1 / 24

Excitation of nucleon resonances in charge-exchange reactions

Excitation of nucleon resonances in charge-exchange reactions. J. Benlliure. Universidad de Santiago de Compostela Spain. 27 A( 20 Ne ,20 Na) @ 900 MeV/u. Energy(MeV). Motivation. Charge-exchange reactions are unique probes to investigate spin-isopin properties of nuclei.

gareth-cummings
Download Presentation

Excitation of nucleon resonances in charge-exchange reactions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Excitation of nucleon resonances in charge-exchange reactions J. Benlliure Universidad de Santiago de Compostela Spain

  2. 27A(20Ne,20Na) @ 900 MeV/u Energy(MeV) Motivation Charge-exchange reactions are unique probes to investigate spin-isopin properties of nuclei. - Contrary to b-decay, these reactions may excite spin-isospin modes over a broad range in energy. - Spin-isospin excitations manifest in two different energy domains • at low energies: particle-hole excitations (Gamow-Teller, spin-dipole, spin- quadrupole or quasi-elastic). - Gamow-Teller: BGT transition strengths - spin-dipole: radial distributions of protons and neutrons A. Krasznahorkay et al. NPA 731 (2004) 224 • at high energies: excitation of nucleon resonances (e.g. D resonance) • - In-medium properties of baryon resonances (downward shift of the D mass • when excited in nuclei) . C. Bachelier et al. PLB 172 (1986) 23 Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  3. p n Do p- po p p Motivation Subnucleonic degrees of freedom play a role in ground-state and structural properties of nuclei. • Gamow-Teller strength quenching. role of D-h excitations • Three-body nuclear forces. role of D(1232) and Roper(1440) The relative probability for inelastic (n,p) and (p,n ) reactions can be used to prove the abundance of protons and neutrons at the nuclear periphery. • Because of the strong absorption isobar charge- • exchange reactions are peripheral processes. Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  4. 124Sb p n 208Pb(1000 MeV/u)+p,d Do 124Sn n p p- po 124In p+ ----p(208Pb,208Bi) ---- d(208Pb,208Bi) p p p n A. Kelic et al., PR.C 70 (2004) 64608 Motivation To investigate spin-isospin excitations at nuclear and subnucleonic level in asymmetric nuclear matter inducing isobar charge-exchange reactions, (p,n) and (n,p), on radioactive relativistic projectiles p,n p+,- p N n D p n N N The momentum recoil induced by the pion emission proves the excitation of the resonance. Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  5. 124Sb 124Sn 124In Experimental requirements Quasi-elastic and inelastic isobar charge-exchange reactions, (p,n) and (n,p), in asymmetric nuclear matter: • relativistic heavy-ion collisions induced by exotic projectiles (isospin asymmetry and radial distributions of protons and neutrons) • isobar charge-exchange (clean reaction channel) Observables: • cross sections for both charge-exchange reactions and channels • missing-energy spectra of the projectile residues Requirements for the setup: • isotopic identification of relativistic projectile residues • separation of elastic and resonant charge-exchange channels • (magnetic analysis of the projectile residues) Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  6. GSI The experiment Inverse kinematics DE ~ 25 MeV (124Sn @ 1000 MeV/u) DZ/Z ~ 7 10-3 DA/A ~ 2.4 10-3 Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  7. Te 120 Te 121 Te 122 Te 123 Te 124 Te 125 Te 126 Sb 123 Sb 123 Sb 123 Sn 106 Sn 107 Sn 108 Sn 109 Sn 110 Sn 111 Sn 112 Sn 113 Sn 114 Sn 115 Sn 116 Sn 117 Sn 118 Sn 119 Sn 120 Sn 121 Sn 122 Sn 123 Sn 124 Sn 125 In 115 The experiment Reactions investigated: • 124Sn+CH2,C, Cu, Pb 124Sb,124In @ 1000 A MeV • 124Sn+Be  120Sn+CH2,C  120Sb,120In @ 1000 A MeV • 112Sn+CH2,C,Cu,Pb 112Sb,112In @ 400, 700, 1000 A MeV • 112Sn+Be  110Sn+CH2,C  110Sb,110In @ 1000 A MeV Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  8. Results Isotopic identification of isobaric charge-exchange residues Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  9. Results Missing-energy spectra in isobar charge-changing reactions induced by 112Sn (p,n) (n,p) Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  10. Results Missing-energy spectra in isobar charge-changing reactions induced by 112Sn C. Bachelier et al. PLB 172 (1986) 23 • The observed spectra are in good qualitative agreement with previous measurements at Saturne • (France) Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  11. Results Unfolding the missing-energy spectrum with the experimental response function Y: measured spectrum H: experimental response function X: observable The primary beam centred through the FRS constitutes our response function H J. Vargas, J.B. and M. Caamaño NIMA 707 (2013) 16 Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  12. Results Unfolding the missing-energy with the experimental response function 112Sn(63Cu,X)112Sb • The unfolding procedure improves the resolution of the final spectra Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  13. Results Excitation of nucleon resonances a(p,X)a’@ 4.2 GeV 112Sn(63Cu,X)112Sb D(1232) N*(1440) D(1600) ? H.P. Morsch et al., PRL 69, 1336 (1992) • Unfolded spectra show additional structures in the inelastic charge-exchange peak that can be • associated to the excitation of different nucleon resonances as the D and Roper resonances. Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  14. Recent measurements with the FRS Resolving nucleon resonances Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  15. Results Energy and target dependence of the resonance excitation 112Sn(12C,12B)112Sb 112Sn(C,X)112Sb+p- 1000 A MeV 700 A MeV 400 A MeV In nucleus-nucleus collisions D-resonance excitation may occurs below the pion production threshold: - Fermi momentum of the nucleons Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  16. Results Energy and target dependence of the resonance excitation 112Sn(12C,12B)112Sb 112Sn(C,C)112Sb+p- 112Sn(p,n)112Sb+p- 1000 A MeV 112Sn(C,B)112Sb+p+ 700 A MeV 400 A MeV • In nucleus-nucleuscollisionsD-resonanceexcitation • occursbelowthe pion productionthreshold: • Fermi momentum of thenucleons • Lowerenergy of theD-resonance Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  17. Results Charge-exchange cross sections • Both cross sections are sensitive to the neutron excess at projectile periphery s(n,p) > s(p,n) • and the projectile size s(124Sb) > s(112Sb) • Elastic (n,p) reactions in the projectile are inhibited in heavy targets by charge conservation • Simple targets such as protons or carbons seem better suited to link these cross sections to the relative abundance of protons and neutrons at the projectile periphery but model calculations are required Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  18. Model calculations Differential cross sections: Isaac Vidaña, U. Coimbra Free NN cross sections: Scattering amplitudes: + target excitations ….. Vertices: Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  19. Model calculations Isaac Vidaña, U. Coimbra Preliminary calculations • Preliminary model calculations provide a good qualitative description of the measured distributions • The calculations clearly show the contribution of different resonances but also their excitation in the projectile but also in the target nucleus • Measurements with proton and carbon targets will be used to extract the properties of the observed resonances Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  20. Future plans at Experimental programme at the Super-FRS Projectile excitations • Exclusive measurements: • Pion detection: • Projectile and target excitations • Identification of resonance isobars Target excitations • Measurements with secondary beams: • Higher secondary beam intensities • Contaminants suppresion • Thinner reaction targets Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  21. Conclusions • A high-resolving power magnetic spectrometer has been proven to be an excellent tool to identify • nucleonic excitations in heavy-ion charge-exchange reactions: - several baryon resonances were identified in the projectile missing energy spectra - cross sections for the elastic and inelastic (p,n) and (n,p) channels where also measured - in-medium properties of these baryons and relative abundance of protons and neutrons at the nuclear periphery are investigated using reliable model calculations • The Super-FRS at FAIR will offer unique opportunities for these investigations - extremely asymmetric nuclear matter - improved separation capabilities (pre-separator) and resolution - exclusive measurements detecting pions in coincidence Collaborators: U. Santiago de Compostela: J. Vargas, Y. Ayyad, S. Beceiro, D. Cortina, P. Díaz, M. Mostazo, C. Paradela GSI: T. Aumann, J. Atkinson, K. Boretzky, A. Estrade, H. Geissel, A. Kelic, Y. Litvinov, S. Pietri, A. Prochazka, M. Takechi, J. Winfield CEA/DAM: A. Chatillon, J. TaiebU. Coimbra: I. Vidaña U. Giessen: H. Lenske Tokyo, Japan, June 2014 José Benlliure, ARIS 2014

  22. Recent measurements with the FRS Missing-energy spectra with secondary beams 112Sn 110Sn 110Sn(C,X)110Sb+p- 110Sb Main difficulties: - Low statistics - Thick S2 target (1 g/cm2 C) - Important background at S2 José Benlliure SuperFRS collaboration meeting, October 2013

  23. 136I (p,n) D++D++ Recent measurements with the FRS Unfolding and regularization of the missing-energy spectrum The most reliable unfolding techniques are based on iterative procedures (Richardson-Lucy) Regularization methods are needed to determine the optimum number of iterations J. Vargas, J.B. and M. Caamaño NIMA 707 (2013) 16 José Benlliure SuperFRS collaboration meeting, October 2013

  24. 132Sb 132Sn 132In Proposal To investigate the isospin dependence of spin-isospin excitations at low and high momentum transfer for both isobar charge-exchange channels (p,n) and (n,p) using relativistic exotic projectiles. • In-medium properties of baryon resonance in isospin asymmetric nuclear matter. (mean energy and width of the resonance) • Gamow-Teller transition strengths • Radial distributions of neutrons and protons. • Nuclear matrix elements for inelastic neutrino interactions. José Benlliure SuperFRS collaboration meeting, February 2014

More Related