Mueller Matrix Polarimetry with Invariant Polarization Pattern Beams

A wide class of nonuniformly totally polarized beams that preserve their transverse polarization pattern during paraxial propagation was studied. Beams of this type are of interest, in particular, in polarimetric techniques that use a single input beam for the determination of the Mueller matrix of a homogeneous sample. In these cases, in fact, it is possible to test the sample response to several polarization states at once. The propagation invariance of the transverse polarization pattern is an interesting feature for beams used in these techniques, because the polarization state of the output beam can be detected at any transverse plane after the sample, without the use of any imaging/magnifying optical system. Furthermore, exploiting the great variety of the beams of this class, the ones that better fit specific experimental constrains can be chosen. In particular, the class also includes beams that present all possible polarization states across their transverse section (the full Poincaré beams (FPB)). The use of the latter has recently been proposed to increase the accuracy of the recovered Mueller matrix elements. Examples of FPBs with propagation-invariant polarization profiles and its use in polarimetry are discussed in detail. The requirement of invariance of the polarization pattern can be limited to the propagation in the far field. In such a case, less restrictive conditions are derived, and a wider class of beams is found.

Measurement of the transverse polarization of electrons emitted in neutron decay – nTRV experiment

This paper recalls the main achievements of the nTRV experiment which measured two components of the transverse polarization (\sigma_{T_{1}}σT1, \sigma_{T_{2}}σT2) of electrons emitted in the \betaβ-decay of polarized, free neutrons and deduced two correlation coefficients, RR and NN, that are sensitive to physics beyond the Standard Model. The value of time-reversal odd coefficient RR, 0.004\pm±0.012\pm±0.005, significantly improved limits on the relative strength of imaginary scalar coupling constant in the weak interaction. The value obtained for the time-reversal even correlation coefficient NN, 0.067\pm±0.011\pm±0.004, agrees with the Standard Model expectation, providing an important sensitivity test of the electron polarimeter. One of the conclusions of this pioneering experiment was that the transverse electron polarization in the neutron \betaβ-decay is worth more systematic exploring by measurements of yet experimentally not attempted correlation coefficients such as HH, LL, SS, UU and VV. This article presents a brief outlook on that questions.

Muon Decay

The decay of the muon has been studied at PSI with several precision measurements: The longitudinal polarization P_{\mathrm{L}}(E)PL(E) with the muon decay parameters \xi'ξ′, \xi''ξ″, the Time-Reversal Invariance (TRI) conserving transverse polarization P_{\mathrm{T_{1}}}(E)PT1(E) with the muon decay parameters \etaη, \eta''η″, the TRI violating transverse polarization P_{\mathrm{T_{2}}}(E)PT2(E), with \alpha'/Aα′/A, \beta'/Aβ′/A and the muon decay asymmetry with P_{\mu}\xiPμξ. The detailed theoretical analysis of all measurements of normal and inverse muon decay has led for the first time to a lower limit |g^{V}_{LL}| > 0.960|gLLV|>0.960 (“V-AV−A”) and upper limits for nine other possible complex couplings, especially the scalar coupling |g^{S}_{LL}| < 0.550|gLLS|<0.550 which had not been excluded before.

CEPC Z-pole polarization design studies

In this paper, we give preliminary designs of beam polarization manipulations by inserting three different types of insertions in the Circular Electron–Positron Collider (CEPC) at center-of-mass energies of 91 GeV (Z-pole). With the wigglers in the collider ring, we can obtain 5% transverse polarization in 1.1 h for the precise energy measurement. To overcome depolarization effects as the beam energy rises from 10 GeV to 45.5 GeV in the booster ring, Siberian snakes based on helical magnets are adopted. Finally, for longitudinally polarized beam collisions, a schematic design of spin rotators based on solenoids in the collider ring is studied.

The transverse polarization of $$\Lambda $$ hyperons in $$e^+e^-\rightarrow \Lambda ^\uparrow h X$$ processes within TMD factorization

We investigate the transverse polarization of the $$\Lambda $$ Λ hyperon in the processes $$e^+e^-\rightarrow \Lambda ^\uparrow \pi ^\pm X$$ e + e - → Λ ↑ π ± X and $$e^+e^-\rightarrow \Lambda ^\uparrow K^\pm X$$ e + e - → Λ ↑ K ± X within the framework of the transverse momentum dependent (TMD) factorization. The transverse polarization is contributed by the convolution of the transversely polarizing fragmentation function (PFF) $$D_{1T}^\perp $$ D 1 T ⊥ of the lambda hyperon and the unpolarized fragmentation function $$D_1$$ D 1 of pion/kaon. We adopt the spectator diquark model result for $$D_{1T}^{\perp }$$ D 1 T ⊥ to numerically estimate the transverse polarization in $$e^+e^-\rightarrow \Lambda ^\uparrow h X$$ e + e - → Λ ↑ h X process at the kinematical region of Belle Collaboration. To implement the TMD evolution formalism of the fragmentation functions, we apply two different parametrizations on the nonperturbative Sudakov form factors associated with the fragmentation functions of the $$\Lambda $$ Λ , pion and kaon. It is found that our prediction on the polarization in the $$\Lambda \pi ^+$$ Λ π + production and $${\bar{\Lambda }} \pi ^-$$ Λ ¯ π - is consistent with the recent Belle measurement in size and sign, while the model predictions on the polarizations in $$\Lambda \pi ^-$$ Λ π - and $$\Lambda K^\pm $$ Λ K ± productions show strong disagreement with the Belle data. The reason for the discrepancies is discussed and possible approaches to improve the calculation in the future are also discussed.

Эффективная диэлектрическая проницаемость анизотропного композита из сфероидных частиц в диэлектрической матрице

The concentration dependences of the effective permittivity of an anisotropic composite containing co-directional particles in the form of oblate or elongated ellipsoids of rotation – spheroids – in the dielectric matrix are obtained. The calculation is made by the numerical solution of a system of coupled quadratic and integral equations obtained by a strict modification of the quasi-static Bruggeman theory. It is shown that the traditional (simplified) modification of the Bruggeman theory, widely used for calculating anisotropic composites, gives errors of different signs for the longitudinal and transverse polarization of electromagnetic waves relative to the axis of spheroids. In this case, the dependences of errors on the concentration of particles are non-monotonic, and the extremes observed on them can exceed 100%. Moreover, the position and magnitude of the extremes strongly depend on the ellipticity of the particles, as well as on the contrast of their permittivity with the matrix.