excitation of nucleon resonances in charge-exchange reactions j. benlliure universidad de santiago...
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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
José Benlliure, ARIS 2014 Tokyo, Japan, June 2014
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
José Benlliure, ARIS 2014 Tokyo, Japan, June 2014
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
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 112Sn
José Benlliure, ARIS 2014 Tokyo, Japan, June 2014
(p,n) (n,p)
Results
Missing-energy spectra in isobar charge-changing reactions induced by 112Sn
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 FRSconstitutes 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
112Sn(63Cu,X)112Sb
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) ?
112Sn(63Cu,X)112Sb(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 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
José Benlliure, ARIS 2014 Tokyo, Japan, June 2014
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
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 (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 …..
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 2013José Benlliure
112Sn
110Sn
110Sb
Main difficulties:
- Low statistics
- Thick S2 target (1 g/cm2 C)
- Important background at S2
110Sn(C,X)110Sb+-
Recent measurements with the FRS
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
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