Publications (34)82.01 Total impact
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ABSTRACT: Coulomb breakup at high energy in inverse kinematics of protonrich 31Cl was used to constrain the thermonuclear 30S(p,γ)31Cl capture reaction rate under typical Type I xray burst conditions. This reaction is abottleneck during rapid protoncapture nucleosynthesis (rp process), where its rate depends predominantly on the nuclear structure of 31Cl. Two lowlying states just above the protonseparation threshold of Sp=296(50) keV in31Cl have been identified experimentally using the R3BLAND setup at the GSI Helmholtzzentrum f¨ ur Schwerionenforschung GmbH. Both states are considered to play a key role in the thermonuclear 30S(p,γ)31Cl capture reaction. Excitation energies of the first Jπ =1/2+,5/2+ states have been extracted and the reaction rate for proton capture on 30S under typical rpprocess temperatures has been investigated. 
Dataset: NIMPR 637 60 20111
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ABSTRACT: The electron–ion scattering experiment ELISe is part of the installations envisaged at the new experimental storage ring at the International Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany. It offers an unique opportunity to use electrons as probe in investigations of the structure of exotic nuclei. The conceptual design and the scientific challenges of ELISe are presented.  [Show abstract] [Hide abstract]
ABSTRACT: The relativistic distortedwave impulse approximation is used to describe the 3He(e, e′ p)2H process. We describe the 3He nucleus within the adiabatic hyperspherical expansion method with realistic nucleonnucleon interactions. The overlap between the 3He and the deuteron wave functions can be accurately computed from a threebody calculation. The nucleons are described by solutions of the Dirac equation with scalar and vector (S–V) potentials. The wave function of the outgoing proton is obtained by solving the Dirac equation with a S–V optical potential fitted to elastic proton scattering data on the residual nucleus. Within this theoretical framework, we compute the cross section of the reaction and other observables like the transverselongitudinal asymmetry, and compare them with the available experimental data measured at JLab.  [Show abstract] [Hide abstract]
ABSTRACT: We measured with unprecedented precision the induced polarization P(y) in (4)He(e,e'p)(3)H at Q(2)=0.8 and 1.3 (GeV/c)(2). The induced polarization is indicative of reactionmechanism effects beyond the impulse approximation. Our results are in agreement with a relativistic distortedwave impulse approximation calculation but are overestimated by a calculation with strong chargeexchange effects. Our data are used to constrain the strength of the spinindependent chargeexchange term in the latter calculation.  [Show abstract] [Hide abstract]
ABSTRACT: The electric form factor of the neutron was determined from studies of the reaction 3He(e,e'n)pp in quasielastic kinematics in Hall A at Jefferson Lab. Longitudinally polarized electrons were scattered off a polarized target in which the nuclear polarization was oriented perpendicular to the momentum transfer. The scattered electrons were detected in a magnetic spectrometer in coincidence with neutrons that were registered in a largesolidangle detector. More than doubling the Q2 range over which it is known, we find G(E)(n)=0.0236±0.0017(stat)±0.0026(syst), 0.0208±0.0024±0.0019, and 0.0147±0.0020±0.0014 for Q(2)=1.72, 2.48, and 3.41 GeV2, respectively.  [Show abstract] [Hide abstract]
ABSTRACT: Proton recoil polarization was measured in the quasielastic 4He(e,e'p)3H reaction at Q{2}=0.8 and 1.3 (GeV/c){2} with unprecedented precision. The polarizationtransfer coefficients are found to differ from those of the 1H(e,e'p) reaction, contradicting a relativistic distortedwave approximation and favoring either the inclusion of mediummodified proton form factors predicted by the quarkmeson coupling model or a spindependent chargeexchange finalstate interaction. For the first time, the polarizationtransfer ratio is studied as a function of the virtuality of the proton.  [Show abstract] [Hide abstract]
ABSTRACT: A Coulomb dissociation experiment on the protonrich 32Ar and 34Ar isotopes was performed at the ALADINLAND setup at GSI in Darmstadt. Recent RQRPA calculations show a lowlying E1 softvibrational mode at an excitation energy Ex ≈ 9 MeV for protonrich argon isotopes at the dripline. In a macroscopic picture, this can be understood as an outofphase oscillation of a thin proton skin against the isospinsaturated core, similar to the neutron pygmy resonance at the neutron dripline. On the other hand, the measured (γ, p) reactions are interesting for the calculation of reaction crosssections and radiative proton capture rates for the rpprocess. In this hydrogen burning process a lot of nuclear structure inputs are still missing. Especially in the argon region a bottleneck for the reaction flow is assumed at 30S and 34Ar. The impact of the predicted proton pygmy resonance on the reaction flow is not yet clear. The experimental motivation and the experiment itself are described. Identification plots for incoming and outgoing particles are shown and a tracking algorithm is applied and shows to work succesfully. 
Article: Spin asymmetry for the 16O() reaction in the Δ(1232) region within an effective Lagrangian approach
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ABSTRACT: The spin asymmetry of the photon in the exclusive reaction is computed employing a recently developed fully relativistic model based on elementary pion production amplitudes that include a consistent treatment of the spin3/2 nucleon resonances. We compare the results of this model to the only available data on Oxygen [K. Hicks, et al., Phys. Rev. C 61 (2000) 054609] and find that, contrary to other models, the predicted spin asymmetry compares well to the available experimental data in the Δ(1232) region. Our results indicate that no major medium modifications in the Δ(1232) properties are needed in order to describe the measured spin asymmetries.  [Show abstract] [Hide abstract]
ABSTRACT: A long standing question in nuclear physics is the effect of the nuclear medium on the properties of the nucleon. In this paper, we present a review of past and present efforts in the search for evidence of possible modifications of the nucleon form factors inside the nuclear medium, using the (e, e p) reaction. Particularly, we discuss the E89044 experiment, which studied the quasielastic 3 He(e, e p) 2 H reaction at a transfer momentum Q 2 = 1.5 (GeV/c) 2 and two different beam energies of 1255 and 4807 MeV in the Hall A of Jefferson Laboratory. The extraction of the 3 He(e, e p) 2 H cross section has been performed with a fitting procedure method, using the simulation program MCEEP (Monte Carlo for ElectroNuclear Coincidence Experiments), taking into account the effects of internal and external radiation and spectrometer resolutions. Unpolarized nuclear response functions have been separated for two different values of the longitudinal polarization of the exchanged photon . Possible changes in the structure of nucleons embedded in a nucleus are studied indirectly, via the ratio of Longitudinal and Transverse nuclear response functions. A comparison of extracted data using the Polarization Technique in the 4 He(e, e p) reaction, with the predictions of the Relativistic Distorted Wave Impulse Approximation Madrid code is also showed.  [Show abstract] [Hide abstract]
ABSTRACT: The energy distributions of the GamowTeller strength are studied for eveneven Xe isotopes with mass numbers from 124 to 142. A selfconsistent microscopic formalism is used to generate the single particle basis, using a deformed Skyrme HartreeFock mean field with pairing correlations in BCS approximation. The GamowTeller transitions are obtained within a quasiparticle random phase approximation (QRPA) approach using a residual spinisospin interaction in the particlehole and particleparticle channels. We then discuss the pairing BCS treatment and the determination of the ph and pp residual interaction coupling constants. We study the GT+ and GT strength distributions for the equilibrium nuclear shapes, which are an essential information for studies of chargeexchange reactions and doublebeta processes involving these isotopes. Comment: 15 pages, 5 figures. To appear in Phys Rev C  [Show abstract] [Hide abstract]
ABSTRACT: We have measured the 4He(e, e’p)3H reaction at missing momenta of 130300 MeV/c using the threespectrometer facility at the Mainz microtron MAMI. Data were taken in perpendicular kinematics to allow us to determine the response function R LT and the asymmetry term A TL. The data are compared to both relativistic and nonrelativistic calculations.  [Show abstract] [Hide abstract]
ABSTRACT: At present there exists a great interest in the search for evidence of possible modification of the nucleon form factors inside the nuclear medium. Recent theoretical work predict changes in the form factors within the experimental limits. Importantly, the longitudinal to sideways transferred polarization ratio has been identified as being ideally suited for such studies, as these polarization observables are believed to be the least sensitive to most standard nuclear structure uncertainties while their ratio shows a high sensitivity to the ratio of the electric to magnetic form factors. The kinematic regime where the measurements have been undertaken is at relatively high energy and it is clear that relativistic effects in wave functions and operators are essential. In this work we focus on the analysis of polarized $^{16}O(\vec{e},e'\vec{p})^{15}N$ observables. Our aim is to explore a selected set of model dependences that could contaminate any attempt to infer medium modifications, mainly related to the description of FSI and to the role played by relativity. 
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ABSTRACT: The physics program in Hall A at Jefferson Lab commenced in the summer of 1997 with a detailed investigation of the 16O (e, e' p) reaction in quasielastic, constant (q,ω) kinematics at Q2 ≈0.8 (GeV/c)2 , q≈1 GeV/c , and ω≈445 MeV . Use of a selfcalibrating, selfnormalizing, thinfilm waterfall target enabled a systematically rigorous measurement. Fivefold differential crosssection data for the removal of protons from the 1p shell have been obtained for 0< pmiss <350 MeV/c . Sixfold differential crosssection data for 0< Emiss <120 MeV were obtained for 0< pmiss <340 MeV/c . These results have been used to extract the ALT asymmetry and the RL , RT , RLT , and RL+TT effective response functions over a large range of Emiss and pmiss . Detailed comparisons of the 1p shell data with Relativistic DistortedWave Impulse Approximation (RDWIA), Relativistic OpticalModel Eikonal Approximation (ROMEA), and Relativistic MultipleScattering Glauber Approximation (RMSGA) calculations indicate that twobody currents stemming from mesonexchange currents (MEC) and isobar currents (IC) are not needed to explain the data at this Q2 . Further, dynamical relativistic effects are strongly indicated by the observed structure in ALT at pmiss ≈300 MeV/c . For 25< Emiss <50 MeV and pmiss ≈50 MeV/c , proton knockout from the 1 s1/2 state dominates, and ROMEA calculations do an excellent job of explaining the data. However, as pmiss increases, the singleparticle behavior of the reaction is increasingly hidden by more complicated processes, and for 280< pmiss <340 MeV/c , ROMEA calculations together with twobody currents stemming from MEC and IC account for the shape and transverse nature of the data, but only about half the magnitude of the measured cross section. For 50< Emiss <120 MeV and 145< pmiss <340 MeV/c , (e, e' pN) calculations which include the contributions of central and tensor correlations (twonucleon correlations) together with MEC and IC (twonucleon currents) account for only about half of the measured cross section. The kinematic consistency of the 1p shell normalization factors extracted from these data with respect to all available 16O (e, e' p) data is also examined in detail. Finally, the Q2 dependence of the normalization factors is discussed.  [Show abstract] [Hide abstract]
ABSTRACT: Recoil nucleon transferred polarization observables in coincidence quasielastic electron scattering are studied within the relativistic distorted wave impulse approximation. Results for response functions and polarization asymmetries are discussed for proton knockout from p1∕2, p3∕2, and s1∕2 shells in 16O. The impact of spinor distortion is examined by comparing the fully relativistic calculation with results obtained by projecting out the negativeenergy components. In particular, a careful analysis of effects linked to the description of the bound and scattered relativistic nucleon wave functions is presented. The high sensitivity of some polarization observables to the dynamical enhancement of the lower components, already shown within the relativistic plane wave impulse approximation, is proven to be maintained in the relativistic distorted wave approach. Semirelativistic approaches based on the effective momentum approximation are also studied. Finally, comparison with experimental data and a brief analysis of effects linked to medium modified form factors is presented.  [Show abstract] [Hide abstract]
ABSTRACT: We study the occurrence of factorization in polarized and unpolarized observables in coincidence quasielastic electron scattering. Starting with the relativistic distorted wave impulse approximation, we reformulate the effective momentum approximation and show that the latter leads to observables which factorize under some specific conditions. Within this framework, the role played by final state interactions and, in particular, by the spinorbit term is explored. Connection with the nonrelativistic formalism is studied in depth. Numerical results are presented to illustrate the analytical derivations and to quantify the differences between factorized and unfactorized approaches.  [Show abstract] [Hide abstract]
ABSTRACT: The polarization transfer in the 4He(e,e′,p)3H reaction was measured over the range of Q2 from 0.5 to 2.6 (GeV/c)2. Results showed that the recoil polarization at the lowest Q2 agreed well with previously reported measurements. The polarization transfer characteristics were found to be only slightly dependent on nuclear structure defects and fine details of the reaction mechanism.  [Show abstract] [Hide abstract]
ABSTRACT: We have measured the proton recoil polarization in the 4He(e>,e(')p>)4H reaction at Q(2)=0.5, 1.0, 1.6, and 2.6 (GeV/c)(2). The measured ratio of polarization transfer coefficients differs from a fully relativistic calculation, favoring the inclusion of a medium modification of the proton form factors predicted by a quarkmeson coupling model. In addition, the measured induced polarizations agree reasonably well with the fully relativistic calculation indicating that the treatment of finalstate interactions is under control.  [Show abstract] [Hide abstract]
ABSTRACT: Coincidence scattering of polarized electrons from nuclei with polarization transfer to outgoing nucleons is studied within the context of relativistic mean field theory. Effects introduced by the dynamical enhancement of the lower components of the bound and scattered nucleon wave functions are analyzed for the polarized response functions and transferred polarization asymmetries. Results obtained by projecting out the negativeenergy components are compared with the fullyrelativistic calculation. The crucial role played by the relativistic dynamics in some spindependent observables is clearly manifested even for low/medium values of the missing momentum. Kinematical relativistic effects are also analyzed. A discussion of the factorization approach and the mechanism for its breakdown is also briefly presented.
Publication Stats
389  Citations  
82.01  Total Impact Points  
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Institutions

20102011

Instituto de Estructura de la Materia
Madrid, Madrid, Spain


2007

University Joseph Fourier  Grenoble 1
 Laboratoire de Physique Subatomique et Cosmologie
Grenoble, RhôneAlpes, France


20002006

Complutense University of Madrid
 Department of Atomic, Molecular and Nuclear Physics
Madrid, Madrid, Spain
