1. In-medium excitation of nucleon resonances using heavy-ion charge exchange reactions J. Benlliure University of Santiago de Compostela, Spain International Workshop XLIII on Gross Properties of Nuclei and Nuclear Excitations Hirschegg, Kleinwalsertal, Austria, January 11 - 17, 2015

2. Motivation José Benlliure 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 27 A( 20 Ne,20 Na) @ 900 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 Hirschegg Int. Workshop, January 2015

3. Motivation José Benlliure 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 N*(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. Hirschegg Int. Workshop, January 2015 Role of nucleon excitations in compact and massive neutron stars. Renewed interest in the in-medium properties of the  -resonance

4. Outline José Benlliure Previous investigations on nucleon resonances excitations using heavy-ion charge- exchange reactions. Recent measurements at FRS@GSI. experimental requirements improved resolution preliminary results Hirschegg Int. Workshop, January 2015 First model calculations. Future perspectives. first exclusive measurements at FRS@GSI nucleon resonances excitation in asymmetric nuclear matter at SuperFRS@FAIR Isobar charge-exchange reactions and the ejectile missing-energy spectra.

5. Isobar charge-exchange reactions Isobar charge-exchange reactions investigated in inverse kinematics allow for the direct observation of in-medium excitation of the Delta resonance for both (p,n) and (n,p) channels. np ++ p n n p oo p p -- oo p n n p  p,n  +,- N N N 20 F 20 Ne 20 Na The momentum recoil induced by the pion emission proves the excitation of the resonance. José Benlliure Hirschegg Int. Workshop, January 2015 C. Bachelier et al. PLB 172 (1986) 23 In the inelastic charge-exchange process the pion must scape in order to preserve the isobar character of the reaction.

6. Isobar charge-exchange reactions at Saturne José Benlliure Hirschegg Int. Workshop, January 2015 Systematic investigations with stable light and medium-mass projectiles were performed measuring the missing-energy spectra of the ejectiles with the SPES 4 spectrometer. A downward shift of about 70 MeV in the mass of the Delta resonance was observed when excited with composite targets. Many theoretical works tried to explain the origin of the shift as due to in-medium effects. F. Osterfeld. Rev. Mod. Phys. 64 (1992) 491 D. Contardo et al.. PLB 168 (1986) 331 Other experiments at: Gatchina: V.N. Baturin et al. Sov. J. NP 31 (1980) 207 Lampf: D.A Lind, Can. J. Phys. 65 (1987) 637 Dubna: V.G. Ableev et al., Jetp. Lett. 40 (1984) 763

7. Isobar charge-exchange reactions at Saturne José Benlliure Hirschegg Int. Workshop, January 2015 The observable used to identify the excitation of the Delta resonance, missing-energy spectra of the ejectiles, is sensitive to excitation in the projectile and the target nucleus. Projectile excitations Target excitations 3 He d  t  N T He = 2 GeV Detailed calculations showed that projectile and target excitations lead to missing-energy spectra with different shapes that contribute to the observed mass shift. E. Oset et al.PLB 224 (1989) 249

8. Direct observation of the Roper resonance at Saturne José Benlliure Hirschegg Int. Workshop, January 2015 Direct observation of the Roper resonance in the missing energy spectra in (  ’ ) reactions on a proton target. H. P. Morsch et al., PRL 69 (1992) 1336

9. Direct observation of the Roper resonance at Saturne José Benlliure Hirschegg Int. Workshop, January 2015 Direct observation of the Roper resonance in the missing energy spectra in (  ’ ) reactions on a proton target.

10. Direct observation of the Roper resonance at Saturne José Benlliure Hirschegg Int. Workshop, January 2015 The unknown nature of the Roper resonance. N*(1440) as a collective excitation (breathing mode). - Bag model: monopole vibration of the bag surface (G. Brown et al. NPA 397 (1983) 447) - Quarks in a deformed oscillator potential: rotational state (H. Toki et al. ) N*(1440) with an exotic nature. - Hybrid state qqqG (S. Capstick et al. PRD 60 (1999) 111501) - Dual nature qqq and qqqqq ( B. Julia-Diaz and D. Riska NPA 780 (2006) 175) …… Taken from L. Alavarez-Ruso arXiv:1011.0609v1 In a quark model with and oscillator potential the Roper would be the second excited state

11. First observation of the  -resonance in (n,p) isobaric charge-exchange reactions at the FRS A. Kelic et al., Phys. Rev. C 70 (2004) 64608 ---- p( 208 Pb, 208 Bi) ---- d( 208 Pb, 208 Bi) 208 Pb(1000 MeV/u)+p,d José Benlliure Hirschegg Int. Workshop, January 2015 Isobar charge-exchange reactions at FRS@GSI

12. A new exploratory experiment at FRS@GSI 124 Sn+CH 2,C  124 Sb, 124 In @ 1000 A MeV 124 Sn+Be  120 Sn+CH 2,C  120 Sb, 120 In @ 1000 A MeV 112 Sn+CH 2,C,Cu,Pb  112 Sb, 112 In @ 400, 700, 1000 A MeV 112 Sn+Be  110 Sn+CH 2,C  110 Sb, 110 In @ 1000 A MeV José Benlliure Hirschegg Int. Workshop, January 2015 To investigate the feasibility of accurate measurements of nucleon resonances excited in isobar charge-exchange reactions induced by stable and unstable projectiles using the inverse kinematic technique.

13. Experimental requirements Requirements for the setup: isotopic identification of reaction ejectiles separation of elastic and resonant charge-exchange channels magnetic analysis of the reaction ejectiles 132 In 132 Sn 132 Sb Observables: cross sections for both charge exchange reactions and channels missing-energy spectra mean energy and width of the  -resonance José Benlliure Hirschegg Int. Workshop, January 2015

14. Experimental setup  -resonance and quasi-elastic charge-exchange reactions identified at the FRS: (standar detection setup) José Benlliure Hirschegg Int. Workshop, January 2015 primary target secondary target  Z/Z ~ 7 10 -3  A/A ~ 2.4 10 -3  E ~ 30 MeV ( 124 Sn, 112 Sn @ 1000 MeV/u) - Reactions with stable beams induced at the primary target - Unstable beams produced at the primary target and charge-exchange reactions induced in the secondary target

15. Recent measurements with the FRS Isotopic identification of isobaric charge-exchange residues José Benlliure Hirschegg Int. Workshop, January 2015 12 C( 112 Sn, 112 Sb)X 12 C( 112 Sn, 112 In)X 112 Sn 49+

16. Recent measurements with the FRS Missing-energy spectra in isobar charge-changing reactions induced by 112 Sn José Benlliure Hirschegg Int. Workshop, January 2015 (p,n)(n,p)

17. Recent measurements with the FRS Comparison with the Saturne data José Benlliure C. Bachelier et al. PLB 172 (1986) 23 Hirschegg Int. Workshop, January 2015 (p,n) (n,p)

18. Recent measurements with the FRS Comparison with the Saturne data José Benlliure ( 124 Sn, 124 Sb) Hirschegg Int. Workshop, January 2015 (n,p)

19. Recent measurements with the FRS Unfolding the missing-energy spectrum with the experimental response function José Benlliure  Y: measured spectrum H: experimental response function X: observable The primary beam centred through the FRS constitutes our response function H Hirschegg Int. Workshop, January 2015

20. Recent measurements with the FRS 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) A stopping condition is needed to determine the optimum number of iterations Hirschegg Int. Workshop, January 2015 Unfolding the missing-energy spectrum with the experimental response function

21. Recent measurements with the FRS Unfolding the missing-energy with the experimental response function José Benlliure 63 Cu( 112 Sn, 112 Sb)X Hirschegg Int. Workshop, January 2015 Final resolution after deconvolution  E ~ 15 MeV ( 124 Sn, 112 Sn @ 1000 A MeV)

22. Excitation of nucleon resonances  (1230)   (1440) ?? 63 Cu( 112 Sn, 112 Sb)X José Benlliure Recent measurements with the FRS Hirschegg Int. Workshop, January 2015 The unfolded data show clear structures in the inelastic component The second substructure is tentatively identified as the Roper resonance p ,  ’)X  @ 4.2 GeV H.P. Morsch et al., PRL 69, 1336 (1992)   (1440)

23. Recent measurements with the FRS Unfolding the missing-energy with the experimental response function José Benlliure Hirschegg Int. Workshop, January 2015

24. Isobar charge-exchange reactions at relativistic energies p( 112 Sn, 112 Sb)X 12 C( 112 Sn, 112 Sb)X 1000 A MeV 700 A MeV 400 A MeV 12 C( 112 Sn, 112 Sb)X José Benlliure Recent measurements with the FRS Hirschegg Int. Workshop, January 2015 The excitation probability of the resonances scales with energy as expected A downward shift in the energy of the resonances is also observed with composite targets

25. Recent measurements with the FRS Missing-energy spectra with secondary beams José Benlliure 112 Sn 110 Sn 110 Sb Main difficulties: - Low statistics - Thick S2 target (1 g/cm 2 C) - Important background at S2 12 C( 110 Sn, 110 Sb)X Hirschegg Int. Workshop, January 2015 110 Sn

26. José Benlliure Recent measurements with the FRS: conclusions Hirschegg Int. Workshop, January 2015 The feasibility of experiments aiming to investigate the in-medium excitation of nucleon resonances using isobar charge-exchange reactions has been proven. The measured missing-energy spectra show a clear separation between the quasi-elastic and resonant charge-exchange channels. The evolution of the missing-energy spectra with the target is in qualitative agreement with previous measurements at Saturne. The resolution has been improved with respect to previous experiments by using thin targets and unfolding the measured spectra from the response function of the spectrometer. The improved resolution allows us to observe substructures in the inelastic charge- exchange peak. The largest component in the inelastic peak is associated to the excitation of the  resonance while the second substructure is tentatively associated to the Roper resonance. Heavier resonances may also be present in the spectra. Measurements from secondary beams suffered from low statistics and the straggling induced by the use of thick targets

27. Differential cross sections: José Benlliure Model calculations Isaac Vidaña, U. Coimbra Hirschegg Int. Workshop, January 2015 Elemental processes: R= ,N*

28. José Benlliure Model calculations Quasi-elastic channel Hirschegg Int. Workshop, January 2015 Elemental processes: Isaac Vidaña, U. Coimbra Scattering amplitudes are calculated in the Born approximation one pion exchange short-range correlations

29. José Benlliure Model calculations Elemental processes: Isaac Vidaña, U. Coimbra Inelastic channels Invariant mass of the resonances for target excitations: Invariant mass of the resonances for projectile excitations:  Hirschegg Int. Workshop, January 2015 R= ,N*

30. José Benlliure Model calculations Projectile and target resonance excitations: Isaac Vidaña, U. Coimbra Hirschegg Int. Workshop, January 2015 target excitations projectile excitations

31. José Benlliure Model calculations Benchmarking with elemental processes (pp  pn   ): Isaac Vidaña, U. Coimbra Hirschegg Int. Workshop, January 2015 data: G. Glass et al., PRD 15 (1977) 37

32. José Benlliure Model calculations Effective number of elementary processes in heavy-ion collisions: Isaac Vidaña, U. Coimbra Hirschegg Int. Workshop, January 2015 Overlapping nucleon density: Transmission function: Pion survival probability:

33. José Benlliure Model calculations Effective number of elementary processes in heavy-ion collisions: Isaac Vidaña, U. Coimbra Hirschegg Int. Workshop, January 2015

34. Model calculations José Benlliure 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 and their excitation in the projectile but also in the target nucleus Preliminary calculations Hirschegg Int. Workshop, January 2015

35. José Benlliure Model calculations Hirschegg Int. Workshop, January 2015 Isaac Vidaña, U. Coimbra Preliminary calculations Reactions induced on protons are the more selective to the excitation of the Delta and the Roper. 1000 A MeV 700 A MeV 400 A MeV 12 C( 112 Sn, 112 Sb)X Measurements at different energies can also be used to select the Delta and Roper in carbon

36. José Benlliure Model calculations: conclusions Hirschegg Int. Workshop, January 2015 New model calculations of isobaric charge-exchange reactions are under development. This model describes both the quasi-elastic and resonant channels including for the moment the excitation of the Delta and Roper resonances in target and projectile nuclei. The model describe reasonably well elemental charge-exchange reactions pp  pn  +. The description of nucleus-nucleus charge-exchange reactions requires a realistic description of the proton and neutron densities (transmission function) and of the absorption probability of pions. The combination of both selects a narrow window in impact parameter at the nuclear periphery. The present version of the model provides a qualitative description of the data measured at GSI. These calculations show a complicated mixing of excitations in the target and projectile nuclei. These results suggest that reactions induced on protons and carbon could be used to extract the properties of the resonances excited in these reactions.

37. José Benlliure Next steps Hirschegg Int. Workshop, January 2015 A new experimental proposal at FRS@GSI - improved momentum resolution with the FRS: stripped target, better tracking detectors - exclusive measurements detecting projectile pions in coincidence - the required setup strongly overlap with the one required for hypernuclei studies From T. Saito

38. José Benlliure Next steps Hirschegg Int. Workshop, January 2015 A new experimental proposal at FRS@GSI - improved momentum resolution with the FRS: strip target, better tracking detectors - exclusive measurements detecting pions in coincidence An experimental program at SuperFRS@FAIR - larger acceptance and resolution at the SuperFRS - exclusive measurements detecting projectile and target pions in coincidence - measurements with intense secondary beams: excitation of nucleon resonances in asymmetric nuclear matter

39. Conclusions A high-resolving power magnetic spectrometer has been proven to be an excellent tool to identify nucleonic excitations in heavy-ion isobaric charge-exchange reactions: - several baryon resonances were identified in the projectile remnant missing-energy spectra - cross sections for elastic and inelastic, (p,n) and (n,p) reactions were also measured - in-medium properties of these baryons and the relative abundance of protons and neutrons at the nuclear periphery will be 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

40. Collaborators José Benlliure 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, H. Weick, J. Winfield CEA/DAM : A. Chatillon, J. Taieb U. Coimbra : I. Vidaña U. Giessen : H. Lenske