Few-body studies at HIgS
Sean Stave
Duke University & Triangle Universities Nuclear Laboratory (TUNL)
And Mohammad Ahmed, Henry Weller
Supported in-part by DOE grant DE-FG02-97ER41033
www.tunl.duke.edu
Sept. 1, 2009
www.tunl.duke.edu/higs/
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Bonn, Germany
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Few-body experiments at HIgS
Exploring A=2 and 3
Photodisintegration of the Deuteron & 3He
• Importance
• Theoretical understanding of A=2,3 systems
• Global state of the experiments
• The role HIGS plays in the understanding of these systems
• What is on the horizon for HIGS
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Overview of A=2
The BBN Importance
“Baryometer”
The Deuteron
Ideal Laboratory for
the study of 2-body
NP system
Fundamental
Sum Rules
• Test of EFT and PM
Calculations
d
Beam
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Target
d
3
Understanding Few-Nucleon Systems
2H,
the simplest of Few-Body Systems
The Theoretical Framework, A=2
• Potential Model
• Effective Field Theory
• Sum Rules for Deuteron:
Gerasimov-Drell-Hearn (GDH) &
Forward Spin Polarizability (g0)
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The A=2 Theoretical Framework
Potential Model Calculations [H. Arenhovel, M. Schwamb et al.]
• High precision NN-potentials, MEC, RC and D degrees of freedom
The Pion-less Effective Field Theory Approach (EFT)
[M. Savage, J-W. Chen & G. Rupak]
• E1 is computed up to N4LO and M1 is calculated up to N2LO,
n-p radiative capture cross section predicted to an accuracy of
1% at CM energies ~ 1 MeV
Most accurate theory describing 2-Nucleon system,
Minimal data exist to test the predictions in this energy region
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The Experimental Effort at HIgS
Few-Body Studies at TUNL are carried out at HIgS
Duke Free-Electron Laser Laboratory
(HIgS)
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HIgS g-ray beam generation
High Intensity Gamma-Ray Source:
RF Cavity
Optical Klystron
FEL
Booster Injector
Mirror
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LINAC
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HIgS Parameters
•Circularly and Linearly Polarized
nearly monoenergetic g-Rays
from 2 to 60 MeV
(90 MeV in the next 1 to 2 years)
•Total Gamma-Ray Flux
~ 108 to 109 g/s
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A=2 Experiments at HIgS
•S(135°)
•S(90°)
•s(q); S(q)
•S(90°)
•s(q); S(q)
•s(q); stotal
Eg = 3.58 MeV
Eg = 2.39 to 4.05 MeV
Eg = 4 to 10 MeV
Eg = 2.44 to 4.0 MeV
Eg = 14 and 16 MeV
Eg = 2.44 to 4.0 MeV
Eric Schrieber et al., 2000
Werner Tornow et al., 2003
Brad Sawatsky et al., 2005
Mohammad Ahmed et al., 2007
Matthew Blackston et al., 2007
Mohammad Ahmed et al., 2008
All experiments were performed using linearly polarized beams
Liquid Scintillating
Detectors
Schreiber
Tornow
Sawatsky
Blackston
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Liquid Scintillating
Detectors in
Blowfish Array
Sawatsky
Blackston
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Li-Glass
Detectors in
an Array
Ahmed
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Status of the “baryometer”
• Very little
data in
energy
region for
BBN
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d(g,n)p Cross section Expansion
Polarized beam, unpolarized target
(M1)
(E1)
Photon analyzing power measurement is proportional to
the %E1 contribution to the total cross section
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A=2 Results at HIgS
Tornow et al.
[PLB 574, 8 (2003)]
Excellent agreement between
data and PM and EFT
4-neutron detectors at a
polar angle of 90 degrees and
azimuthal angles of
0,90,180, and 270 degrees
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PRC 61, 061604 (2000)
Curves from EFT (Rupak et al.)
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d(g,n)p at HIgS: Ahmed et al.
4.0 MeV
3.5 MeV
No significant
d-wave
contributions
are present
at these low
energies
2.44 MeV
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Sum Rules for the Deuteron
Spin-flip part of forward Compton scattering amplitude:
GDH :
Arenhoevel et al.
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GDH on the deuteron: Theory
With
relativistic
corrections
Without
relativistic
corrections
Negative at
low energies
Crosses zero
at low energies
Arenhoevel et al.
[NPA 631, 612c (1998)]
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Cross section difference expansion
Polarized beam, polarized target
]
If ignore d-waves and splitting of p-waves
at low energies then
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A=2 Global Impact
Remember Ds =-3s(M1)
First-ever
indirect
determination
of the GDH Sum
Rule
for Deuteron at
low energies:
-603 ± 43 mb
(Fit from thr. to
4 MeV,
integrated from
thr. to 6 MeV)
Ahmed et al. [PRC 77, 044005 (2008)]
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A=2 GDH Comparison: Data and Theory
• Theory and Data integrated from
threshold to 6 MeV
• Data:
• Arenhoevel:
• -3sM1:
-603 ± 43 mb
-627 mb
-662 mb
• Experimentally confirmed
negative value at low energy
Ahmed et al. [PRC 77, 044005 (2008)]
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A=2 Results at HIgS
Blowfish
• 88-cell Liquid Scintillating
detector array
• 25% of 4p coverage
• q = 22.5 to 157.5 degrees
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d(g,n)p: Weller/Blackston’s Results
Blackston et al. [PRC 78, 034003 (2008)]
16 MeV
•Cross section and analyzing power at 16 MeV as a function of
angle compared with Schwamb/Arenhoevel potential model
•High quality of data allowed a fit using 7 reduced transition
matrix element amplitudes (phases fixed by np elastic
scattering, SAID)
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d(g,n)p: Weller/Blackston’s Results
16 MeV
Note: d-wave
results negligible
and consistent with
theory
Value if no
p-wave splitting
First-ever
observation of the
splittings of the
E1 (p-wave)
amplitudes in low
energy
deuteron photodisintegration
[PRC 78, 034003
(2008)]
Compared with Schwamb/Arenhoevel Potential Model
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A=2 Global Impact
First-ever observation of the p-wave splittings and
confirmation of the relativistic corrections in the theory
[PRC 78, 034003 (2008)]
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Sum Rules for the Deuteron
Spin-flip part of forward Compton scattering amplitude:
Forward Spin-Polarizability:
NLO, EFT calculation by X. Ji et al.
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A=2 g0 Comparison: Data and Theory
First-ever indirect determination of g0
for deuteron at low energies
Data integrated from threshold to 6
MeV
• Data:
3.75 ± 0.18 fm4
• Ji-LO:
3.762 fm4
• Ji-NLO:
4.262 fm4
• Arenhoevel:
4.1 fm4
Ahmed et al. [PRC 77, 044005 (2008)]
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What is our understanding of Few-Nucleon systems?
3He,
the simplest of Few-body Systems with
3NF and no excitation spectrum
System being considered
•3He breakup
•Two-body
•Three-body
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The A=3 Experiments at HIgS
• Photodisintegration of 3He between 7 and 20 MeV
• Total and differential Cross Section
• Total cross section for the 2-body breakup from 7 to 20 MeV,
Tornow et al.
• Total and differential cross sections for the 3-body breakup,
12.8, 13.5, and 14.7 MeV, Perdue et al.
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The A=3 Theoretical Framework
Recent efforts in understanding 3-body systems
[Deltuva, Fonseca, Sauer]
• Coulomb Interaction in the 2- and 3-body
photodisintegration channels
• CD-Bonn + D, with D isobar mediating an effective 3NF and
2-, 3-nucleon currents, and still consistent with 2NF
• Still has issues at low-energies
(3 Nucleon Analyzing Power Puzzle still stands!)
The problem is also being worked upon by
[Witala, Glockle, Nogga, and Golak, et al.]
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Current Status of the 3He breakup cross section
2-body
3-body
total
Factor of 3
below theory
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Shima & Nagai
[PRC 73, 034003 (2006)]
Compared with previous data
and AV18 and AV18+Urbana IX
• No measurement that is
consistent across the
energy range
• Clearly calls for a set of
measurements with the
same experimental
conditions across the
energy range
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A=3 at HIgS: 2-body breakup of 3He, Tornow et al.
• High Pressure 3He/Xe cell
Data are still under analysis for absolute normalization
Two-body peaks clearly separated
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3He
3-body Breakup at HIgS: Weller, Perdue et al.
12.8, 13.5, and 14.7 MeV
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3He
3-body Breakup: Theoretical Framework
No coulomb
interaction
With coulomb
interaction
No sensitivity to
coulomb interaction
in the analyzing
power
Deltuva et al.
[PRC 72, 054004 (2005)]
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Weller, Perdue et al. Initial Results
From an APS talk by B. Perdue
- HIgS Data
- Deltuva
- 3-body phase space
•Phase-Space (PS) to
PS + NP transition near
12.8 MeV
•About 25% below theory
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Summary
What have we accomplished?
• Confirmation of PM/EFT for the deuteron near BBN region
•First determination of the splitting of the p-waves in the
photodisintegration of the deuteron
• First confirmation of GDH sum rule for the deuteron
•Confirmed large negative strength
•Confirmed positive going above 8 MeV and that it arises from
the splitting of the p-waves
• First determination of the g0 sum rule for deuteron
•Precision 3-body photodisintegration cross section for 3He
disagree with state-of-the-art theory at low energies
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Future plans at HIgS
New era of precision measurements at HIgS PAC-09 has approved the following
experiments for the next two years:
• Continue to measure deuteron photodisintegration cross section
at lower energies (below 2.4 MeV) (Using OTPC)
• Direct measurements of the GDH on deuteron
• Compton scattering on the deuteron
• Measurement of two- and three-body cross sections of g + 3He
• GDH Sum rule for 3He
• Cross section measurement of g + 4He
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Acknowledgments
•Calvin Howell et al.
•Werner Tornow et al.
•Henry Weller et al.
•Ying Wu et al.
Thank you!
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• Additional slides
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Weller, Perdue et al. Initial Results
• Results from Gorbunov (1976) coarsely
binned but consistent with current results
8-12 MeV
12-16 MeV
A. N. Gorbunov, Proc. Of the P.N. Lebedev Phys. Inst., p. 1 (1976)
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A=2 Introduction
Few-Nucleon Systems and BBN Network
(d,p)
(p,γ)
(d,n)
(n,γ)
Light-element abundances depends
on
WMAP determines
(d,p)
and 11 nuclear reaction rates
n-p capture reaction rate becomes a “baryometer”
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Understanding the photodisintegration of the deuteron
In 1936, H. A. Bethe and R. F. Bacher wrote …
“… the transition from the ground state to the state of positive energy . . .
can be produced by a magnetic moment, this ‘magnetic dipole’ photoelectric
effect is, however, small compared to the ‘electric dipole’ effect …, except for
very low energies . . . the final state must be a P-state”
[ Rev. Mod. Phys. 8, 82-229 (1936) ]
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The A=2 Experiments at HIgS
In the near-threshold region, the photodisintegration
cross section can be expanded in terms of S and P wave
amplitudes. We can ignore the D-waves and
The P-wave splittings (evidence will be presented soon) :
Bethe, 1936
Photon analyzing power measurement is proportional to
the %E1 contribution to the total cross section
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A=2 Global Impact (Ahmed et al.)
•First-ever
indirect
determination of
g0 for deuteron
at low energies
Ahmed et al. [PRC 77, 044005 (2008)]
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