Spin-flip Amplitude Research Articles

Absorptive corrections to the electromagnetic form factor in high-energy elastic proton-proton scattering

Recently, it was noted that absorptive corrections to the electromagnetic form factor in high-energy proton-proton scattering are important for the theoretical interpretation of the p↑p and p↑A analyzing power AN(t) measurements with the Hydrogen Jet Target polarimeter (HJET) at RHIC. Here, a concise expression for the absorptive correction was derived within the eikonal approach. The resulting analysis reveals a systematic bias, nearly independent of the beam energy, in the experimental determination of the real-to-imaginary ratio ρ when absorption effects are overlooked in the data analysis. Quantification of this bias, as ρmeas=ρ+(0.036±0.016)bias, was achieved using a Regge fit applied to available proton-proton measurements of ρmeas(s) and σtotmeas(s). Considering the potential impact of such an effect on the experimentally determined AN(t), one may enhance consistency between the HJET and STAR measurements of the hadronic spin-flip amplitude. While the sign of the bias in the value of ρ aligns with the anticipated effective increase in the proton charge radius in pp scattering due to absorption, it amplifies the observed discrepancy between σtotmeas and ρmeas values at s=13 TeV as measured in the TOTEM experiment. Evaluation (using published TOTEM data) of the measured proton-proton dσ/dt dependence on the absorptive corrections indicated that possible soft photon corrections to the hadronic amplitude slope may be essential for such data analysis. Published by the American Physical Society 2024

Feasibility study for precisely measuring the EIC He3 beam polarization with the Polarized Atomic Hydrogen Gas Jet Target polarimeter at RHIC

The Polarized Atomic Hydrogen Gas Jet Target polarimeter (HJET) is used to measure the absolute proton beam polarization, $\sigma_P^\text{syst}/P\!\lesssim\!0.5\%$, at the Relativistic Heavy Ion Collider. Here I consider the possibility of employing HJET to measure the ${}^3\text{He}$ ($h$) beam polarization at the Electron-Ion Collider (EIC). The dominant contribution to the ratio of the $h^\uparrow{p}$ and $p^\uparrow{h}$ analyzing powers, which is needed for such measurements, can be easily calculated using well-known values of the proton and helion magnetic moments, but some corrections should be applied to achieve the required accuracy. It was found that corrections due to absorption and ${}^3\text{He}$ breakup effectively cancel in the ratio and a correction due to hadronic spin-flip amplitudes can be derived from the proton beam measurements. As a result, the anticipated systematic uncertainty in the measured ${}^3\text{He}$ beam polarization can satisfy the EIC requirement $\sigma_P^\text{syst}/P\!\lesssim\!1\%$.

Coulomb phase corrections to the transverse analyzing power AN(t) in high-energy forward proton-proton scattering

Study of polarized proton-proton elastic scattering in the Coulomb-nuclear interference region allows one to measure the forward hadronic single spin-flip amplitude including its phase. However, in a precision experimental data analysis, a phase-shift correction ${\ensuremath{\delta}}_{C}$ due to the long distance Coulomb interaction should be taken into account. For unpolarized scattering, ${\ensuremath{\delta}}_{C}$ is commonly considered as well established. Here, we evaluate the Coulomb phase shifts for the forward elastic proton-proton single spin-flip electromagnetic and hadronic amplitudes. Only a small discrepancy between the spin-flip and nonflip phases was found which can be neglected in the high-energy forward elastic $pp$ studies involving transverse spin. Nonetheless, the effective alteration of the hadronic spin-flip amplitude by the long-distance electromagnetic corrections can be essential for interpretation of the experimental results.

Probing the Pomeron spin structure with Coulomb-nuclear interference

Polarized pp elastic scattering at small angles in the Coulomb-nuclear interference (CNI) region offers a unique opportunity to study the spin structure of the Pomeron. Electromagnetic effects in elastic amplitude can be equivalently treated either as Coulomb corrections to the hadronic amplitude (Coulomb phase), or as absorption corrections to the Coulomb scattering amplitude. We perform the first calculation of the Coulomb phase for the spin-flip amplitude and found it significantly exceeding the widely used non-flip Coulomb phase. The alternative description in terms of absorption corrections, though equivalent, turned out to be a more adequate approach for the Coulomb corrected spin-flip amplitude. Inspired by the recent high statistics measurements of single-spin asymmetry with the HJET polarimeter at the BNL, we also performed a Regge analysis of data, aiming at disentangling the Pomeron contribution. However, in spite of an exceptional accuracy of the data, they do not allow to single out the Pomeron term, which strongly correlates with the major sub-leading Reggeons. A stable solution can be accessed only by making additional ad hoc assumptions, e.g. assuming the Pomeron to be a simple Regge pole, or fixing some unknown parameters. Otherwise, in addition to the STAR data at s=200GeV new measurements, say at 100GeV or 500GeV, could become decisive.

Nucleon Structure and Spin Effects in Elastic Hadron Scattering

Soft diffraction phenomena in elastic nucleon scattering are considered from the viewpoint of the spin dependence of the interaction potential. Spin-dependent pomeron effects are analyzed for elastic pp scattering, and spin-dependent differential cross sections and spin correlation parameters are calculated. The spin correlation parameter AN is examined on the basis of experimental data from s=4.9 GeV up to 23.4GeV in the framework of the extended High Energy Generalized Structure (HEGS) model. It is shown that the existing experimental data of proton-proton and proton-antiproton elastic scattering at high energy in the region of the diffraction minimum and at large momentum transfer give the support of the existence of the energy-independent part of the hadron spin flip amplitude.

Corrections to the elastic proton-proton analyzing power parametrization at high energies

The HJET Polarized Atomic Hydrogen Gas Jet Target polarimeter (HJET) polarimeter was designed to measure the absolute polarization of the proton beams at the Relativistic Heavy Ion Collider. In these measurements, the small scattering angle elastic $pp$ single $A_N(t)$ and double $A_{NN}(t)$ spin analyzing powers can be precisely determined. The experimental accuracy achieved at HJET requires corrections to the $A_N(t)$ parametrization, conventionally used for such studies. In this paper we evaluate the corrections to the analyzing powers due to (i) the differences between the electromagnetic and hadronic form factors and (ii) the $m_p^2/s$ terms in the elastic spin-flip $pp$ electromagnetic amplitude. The corresponding alterations of the evaluated hadronic spin-flip amplitudes are about the same as the experimental uncertainties of the HJET measurements. The proposed corrections may have implications for the elastic $pp$ forward real-to-imaginary amplitude ratios $\rho$ determined in unpolarized $pp$ experiments.

A study of the critical minima and spin polarization in the elastic electron scattering by the lead atom

A complex optical potential, in the framework of Dirac partial wave analysis, is employed to study the minima in the differential cross sections (DCSs) and the spin polarization due to the elastic scattering of electron by Pb atom. In addition, integral, momentum-transfer, absorption, viscosity and total cross sections are also reported for the energy region 6 eV ≤ Ei ≤10 keV. This complex optical potential comprises the static, exchange, polarization and absorption components. We obtain, in total, 12 critical minima (CM) positions, where DCS attains its smallest values and 22 points with of the maximum values of spin polarization (MSP). CM and MSP are found to be correlated in terms of Ei and scattering angles where the spin-flip amplitude overrides the magnitude of their direct counterpart. As per as we know, there is neither any experimental nor any theoretical study on CM of e-Pb scattering available in the literature. A detailed comparison shows a good agreement between our predicted results with the available experimental and other theoretical findings.

The First Asymmetry Measurements in High-Energy Polarized Proton-Nucleus Collision at PHENIX-RHIC

The single spin asymmetries in very forward neutron production had been first observed about a decade ago at RHIC in transversely polarized proton + proton collision at √s = 200 GeV. Although neutron production near zero degrees is well described by the one-pion exchange (OPE) framework, the OPE appeared to be not satisfactory to describe the observed analyzing power A N . The absorptive correction to the OPE generates the asymmetry as a consequence of a phase shift between the spin flip and non-spin flip amplitudes. However the amplitude predicted by the OPE is too small to explain the large observed asymmetries. Only the model which introduces interference between major pion and small a 1 -Reggeon exchange amplitudes has been successful in reproducing the experimental data. During RHIC Run-15, RHIC delivered polarized proton collisions with Au and Al for the first time, enabling the exploration of the mechanism of transverse single-spin asymmetries with nuclear collisions. A very striking A-dependence was discovered in very forward neutron production at PHENIX in transversely polarized proton + nucleus collision at √s = 200 GeV. Such a dependence has not been predicted from the existing framework which has been succesful in proton + proton collision. In this report, experimental and theoretical efforts are discussed to disentangle the mysterious A-dependence in the very forward neutron asymmetry.

Polarization Effects in Adron-Nuclei Scattering at High Energy

Abstract: The available experimental data point to the absence of the energy interval of scattering. This makes a basis for the hypothesis about the existence of a non-zero polarization research on the future accelerators will provide information about the structure of the nucleon interaction at large distances. Using different hypotheses about the property of the nucleon interaction at large distances a number of model approaches lead to the nondisappearing polarization in high -energy processes at small transfer moment. In this investigation we regard the model results for the polarization effects of nucleon-nuclei scattering. In the framework of the hypothesis concerning the exis¬tence of quark bag in nuclei we managed to describe the behaviour of the formfactors of nuclei at large q and structure functions of nuclei. The parameters of quark distribution in the bag at k>>k0 (the parameter k0 may in principle be different for different bags) extracted from the data on formfactors and on deep inelastic scattering of nucleons on nuclei proved to be very close. This result allows us to suppose that the contribution of the nucleon to the main terms in the spin-flip amplitude. The hypothesis will be proved in this work. The analysis shows that when the preasymptotic corrections are absent, we have the zero polarisations. The parameters in the spin-flip amplitude determined from one reaction, for example nucleon-nuclei scattering, allow us to obtain a wide circle of results for the polarisation effects of elastic pp or meson-nucleon scattering at high energies.

Relativistic effects in double ionization of helium via Compton scattering

In this article we present the relativistic calculations, based on the QED theory, for double ionization of helium by the Compton scattering. In particular, we calculate the contribution of the spin–flip amplitude to the total cross section. Due to this amplitude the final triplet spin state of the ejected electrons is possible. In the calculations based on the non–relativistic A2 term of the electron–photon interaction only the singlet spin state for the final electrons is allowed. We further assume the shake-off mechanism for process of double ionization. For the ground state of helium we use both the non–correlated and highly correlated wave function. We also discuss a degree of the scattered photon polarization in correlation with the formation of spin triplet state. Our calculations cover the photon impact energy range from 150 to 1000keV.

The First Transverse Single Spin Measurement in High Energy Polarized Proton-Nucleus Collision at the PHENIX experiment at RHIC

Large single spin asymmetries in very forward neutron production seen using the PHENIX zero-degree calorimeters are a long established feature of transversely polarized proton-proton collisions at RHIC. Neutron production near zero degrees is well described by the one-pion exchange framework. The absorptive correction to the OPE generates the asymmetry as a consequence of a phase shift between the spin flip and non-spin flip amplitudes. However, the amplitude predicted by the OPE is too small to explain the large observed asymmetries. A model introducing interference of pion and a1-Reggeon exchanges has been successful in reproducing the experimental data. During the RHIC experiment in year 2015, RHIC delivered polarized proton collisions with Au and Al nuclei for the first time, enabling the exploration of the mechanism of transverse single-spin asymmetries with nuclear collisions. The observed asymmetries showed surprisingly strong A-dependence in the inclusive forward neutron production, while the existing framework which was successfull in p+p only predicts moderate A- dependence. Thus the observed data are absolutely unexpected and unpredicted. In this report, experimental and theoretical efforts are discussed to disentangle the observed A-dependence using somewhat semi-inclusive type measurements and Monte-Carlo study, respectively.

High energy hadron spin flip amplitude

The high energy part of the hadron spin flip amplitude is examined in the framework of the new high energy general structure (HEGS) model of the elastic hadron scattering at high energies. The different forms of the hadron spin flip amplitude are compared in the impact parameters representation. It is shown that the existing experimental data of the proton-proton and proton-antiproton elastic scattering at high energy in the region of the diffraction minimum and at large momentum transfer give support in the presence of the energy-independent part of the hadron spin flip amplitude with the momentum dependence proposed in the works by Galynskii-Kuraev.

Transverse Spin Asymmetries in the CNI Region of Elastic Proton-Proton Scattering at s=200 GeV

Precise measurements of transverse spin asymmetries in proton-proton elastic scattering at very small values of four-momentum transfer squared, [Formula: see text], have been performed using the Relativistic Heavy Ion Collider (RHIC) polarized proton beams. The measurements of both single and double spin asymmetries were made at the center-of-mass energy [Formula: see text] GeV and in the region [Formula: see text] [Formula: see text], which was accessed using Roman Pot devices incorporated into the STAR experimental setup. The obtained set of asymmetries is sensitive to the poorly known hadronic contribution to the spin-flip amplitudes and provide significant constraints for the theoretical descriptions of the reaction mechanism of proton-proton elastic scattering at high energies.

Nucleon structure and the high energy interactions

On the basis of the representation of the generalized structure of nucleons a new model of the hadron interaction at high energies is presented. A new $t$ dependence of the generalized parton distributions is obtained from the comparative analysis of different sets of the parton distribution functions, based on the description of the entire set of experimental data for the electromagnetic form factors of the proton and neutron. Taking into account the different moments of the generalized parton distributions of the hadron, quantitative descriptions of all existing experimental data of the proton-proton and proton-antiproton elastic scatterings from $\sqrt{s}=9.8\text{ }\text{ }\mathrm{GeV}$ to 8 TeV, including the Coulomb range and large momentum transfers up to $\ensuremath{-}t=15\text{ }\text{ }{\mathrm{GeV}}^{2}$, are obtained with a few free high-energy fitting parameters. The real part of the hadronic elastic scattering amplitude is determined only through the complex $s$ that satisfies the dispersion relations. The negligible contributions of the hard Pomeron and the presence of the non-small contributions of the maximal Odderon are obtained. The non-dying form of the spin-flip amplitude is examined as well. The structures of the Born term and unitarized scattering amplitude are analyzed. It is shown that the black disk limit for the elastic scattering amplitude is not reached at LHC energies. Predictions for LHC energies are made.

Donor-driven spin relaxation in multivalley semiconductors.

The observed dependence of spin relaxation on the identity of the donor atom in n-type silicon has remained without explanation for decades and poses a long-standing open question with important consequences for modern spintronics. Taking into account the multivalley nature of the conduction band in silicon and germanium, we show that the spin-flip amplitude is dominated by short-range scattering off the central-cell potential of impurities after which the electron is transferred to a valley on a different axis in k space. Through symmetry arguments, we show that this spin-flip process can strongly affect the spin relaxation in all multivalley materials in which time-reversal cannot connect distinct valleys. From the physical insights gained from the theory, we provide guidelines to significantly enhance the spin lifetime in semiconductor spintronics devices.

Tunnel magnetoresistance in organic spin valves in the regime of multistep tunneling

A model of a spin valve in which electron transport between the magnetized electrodes is due to multistep tunneling is analyzed. Motivated by recent experiments on organic spin valves, we assume that spin memory loss in the course of transport is due to random hyperfine fields acting on electron while it waits for the next tunneling step. Amazingly, we identify the three-step configurations of sites, for which the tunnel magnetoresistance (TMR) is negative in the absence of interfacial effects, suggesting that the resistance for antiparallel magnetizations of the electrodes is smaller than for parallel magnetizations. We analyze the phase volume of these configurations with respect to magnitudes and relative orientations of the on-site hyperfine fields. The effect of sign reversal of TMR is exclusively due to interference of the spin-flip amplitudes on each site; it does not emerge within commonly accepted probabilistic description of spin transport. Another feature specific to multistep inelastic tunneling is bouncing of electron between nearest neighbors while awaiting a ``hard'' hop. We demonstrate that this bouncing, being absolutely insignificant for conduction of current, can strongly affect the spin memory loss. This effect is also of interference origin.

Inclusive cross section and single transverse spin asymmetry for very forward neutron production in polarizedp+pcollisions ats=200 GeV

The energy dependence of the single-transverse-spin asymmetry, A_N, and the cross section for neutron production at very forward angles were measured in the PHENIX experiment at RHIC for polarized p+p collisions at sqrt(s)=200 GeV. The neutrons were observed in forward detectors covering an angular range of up to 2.2 mrad. We report results for neutrons with momentum fraction of x_F=0.45 to 1.0. The energy dependence of the measured cross sections were consistent with x_F scaling, compared to measurements by an ISR experiment which measured neutron production in unpolarized p+p collisions at sqrt(s)=30.6--62.7 GeV. The cross sections for large x_F neutron production for p+p collisions, as well as those in e+p collisions measured at HERA, are described by a pion exchange mechanism. The observed forward neutron asymmetries were large, reaching A_N=-0.08+/-0.02 for x_F=0.8; the measured backward asymmetries, for negative x_F, were consistent with zero. The observed asymmetry for forward neutron production is discussed within the pion exchange framework, with interference between the spin-flip amplitude due to the pion exchange and nonflip amplitudes from all Reggeon exchanges. Within the pion exchange description, the measured neutron asymmetry is sensitive to the contribution of other Reggeon exchanges even for small amplitudes.

Single spin asymmetry [formula omitted] in polarized proton–proton elastic scattering at [formula omitted

We report a high precision measurement of the transverse single spin asymmetry AN at the center of mass energy s=200 GeV in elastic proton–proton scattering by the STAR experiment at RHIC. The AN was measured in the four-momentum transfer squared t range 0.003⩽|t|⩽0.035 (GeV/c)2, the region of a significant interference between the electromagnetic and hadronic scattering amplitudes. The measured values of AN and its t-dependence are consistent with a vanishing hadronic spin-flip amplitude, thus providing strong constraints on the ratio of the single spin-flip to the non-flip amplitudes. Since the hadronic amplitude is dominated by the Pomeron amplitude at this s, we conclude that this measurement addresses the question about the presence of a hadronic spin flip due to the Pomeron exchange in polarized proton–proton elastic scattering.

Single transverse-spin asymmetry of very forward neutron production in polarized p + p collisions at PHENIX

The cross section and xF dependence of AN of very forward neutron production in polarized p + p collisions at = 200 GeV were measured in the PHENIX experiment at RHIC. The measured cross sections were consistent with the xF scaling claimed by the ISR experiment which measured neutron production in p + p collisions at from 30.6 to 62.7 GeV. These cross sections for large xF neutron production, as well as those in e + p collisions at HERA, are mainly described by one-pion exchange. At PHENIX, significant negative AN was observed in the forward region, and no significant backward AN was observed. We also measured and pT dependence of AN of very forward neutron production at from 62.4 to 500 GeV. The observed large asymmetry of neutron production is considered to come from the interference between the spin-flip amplitude of the pion exchange and spin-non-flip amplitude of all Reggeon exchange. Therefore, the neutron asymmetry has a sensitivity to other Reggeon exchange amplitude even if it is a small amplitude.

THE EFFECTS OF THE SMALL-t PROPERTIES OF HADRONIC SCATTERING AMPLITUDE ON THE DETERMINATION OF ITS REAL PART

Taking into account the different forms of the Coulomb-hadron interference phase and the possible spin-flip contribution the new analysis of the experimental data of the proton–antiproton elastic scattering at 3.8<pL<6.0 GeV/c and small momentum transfer is carried out. It is shown that the size of the spin-flip amplitude can be determined from the form of the differential cross-sections at small-t, and the deviation of ρ(s, t) obtained from the examined experimental data of the [Formula: see text] scattering from the analysis1, based on the dispersion relations, is conserved in all examined assumptions. The analysis of the proton–proton elastic scattering at 9<pL<70 GeV/c also shows the impact of the examined effects on the form of the differential cross-sections.