1

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

2

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.

3

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

4

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

5

Need data to untangle deformation effects from isospin dependences

6

3 Setup and Collaboration

12

3

The new epoch in photon-induced reaction studies:

The coincidence setup

3

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

7

Enhanced sensitivity via coincidence measurements

8

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.

9

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–

20

2

01

1021

Mm

mGt

e

iJnpkkkkJnpf

Kpn

nP

JkkJ nnpp

JJjjK

ccJJJJcc

JnnJppJjj

Jjj

JM pn

0~~0

'"'':''

1'21

†'

†'

''

',,, ''

'0

2211

21

'

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

10

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

11

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.

12

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

13

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

20

14

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

Consequence: shallow nn 1S0 bound state

15

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

16

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

17

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

18

Chiral Expansion of the Nuclear Forces

19

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.

20

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

Electric and Magnetic Polarizabilities of the nucleons

2014 TAC Visit

21

The Status of Nucleon EM Polarizabilities

2014 TAC Visit

22

EFT Extractions – HWG, JAMcG, DRP, GF

PDG - 2013 HWG, JAMcG, DRP, GF, PPNP, 67 (2012) 841-897JAMcG, DRP, HWG, EJP, A 49 (2013) 12

Setup for EM measurements at HIGS

23

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

2014 TAC Visit

24

HIGS Cryogenic Target ( TUNL + GWU Joint Effort)

25

GDH sum rule on the deuteron: 2H(, n)