In-medium excitation of nucleon resonances using heavy-ion charge exchange reactions J. Benlliure...
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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.
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
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.
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
C. Bachelier et al. PLB 172 (1986) 23
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
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) 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
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
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
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
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.
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
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
José Benlliure Hirschegg Int. Workshop, January 2015
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
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.
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
José Benlliure Hirschegg Int. Workshop, January 2015
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
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
José Benlliure Hirschegg Int. Workshop, January 2015
12C(112Sn,112Sb)X 12C(112Sn,112In)X
112Sn49+
Recent measurements with the FRS
Missing-energy spectra in isobar charge-changing reactions induced by 112Sn
José Benlliure Hirschegg Int. Workshop, January 2015
(p,n) (n,p)
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) (p,n) (n,p)(n,p)
Recent measurements with the FRS
Comparison with the Saturne data
José Benlliure
(124Sn,124Sb)
Hirschegg Int. Workshop, January 2015
(n,p)(n,p)(n,p)
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 FRSconstitutes our response function H
Hirschegg Int. Workshop, January 2015
Recent measurements with the FRS
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
Hirschegg Int. Workshop, January 2015
Unfolding the missing-energy spectrum with the experimental response function
Recent measurements with the FRS
Unfolding the missing-energy with the experimental response function
José Benlliure
63Cu(112Sn,112Sb)X
Hirschegg Int. Workshop, January 2015
Final resolution after deconvolution E ~ 15 MeV (124Sn, 112Sn @ 1000 A MeV)
Excitation of nucleon resonances
(1230)
(1440)
?
63Cu(112Sn,112Sb)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)
Recent measurements with the FRS
Unfolding the missing-energy with the experimental response function
José Benlliure Hirschegg Int. Workshop, January 2015
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
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
Recent measurements with the FRS
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
Hirschegg Int. Workshop, January 2015
110Sn
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
Differential cross sections:
José Benlliure
Model calculations
Isaac Vidaña, U. Coimbra
Hirschegg Int. Workshop, January 2015
Elemental processes:
R=,N*
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
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*
José Benlliure
Model calculations
Projectile and target resonance excitations: Isaac Vidaña, U. Coimbra
Hirschegg Int. Workshop, January 2015
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
Hirschegg Int. Workshop, January 2015
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
Hirschegg Int. Workshop, January 2015
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
José Benlliure
Model calculations
Hirschegg Int. Workshop, January 2015
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
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 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
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
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
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