In-medium excitation of nucleon resonances using heavy-ion charge exchange reactions J. Benlliure University of Santiago de Compostela, Spain International.

In-medium excitation of nucleon resonancesusing heavy-ion charge exchange reactions

J. BenlliureUniversity of Santiago de Compostela, Spain

International Workshop XLIII on Gross Properties of Nuclei and Nuclear Excitations

Hirschegg, Kleinwalsertal, Austria, January 11 - 17, 2015

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

27A(20Ne,20Na) @ 900 MeV/u

Energy(MeV)

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

C. Bachelier et al. PLB 172 (1986) 23

Hirschegg Int. Workshop, January 2015

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.


Role of nucleon excitations in compact and massive neutron stars.

Renewed interest in the in-medium properties of the -resonance

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


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.

Isobar charge-exchange reactions

Isobar charge-exchange reactions investigated in inverse kinematics allow for the direct observationof in-medium excitation of the Delta resonance for both (p,n) and (n,p) channels.

n p

+

p n

n p

o

p p

-

o

pn

np

p,n +,-

N

N

N

20F

20Ne

20Na

The momentum recoil induced by the pionemission proves the excitation of the resonance.

José Benlliure Hirschegg Int. Workshop, January 2015


In the inelastic charge-exchange process the pion mustscape in order to preserve the isobar character of the reaction.

Isobar charge-exchange reactions at Saturne


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) 207Lampf: D.A Lind, Can. J. Phys. 65 (1987) 637Dubna: V.G. Ableev et al., Jetp. Lett. 40 (1984) 763

Isobar charge-exchange reactions at Saturne


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

3He d t N

THe = 2 GeVDetailed 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

Direct observation of the Roper resonance at Saturne


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



Direct observation of the Roper resonance in the missing energy spectra in (’) reactions on a proton target.



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

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(208Pb,208Bi)

---- d(208Pb,208Bi)

208Pb(1000 MeV/u)+p,d


Isobar charge-exchange reactions at FRS@GSI

A new exploratory experiment at FRS@GSI

Sn106

Sn107

Sn108

Sn109

Sn110

In115

Sn125

Sn124

Sn123

Sn122

Sn121

Sn120

Sn119

Sn118

Sn117

Sn116

Sn115

Sn114

Sn113

Sn112

Sn111

Sb123

Sb123

Sb123

Te126

Te125

Te124

Te123

Te122

Te121

Te120

124Sn+CH2,C 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


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.

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

132In

132Sn

132SbObservables:

cross sections for both charge exchange reactions and channels

missing-energy spectra

mean energy and width of the-resonance


Experimental setup

-resonance and quasi-elastic charge-exchange reactions identified at the FRS:(standar detection setup)


primary target

secondary target

Z/Z ~ 7 10-3

A/A ~ 2.4 10-3

4102

BB

E ~ 30 MeV (124Sn, 112Sn @ 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

Recent measurements with the FRS

Isotopic identification of isobaric charge-exchange residues


12C(112Sn,112Sb)X 12C(112Sn,112In)X

112Sn49+


Missing-energy spectra in isobar charge-changing reactions induced by 112Sn


(p,n) (n,p)


Comparison with the Saturne data

José Benlliure



(p,n) (p,n) (n,p)(n,p)


Comparison with the Saturne data

José Benlliure

(124Sn,124Sb)


(n,p)(n,p)(n,p)


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 FRSconstitutes our response function H



José Benlliure

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


Unfolding the missing-energy spectrum with the experimental response function


Unfolding the missing-energy with the experimental response function

José Benlliure

63Cu(112Sn,112Sb)X


Final resolution after deconvolution E ~ 15 MeV (124Sn, 112Sn @ 1000 A MeV)

Excitation of nucleon resonances

(1230)

(1440)

?

63Cu(112Sn,112Sb)X

José Benlliure



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)


Unfolding the missing-energy with the experimental response function


Isobar charge-exchange reactions at relativistic energies

p(112Sn,112Sb)X12C(112Sn,112Sb)X

1000 A MeV

700 A MeV

400 A MeV

12C(112Sn,112Sb)X

José Benlliure



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


Missing-energy spectra with secondary beams

José Benlliure

112Sn

110Sn

110Sb

Main difficulties:

- Low statistics

- Thick S2 target (1 g/cm2 C)

- Important background at S2

12C(110Sn,110Sb)X


110Sn

José Benlliure

Recent measurements with the FRS: conclusions


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

Differential cross sections:

José Benlliure

Model calculations

Isaac Vidaña, U. Coimbra


Elemental processes:

R=,N*

José Benlliure

Model calculations

Quasi-elastic channel


Elemental processes: Isaac Vidaña, U. Coimbra

Scattering amplitudes are calculated in the Born approximation

one pion exchange short-range correlations

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:


R=,N*

José Benlliure

Model calculations

Projectile and target resonance excitations: Isaac Vidaña, U. Coimbra


target excitations projectile excitations

José Benlliure

Model calculations

Benchmarking with elemental processes (pppn): Isaac Vidaña, U. Coimbra

Hirschegg Int. Workshop, January 2015data: G. Glass et al., PRD 15 (1977) 37

José Benlliure

Model calculations

Effective number of elementary processes in heavy-ion collisions: Isaac Vidaña, U. Coimbra


Overlapping nucleon density:

Transmission function:

Pion survival probability:

José Benlliure

Model calculations

Effective number of elementary processes in heavy-ion collisions: Isaac Vidaña, U. Coimbra


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


José Benlliure

Model calculations


Isaac Vidaña, U. CoimbraPreliminary 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

12C(112Sn,112Sb)X

Measurements at different energies can also be used to select the Delta and Roper in carbon

José Benlliure

Model calculations: conclusions


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 pppn+.

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.

José Benlliure

Next steps


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

José Benlliure

Next steps


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

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

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

In-medium excitation of nucleon resonances using heavy-ion charge exchange reactions J. Benlliure University of Santiago de Compostela, Spain International.

Documents

n reactions

inelastic chargeexchange

nucleon resonances excitations

role of nucleon excitations

spin quadrupole

spaininternational workshop

d resonance

inelastic n