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

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

Motivation Tokyo, Japan, June 2014 José Benlliure, ARIS 2014 Subnucleonic degrees of freedom play a role in ground-state and structural properties of nuclei. Gamow-Teller strength quenching. role of  -h excitations Three-body nuclear forces. role of  (1232) and Roper(1440) Because of the strong absorption isobar charge- exchange reactions are peripheral processes. 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. n p oo p p -- oo

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 A. Kelic et al., PR.C 70 (2004) p( 208 Pb, 208 Bi) ---- d( 208 Pb, 208 Bi) 208 Pb(1000 MeV/u)+p,d np ++ p n n p oo p p -- oo p n n p  p,n  +,- N N N 124 In 124 Sn 124 Sb The momentum recoil induced by the pion emission proves the excitation of the resonance. José Benlliure, ARIS 2014 Tokyo, Japan, June 2014

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) Requirements for the setup: isotopic identification of relativistic projectile residues separation of elastic and resonant charge-exchange channels (magnetic analysis of the projectile residues) 124 In 124 Sn 124 Sb Observables: cross sections for both charge-exchange reactions and channels missing-energy spectra of the projectile residues José Benlliure, ARIS 2014 Tokyo, Japan, June 2014

GSI Inverse kinematics  E ~ 25 MeV ( MeV/u)  Z/Z ~  A/A ~ The experiment José Benlliure, ARIS 2014 Tokyo, Japan, June 2014

Reactions investigated: 124 Sn+CH 2,C, Cu, Pb  124 Sb, A MeV 124 Sn+Be  120 Sn+CH 2,C  120 Sb, A MeV 112 Sn+CH 2,C,Cu,Pb  112 Sb, , 700, 1000 A MeV 112 Sn+Be  110 Sn+CH 2,C  110 Sb, A MeV The experiment José Benlliure, ARIS 2014 Tokyo, Japan, June 2014

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

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

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

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 José Benlliure, ARIS 2014 Tokyo, Japan, June 2014 J. Vargas, J.B. and M. Caamaño NIMA 707 (2013) 16

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

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

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

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

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

Results Charge-exchange cross sections José Benlliure, ARIS 2014 Tokyo, Japan, June 2014 Both cross sections are sensitive to the neutron excess at projectile periphery  (n,p) >  (p,n) and the projectile size  ( 124 Sb) >  ( 112 Sb) 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

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

Model calculations José Benlliure, ARIS 2014 Tokyo, Japan, June 2014 Isaac Vidaña, U. Coimbra 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 Preliminary calculations

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

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 José Benlliure, ARIS 2014 Tokyo, Japan, June 2014 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. Taieb U. Coimbra: I. Vidaña U. Giessen: H. Lenske

Recent measurements with the FRS Missing-energy spectra with secondary beams SuperFRS collaboration meeting, October 2013 José Benlliure 112 Sn 110 Sn 110 Sb Main difficulties: - Low statistics - Thick S2 target (1 g/cm 2 C) - Important background at S2 110 Sn(C,X) 110 Sb+  -

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

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. 132 In 132 Sn 132 Sb Radial distributions of neutrons and protons. Gamow-Teller transition strengths In-medium properties of baryon resonance in isospin asymmetric nuclear matter. (mean energy and width of the resonance) Nuclear matrix elements for inelastic neutrino interactions. SuperFRS collaboration meeting, February 2014 José Benlliure