrum above the threshold of e ⁺ e ⁻ pair production, i.e., at energies 10¹⁵–10¹⁷ eV, may be absent due to the synchrotron radiation by the electron component of the extragalactic ultrahigh-energy cosmic rays (UHE CRs) in the Galactic magnetic field. The mechanism we propose requires small (<2×10⁻¹² G) extragalactic magnetic fields and a large photon fraction in the UHE CRs. For a typical photon flux expected in top-down scenarios of UHE CRs, the predicted flux in the region of the dip is close to the existing experimental limit. The sensitivity of our mechanism to the extragalactic magnetic field may be used to improve existing bounds on the latter by two orders of magnitude. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 8, 487–492 (25 October 1999) Published in English in the original Russian journal. Edited by Steve Torstveit.