Recoil Polarization Research Articles

Electromagnetic radii of the nucleon in soft-wall holographic QCD

We revisit the electromagnetic form factors of the proton and neutron in the original-minimal soft-wall holographic QCD, which has only two parameters, i.e., the mass scale κ and the twist parameter of the nucleon τ. We first fix τ=3 by the hard scattering rule, and extract κ=0.402 GeV from the world data (including the Mainz A1 data) of the Sachs magnetic form factor of the proton GMp. We then predict among others, the charge radius of the proton to be rp=0.831±0.008 fm, in perfect agreement with the recent charge radius of the proton measured by the PRad collaboration at Jefferson Lab, and in agreement with the muonic hydrogen experiments. Our prediction for the proton elastic form factor ratio μpGEp/GMp is also in very good agreement with the recent high precision Jefferson Lab recoil polarization experiment E08-007 for Q2=0.3−0.6 GeV2, and with the recent high precision Mainz A1 experiment for Q2<0.13 GeV2.

Complex-scaled ab initio QED approach to autoionizing states

Ab initio method based on a complex-scaling approach and aimed at a rigorous QED description of autoionizing states is worked out. The autoionizing-state binding energies are treated nonperturbatively in $\alpha Z$ and include all the many-electron QED contributions up to the second order. The higher-order electron correlation, nuclear recoil, and nuclear polarization effects are taken into account as well. The developed formalism is demonstrated on the $LL$ resonances in heliumlike argon and uranium. The most accurate theoretical predictions for the binding energies are obtained.

Laser ionisation detection of O(3 P j ) atoms in the VUV; application to photodissociation of O2

Detection of O() atoms using one-photon resonant excitation to the state at nm followed by near-threshold ionisation, i.e. 1 + 1' resonance-enhanced multi-photon ionisation, has been investigated. The aim was to achieve low ion recoil, improved sensitivity, and reliable angular momentum polarisation information, with an as simple as possible laser setup. An efficient 1 + 1' scheme has been found where the VUV light for the first step is generated by difference frequency () VUV generation, and the ionisation step 1' uses around 289 nm. The presented scheme induces 9 m/s recoil of the O ion using a two-dye laser system, and zero recoil should be possible by generating 302 nm radiation with a third dye laser. While this approach is much more sensitive than a previous 1 + 1' scheme using 212.6 nm for the 1' step, we found that the relatively intense radiation of the beam does not saturate the 1' step. To test the ability of this scheme to accurately determine branching ratios, fine structure yields, and angular distributions including polarisation information, it has been applied to O photodissociation around 130 nm with subsequent O() fragment detection.

K^{+}Lambda photoproduction at forward angles and low momentum transfer

gamma p rightarrow K^{+} Lambda differential cross sections and recoil polarisation data from threshold for extremely forward angles are presented. The measurements were performed at the BGOOD experiment at ELSA, utilising the high angular and momentum resolution forward spectrometer for charged particle identification. The high statistics and forward angle acceptance enables the extraction of the cross section as the minimum momentum transfer to the recoiling hyperon is approached.

Comparison of recoil polarization in the [formula omitted] process for protons extracted from s and p shells

We present the first measurements of the double ratio of the polarization-transfer components (Px′/Pz′)p/(Px′/Pz′)s for knock-out protons from the s and p shells in C12 measured by the C12(e→,e′p→) reaction in quasi-elastic kinematics. The data are compared to theoretical predictions in the relativistic distorted-wave impulse approximation. Our results show that the differences between s- and p-shell protons, observed when compared at the same initial momentum (missing momentum), largely disappear when the comparison is done at the same proton virtuality. We observe no difference in medium modifications between protons from the s and p shells with the same virtuality in spite of the large differences in the respective nuclear densities.

Proton form factor ratio μpGEp/GMp from double spin asymmetry

The ratio of the electric and magnetic form factor of the proton, $\mu_p G_E^p/G_M^p$, has been measured for elastic electron-proton scattering with polarized beam and target up to four-momentum transfer squared, $Q^2=5.66$ (GeV/c)$^2$ using the double spin asymmetry for target spin orientation aligned nearly perpendicular to the beam momentum direction. This measurement of $\mu_p G_E^p/G_M^p$ agrees with the $Q^2$ dependence of previous recoil polarization data and reconfirms the discrepancy at high $Q^2$ between the Rosenbluth and the polarization-transfer method with a different measurement technique and systematic uncertainties uncorrelated to those of the recoil-polarization measurements. The form factor ratio at $Q^2$=2.06 (GeV/c)$^2$ has been measured as $\mu_p G_E^p/G_M^p = 0.720 \pm 0.176_{stat} \pm 0.039_{sys}$, which is in agreement with an earlier measurement with the polarized target technique at similar kinematics. The form factor ratio at $Q^2$=5.66 (GeV/c)$^2$ has been determined as $\mu_p G_E^p/G_M^p=0.244\pm0.353_{stat}\pm0.013_{sys}$, which represents the highest $Q^2$ reach with the double spin asymmetry with polarized target to date.

Study of light nuclei by polarization observables in electron scattering

Electron-induced proton, neutron and deuteron knock-out remains the most versatile probe of the electro-magnetic properties and spin structure of light nuclei. The advent of highly polarized beams and targets and improvements in recoil polarization methods, as well as analysis and simulation techniques, have enabled us to study the static and dynamical properties of few-body systems with unprecedented precision. Recent experiments at Jefferson Lab and MAMI are presented and put into perspective of state-of-the art Faddeev calculations, with focus on the ^\mathbf{3}\mathbf{He}3𝐇𝐞 nucleus.

Non-strange baryons (CLAS)

Baryon spectroscopy is an essential tool in the study of nucleon resonances. The use of polarization observables can greatly clarify the spectrum of broad and overlapping nucleon excitations. The N* program with the CEBAF Large Acceptance Spectrometer (CLAS) at the Thomas Jefferson National Accelerator Facility includes experimental studies with linearly- and circularly-polarized tagged-photon beams, longitudinally- and transversely-polarized nucleon targets, and recoil polarizations. An overview of these experimental studies and recent results are presented.

QED calculation of electron-electron correlation effects in heliumlike ions

Fully relativistic approach to evaluate the correlation effects in highly charged ions is presented. The interelectronic-interaction contributions of first and second orders in $1/Z$ are treated rigorously within the framework of bound-state quantum electrodynamics, whereas the calculations of the third- and higher-order contributions are based on the Dirac-Coulomb-Breit Hamiltonian. The developed approach allows one to deal with single as well as degenerate or quasi-degenerate states. We apply this approach to the calculations of the correlation contributions to the $n=1$ and $n=2$ energy levels in heliumlike ions. The obtained contributions are combined with the one-electron and screened QED corrections, nuclear recoil and nuclear polarization corrections to get the total theoretical predictions for the ionization and transition energies in high-$Z$ heliumlike ions.

HCAL-J: hadron calorimeter for the study of nucleon form factors at Jefferson Lab

ABSTRACTHCAL-J is a hadron calorimeter under construction at JLAB in Newport News, VA (USA).The main interest of the JLAB physics is the study of the hadron matter properties, using a longitudinally polarised electron beam; in particular, researchers investigate the electromagnetic form factors of nuclei and nucleons using the Continuous Electron Beam Accelerator Facility (CEBAF) accelerator, which provides a beam of 12 GeV electrons. The upgrade to higher energies allows measurements at high values of Q2 and a more in-depth study of the internal structure of the hadron matter.To this purpose, Hall A collaboration is building the SuperBigBite Spectrometer (SBS), which consists of a series of elements including a dipole magnet to curve the trajectory of the recoil particles, and a series of Gas Electron Multiplier (GEM) to track the particles. Moreover, two analyzers for the measurement of the polarisation components and a hadron calorimeter, HCAL-J, to measure the particle energy, are used in order to apply the so-called recoil polarisation method, which consists in measuring both the longitudinal and transverse polarisation of the scattered nucleon.The study, through SBS, of the electromagnetic form factors of nucleons allows obtaining the ratio between these two components, which results to be proportional to the ratio between the electric and magnetic form factors of the nucleon.HCAL-J is a sampling calorimeter useful to measure the energy of the recoil nucleon; its active area consists of 288 modules that include a matrix with 24 modules in height and 12 in width. There are optical fibres in between each module, connected to a photomultiplier, in order to look at the light from the scintillating material and convert it into an electric signal, related to the energy of the incident particle.

Determination of the Polarization Observables $${{\varvec{C}}}_{{\varvec{x}}}$$, $${{\varvec{C}}}_{{\varvec{z}}}$$, and $${{\varvec{P}}}_{{\varvec{y}}}$$ for the Quasi-Free Mechanism in the Reaction $${\varvec{\overrightarrow{\gamma }}}{\varvec{d}}\varvec{\rightarrow } {\varvec{K}}^{\varvec{+}}{\varvec{\overrightarrow{\varLambda }}} {{\varvec{n}}}$$

The study of the excited-nucleon ( $$N^*$$ ) spectrum is fundamental for the quest to understand non-perturbative quantum chromodynamics. Measured kinematical evolutions of experimental observables, such as polarizations and unpolarized cross sections, for exclusive meson photoproduction off proton and neutron, are the foundation of theoretical and phenomenological analyses that identify the $$N^*$$ states excited in these reactions and determine their parameters. While free proton targets are readily available, experiments typically use bound neutrons, such as in the deuteron, to estimate observables for photoproduction off the free neutron. Even though exclusivity allows to select event samples dominated by quasi-free scattering (QF), it is not clear if the obtained observables are unbiased estimates of the observables for photoproduction off the free neutron. Studies assessing the possible sources of bias, such as the neutron binding and final-state interactions (FSI), are sparse and primarily focused on the unpolarized cross sections. The comparison between observables for production off the free and off the bound proton in high-statistics reactions, seems to be the natural way to study and to quantify these effects experimentally. Alternatively, one can map the evolution of the QF observables with target-neutron momentum and potentially extrapolate it to the “free”-neutron point of zero momentum. In this work, we determine the recoil polarization $$P_y$$ of the $$\varLambda $$ hyperon and the polarization transfers $$C_x$$ and $$C_z$$ from circularly-polarized photons to the $$\varLambda $$ for the quasi-free mechanism of the reaction $$\overrightarrow{\gamma }d\rightarrow K^+\overrightarrow{\varLambda } n$$ , i.e., for photoproduction off the bound proton. The data were taken with the CLAS detector at the Thomas Jefferson National accelerator facility (JLab) during the E06-103 (g13a) experiment and cover $$E_{\gamma }$$ between 0.9 and 2.6 GeV and $$\cos \theta _{KCM}$$ between $$-\,0.3$$ and 0.8. For several kinematic bins, the dependence of the polarizations on the target-proton momentum is studied. Our work can be used as a benchmark to develop analysis strategies to reduce potential bias due to FSI and the binding of the neutron in the deuteron in reported polarization observables for quasi-free meson photoproduction off the bound neutron.

Nucleon Spectroscopy with CLAS

Meson photoproduction is an important tool in the study of nucleon resonances. The spectrum of broad and overlapping nucleon excitations can be greatly clarified by use of polarization observables. The N* program at Jefferson Lab with the CEBAF Large Acceptance Spectrometer (CLAS) includes experimental studies with linearly- and circularly-polarized tagged-photon beams, longitudinally- and transversely-polarized nucleon targets, and recoil polarizations. Selected results from these experimental studies will be presented.

Slowing down of alpha particles in ICF DT plasmas

With the effects of the projectile recoil and plasma polarization considered, the slowing down of 3.54 MeV alpha particles is studied in inertial confinement fusion DT plasmas within the plasma density range from 1024 to 1026 cm−3 and the temperature range from 100 eV to 200 keV. It includes the rate of the energy change and range of the projectile, and the partition fraction of its energy deposition to the deuteron and triton. The comparison with other models is made and the reason for their difference is explored. It is found that the plasmas will not be heated by the alpha particle in its slowing down the process once the projectile energy becomes close to or less than the temperature of the electron or the deuteron and triton in the plasmas. This leads to less energy deposition to the deuteron and triton than that if the recoil of the projectile is neglected when the temperature is close to or higher than 100 keV. Our model is found to be able to provide relevant, reliable data in the large range of the density and temperature mentioned above, even if the density is around 1026 cm−3 while the deuteron and triton temperature is below 500 eV. Meanwhile, the two important models [Phys. Rev. 126, 1 (1962) and Phys. Rev. E 86, 016406 (2012)] are found not to work in this case. Some unreliable data are found in the last model, which include the range of alpha particles and the electron-ion energy partition fraction when the electron is much hotter than the deuteron and triton in the plasmas.

Ground-state ionization energies of boronlike ions

High-precision QED calculations of the ground-state ionization energies are performed for all boronlike ions with the nuclear charge numbers in the range $16 \leqslant Z\leqslant 96$. The rigorous QED calculations are performed within the extended Furry picture and include all many-electron QED effects up to the second order of the perturbation theory. The contributions of the third- and higher-order electron-correlation effects are accounted for within the Breit approximation. The nuclear recoil and nuclear polarization effects are taken into account as well. In comparison with the previous evaluations of the ground-state ionization energies of boronlike ions the accuracy of the theoretical predictions has been improved significantly.

Differential cross sections and polarization observables from CLAS K⁎ photoproduction and the search for new N⁎ states

The reaction γp→K⁎+Λ was measured using the CLAS detector for photon energies between the threshold and 3.9 GeV at the Thomas Jefferson National Accelerator Facility. For the first time, spin-density matrix elements have been extracted for this reaction. Differential cross sections, spin density matrix elements, and the Λ recoil polarization are compared with theoretical predictions using the BnGa partial wave analysis. The main result is the evidence for significant contributions from N(1895)1/2− and N(2100)1/2+ to the reaction. Branching ratios for decays into K⁎Λ for these resonances and further resonances are reported.

Electromagnetic proton form factors in dual large-Nc QCD: An update

An updated determination is presented of the electric and magnetic form factors of the proton, in the framework of a dual-model realization of quantum chromodynamics (QCD) in the limit of an infinite number of colors. Very good agreement with data is obtained in the space-like region up to [Formula: see text]. In particular, the ratio [Formula: see text] is predicted in very good agreement with recoil polarization measurements from Jefferson Lab, up to [Formula: see text].

Recoil polarization measurements

Polarization observables in photon-induced meson production off nucleons have long been recognized to hold the promise of a detailed understanding of the excited states in the excitation spectrum of the nucleon. Photon beam and proton target polarization are routinely used at the ELSA facility in the Crystal Barrel/TAPS experiment and have yielded a wealth of data on contributing partial waves and nucleon resonances. A detector study on how to complement these ongoing studies by recoil polarization measurements that offer an orthogonal approach with otherwise unmeasurable observables in the field of non-strange meson photoproduction has been performed.Building on experience with silicon detectors operated in the photon beamline environment, first possible layouts of Si detector telescopes for recoil protons were developed. Various geometries, e.g. Archimedean spiral design of annular sensors, sector shapes and rectangular sensors were studied and have been used during test measurements. A prototype for the recoil polarimeter was built and subjected to performance tests in protonproton scattering at the COSY-accelerator in Julich.

Baryon Spectroscopy with Polarization Observables from CLAS

The spectrum of nucleon excitations is dominated by broad and overlapping resonances. Polarization observables in photoproduction reactions are key in the study of these excitations. They give indispensable constraints to partial-wave analyses and help clarify the spectrum. A series of polarized photoproduction experiments have been performed at the Thomas Jefferson National Accelerator Facility with the CEBAF Large Acceptance Spectrometer (CLAS). These measurements include data with linearly and circularly polarized tagged-photon beams, longitudinally and transversely polarized proton and deuterium targets, and recoil polarizations through the observation of the weak decay of hyperons. An overview of these studies and recent results will be given.

Ionization energies along beryllium isoelectronic sequence

Ionization energies for the ground state of berylliumlike ions with nuclear charge numbers in the range Z=16-96 are rigorously evaluated. The calculations merge the ab initio QED treatment in the first and second orders of the perturbation theory in the fine-structure constant $\alpha$ with the third- and higher-order electron-correlation contributions evaluated within the Breit approximation. The nuclear recoil and nuclear polarization effects are taken into account. The accuracy of the ionization energies obtained has been significantly improved in comparison with previous calculations.

K¯+N→K+Ξreaction andS=−1hyperon resonances

The $\bar{K} + N \to K + \Xi$ reaction is studied for center-of-momentum energies ranging from threshold to 3 GeV in an effective Lagrangian approach that includes the hyperon $s$- and $u$-channel contributions as well as a phenomenological contact amplitude. The latter accounts for the rescattering term in the scattering equation and possible short-range dynamics not included explicitly in the model. Existing data are well reproduced and three above-the-threshold resonances were found to be required to describe the data, namely, the $\Lambda(1890)$, $\Sigma(2030)$, and $\Sigma(2250)$. For the latter resonance we have assumed the spin-parity of $J^P=5/2^-$ and a mass of 2265 MeV. The $\Sigma(2030)$ resonance is crucial in achieving a good reproduction of not only the measured total and differential cross sections, but also the recoil polarization asymmetry. More precise data are required before a more definitive statement can be made about the other two resonances, in particular, about the $\Sigma(2250)$ resonance that is introduced to describe a small bump structure observed in the total cross section of $K^- + p \to K^+ + \Xi^-$. The present analysis also reveals a peculiar behavior of the total cross section data in the threshold energy region in $K^- + p \to K^+ + \Xi^-$, where the $P$- and $D$-waves dominate instead of the usual $S$-wave. Predictions for the target-recoil asymmetries of the $\bar{K} + N \to K + \Xi$ reaction are also presented.