Polarization Transfer Measurements Research Articles

Measurement of polarization transfer in the quasi-elastic [formula omitted] process

Polarization transfer to a bound proton in polarized electron knock-out reactions, A(e→,e′p→), is a powerful tool to look for an in-medium modification of the bound proton. It requires comparison to calculations that consider the many-body effects accompanying the quasi-free process. We report here measured components Px′, Pz′, and their ratio Px′/Pz′, of polarization transfer to protons bound in Ca40, which is described well by the shell model and for which reliable calculations are available. While the calculations capture the essence of the data, our statistical precision allows us to observe deviations that cannot be explained by simple scaling, including by varying the proton electromagnetic form factor ratio GE/GM. We further explore the deviations of the ratio of the polarization transfer components from that of a free proton, (Px′/Pz′)A/(Px′/Pz′)H, and its dependence on the bound-proton virtuality.

Dressed-state control of effective dipolar interaction between strongly-coupled solid-state spins

Strong interactions between defect spins in many-body solid-state quantum systems are a crucial resource for exploring non-classical states. However, they face the key challenge of controlling interactions between the defect spins, since they are spatially fixed inside the host lattice. In this work, we present a dressed state approach to control the effective dipolar coupling between solid-state spins and demonstrate this scheme experimentally using two strongly-coupled nitrogen vacancy (NV) centers in diamond. Through Ramsey spectroscopy on the sensor spin, we detect the change of the effective dipolar field generated by the control spin prepared in different dressed states. To observe the change of interaction dynamics, we deploy spin-lock-based polarization transfer measurements between the two NV spins in different dressed states. This scheme allows us to control the distribution of interaction strengths in strongly interacting spin systems, which can be a valuable tool for generating multi-spin correlated states for quantum-enhanced sensing.

Monte Carlo simulation of the effective Sherman function for electron polarimetry in the few-MeV energy range

The effective analyzing power in Mott scattering was computed with a Monte Carlo simulation and compared to experimental results for electron-beam energies between 1.0 and 3.5 MeV. The dependence on target thickness and beam energy was analyzed, and possible parametrizations were discussed. The optimal target thickness and scattering angle for the measurement of polarization transfer in Møller scattering were determined.

Using as a spin polarimeter * *Partly supported by the National Natural Science Foundation of China NSFC (11875262, 11875115), Joint Large-Scale Scientific Facility Funds of the NSFC and Chinese Academy of Sciences (U2032110)

Polarization transfer measurement plays an important role in the search for new physics processes in charmed baryon decays. The measurement of the decay is suggested as a spin polarimeter. A general description of the decay is developed using Euler angles, and the polarization parameters are derived. Its relationship with parity violation is found using the phenomenological amplitude model. A Monte-Carlo simulation is performed, and the results show that charmed baryon polarization is well determined using a set of Monte-Carlo events with selected asymmetry parameters. The experimental measurement of these asymmetry parameters is suggested.

Measurement of polarization transfer in Møller scattering of relativistic electrons

A dedicated Mott polarimeter was designed to study the final spin state in M\o{}ller scattering of transversely polarized electron beams in the relativistic energy range. The polarization transfer was measured for two incident-beam polarization orientations with respect to the M\o{}ller scattering plane, at 3 MeV incident-beam energy. The results are found to be in agreement with the predictions of relativistic quantum mechanics. Estimates for the measurement of quantum spin correlations in M\o{}ller scattering, based on a simultaneous determination of the spin projections for both electrons in the final state, are also presented.

Polarization transfer in $$\varvec{e}^+p \rightarrow e^+ \varvec{p}$$ scattering using the Super BigBite Spectrometer

The effects of multi-photon-exchange and other higher-order QED corrections on elastic electron-proton scattering have been a subject of high experimental and theoretical interest since the polarization transfer measurements of the proton electromagnetic form factor ratio \(G_E^p/G_M^p\) at large momentum transfer \(Q^2\) conclusively established the strong decrease of this ratio with \(Q^2\) for \(Q^2 \gtrsim 1\) \(\hbox {GeV}^2\). This result is incompatible with previous extractions of this quantity from cross section measurements using the Rosenbluth Separation technique. Much experimental attention has been focused on extracting the two-photon exchange (TPE) effect through the unpolarized \(e^+p/e^-p\) cross section ratio, but polarization transfer in polarized elastic scattering can also reveal evidence of hard two-photon exchange. Furthermore, it has a different sensitivity to the generalized TPE form factors, meaning that measurements provide new information that cannot be gleaned from unpolarized scattering alone. Both \(\epsilon \)-dependence of polarization transfer at fixed \(Q^2\), and deviations between electron-proton and positron-proton scattering are key signatures of hard TPE. A polarized positron beam at Jefferson Lab would present a unique opportunity to make the first measurement of positron polarization transfer, and comparison with electron-scattering data would place valuable constraints on hard TPE. Here, we propose a measurement program in Hall A that combines the Super BigBite Spectrometer for measuring recoil proton polarization, with a non-magnetic calorimetric detector for triggering on elastically scattered positrons. Though the reduced beam current of the positron beam will restrict the kinematic reach, this measurement will have very small systematic uncertainties, making it a clean probe of TPE.

Two-photon exchange from intermediate state resonances in elastic electron-proton scattering

We use a recently developed dispersive approach to compute the two-photon exchange (TPE) correction to elastic electron-proton scattering, including contributions from hadronic $J^P=1/2^\pm$ and $3/2^\pm$ resonant intermediate states below~1.8~GeV. For the transition amplitudes from the proton ground state to the resonant excited states we employ new exclusive meson electroproduction data from CLAS at $Q^2 \lesssim 5$~GeV$^2$, and we explore the effects of both fixed and dynamic widths for the resonances. Among the resonant states, the $N(1520)~\!3/2^-$ becomes dominant for $Q^2 \gtrsim 2$~GeV$^2$, with a sign opposite to the comparably sized $\Delta(1232)~\!3/2^+$ contribution, leading to an overall increase in the size of the TPE correction to the cross section relative to the nucleon only contribution at higher $Q^2$ values. The results are in good overall agreement with recent $e^+ p$ to $e^- p$ cross section ratio and polarization transfer measurements, and provide compelling evidence for a resolution of the electric to magnetic form factor ratio discrepancy.

Octet baryon electromagnetic form factor double ratios (GE*/GM*)/(GE/GM) in a nuclear medium

The ratios of the baryon electric ($G_E$) to magnetic ($G_M$) form factors, $G_E/G_M$, can provide us with important information on the structure of baryons in vacuum as demonstrated in recent studies for the proton and neutron systems. It has been argued that the corresponding in-medium ratios, $G_E^\ast/G_M^\ast$, can also provide useful information on the electromagnetic structure of baryons in a nuclear medium. Although the ratios may not be measured directly in experiments except for the proton at present, the double ratios $(G_E^\ast/G_M^\ast)/(G_E/G_M)$ can be directly related to the polarization-transfer measurements of bound baryons. In the present work we estimate, for the first time, the double ratios $(G_E^\ast/G_M^\ast)/(G_E/G_M)$ for all the members of octet baryons in symmetric nuclear matter in the range $Q^2=0$--3 GeV$^2$, where $Q^2=- q^2$ with $q$ being the four-momentum transfer.

Quasi-elastic polarization-transfer measurements on the deuteron in anti-parallel kinematics

We present measurements of the polarization-transfer components in the H2(e→,e′p→) reaction, covering a previously unexplored kinematic region with large positive (anti-parallel) missing momentum, pmiss, up to 220MeV/c, and Q2=0.65(GeV/c)2. These measurements, performed at the Mainz Microtron (MAMI), were motivated by theoretical calculations which predict small final-state interaction (FSI) effects in these kinematics, making them favorable for searching for medium modifications of bound nucleons in nuclei. We find in this kinematic region that the measured polarization-transfer components Px and Pz and their ratio agree with the theoretical calculations, which use free-proton form factors. Using this, we establish upper limits on possible medium effects that modify the bound proton's form factor ratio GE/GM at the level of a few percent. We also compare the measured polarization-transfer components and their ratio for 2H to those of a free (moving) proton. We find that the universal behavior of 2H, 4He and 12C in the double ratio (Px/Pz)A(Px/Pz)H1 is maintained in the positive missing-momentum region.

Technical supplement to “Polarization transfer observables in elastic electron-proton scattering at [formula omitted] and [formula omitted

The GEp-III and GEp-2γ experiments, carried out in Jefferson Lab’s Hall C from 2007–2008, consisted of measurements of polarization transfer in elastic electron–proton scattering at momentum transfers of Q2=2.5,5.2,6.8, and 8.54 GeV 2. These measurements were carried out to improve knowledge of the proton electromagnetic form factor ratio R=μpGEp∕GMp at large values of Q2 and to search for effects beyond the Born approximation in polarization transfer observables at Q2=2.5GeV2. The final results of both experiments were reported in a recent archival publication. A full reanalysis of the data from both experiments was carried out in order to reduce the systematic and, for the GEp-2γ experiment, statistical uncertainties. This technical note provides additional details of the final analysis omitted from the main publication, including the final evaluation of the systematic uncertainties.

Polarization-transfer measurement to a large-virtuality bound proton in the deuteron

We report the measurement of the ratio of polarization-transfer components, Px/Pz, in the H2(e→,e′p→)n reaction at low and high missing momenta, in search of differences between free and bound protons. The observed deviation of Px/Pz from that of a free proton, which is similar to that observed in 4He, indicates that the effect in nuclei is a function of the virtuality of the knock-out proton and the missing momentum direction, but notthe average nuclear density. There is a general agreement between the data and calculations, which assume free proton form factors, however, the measurements are consistently about 10% higher.

Reanalysis of Rosenbluth measurements of the proton form factors

We present a reanalysis of the data from Stanford Linear Accelerator Center (SLAC) experiments E140 [R. C. Walker et al., Phys. Rev. D 49, 5671 (1994)] and NE11 [L. Andivahis et al., Phys. Rev. D 50, 5491 (1994)] on elastic electron-proton scattering. This work is motivated by recent progress in calculating the corresponding radiative corrections and by the apparent discrepancy between the Rosenbluth and polarization transfer measurements of the proton electromagnetic form factors. New, corrected values for the scattering cross sections are presented, as well as a new form factor fit in the $Q^2$ range from 1 to 8.83 $\text{GeV}^2$. We also provide a complete set of revised formulas to account for radiative corrections in single-arm measurements of unpolarized elastic electron-proton scattering.

Development of Neutron Polarization Measurement System for Studying NN interaction in Nuclear Medium

We have developed the neutron polarization measurement system to perform the first polarization-transfer measurement for the exclusive [Formula: see text] reaction. For the neutron polarization measurement, we have reconstructed the neutron polarimeter NPOL3. The NPOL3 system has been calibrated by using the polarized neutron from the [Formula: see text] reaction, and the resulting effective analyzing power is [Formula: see text]. For the exclusive measurement, the Large Acceptance Spectrometer (LAS) has been used for the recoil proton detection. The energy resolution of 6 MeV is achieved for separation energy, which is sufficient to separate the [Formula: see text] and [Formula: see text] orbits for light nuclei.

Radiative corrections to polarization observables in electron-proton scattering

We consider radiative corrections to polarization observables in elastic electron-proton scattering, in particular, for the polarization transfer measurements of the proton form factor ratio $\mu G_E/G_M$. The corrections are of two types: two-photon exchange (TPE) and bremsstrahlung (BS); in the present work we pay special attention to the latter. Assuming small missing energy or missing mass cut-off, the correction can be represented in a model-independent form, with both electron and proton radiation taken into account. Numerical calculations show that the contribution of the proton radiation is not negligible. Overall, at high $Q^2$ and energies the total correction to $\mu G_E/G_M$ grows, but is dominated by TPE. At low energies both TPE and BS may be significant; the latter amounts to ~ 0.01 for some reasonable cut-off choices.

Measurement of theH1(γ⃗, p⃗)π0Reaction Using a Novel Nucleon Spin Polarimeter

We report the first large-acceptance measurement of polarization transfer from a polarized photon beam to a recoiling nucleon, pioneering a novel polarimetry technique with wide application to future nuclear and hadronic physics experiments. The commissioning measurement of polarization transfer in the $^{1}H$($\vec{\gamma}$,$\vec{p}$)$\pi^{0}$ reaction in the range $0.4<E_{\gamma}<1.4$ GeV is highly selective regarding the basic parameterizations used in partial wave analyses to extract the nucleon excitation spectrum. The new data strongly favor the recently proposed Chew-Mandelstam formalism.

Nuclear density dependence of in-medium polarization

It is shown that polarization transfer measurements $(\vec{e},e'\vec{p})$ on a specific target nucleus can provide constraints on the ratio of the in-medium electric to magnetic form factor. Thereby one exploits the fact that proton knockout from single-particle levels exhibit a specific sensitivity to the effective nuclear density. It is shown that in $^{12}$C the effective nuclear density for $s$-shell knockout is about twice as high as for $p$-shell knockout. With current model predictions for the in-medium form factors, one obtains measurable modifications of the order of 5% in the ratios of the double polarization observables between those single-particle levels.

Δ-resonance contribution to the two-photon exchange amplitude

We consider two-photon exchange (TPE) in the elastic electron-proton scattering and study the contribution arising from the production of Delta(1232) resonance in the intermediate state. We calculate all three TPE amplitudes (generalized form factors), and find that the Delta contribution mainly influences generalized electric form factor (contrary to the elastic contribution, which affects magnetic form factor), and the effect grows with Q^2. If the corresponding correction is applied to the recent polarization transfer measurements of proton form factors, their results will change markedly. Thus we suggest that TPE corrections due to inelastic intermediate states are important to polarization experiments at high Q^2, and should not be neglected.

New N-Substituted (E)-4-Arylidene Isoquinoline-1,3-dione Derivatives: NMR Spectroscopic Investigation and Antibacterial Activity

New N-substituted 4-arylidene-isoquinoline-1,3-dione derivatives were obtained as one geometrical isomer by aldol condensation of the appropriate aldehyde and the corresponding N-substituted homophthalimides. The structural elucidation of compounds 3a–h was established by infrared and NMR spectroscopy including 1H, 13C, CH CORR, and distortionless enhancement by polarization transfer measurements. Compounds 3d–h were evaluated for their antibacterial activity against some strains of bacteria using the disc diffusion method and microdilution tests.

Medium Modifications of Hadron Properties and Partonic Processes

Chiral symmetry is one of the most fundamental symmetries in QCD. It is closely connected to hadron properties in the nuclear medium via the reduction of the quark condensate < q̄q >, manifesting the partial restoration of chiral symmetry. To better understand this important issue, a number of Jefferson Lab experiments over the past decade have focused on understanding properties of mesons and nucleons in the nuclear medium, often benefiting from the high polarization and luminosity of the CEBAF accelerator. In particular, a novel, accurate, polarization transfer measurement technique revealed for the first time a strong indication that the bound proton electromagnetic form factors in 4He may be modified compared to those in the vacuum. Second, the photoproduction of vector mesons on various nuclei has been measured via their decay to e+ e− to study possible in-medium effects on the properties of the ρ meson. In this experiment, no significant mass shift and some broadening consistent with expected collisional broadening for the ρ meson has been observed, providing tight constraints on model calculations. Finally, processes involving in-medium parton propagation have been studied. The medium modifications of the quark fragmentation functions have been extracted with much higher statistical accuracy than previously possible.

Study of spin-dipole strengths in 16F via complete polarization transfer measurements

A complete set of polarization transfer observables has been measured for the 16O(p, n) reaction at Tp = 296 MeV and θlab = 0°. The measured polarization transfer observables are used in order to investigate the spin-parity of the spin-dipole resonance in 16F. A possible indication of 0− state has been found at Ex = 11.0 MeV. The obtained results also show the energy hierarchy Ex(2−) < Ex(0−) < Ex(l−), which suggests the importance of the tensor correlations.