Sokolov-Ternov Effect Research Articles

Production and decay of hyperons in a transversely polarized electron-positron collider

The self-polarization of relativistic electrons or positrons moving in a magnetic field at a storage ring occurs through the emission of spin-flip synchrotron radiation, known as the Sokolov-Ternov effect. The resulting transverse polarizations of the colliding electrons and positrons, away from the depolarization resonances, allow for precise investigation of the spin entangled hyperon-antihyperon pairs via virtual photon or charmonium decay. The feasibility study reveals a promising increase in the statistical sensitivity of the CP violation signal after considering the transverse polarizations of the lepton beams. Published by the American Physical Society 2024

Radiative polarization dynamics of relativistic electrons in an intense electromagnetic field

We propose a self-consistent model which utilizes the polarization vector to theoretically describe the evolution of spin polarization of relativistic electrons in an intense electromagnetic field. The variation of radiative polarization due to instantaneous no photon emission is introduced into our model, which extends the applicability of the polarization vector model derived from the nonlinear Compton scattering under local constant crossed-field approximation to the complex electromagnetic environment in laser plasma interaction. According to this model, we develop a Monte Carlo method to simulate the electron spin under the influence of radiation and precession simultaneously. Our model is consistent with the quantum physical picture that spin can only be described by a probability distribution before measurement, and it contains the entire information on the spin. The correctness of our model is confirmed by the successful reproduction of the Sokolov-Ternov effect and the comparison of the simulation results with other models in the literature. The results show the superiority in accuracy, applicability, and computational efficiency of our model, and we believe that our model is a better choice to deal with the electron spin in particle-in-cell simulation for laser plasma interaction.

Scaling laws for the depolarization time of relativistic particle beams in strong fields

The acceleration of polarized electrons and protons in strong laser and plasma fields is a very attractive option to obtain polarized beams in the GeV range. We investigate the feasibility of particle acceleration in strong fields without destroying an initial polarization, taking into account all relevant mechanisms that could cause polarization losses, i.e. the spin precession described by the T-BMT equation, the Sokolov-Ternov effect and the Stern-Gerlach force. Scaling laws for the (de-)polarization time caused by these effects reveal that the dominant polarization limiting effect is the rotation of the single particle spins around the local electromagnetic fields. We compare our findings to test-particle simulations for high energetic electrons moving in a homogeneous electric field. For high particle energies the observed depolarization times are in good agreement with the analytically estimated ones.

The Bloch equation for spin dynamics in electron storage rings: Computational and theoretical aspects

In this paper, we describe our work on spin polarization in high-energy electron storage rings which we base on the Full Bloch equation (FBE) for the polarization density and which aims towards the [Formula: see text] option of the proposed Future Circular Collider (FCC-ee) and the proposed Circular Electron Positron Collider (CEPC). The FBE takes into account non spin-flip and spin-flip effects due to synchrotron radiation including the spin-diffusion effects and the Sokolov–Ternov effect with its Baier–Katkov generalization as well as the kinetic-polarization effect. This mathematical model is an alternative to the standard mathematical model based on the Derbenev–Kondratenko formulas. For our numerical and analytical studies of the FBE, we develop an approximation to the latter to obtain an effective FBE. This is accomplished by finding a third mathematical model based on a system of stochastic differential equations (SDEs) underlying the FBE and by approximating that system via the method of averaging from perturbative ODE theory. We also give an overview of our algorithm for numerically integrating the effective FBE. This discretizes the phase space using spectral methods and discretizes time via the additive Runge–Kutta (ARK) method which is a high-order semi-implicit method. We also discuss the relevance of the third mathematical model for spin tracking.

Theory of radiative electron polarization in strong laser fields

Radiative polarization of electrons and positrons through the Sokolov-Ternov effect is important for applications in high-energy physics. Radiative spin-polarization is a manifestation of quantum radiation reaction affecting the spin-dynamics of electrons. We recently proposed that an analogue of the Sokolov-Ternov effect could occur in the strong electromagnetic fields of ultra-high-intensity lasers, which would result in a build-up of spin-polarization in femtoseconds. In this paper we develop a density matrix formalism for describing beam polarization in strong electromagnetic fields. We start by using the density matrix formalism to study spin-flips in non-linear Compton scattering and its dependence on the initial polarization state of the electrons. Numerical calculations show a radial polarization of the scattered electron beam in a circularly polarized laser, and we find azimuthal asymmetries in the polarization patterns for ultra-short laser pulses. A degree of polarization approaching 9 % is achieved after emitting just a single photon. We develop the theory by deriving a local constant crossed field approximation (LCFA) for the polarization density matrix, which is a generalization of the well known LCFA scattering rates. We find spin-dependent expressions that may be included in electromagnetic charged-particle simulation codes, such as particle-in-cell plasma simulation codes, using Monte-Carlo modules. In particular, these expressions include the spin-flip rates for arbitrary initial polarization of the electrons. The validity of the LCFA is confirmed by explicit comparison with an exact QED calculation of electron polarization in an ultrashort laser pulse.

Spin polarization of electrons by ultraintense lasers

In a strong magnetic field, ultra-relativistic electrons or positrons undergo spin flip transitions as they radiate, preferentially spin polarizing in one direction -- the Sokolov-Ternov effect. Here we show that this effect could occur very rapidly (in less than 10 fs) in high intensity ($I\gtrsim10^{23}$ W/cm$^{2}$) laser-matter interactions, resulting in a high degree of electron spin polarization (70%-90%).

ON THE RELATION BETWEEN UNRUH AND SOKOLOV–TERNOV EFFECTS

We show that the Sokolov–Ternov effect — the depolarization of particles in storage rings coming from synchrotron radiation due to spin flip transitions — is physically equivalent to the Unruh effect for circular acceleration if one uses a spin-1/2 particle as the Unruh–DeWitt detector. It is shown that for the electron, with gyromagnetic number g ≈ 2, the exponential contribution to the polarization, which usually characterizes the Unruh effect, is "hidden" in the standard Sokolov–Ternov effect making it hard to observe. Thus, our conclusions are different in detail from previous work.

On the physical meaning of the Unruh effect

Simple arguments are presented that detectors moving with constant acceleration (even acceleration for a finite time) should detect particles. The effect is seen to be universal. Moreover, detectors undergoing linear acceleration and uniform circular motion both detect particles for the same physical reason. It is shown that the Unruh effect for a circularly orbiting electron in a constant external magnetic field used as a Unruh-DeWitt detector physically coincides with the experimentally verified Sokolov-Ternov effect.

Precision measurement with the transverse polarimeter at HERA II

The HERA ep–collider provides a longitudinally polarised positron beam to the three experiments HERMES, H1 and ZEUS. The degree of polarisation is determined with two Compton polarimeters, one measuring the transverse polarisation that naturally builds up in a sufficiently planar ring via the Sokolov–Ternov effect, the other one measuring the longitudinal polarisation between the HERMES spin rotators. The future physics program of the collider experiments requires polarimetry with a precision of better than 1%. To meet this goal, the Transverse Polarimeter has been upgraded in 2001 with a new data acquisition system and a silicon strip detector complementing the main calorimeter. A new analysis, which allows an in–situ calibration in parallel to the polarisation measurement without relying on testbeam results obtained under different conditions, is presented in this paper. The new method uses a fit of the double–differential Compton cross section (folded with detector effects) to the measured two–dimensional spectra in energy and position of the scattered photon. In March 2003, HERA succeeded to deliver up to 50% of longitudinal polarisation to all three experiments as well as collisions for H1 and ZEUS. Some first results of the new analysis on polarised HERA II data are shown. PACS: 29.27.Hj Polarized beams – 13.88.+e Polarization in interactions and scattering

Radiational self-polarization of electrons moving in the electromagnetic plane-wave field

The radiational self-polarization effect induced by spontaneous radiation is shown to be possible for an electron moving in the electromagnetic plane-wave field. It is quite similar to the well-known Sokolov-Ternov effect, as regards the synchrotron radiation. The physical analysis of the self-polarization process is given and qualitative estimates for experimental observation of the predicted effect are discussed.