Spin and Polarization Effects in the Annihilation of Triplet Positronium

Drisko, R.M.

doi:10.1103/physrev.102.1542

Cited by 30 publications

(13 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This effect, which will not affect f d after around 0.75 T [69], reduces the amount of long lived Ps present by mixing m = 0 triplet and singlet states [70]. However, increasing the magnetic field also increases the positron beam density, and the increased Ps yield due to e-h pair production partially compensates for the magnetic quenching, otherwise the difference in percent delayed fractions would be around 40 % [71,54]. Figure 5 shows the Ps yield as a function of temperature for the n-Ge (a) and n-Si (b) samples.…”

Section: B Ps Yieldmentioning

confidence: 99%

“…Note that η =1 would be expected for an ideal version of our experiment in which the total energy of 2 and 3 photon decays both contribute equally to the detector response. A smaller value of η would result from the preferential absorption of the lower energy 3γ decay photons in the chamber walls and surrounding materials, and also from the directionality of the 3γ decays in a strong magnetic field which do not favor detection of |m|=1 ortho Ps decays in a plane perpendicular to the magnetic field direction [57]. A larger value of η would result if the total number of photons were an important factor, for example due to preferential scattering of the lower energy 3γ annihilation photons into the detector.…”

Section: B Single Shot Lifetime Measurementsmentioning

confidence: 99%

See 1 more Smart Citation

Positronium formation via excitonlike states on Si and Ge surfaces

et al. 2011

View full text Add to dashboard Cite

Recent experiments combining lifetime and laser spectroscopy of positronium (Ps) show that these atoms are emitted from p-Si(100) at a rate that depends on the sample temperature, suggesting a thermal activation process, but with an energy that does not, precluding direct thermal activation as the emission mechanism. Moreover, the amount of Ps emitted is substantially increased if the target is irradiated with 532 nm laser light just prior to the implantation of the positrons. Our interpretation of these data was that the Ps was emitted via an exciton-like positron-electron surface state, not dissimilar to an electronic surface exciton observed on Si in two-photon photoemission measurements. The hypothesis that this state may be populated by electrons from one of the occupied electronic surface states, either thermally or by laser excitation, is consistent with our observations and suggests that one should expect a high Ps yield at room temperature from an n-doped Si(100) sample, since in this case the same surface states will already be occupied. Here we present data obtained with an n-Si(100) target that supports our model, and also reveals the unexpected result that the kinetic energy of Ps emitted from this material actually decreases when it is heated, an effect we attribute to shifts in the surface energy levels due to the presence of a high density of thermally generated electrons. We show data obtained with a Ge(100) sample that corroborate the idea that the effects we observe are related to surface electron states, and hence should occur for any indirect band gap semiconductor with dangling bond states. Our model is further confirmed by the observation that the Ps yield from p-Si depends linearly on the surface density of the implanted positrons due to the effects of electron-hole pairs created as the positrons slow down.

show abstract

Section: B Ps Yieldmentioning

confidence: 99%

Section: B Single Shot Lifetime Measurementsmentioning

confidence: 99%

Positronium formation via excitonlike states on Si and Ge surfaces

et al. 2011

View full text Add to dashboard Cite

show abstract

“…Drisko [201] calculated the angular distributions for photons emitted in triplet state decays and showed that the distribution of annihilation gamma rays depends on the azimuthal quantum number m. We can immediately see why this must be the case; for m = 0 decays three photons with helicity = +1 are emitted, but the total angular momentum projected along the quantization axis must be zero. This limits the possible angles with which annihilation photons from m = 0 states can be emitted and still conserve momentum in a different way from the restrictions on the m = 1 states.…”

Section: Ps Annihilationmentioning

confidence: 99%

“…This limits the possible angles with which annihilation photons from m = 0 states can be emitted and still conserve momentum in a different way from the restrictions on the m = 1 states. The number of photons emitted as a function of angle for the different m states was found to be [201] …”

Section: Ps Annihilationmentioning

confidence: 99%

Experimental progress in positronium laser physics

2018

View full text Add to dashboard Cite

Abstract. The field of experimental positronium physics has advanced significantly in the last few decades, with new areas of research driven by the development of techniques for trapping and manipulating positrons using Surko-type buffer gas traps. Large numbers of positrons (typically ≥10 6 ) accumulated in such a device may be ejected all at once, so as to generate an intense pulse. Standard bunching techniques can produce pulses with ns (mm) temporal (spatial) beam profiles. These pulses can be converted into a dilute Ps gas in vacuum with densities on the order of 10 7 cm −3 which can be probed by standard ns pulsed laser systems. This allows for the efficient production of excited Ps states, including long-lived Rydberg states, which in turn facilitates numerous experimental programs, such as precision optical and microwave spectroscopy of Ps, the application of Stark deceleration methods to guide, decelerate and focus Rydberg Ps beams, and studies of the interactions of such beams with other atomic and molecular species. These methods are also applicable to antihydrogen production and spectroscopic studies of energy levels and resonances in positronium ions and molecules. A summary of recent progress in this area will be given, with the objective of providing an overview of the field as it currently exists, and a brief discussion of some future directions.

show abstract

“…It was shown in Ref. 55 that the amplitudes for the three-photon annihilation of orthopositronium H f i (X 1,+1 , X 1,0 , X 1,−1 ) can be written as 21) where the vector u 1 is a function of the photon polarization vectors:…”

Section: )mentioning

confidence: 99%

The diagonal spin basis and calculation of processes involving polarized particles

Galynskii¹

1998

Phys. Part. Nucl.

View full text Add to dashboard Cite

The review of recently developed by the authors new techniques for covariant calculation of matrix elements in QED, the so-called formalism of "Diagonal Spin Basis" (DSB), is presented. In DSB spin 4-vectors of in-and out-fermions are expressed just in terms of their 4-momenta. In this approach the little Lorentz group, common for the initial and final states, is realized. This brings the spin operators of in-and out-particles to coincidence, allowing to separate in a covariant way the interactions with and without change of the spin states of the particles involved in the reaction and to follow in details the whole dynamics of the spin interactions. In contrast to methods of CALCUL group and others, the developed approach is valid for both massive fermions and massless ones. It is not necessary to introduce auxiliary vectors in DSB. Just 4-momenta of particles participating in reactions are required in it to construct the mathematical apparatus for calculations of matrix elements. We apply this formalism to the following processes: 1) Möller and Bhabha bremsstrahlung (e ± e − → e ± e − γ) in the ultrarelativistic (massless) limit when initial particles and photon are helicity polarized; 2) Compton back-scattering of photons of intensive circularly polarized laser wave focused on a beam of longitudinally polarized ultrarelativistic electrons (e + nγ 0 → e + γ); 3) e + e − -pair production by a hard photon in simultaneous collision with several laser beam photons (γ + nγ 0 → e + + e − ); 4) Bethe-Heitler process in the case of a linearly polarized photon emission by an electron with account for proton recoil and form factors; 5) the reaction ep → epγ with proton polarizability being taken into account in the kinematics when proton bremsstrahlung dominates; 6) orthopositronium 3-photon annihilation (e + e − → 3γ). The results obtained with the help of the developed DSB-formalism certify its efficiency for calculating of multiparticle processes when polarization is to be taken into account.

show abstract

Spin and Polarization Effects in the Annihilation of Triplet Positronium

Cited by 30 publications

References 7 publications

Positronium formation via excitonlike states on Si and Ge surfaces

Positronium formation via excitonlike states on Si and Ge surfaces

Experimental progress in positronium laser physics

The diagonal spin basis and calculation of processes involving polarized particles

Contact Info

Product

Resources

About