Search

The low-lying M1 strength of the open-shell nucleus 50Cr has been studied with the method of nuclear resonance fluorescence up to 9.7 MeV using bremsstrahlung at the superconducting Darmstadt linear electron accelerator S-DALINAC and Compton backscattered photons at the High Intensity γ-ray Source (HIγS) facility between 6 and 9.7 MeV of the initial photon energy. Fifteen 1+ states have been observed between 3.6 and 9.7 MeV. Following our analysis the lowest 1+ state at 3.6 MeV can be considered as an isovector orbital mode with some spin admixture. The obtained results generally match the estimations and trends typical for the scissors-like mode. Detailed calculations within the Skyrme quasiparticle random-phase-approximation method and the large-scale shell model justify our conclusions. The calculated distributions of the orbital current for the lowest 1+-state suggest the schematic view of Lipparini and Stringari (isovector rotation-like oscillations inside the rigid surface) rather than the scissors-like picture of Lo Iudice and Palumbo. The spinM1 resonance is shown to be mainly generated by spin-flip transitions between the orbitals of the fp shell. [ABSTRACT FROM AUTHOR]

The cosmic microwave background (CMB) energy spectrum is a near-perfect blackbody. The standard model of cosmology predicts small spectral distortions to this form, but no such distortion of the skyaveraged CMB spectrum has yet been measured. We calculate the largest expected distortion, which arises from the inverse Compton scattering of CMB photons off hot, free electrons, known as the thermal Sunyaev-Zel'dovich (TSZ) effect. We show that the predicted signal is roughly one order of magnitude below the current bound from the COBE-FIRAS experiment, but it can be detected at enormous significance (> 1 OOOcr) by the proposed Primordial Inflation Explorer (PIXIE). Although cosmic variance reduces the effective signal-to-noise ratio to 230er, this measurement will still yield a subpercent constraint on the total thermal energy of electrons in the observable Universe. Furthermore, we show that PIXIE can detect subtle relativistic effects in the sky-averaged TSZ signal at 30

Photodisintegration of 9Be through the l/2+ state near neutron threshold and cluster dipole resonance below giant dipole resonance was measured with quasi-monochromatic γ-ray beams produced in the inverse Compton scattering of laser photons. The cross section for the l/2+ state is revisited, being consistent with the 2001 data. The cross section for the cluster dipole resonance is consistent with the cluster dipole sum-rule which however degenerates for the two-body (n-8Be) and three-body(n-α-α) configurations. [ABSTRACT FROM AUTHOR]

The feasibility of the generation of bright ultrashort gamma-ray pulses is demonstrated in the interaction of a relativistic electron bunch with a counterpropagating tightly focused superstrong laser beam in the radiation-dominated regime. The Compton scattering spectra of gamma radiation are investigated using a semiclassical description for the electron dynamics in the laser field and a quantum electrodynamical description for the photon emission. We demonstrate the feasibility of ultrashort gamma-ray bursts of hundreds of attoseconds and of dozens of megaelectronvolt photon energies in the near-backwards direction of the initial electron motion. The tightly focused laser field structure and the radiation reaction are shown to be responsible for such short gamma-ray bursts, which are independent of the durations of the electron bunch and of the laser pulse. The results are measurable with the laser technology available in the near future. [ABSTRACT FROM AUTHOR]

The article reports on Thomas Jefferson National Accelerator Facility (Jefferson Lab) experiment E00-110, focusing on the photon electroproduction cross section in the deeply virtual Compton scattering (DVCS) regime and the valence quark region. It discusses the results of both helicity-dependent and helicity-independent cross sections. Topics include the kinematic settings of the photon electroproduction cross sections and the dominance of the twist-2 handbag amplitude.

Double-polarization observables in the reaction ... have been measured at Q²2 = 0.33 (GeV/c)². The experiment was performed at the spectrometer setup of the A1 Collaboration using the 855 MeV polarized electron beam provided by the Mainz Microtron (MAMI) and a recoil proton polarimeter. From the double-polarization observables the structure function PYT is extracted for the first time, with the value (-15.4 ± 3.3(stat.) -2.4 (syst.)/+1.5) GeV-2, using the low-energy theorem for virtual Compton scattering. This structure function provides a hitherto unmeasured linear combination of the generalized polarizabilities of the proton. [ABSTRACT FROM AUTHOR]

Wide-angle exclusive Compton scattering and single-pion photoproduction from the proton have been investigated via measurement of the polarization transfer from a circularly polarized photon beam to the recoil proton. The wide-angle Compton scattering polarization transfer was analyzed at an incident photon energy of 3.7 GeV at a proton scattering angle of θcmp=70°. The longitudinal transfer KLL, measured to be 0.645±0.059±0.048, where the first error is statistical and the second is systematic, has the same sign as predicted for the reaction mechanism in which the photon interacts with a single quark carrying the spin of the proton. However, the observed value is ~3 times larger than predicted by the generalized-parton-distribution-based calculations, which indicates a significant unknown contribution to the scattering amplitude. [ABSTRACT FROM AUTHOR]

Differential cross sections for elastic scattering of photons from the deuteron have recently been measured at the Tagged-Photon Facility at the MAX IV Laboratory in Lund, Sweden. These first new measurements in more than a decade further constrain the isoscalar electromagnetic polarizabilities of the nucleon and provide the first-ever results above 100 MeV, where the sensitivity to the polarizabilities is increased. We add 23 points between 70 and 112 MeV, at angles 60°, 120°, and 150°. Analysis of these data using a chiral effective field theory indicates that the cross sections are both self-consistent and consistent with previous measurements. Extracted values of αs=[12.1±0.8(stat)±0.2(BSR)±0.8(th)]××10-4fm3 and βs=[2.4±0.8(stat)±0.2(BSR)±0.8(th)]×10-4fm3 are obtained from a fit to these 23 new data points. This paper presents in detail the experimental conditions and the data analysis used to extract the cross sections. [ABSTRACT FROM AUTHOR]

Forty-six decay chains, assigned to the decay of 288115, were produced using the 243Am)(48,3n)288115 reaction at the Lawrence Berkeley National Laboratory 88-in. cyclotron. The resulting series of α decays were studied using α-photon and α-x-ray spectroscopies. Multiple α-photon coincidences were observed in the element 115 decay chain members, particularly in the third- and fourth-generation decays (presumed to be 280Rg and 276Mt, respectively). Upon combining these data with those from 22 288115 decay chains observed in a similar experiment, updated level schemes in 276Mt and 272Bh (populated by the α decay of 280Rg and 276Mt, respectively) are proposed. Photons were observed in the energy range expected for K x rays coincident with the α decay of both 280Rg and 276Mt. However, Compton scattering of higher-energy γ rays and discrete transitions are present in the K x-ray region preventing a definitive Z identification to be made based on observation of characteristic K x-ray energies. [ABSTRACT FROM AUTHOR]

Relativistic electrons counterpropagating through the center of a radially polarized J1 optical Bessel beam in vacuum will emit radiation in a manner analogous to the channeling radiation that occurs when charged particles traverse through a crystal lattice. However, since this interaction occurs in vacuum, problems with scattering of the electrons by the lattice atoms are eliminated. Contrary to inverse Compton scattering, the emitted frequency is also determined by the amplitude of the laser field, rather than only by its frequency. Adjusting the value of the laser field permits the tuning of the emitted frequency over orders of magnitude, from terahertz to soft X rays. High flux intensities are predicted (∼100 MW/cm2). Extended interaction lengths are feasible due to the diffraction-free properties of the Bessel beam and its radial field, which confines the electron trajectory within the center of the Bessel beam. [ABSTRACT FROM AUTHOR]

The study of exclusive processes in the future electron-ion (eA) colliders will be an important tool to investigate the QCD dynamics at high energies as they are in general driven by the gluon content of the target which is strongly subject to parton saturation effects. In this paper we compute the coherent and incoherent cross sections for the deeply virtual Compton scattering (DVCS) process relying on the color dipole approach and considering different models for the dipole-proton scattering amplitude. The dependencies of the cross sections with the energy, photon virtuality, nuclear mass number, and squared momentum transfer are analyzed in detail. We demonstrate that the ratio between the incoherent and coherent cross sections decreases at smaller values of Q² and increases at smaller values of A. We show that the coherent cross section dominates at small t and exhibits the typical diffractive pattern, with the number of dips in the range |t| ≤ 0.3 GeV² increasing with the mass atomic number. Our results indicate that the position of the dips are independent of the model used to treat the dipole-proton interaction as well as of the center-of-mass energy. [ABSTRACT FROM AUTHOR]

Bonding characteristics of liquid boron at 2500 K are studied by using high-resolution Compton scattering. An excellent agreement is found between the measurements and the corresponding Car- Parrinello molecular dynamics simulations. Covalent bond pairs are clearly shown to dominate in liquid boron along with the coexistence of diffuse pairs. Our study reveals the complex bonding pattern of liquid boron and gives insight into the unusual properties of this high-temperature liquid. [ABSTRACT FROM AUTHOR]

First measurement of the beam asymmetry Σ for Compton scattering off the proton in the energy range Ey = 0.85-1.25 GeV is presented. The data reveal two narrow structures at Er = 1.036 and Ey = 1.119 GeV. They may signal narrow resonances with masses near 1.68 and 1.72 GeV, or they may be generated by the subthreshold K A and cop production. Their decisive identification requires additional theoretical and experimental efforts. [ABSTRACT FROM AUTHOR]

The spin polarizabilities of the nucleon describe how the spin of the nucleon responds to an incident polarized photon. The most model-independent way to extract the nucleon spin polarizabilities is through polarized Compton scattering. Double-polarized Compton scattering asymmetries on the proton were measured in the Δ(1232) region using circularly polarized incident photons and a transversely polarized proton target at the Mainz Microtron. Fits to asymmetry data were performed using a dispersion model calculation and a baryon chiral perturbation theory calculation, and a separation of all four proton spin polarizabilities in the multipole basis was achieved. The analysis based on a dispersion model calculation yields γE1E1=-3.5±1.2, γM1M1=3.16±0.85, γE1M2=-0.7±1.2, and γM1E2=1.99±0.29, in units of 10- 4fm4. [ABSTRACT FROM AUTHOR]

We present an incisive spectroscopic technique for directly probing redox orbitals based on bulk electron momentum density measurements via high-resolution x-ray Compton scattering. Application of our method to spinel LixMn2O4, a lithium ion battery cathode material, is discussed. The orbital involved in the lithium insertion and extraction process is shown to mainly be the oxygen 2p orbital. Moreover, the manganese 3d states are shown to experience spatial delocalization involving 0.16 ± 0.05 electrons per Mn site during the battery operation. Our analysis provides a clear understanding of the fundamental redox process involved in the working of a lithium ion battery. [ABSTRACT FROM AUTHOR]

A measurement of the electroproduction of photons off protons in the deeply inelastic regime was performed at Jefferson Lab using a nearly 6 GeV electron beam, a longitudinally polarized proton target, and the CEBAF Large Acceptance Spectrometer. Target-spin asymmetries for ep → e'p'γ events, which arise from the interference of the deeply virtual Compton scattering and the Bethe-Heitler processes, were extracted over the widest kinematics in Q2,xB,t, and ϕ, for 166 four-dimensional bins. In the framework of generalized parton distributions, at leading twist the t dependence of these asymmetries provides insight into the spatial distribution of the axial charge of the proton, which appears to be concentrated in its center. These results also bring important and necessary constraints for the existing parametrizations of chiral-even generalized parton distributions. [ABSTRACT FROM AUTHOR]

Photoneutron cross sections were measured for five stable Nd isotopes, 143,144,145,146,148Nd, near neutron threshold with highly monochromatic laser-Compton scattering γ rays. The photoneutron data were compared with the calculations performed with the talys reaction code with inputs of the Skyrme Hartree-Fock-Bogoliubov (HFB) plus quasi-particle random phase approximation (QRPA) model and the axially symmetric deformed Gogny HFB plus QRPA model of E1 γ-ray strength. Using the γ-ray strength function constrained by the present photoneutron data, a thorough analysis of the reverse (n,?) cross sections is made. Radiative neutron capture cross sections for an s-process branching-point nucleus in the rare earth region, 147Nd with the half-life 10.98 d, are deduced with the ?-ray strength function method. The impact of the newly evaluated 147Nd(n,γ)148Nd cross section on s-process nucleosynthesis is discussed. [ABSTRACT FROM AUTHOR]

The electromagnetic polarizabilities of the nucleon are fundamental properties that describe its response to external electric and magnetic fields. They can be extracted from Compton-scattering data-and have been, with good accuracy, in the case of the proton. In contradistinction, information for the neutron requires the use of Compton scattering from nuclear targets. Here, we report a new measurement of elastic photon scattering from deuterium using quasimonoenergetic tagged photons at the MAX IV Laboratory in Lund, Sweden. These first new data in more than a decade effectively double the world data set. Their energy range overlaps with previous experiments and extends it by 20 MeV to higher energies. An analysis using chiral effective field theory with dynamical A(1232) degrees of freedom shows the data are consistent with and within the world data set. After demonstrating that the fit is consistent with the Baldin sum rule, extracting values for the isoscalar nucleon polarizabilities, and combining them with a recent result for the proton, we obtain the neutron polarizabilities as αn = [11.55+1.25(stat)+0.2(BSR)+ 0.8(th)] x 10-4 fm3 and βn = [3.65≠ 1.25(stat) +0.2(BSR) ≠ 0.8(th)] x 10-4 fm3, with X2 = 45.2 for 44 degrees of freedom. [ABSTRACT FROM AUTHOR]

The cumulant expansion is a powerful approach for including correlation effects in electronic structure calculations beyond the GW approximation. However, the expansion is not generally valid, as current implementations ignore terms that mix particle and hole states and lead to partial occupation numbers of one-electron states. These limitations are corrected here using a cumulant expansion of the retarded one-electron Green's function that includes both particle and hole contributions. The approach provides a consistent framework that improves on the GW approximation to the spectral function without additional computational effort. The method is illustrated with results for the homogeneous electron gas and comparisons to experiment and other methods. [ABSTRACT FROM AUTHOR]

The article focuses on a study which examines the feasibility of isotope of lithium (6Li) as a target in nuclear Compton scattering experiments. Topics discussed include measurements of Compton-scattering cross sections from 6Li at the High Intensity Gamma-Ray Source (HlyS), nucleon polarizabilities and absolute cross-section extraction for the higher-energy 6Li.

Elastic scattering of photons from l2C has been investigated using quasimonoenergetic tagged photons with energies in the range 65-115 MeV at laboratory angles of 60°, 120°, and 150° at the Tagged-Photon Facility at the MAX IV Laboratory in Lund, Sweden. A phenomenological model was employed to provide an estimate of the sensitivity of the l2C(y,y)l2C cross section to the bound-nucleon polarizabilities. [ABSTRACT FROM AUTHOR]

We present a theoretical study of two-color ionization of hydrogen with keV photons at intensities ranging from 1016 to 1018 W/cm2. We consider the atom in interaction with a superposition of two electromagnetic pulses centered around two frequencies that differ by a few atomic units and we present in detail the case of the frequencies 55 and 50 a.u. We present the electron energy spectra, angular distributions, and ionization rates based on nonperturbative and perturbative calculations. Although the ejected electron energy distribution is dominated by one-photon ionization from each pulse, we are able to identify the contribution of stimulated Compton scattering, a process in which one photon is absorbed while the other is emitted, the photon energy difference being transferred to the electron. This leads to low-energy electrons, and we show in particular that it is of crucial importance to consider the retardation effects on the ionization rates and the electron angular distributions. The relative propagation direction of the two fields also plays an important role; in the case of counterpropagating fields, the ionization by stimulated Compton scattering is dominated by A2 and competes with one-photon ionization at high intensities. [ABSTRACT FROM AUTHOR]

We explore the role of final-state interactions (FSIs) in inclusive deep-inelastic scattering from the deuteron. Relating the inclusive cross section to the deuteron forward virtual Compton scattering amplitude, a general formula for the FSI contribution is derived in the generalized eikonal approximation, utilizing the diffractive nature of the effective hadron-nucleon interaction. The calculation uses a factorized model with a basis of three resonances with mass W < 2 GeV and a continuum contribution for larger W as the relevant set of effective hadron states entering the final-state interaction amplitude. The results show sizeable on-shell FSI contributions for Bjorken x ≿ 0.6 and Q² ≾ 10 GeV², increasing in magnitude for lower Q2, but vanishing in the high-Q² limit because of phase-space constraints. The off-shell rescattering contributes at x ≿ 0.8 and is taken as an uncertainty on the on-shell result. [ABSTRACT FROM AUTHOR]

We present the momentum distributions of the nucleus and of the electrons from double ionization of the helium atom by Compton scattering of photons with hν=40 keV. We find that the doubly charged ion momentum distribution is very close to the Compton profile of the nucleus in the ground state of the helium atom, and the momentum distribution of the singly charged ion to give a precise image of the electron Compton profile. To reproduce these results, nonrelativistic calculations require the use of highly correlated initial- and final-state wave functions. [ABSTRACT FROM AUTHOR]

A setup of a unique x-ray source is put forward employing a relativistic electron beam interacting with two counterpropagating laser pulses in the nonlinear few-photon regime. In contrast to Compton scattering sources, the envisaged x-ray source exhibits an extremely narrow relative bandwidth of the order of 10-4, comparable with an x-ray free-electron laser. The brilliance of the x rays can be an order of magnitude higher than that of a state-of-the-art Compton source. By tuning the laser intensities and the electron energy, one can realize either a single peak or a comblike x-ray source of around keV energy. The laser intensity and the electron energy in the suggested setup are rather moderate, rendering this scheme compact and tabletop size, as opposed to x-ray free-electron laser and synchrotron infrastructures. [ABSTRACT FROM AUTHOR]

A new experimental evaluation of the quenching factor for nuclear recoils in NalfTl] is described. Systematics affecting previous measurements are addressed by careful characterization of the emission spectrum of the neutron source, use of a small scintillator coupled to an ultra-bialkali high-quantum-efficiency photomultiplier, and evaluation of nonlinearities in the electron recoil response via Compton scattering. A trend towards a rapidly diminishing quenching factor with decreasing sodium recoil energy is revealed. Additionally, no evidence for crystal lattice channeling of low-energy recoiling ions is found in a scintillator of known crystallographic orientation. A discussion on how these findings affect dark matter searches employing NalfTl] (e.g., DAMA/LIBRA) is offered. [ABSTRACT FROM AUTHOR]