Unpolarized Particles Research Articles

Impact dynamics and polarization mechanism of BaxSr1−xTiO3 particles reinforced polydimethylsiloxane composites

AbstractBaxSr1−xTiO3 (BST) ceramics have excellent performance of electromechanical conversion, however, the application of BST ceramics in the field of sensing is restricted by the brittle fracture, electromechanical failure, and collateral damage of BST under impact. In this article, unpolarized BST particles reinforced polydimethylsiloxane (PDMS) composites‐BST/PDMS with excellent mechanical properties, flexibility and flexoelectric coefficient have been prepared. Experimental study on the dynamic mechanical behavior and polarization characteristics of BST/PDMS composites under different impact velocity, element ratio and content of BST are carried out. Furthermore, the three‐phase model have been developed, based on that, impact deformation, stress behavior and polarization response have been investigated. The results show that, the duration of elastic deformation stage increases with increasing of BST content, but maximum stress decreases; time‐history curves of polarization voltage are approximately a “sine” function distribution, polarization voltages of Ba0.75Sr0.25TiO3/PDMS are higher than that of Ba0.25Sr0.75TiO3/PDMS; flexoelectric coefficient increases with increasing of BST content, and μzzzz is larger than that of μxxzz and μxzxz; addition of BST particle leads to greater strain gradient, and increases the polarization voltage of PDMS matrix; electric field at the interface increases due to the dielectric effect, which improves the ability of charge migration, voltage difference of 20% Ba0.75Sr0.25TiO3/80% PDMS caused by interfacial potential is smaller (about 9.3%) compared with 10% Ba0.75Sr0.25TiO3/90% PDMS. This work is significant for the development of flexible intelligent sensing materials.Highlights The mechanical behavior and polarization characteristics of BST/PDMS are studied. The polarization voltages of BST/PDMS (x = 0.75) are higher than BST/PDMS (x = 0.25). The flexoelectric coefficient increases with increasing of BST content.

Comment on “Spin correlations in elastic e$$^{+}$$e$$^{-}$$ scattering in QED”

In the previous work, "Spin correlations in elastic $e^+ e^-$ scattering in QED" (Yongram, 2018), spin correlations for entangled electrons and positrons as emergent particles of electron-positron scattering (also known as Bhabha scattering) were calculated at tree level in QED. When trying to reproduce the author's work, we have found different results. In this work, we show the calculation for fully (initial and final polarized states) and partially (just final polarized states) polarized probability amplitudes for electron-positron scattering at all energies. While Yongram claims that violation of Clauser-Horne inequality (CHI) occurs at all energies for both mentioned cases, for fully polarized scattering we found violation of the CHI for speeds $\beta \gtrsim 0.696$, including the high energy limit, supporting the agreement between QED and foundations of quantum mechanics. However, for initially unpolarized particles we found no violation of the CHI.

Study on the Optical Parameters of Different Particle Sizes Considering Particle Group Reflectivity

With the rapid advancements in laser and detection technology, it is now possible to obtain the physical properties of particles. Analyzing the physical properties of particles can establish the foundation for further research on the optical field transmission of particles in the micron range. The transport model of unpolarized particles is constructed by applying the unpolarized transport technology, and the Stokes vector is used to calculate the transport characteristics of the particle to obtain the four-dimensional mathematical vector that represents average light intensity. A random matrix is established with the help of the Markov chain to transmit unpolarized characteristic parameters of particles and to investigate the energy levels of a vast number of particles. According to the Mie scattering theory, the spatial intensity distribution function of light scattering is calculated, and the experiment on the characteristic parameter of the particle is carried out based on the results of a photoelectric detector, and compared with the numerical simulation. By analyzing the mathematical model, the accuracy and effectiveness of the model are verified, which provides theoretical support for further research on particle physics.

Doing Spin Physics with Unpolarized Particles

Twisted, or vortex, particles refer to freely propagating non-plane-wave states with helicoidal wave fronts. In this state, the particle possesses a nonzero orbital angular momentum with respect to its average propagation direction. Twisted photons and electrons have been experimentally demonstrated, and creation of other particles in twisted states can be anticipated. If brought in collisions, twisted states offer a new degree of freedom to particle physics, and it is timely to analyze what new insights may follow. Here, we theoretically investigate resonance production in twisted photon collisions and twisted e^{+}e^{-} annihilation and show that these processes emerge as a completely novel probe of spin and parity-sensitive observables in fully inclusive cross sections with unpolarized initial particles. This is possible because the initial state with a nonzero angular momentum explicitly breaks the left-right symmetry even when averaging over helicities. In particular, we show how one can produce almost 100% polarized vector mesons in unpolarized twisted e^{+}e^{-} annihilation and how to control its polarization state.

On the spin correlations of final leptons produced in the high-energy annihilation and two-photon processes e+e− → μ+ μ−, τ+τ− and γγ → e+e−, μ+μ−, τ+τ−

The electromagnetic processes of annihilation of (e+e−) pairs, into heavy flavor lepton pairs are theoretically studied in the one-photon approximation, using the technique of helicity amplitudes . For the process e+e− − μ+μ−, it is shown that - in the case of the unpolarized electron and positron − the final muons are also unpolarized but their spins are strongly correlated; the structure of their triplet states is analyzed and explicit expressions for the correlation tensor components are derived. On the other hand, the theoretical study of spin structure for the processes of lepton pair production by photon pairs is also performed: for the two-photon process γγ → e+e−, it is found that – quite similarly - in the case of unpolarized photons the spins of final unpolarized particles prove to be strongly correlated, and explicit expressions for the correlation tensor components and relative fractions of singlet and triplet states of the final system are obtained. It is established that in both these processes the spin correlations of final leptons have the purely quantum character, since one of the Bell-type incoherence inequalities for the correlation tensor components is always violated. Analogous analysis can be wholly applied also to the annihilation process e+e− → τ+τ− and to the two-photon processes γγ → μ+μ−, γγ → τ+τ−, becoming possible at considerably higher energies.

Quantum Entanglement in the Nonrelativistic Collision Between Two Identical Fermions with Spin 1/2

In the framework of nonstationary scattering theory, we study the formation of an entangled state of two identical nonrelativistic spin-1/2 particles as a result of their elastic scattering. The measure of particle entanglement in the final channel is described using pair concurrence. For the indicated quantitative criterion, we obtain general expressions in terms of the direct and exchange scattering amplitudes in the cases of pure and mixed spin states of the pair in the initial channel. We consider the violation of Bell’s inequality in the final channel. We show that as a result of a collision between unpolarized particles, a Werner spin state of the pair forms, which is entangled if the singlet component of the angular differential scattering cross section in the center-of-mass reference frame exceeds the triplet component. We use the process of free electron-electron scattering as an example to illustrate the developed formalism.

Approximate Formula for the Total Cross Section for a Moderately Small Eikonal Function

We study the eikonal approximation of the total cross section for the scattering of two unpolarized particles and obtain an approximate formula in the case where the eikonal function χ(b) is moderately small, |χ(b)| ≲ 0.1. We show that the total cross section is given by a series of improper integrals of the Born amplitude AB. The advantage of this representation compared with standard eikonal formulas is that these integrals contain no rapidly oscillating Bessel functions. We prove two theorems that allow relating the large-b asymptotic behavior of χ(b) to analytic properties of the Born amplitude and give several examples of applying these theorems. To check the effectiveness of the main formula, we use it to calculate the total cross section numerically for a selection of specific expressions for AB, choosing only Born amplitudes that result in moderately small eikonal functions and lead to the correct asymptotic behavior of χ(b). The numerical calculations show that if only the first three nonzero terms in it are taken into account, this formula approximates the total cross section with a relative error of O(10−5).

Polarization effects in the reactions p + 3He → π+ + 4He, π+ + 4He → p + 3He and quantum character of spin correlations in the final (p, 3He) system

The general consequences of T invariance for the direct and inverse binary reactions a + b → c + d, c + d → a + b with spin-1/2 particles a, b and unpolarized particles c, d are considered. Using the formalism of helicity amplitudes, the polarization effects are studied in the reaction p + 3He → π+ + 4He and in the inverse process π+ + 4He → p + 3He. It is shown that in the reaction π+ + 4He → p + 3He the spins of the final proton and 3 He nucleus are strongly correlated. A structural expression through helicity amplitudes, corresponding to arbitrary emission angles, is obtained for the correlation tensor. It is established that in the reaction π+ + 4He → p + 3He one of the “classical” incoherence inequalities of the Bell type for diagonal components of the correlation tensor is necessarily violated and, thus, the spin correlations of the final particles have the strongly pronounced quantum character.

Investigating GPDs in the framework of the double distribution model

In this paper, we construct the generalized parton distribution (GPD) in terms of the kinematical variables [Formula: see text], [Formula: see text], [Formula: see text], using the double distribution model. By employing these functions, we could extract some quantities which makes it possible to gain a three-dimensional insight into the nucleon structure function at the parton level. The main objective of GPDs is to combine and generalize the concepts of ordinary parton distributions and form factors. They also provide an exclusive framework to describe the nucleons in terms of quarks and gluons. Here, we first calculate, in the Double Distribution model, the GPD based on the usual parton distributions arising from the GRV and CTEQ phenomenological models. Obtaining quarks and gluons angular momenta from the GPD, we would be able to calculate the scattering observables which are related to spin asymmetries of the produced quarkonium. These quantities are represented by [Formula: see text] and [Formula: see text]. We also calculate the Pauli and Dirac form factors in deeply virtual Compton scattering. Finally, in order to compare our results with the existing experimental data, we use the difference of the polarized cross-section for an initial longitudinal leptonic beam and unpolarized target particles [Formula: see text]. In all cases, our obtained results are in good agreement with the available experimental data.

The Universal Expression for the Amplitude Square in Quantum Electrodynamics

The universal expression for the amplitude square |u_f M u_i|^2 for any matrix of interaction M is derived. It has obvious covariant form. It allows the avoidance of calculation of products of the Dirac's matrices traces and allows easy calculation of cross-sections of any different processes with polarized and unpolarized particles.

Spin structure of the “Forward” nucleon charge-exchange reaction n + p → p + n and the deuteron charge-exchange breakup

The structure of the nucleon charge-exchange process n + p → p + n is investigated basing on the isotopic invariance of the nucleon-nucleon scattering. Using the operator of permutation of the spin projections of the neutron and proton, the connection between the spin matrices, describing the amplitude of the nucleon charge-exchange process at zero angle and the amplitude of the elastic scattering of the neutron on the proton in the “backward” direction, has been considered. Due to the optical theorem, the spin-independent part of the differential cross section of the process n + p → p + n at zero angle for unpolarized particles is expressed through the difference of total cross sections of unpolarized proton-proton and neutron-proton scattering. Meantime, the spin-dependent part of this cross section is proportional to the differential cross section of the deuteron charge-exchange breakup d + p → (pp) + n at zero angle at the deuteron momentum k d = 2 k n (k n is the initial neutron momentum). Analysis shows that, assuming the real part of the spin-independent term of the “forward” amplitude of the process n + p → p + n to be smaller or of the same order as compared with the imaginary part, in the wide range of neutron laboratory momenta k n > 700 MeV/c the main contribution into the differential cross section of the process n + p → p + n at zero angle is provided namely by the spin-dependent term.

Searches for new neutral gauge Z′ bosons at the e + e − International Linear Collider and their identification

The potential of the electron-positron International Linear Collider for searches for and the separation of signals induced by new neutral gauge bosons predicted by various classes of models featuring an extended gauge sector is investigated. The analysis presented in this article was performed for processes of annihilation fermion-pair production and was based on the use of differential polarization observables, which ensure a higher sensitivity (in relation to integrated observables) of the processes being considered to Z′-boson parameters. Thresholds for discovering and identifying new neutral gauge bosons associated with models belonging to the E6 and LR, as well as the ALR and SSM, classes are determined. In particular, it is shown that polarization experiments at a 0.5-TeV electron-positron collider of integrated luminosity 100 fb−1 would make it possible to identify unambiguously the entire set of Z′-boson models (Z′SSM, Z′φ, Z′η, Z′χ, Z′LRS, and Z′ALR) for MZ′ < 6√s and to improve considerably the respective estimates expected from experiments with unpolarized particles.

Quasi-elastic and elastic charge-exchange differential cross sections (critical review)

More than 50 years ago the charge-exchange of one nucleon in the quasi-elastic nucleon deuteron scattering was proposed to determine the spin independent, or the spin dependent parts of the elastic backward neutron proton differential cross section. For this purpose two measurements are to be performed using unpolarized particles only. Such a suggestion was very attractive for experimentalists, since at that time polarized beams were rare and polarized targets were nonexistent. One experiment consists in the inclusive measurement of the charge-exchange quasi-elastic nucleon deuteron differential cross section. The energy of the fast outgoing nucleon is to be approximately the same as that of the incident nucleon. The intrinsic momenta of the remaining two identical nucleons should be small. The impulse approximation has been assumed, i.e. in the final state of the two nucleons their interaction can be neglected. The quasi-elastic result is to be compared with the elastic np differential cross section in the backward direction at the same energy. The theory related the ratio RQE(π) of the quasi-elastic to the elastic np charge-exchange differential cross sections to the spin dependent part of the np backward elastic scattering amplitude. Several experiments in the nucleon kinetic energy interval below 1 GeV were carried out, where the RQE(π) values were determined. Recently the energy interval was extended up to 2 GeV by successful experiments at the JINR VBLHE Nuclotron. The quasi-elastic results can be compared with the values of the analogous quantity Rnp(π) for the np elastic scattering, calculated from the phase shift analyses below 1.3 GeV. The present paper is a critical review checking expressions for Rnp(π) in different amplitude representations, listing numerical values of elastic np quantities and results of existing quasi-elastic experiments. Conclusions and statements of some authors and the validity of the relevant theory is discussed.

Spin correlations in elastic e+e- scattering in QED

Spin correlations are carefully investigated in elastic e+e- scattering in QED, for initially polarized as well as unpolarized particles, with emphasis placed on energy or speed of the underlying particles involved in the process. An explicit expression is derived for the corresponding transition probabilities in closed form to the leading order. These expressions differ from those obtained from simply combining the spins of the relevant particles, which are of kinematic nature. It is remarkable that these explicit results obtained from quantum field theory show a clear violation of Bell's inequality at all energies, in support of quantum theory in the relativistic regime. We hope that our explicit expression will lead to experiments, of the type described in the bulk of this paper, that monitor speed.

Dynamics of polarization buildup by spin filtering

There has been much recent research into polarizing an antiproton beam, instigated by the recent proposal from the PAX (Polarized Antiproton eXperiment) project at GSI Darmstadt. It plans to polarize an antiproton beam by repeated interaction with a polarized internal target in a storage ring. The method of polarization by spin filtering requires many of the beam particles to remain within the ring after scattering off the polarized internal target via electromagnetic and hadronic interactions. We present and solve sets of differential equations which describe the buildup of polarization by spin filtering in many different scenarios of interest to projects planning to produce high intensity polarized beams. These scenarios are: 1) spin filtering of a fully stored beam, 2) spin filtering while the beam is being accumulated, i.e. unpolarized particles are continuously being fed into the beam, 3) the particle input rate is equal to the rate at which particles are being lost due to scattering beyond ring acceptance angle, the beam intensity remaining constant, 4) increasing the initial polarization of a stored beam by spin filtering, 5) the input of particles into the beam is stopped after a certain amount of time, but spin filtering continues. The rate of depolarization of a stored polarized beam on passing through an electron cooler is also shown to be negligible.

Target normal spin asymmetry and charge asymmetry foreμelastic scattering and the crossed processes

Two kinds of asymmetry arise from the interference of the Born amplitude and the box-type amplitude corresponding to two virtual photon exchange, namely, charge-odd and single-spin asymmetries. In the case of unpolarized particles the charge-odd correlation is calculated. It can be measured in a combination of electron-muon and positron-muon experiments. The forward-backward asymmetry is the corresponding quantity which can be measured for the crossed processes. In the case of a polarized muon the single-spin asymmetry for annihilation and scattering channels has been calculated. The additional structure function arising from the interference is shown to suffer from infrared divergencies. The background due to electroweak interaction is discussed.

Speed dependent polarization correlations in QED and entanglement

Exact computations of polarizations correlations probabilities are carried out in QED, to the leading order, for initially polarized as well as unpolarized particles. Quite generally they are found to be speed dependent and are in clear violation of Bells inequality of Local Hidden Variables (LHV) theories. This dynamical analysis shows how speed dependent entangled states are generated. These computations, based on QED are expected to lead to new experiments on polarization correlations monitoring speed in the light of Bells theorem. The paper provides a full QED treatment of the dynamics of entanglement.

Angular correlations in the decays of two unstable identical particles with close momenta

For the decay of two identical particles with close momenta, the angular correlations between the directions of emission of decay products are considered on the basis of the model of independent single-particle sources emitting unstable unpolarized particles of nonzero spin. These correlations reflect spin correlations that are caused by quantum-statistics and final-state-interaction effects. A general theory of angular correlations in the decays of two arbitrarily polarized particles (resonances) is constructed.

Measurement of spin-transfer observables in p p-->Lambda Lambda at 1.637 GeV/c.

Spin-transfer observables for p p-->Lambda Lambda have been measured using a transversely polarized frozen-spin target and a beam momentum of 1.637 GeV/c. Current models of the reaction near threshold are in good agreement with existing measurements performed with unpolarized particles in the initial state but produce conflicting predictions for the spin-transfer observables Dnn and Knn (the normal-to-normal depolarization and polarization transfer), which are measurable only with polarized target or beam. Measurements of Dnn and Knn presented here are found to be in disagreement with predictions from these models.

On classical description of radiation from neutral fermion with anomalous magnetic moment

Electromagnetic radiation from an uncharged spin 1/2 particle with an anomalous magnetic moment moving in the classical electromagnetic external field originates from quantum spin-flip transitions. Although this process has a purely quantum nature, it was observed for certain particular external field configurations that, when quantum recoil is neglected, the radiation power corresponds to the classical radiation from an evolving magnetic dipole. We argue that this correspondence has a more general validity in the case of an unpolarized particle and derive a general formula for radiation in terms of the external field strength and its derivative. A classical dynamics of the spin is described by the Bargmann–Michel–Telegdi equation.