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

Excitation of nucleon resonances in

charge-exchange reactions

J. Benlliure

Universidad de Santiago de CompostelaSpain

Motivation

Tokyo, Japan, June 2014José 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) .

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

Motivation

Tokyo, Japan, June 2014José 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

p p

-

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) 64608

---- p(208Pb,208Bi)

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

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

n p

+

p n

n p

o

p p

-

o

pn

np

p,n +,-

N

N

N

124In

124Sn

124Sb

The momentum recoil induced by the pionemission 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)

124In

124Sn

124Sb

Observables:

cross sections for both charge-exchange reactions and channels

missing-energy spectra of the projectile residues


GSI

Inverse kinematics

4102

BB

E ~ 25 MeV (124Sn @ 1000 MeV/u)

Z/Z ~ 7 10-3

A/A ~ 2.4 10-3

The experiment


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

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

The experiment


Results

Isotopic identification of isobaric charge-exchange residues


Results

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


(p,n) (n,p)

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)

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 FRSconstitutes our response function H


J. Vargas, J.B. and M. Caamaño NIMA 707 (2013) 16

Results

Unfolding the missing-energy with the experimental response function

112Sn(63Cu,X)112Sb


The unfolding procedure improves the resolution of the final spectra

Excitation of nucleon resonances

(1232)

(1440)

(1600) ?

112Sn(63Cu,X)112Sb(p,X)’@ 4.2 GeV

H.P. Morsch et al., PRL 69, 1336 (1992)

Results


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


Energy and target dependence of the resonance excitation

In nucleus-nucleus collisions -resonance excitationmay occurs below the pion production threshold:

- Fermi momentum of the nucleons

1000 A MeV

700 A MeV

400 A MeV

112Sn(C,X)112Sb+-

112Sn(12C,12B)112Sb

Results


112Sn(p,n)112Sb+-

112Sn(C,B)112Sb++

In nucleus-nucleus collisions -resonance excitationoccurs below the pion production threshold:-Fermi momentum of the nucleons-Lower energy of the -resonance

1000 A MeV

700 A MeV

400 A MeV

112Sn(C,C)112Sb+-

112Sn(12C,12B)112Sb

Results

Energy and target dependence of the resonance excitation


Results

Charge-exchange cross sections


Both cross sections are sensitive to the neutron excess at projectile periphery (n,p) > (p,n) and the projectile size (124Sb) > (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

Differential cross sections:

Model calculations

Scattering amplitudes:

Vertices:

Isaac Vidaña, U. Coimbra

+ target excitations …..


Free NN cross sections:

Model calculations


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


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


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


Missing-energy spectra with secondary beams

SuperFRS collaboration meeting, October 2013José Benlliure

112Sn

110Sn

110Sb

Main difficulties:

- Low statistics

- Thick S2 target (1 g/cm2 C)

- Important background at S2

110Sn(C,X)110Sb+-


Unfolding and regularization of the missing-energy spectrum

SuperFRS collaboration meeting, October 2013José Benlliure

136I

+

(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.

132In

132Sn

132Sb

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 2014José Benlliure

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

Documents

oo p n n p p

d np p n n p oo p p

n reactions

inelastic n

pb1000 mevu p

oo slide

experiment jos benlliure

motivation tokyo