Polarized Photon Beam Research Articles

Laser Electron Photon Experiment at SPring-8

A highly polarized photon beam produced via the backward Compton scattering of polarized laser photons off the high energy electron is utilized for nuclear and particle physics experiments at SPring-8. Some recent resultsfrom the first physics run started in 2000 are presented and the future prospects are discussed.

Angular correlation theory for double photoionization in a rare-gas atom: Ionization by polarized photons

This is a sequel to an earlier article on the theory of angular correlation for double photoionization. Here we consider the two-step double photoionization of a rare gas atom under the influence of a polarized photon beam described by appropriate Stokes parameters. Cylindrical mirror analysers (CMA) are used to detect the outgoing electrons. Theoretical values of the correlation functions are obtained for linearly polarized light. Two different situations is handled. Once, the value of the correlation function is obtained keeping the photo-electron in a fixed direction. The other case the direction of the Auger electron is kept fixed. Comparison with experiments on xenon shows excellent agreement for the case of (4d_{5/2}) photoionization followed by a subsequent (N_{5}-O_{23}O_{23} ^{1}S_{0}) Auger decay for a polarized incident photon of energy (94.5eV) {[}J. Phys.B,

Parity Measurements with Completely Polarized Photon Beam

Photon scattering experiments on 52Cr and 138Ba were performed to resolve ambiguous parity assignments below neutron threshold energy by using completely linear-polarized photon beam generated by Laser-Compton backscattering technique. The parity of 5544 keV level in 52Cr was confirmed to be negative. The Ml transition was identified at 5098 keV in 52Cr. The 5644 keV level in 138Ba, which was tentatively assigned as Ml transition by former Compton polarimeter measurement, was clearly assigned as El transition. A parity measurement with a completely linear-polarized photon beam was demonstrated to be simple and straightforward method.

τ magnetic moment in a γγ collider

We analyze different observables to study the magnetic dipole moment of the tau pairs produced by photon linear colliders. We use the circular polarized photon beam and study distributions of polarized $\tau$ final pairs to define sensibly asymmetries to magnetic dipole moment.

Meson photoproduction at GRAAL and baryon resonances

Differential cross sections and polarised photon beam asymmetries for eta, pi(0) and pi(1) photoproduction on the proton, produced by the GRAAL Collaboration, are presented. The results cover wide angular and enegy ranges of 40-170degrees and 550-1496 MeV (707-1496 MeV for eta) respectively, and exhibit an unprecedented level of accuracy. The results are compared with predictions of several models.

Searching for Gluonic Excitations – The Hall D Project at Jlab

Hybrid mesons are produced when the gluonic degrees of freedom are excited within normal mesons. A large fraction of these gluonic excitations can be identified using unique combinations of spin, parity and charge conjugation (J PC ) quantum numbers which are not allowed for ordinary \(q\bar q\) bound states. Photon beams are expected to be particularly favorable for the production of such states, which are required by the quark confining mechanism of QCD. Mapping out the spectrum and decay modes of these hybrid mesons is the necessary first step in understanding the nature of confinement. Plans are underway at Jefferson Lab to upgrade the energy of the electron accelerator to 12 GeV. With 12 GeV electrons, a 9 GeV linearly polarized photon beam will be produced using the coherent bremsstrahlung technique. Along with this energy upgrade, a hermetic detector housed in new experimental hall (Hall D) will be used to collect data on photoproduced mesons with unprecedented statistics.

Hard polarized photon emission in single crystals by high energy electrons for planar crystal orientations

The radiation emission spectra of polarized photons emitted from charged particle in single crystals are obtained in the semiclassical theory in Baier–Katkov–Strakhovenko approximation for planar crystal orientation. Optimal crystal orientations for producing unpolarized and polarized photon beams are also found.

Chargino production and decay in photon–photon collisions

We study the production and leptonic decay of charginos in the collisions of polarized photon beams including the complete spin correlations. The photons can be generated by Compton backscattering of polarized laser pulses off a polarized electron beam. Since the production process is determined only by the electromagnetic coupling of the charginos, this process allows to study their decay dynamics. The cross section and the forward–backward asymmetry of the decay lepton are very sensitive to the gaugino mass parameter M 1 and to the sneutrino mass without any ambiguities.

Generation of Compton backscattering γ-ray beams

The backward scattering of laser light against high-energy electrons may be used to produce highly polarized photon beams of low background, with an energy resolution of a few percent. The general characteristics of Compton backscattering beams are outlined and the application of this technique to different electron accelerators is reviewed. The results from existing facilities are presented with an outlook to planned future installations.

Anomalousf1exchange in vector meson photoproduction asymmetries

We perform an analysis of the elastic production of vector mesons with polarized photon beams at high energy in order to investigate the validity of a recently proposed dynamical mechanism based on the dominance of the f_1 trajectory at large momentum transfer. The density matrix characterizing the angular distributions of the vector meson decays is calculated within an exchange model which includes the Pomeron and the f_1. The asymmetries of these decays turn out to be very useful to disentangle the role of these exchanges since their effect depends crucially on their quantum numbers which are different. The observables analyzed are accessible with present experimental facilities.

Helicity dependence of γp→nπ+ results from the GDH experiment at mamiresults from the GDH experiment at mami

The helicity dependence of the total photoabsorption cross section and partial channels for polarized protons have been measured for incident photon energies from 120 to 800 MeV. We used the large acceptance detector DAPHNE with additional forward components in conjunction with a newly developed frozen spin target and the tagged polarized photon beam facility of the MAMI accelerator in Mainz (Glasgow-Mainz tagger). First preliminary results for the polarized total cross section of the γp→nπ+ channel and its contribution to the GDH integral and the forward spin polarizability are compared with partial wave analysis of DHT and SAID.

Monte Carlo simulation of X-ray fluorescence spectra: Part 4. Photon scattering at high X-ray energies

The photon scattering model of a Monte Carlo simulation code for synchrotron radiation X-ray fluorescence (SRXRF) spectrometers is evaluated at high X-ray energies (60–100 keV) by means of a series of validation experiments performed at Beamline BW5 of HASYLAB. Using monochromatic X-rays, Compton/Rayleigh multiple scattering experiments were performed on polypropylene, Al and Cu samples. Especially in the case of the first two matrices multiple Compton scattering occurs with high probability. This work demonstrates that the simulation model provides a reliable estimate of the spectral distribution of the multiply scattered linearly polarized photon beam as observed by an HPGe detector. Next to variations in sample composition and thickness, the ability of the code to simulate various detection geometries has also been verified. As an application of the code, the achievable detection limits of SRXRF for rare earth elements as obtained with white beam and monochromatic (80 keV) excitation are compared.

Light by light scattering at high energy: a tool to reveal new particles

We point out a few remarkable properties of the γγ→ γγ process at high energy, which should allow to search for effects of new particles and interactions. We give illustrations with threshold effects due to pairs of new charged particles (charginos, charged Higgs particles, sfermions), resonance effects due to s-channel production of neutral scalars (standard or supersymmetric neutral Higgs particles or technipions) and unitarity saturating amplitudes due to a strongly interacting sector. The use of polarized photon beams is also briefly discussed.

Observation of M1 resonance in 206Pb using a highly linear polarized photon beam

More than twenty M1 states were discovered in 206Pb from 6.5 to 8.1 MeV with a high-resolution NRF experiment that used a highly linear-polarized photon beam generated by laser-Compton backscattering. The total reduced transition probability of ΣB( M1 ↑) = 17.4 ± 5.6 μ N 2 agreed well with QPM calculation (16.1 μ N 2) and previous tagged photon experiment (19 ± 2 μ N 2). a fine structure of two bumps at 7.2 and 7.9 MeV which was reproduced reasonably by the QPM calculation was clearly observed in the isovector M1 strength distribution.

Polarization in Pseudoscalar Meson Photoproduction

Two problems of current interest in the use of polarization observables for pseudoscalar meson photoproduction to probe the basic dynamics are discussed. The first one concerns the extraction of the ratio of electric quadrupole to magnetic dipole transition strengths in the photo-excitation of the \(\). The predictions of various models are compared with the recent LEGS and MAMI data obtained with polarized photon beams. The second one is a proposal by Saghai and Tabakin to use the nodal structure of spin observables to unveil underlying dynamics in the production process. We demonstrate with the example of \(\) at \(\) photon energy that the assumption of multipole truncation, which enters into their nodal analysis, is questionable.

Circularly polarized photon beams produced by channeled longitudinally polarized electrons

The spectral distributions and polarization of the radiation of electrons with longitudinal polarization when they move in parallel to crystallographic planes and axes are calculated in the constant field approximation. It is shown that the x= ω/ ε-dependence ( ϵ and ω are the electron and photon energy) of the radiation circular polarization coincides with that for the bremsstrahlung in amorphous media and coherent bremsstrahlung in single crystals, and that the radiation under consideration may serve as a source of intense circularly polarized photons.

New Measurement ofΣBeam Asymmetry forηMeson Photoproduction on the Proton

We present new Sigma beam asymmetry data for eta meson photoproduction on the proton, using a novel tagged, laser backscattered, linearly polarized photon beam up to 1.1 GeV. The data show large, positive asymmetries, at all incident photon energies. In addition to the S-11(1535) and D-13(1520) resonances necessary to reproduce the cross sections, P-13(1720) and D-15(1675) four stars resonances contribute to the Sigma observable, but cannot reproduce the strong forward asymmetries measured at energies higher than 900 MeV.

Optimal spin basis in polarized photon linear colliders

We analyze the spin correlations of the top quark pairs produced at photon linear colliders. We employ the circular polarized photon beams and general spin basis for the top quark pair. We consider general spin bases to find a strong spin correlation between the produced top quark and top antiquark. We show the cross sections in these bases and discuss the characteristics of the results.

Experimental study of the 3He(γ, pp)n reaction with polarized photons

The experimental study of the reaction 3He(γ, pp)n is being carried out in the photon energy range E γ = 200–500 MeV at the Tokyo 1.3 GeV electron synchrotron. By use of the tagged and linearly polarized photon beam, and the π-sr magnetic spectrometer TAGX, a kinematically complete measurement of the reaction 3He(γ, pp)n will be made. The high statistics measurements of dσ dΩ and Σ of the reaction 3He(γ, pp)n will clarify the photon absorption mechanism.

Photoelectron angular distribution measurements of at visible wavelengths

Photoelectron angular distributions for the laser photodetachment process have been measured at six wavelengths in the region 457.9 - 647.1 nm. An intense 10 keV beam was produced in a caesium sputter-type ion source and mass-selected with a bending magnet. The mass-selected ion beam was subsequently crossed at with a linearly polarized, continuous photon beam. Angular distributions were obtained by measuring the laboratory-frame energy spectra of photodetached electrons as a function of the angle between the velocity vector of the ejected electrons and the polarization direction of the linearly polarized photon beam. The photoelectron angular distributions were used to determine asymmetry parameters. The present measurements are in excellent agreement with those of Hall and Siegel at 488.0 and 514.5 nm (1968 J. Chem. Phys. 48 943), and good agreement with a calculation by Cooper and Zare (1968 J. Chem. Phys. 48 942). The photodetachment asymmetry parameters for are compared with a recent measurement of the photodetachment asymmetry parameters for .