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Many-body Nuclear Structure, Few-Nucleon Systems and Hadron Structure: next 5 yearsTUNL Faculty:•M.W. Ahmed, H. Karwowski and H.R. Weller; and
•C.R. Howell, W. Tornow and A. Young
Research Objectives (5-year program):1. Many-body nuclear structure•Studies of collective excitations at HIGS using nuclear resonance fluorescence•Fission studies with neutrons (tandem lab) and -rays at HIGS•Nuclear reactions important for astrophysics , e.g., (, n) at HIGS•(3He, n) cross-section measurements to check wavefunctions used in QRPA calcs. of 0 decay in the tandem lab
2. Advance descriptions of low-energy few-nuclear phenomena in terms of QCD using either models with effective degrees of freedom or Lattice calculations, •few-nucleon measurements with neutron beams in the tandem lab •few-nucleon measurements with -ray beams at HIS•Double polarized photodisintegration of the deuteron•Nucleon polarizabilities with polarized beam Compton scattering at HIGS: Independent measurements of electric and magnetic polarizabilities of proton and neutronSpin polarizabilities of the proton and neutron
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Nuclear Resonance Fluorescence (NRF) Studies at HIS
a) Understanding the Pygmy Dipole Resonance Numerous nuclei investigated.
b) Supporting 0NME Calculations Dipole response of nuclei in the A=40 -150 mass range: If models can’t describe the measured dipole response correctly, you can’t trust their 0 NME predictions. Done 76Ge, 76Se, 136Xe, 136Ba, 130Te and propose to continue in the future: 130Xe is missing, for example.
c) Extending the reach of NRF studies by - coincidences: setup Just starting.
d) Extending the science reach by -n coincidences: 2-n setup Proposing for future.
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Study of Nuclear Dipole Response to Electromagnetic Radiation
Sn
P, n
p n
() (,Xn)
• Giant Dipole Resonance: Ex ~ 10 - 20 MeV, B(E1) ~ 5 - 10 W.u.
• Orbital “Scissors” mode: Ex ~ 3 MeV, B(M1) ~ 3 N2
• Two Phonon Excitation: Ex ~ 4 MeV, B(E1) ~ 10-3 W.u.
• Pygmy Dipole Resonance
M1 E1
p,n n
Xλ ? E1
Ex
Cro
ss S
ectio
n
10 2051
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Example of a Pygmy Resonance Study
E1 strength concentration at 5 – 7 MeV
Fragmented strength
Strength seems to scale with N/Z Collective effect
Nuclear Resonance Fluorescence
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Need data to untangle deformation effects from isospin dependences
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3 Setup and Collaboration
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The new epoch in photon-induced reaction studies:
The coincidence setup
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4 HPGe 60%: very high energy resolution (8 keV) @ 5 MeV, low efficiency4 LaBr 3”x 3” : good energy resolution (80 keV) @ 5 MeV, ~5 times higher efficiency than HPGe
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Enhanced sensitivity via coincidence measurements
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Nuclear Astrophysics Studies at HIS: (,n) Reactions
a) Did (,n) measurement [86Kr(,n)85Kr] to investigate the branching point nucleus 85Kr , s-process nucleosynthesis, continue in future: 87Rb(,n)86Rb to study the branching point nucleus 86Rb.
b) Did (,n) measurement on 26Mg to obtain level information relevant to 22Ne(,n)25Mg neutron source reaction.
c) In the future concentrate on neutron energy measurements (via TOF) rather than only on neutron detection without any energy info. d) Do ’-n coincidence measurements in A(,’n)B reactions using instead of the 3 setup the 2n setup by replacing some of the -ray detectors by neutron detectors.
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Search for 0 decay
udd
uu
u
u ud
d
d
d
W– W–
e–e–
p p
n n A-2d
uu
d
W– W–
e–e–
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1021
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mGt
e
iJnpkkkkJnpf
Kpn
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pnQRPA calculations
J. Suhonen and O. Civitarese, Nucl. Phys. A 847 (2010) 207.
npQRPA calculations can accommodate large model space but are based on simplifying assumptions about the structure of the ground-state of the initial and final nuclei. They assume that the nucleons are arranged in the ground states are in configurations consistent with the BCS approximation.
From April 2014 NSAC report on 0b
(Operate with pair of creation and annihilation operators)
<m> = 17.5 meV
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Concerns about BCS approximation
Relevant Orbits for 0 decay:A = 76, 82
Not included in npQRPA calc., but could exist in nature.
S.J. Freeman and J.P. Shiffer, J. Phys. G: Nucl. Part. Phys. 39, 124004 (2012).
Examples ofExcitations due to pair vibrations
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Cross-section measurements for two-proton drop off reaction on nuclei used in 0 searches
Faculty: A.E. Champagne, C.R. Howell, W. Tornow and A. Young
Thesis Students: Dustin Combs and David Ticehurst
Facility: tandem lab
Objective:Measure cross sections for the(3He, n) reaction for particle transfers to the 0+ ground state and 0+ excited states of the residual nucleus. The ratio of the relative strengths for leaving the residual nucleus in an excited 0+ state relative to that for leaving the nucleus in the ground state provides a test of assumptions about the wavefunctions used in QRPA calculations of the nuclear matrix elements for 0.
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Setup for (3He, n) cross-section measurements
Top view of experimental setup
13-m flight pathfor n tof measurements
Liquid scintillators
Beam defining apertures lined with lead
Status:•Development of a-particle beam pulsing system completed
•Test runs with pulsed 4He beam using (, n) reactions demonstrate that signal-to-background ratio is adequate to proceed with (3He, n) measurements
•Installation of 3He gas recirculation/recovery system on the helium ion source is underway
12C(, n)15Ogs
16O(, n)19Negs
12C(, n)15Oex
E = 20 MeVfp = 3 m
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Planned Cross-section Measurements
Reaction
Target
Nuclei Q (MeV)
Energy (MeV)
(3He, n) 74Ge, 76Ge
74Se, 76Se126Te, 128Te, 130Te132Xe, 134Xe, 136Xe
+8.7, +10.7
+3.7, +5.8
+6.7, +7.7, +8.8
+6.5, +7.6, +8.7
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From 2007 Nuclear Science LRP
Studies of Few-nucleon systems and Hadron Structure
Over arching goal:Develop theoretically consistent descriptions of strongly interacting matter from quark-gluon dof to collective motion phenomena
PQCD
Hybrids (quarks and gluonic combinations)Lattice QCD
Effective Field Theories (EFTs)Meson-exchange interactionsab initio 3N and 4N calculations
Quantum Monte Carlo techniquesQuasi-particle Random Phase ApproximationConfiguration Models (e.g., Shell Model)Density Functional Theory
Region where TUNL groups contribute
Few-nucleon Many-body
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Consequence: shallow nn 1S0 bound state
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A. Siepe et al., Phys. Rev. C 65, 034010 (2002). Calculations: CD-Bonn NN potential
X.C. Ruan et al., Phys. Rev. C 75, 057001 (2007). Calculations: CD-Bonn NN potential
Discrepancy with nn QFS in nd breakupfrom: H. Witała and W. Glöckle, Phys. Rev. C 83, 034004 (2011)
Ep=0
Univ. Bonn, En=26 MeV
CIAE, En=25 MeV
CD Bonn pot.ann = -18.8 fm
CD Bonn pot.reff = 2.79 fm
= 1.18
= 1.18
Witała: Must increase thenn 1S0 strength to fit data
Two-pronged approach
Remeasure nn-QFS
Search for di-neutron bound statevia + 3H -> n + n +p
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R&D for nn QFS measurement in nd breakup
Experiment setup
Locus for nd breakup
CD2
n1 n2
Signal-to-background ratioacceptable will move on to firstPhase of measurements
Faculty: C.R. Howell and W. Tornow
Thesis Student: Ron MaloneFacility: Tandem Lab
Neutron source:2H(d, n)
nd elastic
12Cel
12Cinel
absolute luminosity determined in situ via nd elastic scattering
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2.5.1 Photodisintegration of the triton
Experimental Setup
Status:•Tritium gas target design underway•Detector R&D underway (silicon strip detectors and wire chambers)
Faculty: M.W. Ahmed, C.R. Howell and W. Tornow
Thesis Students: Forrest Friesen and Zhonglin HanFacility: HISnn FSI
~210 Ci of tritium gas in 7 cells
80 cm
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Chiral Expansion of the Nuclear Forces
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Neutron-Deuteron Ay()
AV18, CD BonnNijm1, Nijm2
AV18, CD BonnNijm1, Nijm2 & TM99 3NF
Tornow et al.1983
NLO 2NF
N2LO 2NF
N3LO 2NF
Chiral NN potentialof Epelbaum et al.
N3LO 2NF
N3LO 2NF & N2LO 3NF
N3LO 2NF
N3LO 2NF & N3LO 3NF contact terms and 2 exchange
N3LO 2NF & N3LO 3NFplus (2 - 1exchange
N3LO 2NF & N3LO 3NFplus ring
Calculations : H. Witała et al.
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4N Systems
Esterline et al.
TUNL
p-3He Ay(), T=1 n-3He Ay(), T=0,1
Proposal: Obtain n-3H Ay() data (T=1) at En=2.26 MeV and En=5.54 MeV to check on isospin dependence (p-3H is also T=0,1).
Ec.m.-EB3N
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Electric and Magnetic Polarizabilities of the nucleons
2014 TAC Visit
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The Status of Nucleon EM Polarizabilities
2014 TAC Visit
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EFT Extractions – HWG, JAMcG, DRP, GF
PDG - 2013 HWG, JAMcG, DRP, GF, PPNP, 67 (2012) 841-897JAMcG, DRP, HWG, EJP, A 49 (2013) 12
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Setup for EM measurements at HIGS
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The HINDA Array
Cryo-CoolerCooling Power: 1.5 W @ 4.2 KBase T = 3.5 KL = 20 cm, V = 0.24 Lit D/H/cm2 = 1024
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2014 TAC Visit
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HIGS Cryogenic Target ( TUNL + GWU Joint Effort)
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GDH sum rule on the deuteron: 2H(, n)