Gregory Potel

Evidence for Phonon Mediated Pairing Interaction in the Halo of the Nucleus 11Li

With the help of a unified nuclear structure–direct reaction heory we analyze the reaction 1H(11Li,9Li) 3H. The two halo neutrons are correlated through the bare and the induced (medium polarization) pairing interaction. By considering all dominant reaction processes leading to t he population of the 1 /2 (2.69 MeV) first excited state of9Li, namely multistep transfer (successive, simultaneous a nd non–orthogonality), breakup and inelastic channels, it is possible to show that the experiment provide s, for the first time in nuclear physics, direct evidence of phonon mediated pairing. PACS: 25.40.Hs, 25.70.Hi, 74.20.Fg, 74.50. +r

Calculation of the transition from pairing vibrational to pairing rotational regimes between magic nuclei ¹⁰⁰Sn and ¹³²Sn via two-nucleon transfer reactions.

Absolute values of two-particle transfer cross sections along the Sn-isotopic chain are calculated. They agree with measurements within errors and without free parameters. Within this scenario, the predictions concerning the absolute value of the two-particle transfer cross sections associated with the excitation of the pairing vibrational spectrum expected around the recently discovered closed shell nucleus(50)(132)Sn(82) and the very exotic nucleus (50)(100)Sn(50) can be considered quantitative, opening new perspectives in the study of pairing in nuclei.

Stability properties of |Ψ|2 in Bohmian dynamics

Abstract According to Bohmian dynamics, the particles of a quantum system move along trajectories, following a velocity field determined by the wavefunction Ψ ( x , t ). We show that for simple one-dimensional systems any initial probability distribution of a statistical ensemble approaches asymptotically | Ψ ( x , t )| 2 if the system is subject to a random noise of arbitrarily small intensity.

Structure and Reactions of Be 11: Many-Body Basis for Single-Neutron Halo

The exotic nucleus ^{11}Be has been extensively studied and much experimental information is available on the structure of this system. We treat, within the framework of renormalized nuclear field theory in both configuration and 3D space, the mixing of bound and continuum single-particle states through the coupling to collective vibrations of the ^{10}Be core. We also take care of the Pauli principle acting not only between the single valence particle explicitly considered and those participating in the collective states, but also between fermions involved in two-phonon virtual states dressing the single-particle motion. In this way, it is possible to simultaneously and quantitatively account for the energies of the 1/2^{+}, 1/2^{-} low-lying states, the centroid and line shape of the 5/2^{+} resonance and the one-nucleon stripping and pickup absolute differential cross sections involving ^{11}Be as either target or residual nucleus. Also for the dipole transition connecting the 1/2^{+} and 1/2^{-} parity inverted levels as well as the isotopic shift of the charge radius. Theory provides a unified and exhaustive nuclear structure and reaction characterization of the many-body effects which are at the basis of this paradigmatic one-neutron halo system.

Pairing correlations with single Cooper pair transfer to individual quantal states

G. PotelDepartamento de Fisica Atomica, Molecular y Nuclear, Universidad de Sevilla, Facultadde Fisica, Avda. Reina Mercedes s/n, Spain.R. A. BrogliaDipartimento di Fisica, Universita` di Milano, Via Celoria 16, 20133 Milano, Italy.INFN, Sezione di Milano Via Celoria 16, 20133 Milano, Italy.The Niels Bohr Institute, University of Copenhagen, Blegdamsvej 17, 2100 CopenhagenO, Denmark.

Nuclear field theory predictions for 11Li and 12Be: Shedding light on the origin of pairing in nuclei

Recent data resulting from studies of two-nucleon transfer reaction on 11Li, analyzed through a unified nuclear-structure-direct-reaction theory have provided strong direct as well as indirect confirmation, through the population of the first excited state of 9Li and of the observation of a strongly quenched ground state transition, of the prediction that phonon-mediated pairing interaction is the main mechanism binding the neutron halo of the 8.5-ms-lived 11Li nucleus. In other words, the ground state of 11Li can be viewed as a neutron Cooper pair bound to the 9Li core, mainly through the exchange of collective vibration of the core and of the pigmy resonance arizing from the sloshing back and forth of the neutron halo against the protons of the core, the mean field leading to unbound two-particle states, a situation essentially not altered by the bare nucleon-nucleon interaction acting between the halo neutrons. Two-neutron pick-up data, together with (t, p) data on 7Li, suggest the existence of a pairing vibrational band based on 9Li, whose members can be excited with the help of inverse kinematic experiments as was done in the case of 11Li(p, t)9Li reaction. The deviation from harmonicity can provide insight into the workings of medium polarization effects on Cooper-pair nuclear pairing, let alone specific information concering the “rigidity” of the N = 6 shell closure. Further information concerning these questions is provided by the predicted absolute differential cross sections σabs associated with the reactions 12Be(p, t)10Be(g.s.) and 12Be(p, t)10Be(pv) (≈10Be(p, t)8Be(g.s.)). In particular, concerning this last reaction, predictions of σabs can change by an order of magnitude depending on whether the halo properties associated with the d5/2 orbital are treated selfconsistently in calculating the ground state correlations of the (pair removal) mode, or not.

Pairing Interaction and Two-Nucleon Transfer Reactions

Soon after the formulation of BCS theory [1], it was recognized by Bohr, Mottelson, and Pines that the existence of an energy gap in the intrinsic excitation spectrum of deformed nuclei displayed a suggestive analogy with that observed in the electronic spectra of metallic superconductors and could, like this one, be described at profit in terms of correlated pairs [2]. Their paper represented the starting point of more than fifty years of experimental and theoretical BCS flavored studies of pairing in nuclei [3].

Dynamical processes in the structure of halo nuclei and their experimental evidence

High polarizability and halo phenomena are strongly correlated, as evidenced by the qualitative changes of the nuclear spectrum which arise taking into account the dynamical coupling of the valence neutrons with the collective vibrations of the system. Direct experimental evidence of their role in the induced pairing interaction binding the halo neutrons of 11Li to the core 9Li is provided by the absolute cross section of the reaction 1H(11Li,9Li)3H to the first excited state of 9Li.