Solar p-p chain and the 7Be(p,?)8B S-factor

1
Solar p-p chain and the 7Be(p,?)8B S-factor

• K. A. Snover
• for the
• Seattle/Triumf collaboration
• A.R. Junghans, E.C. Mohrmann, K.A. Snover, T.D.
  Steiger, E.G. Adelberger, J.M. Casandjian, H.E.
  Swanson
• Center for Experimental Nuclear Physics and
  Astrophysics
• University of Washington, Seattle
• L.R. Buchmann, S. Park, A.Y. Zyuzin and A. Laird
• TRIUMF, Vancouver B.C.
• Present address Forschungszentrum Rossendorf,
  Dresden

2
The solar pp chain
p p ? 2H e ?e
p e- p ? 2H ?e

• Sun burns hydrogen to helium in its core T 1.5 .
  107 K
• 4p ? 4He 26.7 MeV

99.75
0.25
2H p ? 3He ?
85
15
10-5
3He p ? 4He e ?e
3He 3He ? 4He 2p
3He 4He ? 7Be ?
0.02
15.07
7Be e- ? 7Li ? ?e
7Be p ? 8B ?
7Li p ? ? ?
3
Fractional uncertainties in the SSMBP00

• Bahcall et al. hep-ph/0111150 v4

• Precise experimental determination of S17 needed
  through direct 7Be(p,?)8B measurement

4
Experimental setup at the University of Washington
Terminal Ion Source p, d, a particles up to 20
?A, 6 MeV
Beam rastering by magnet coils
NaI detector
5
Target fabrication at TRIUMF

• 7Li(p,n)7Be, Ep13 MeV
• 1st reduction/evaporation 7BeO?7Be
• 2nd reduction/evaporation
• ?7Be 40-60 atomic purity on 4mm diameter
  post
• 100, 300 mCi

6
7Be scheme

• 7Be decays via EC to 7Li (10 branch to excited
  state)
• Delayed ? emission unique signature for radiative
  p-capture by 7Be

7
Chamber view
8
Highlights

• Large area uniform beam flux small area target
  
• ?precision determination of beam-target
  interactions
• 7Be(?,?)11C narrow resonance profile
• ?precision determination of target energy
  loss profile
• In situ monitoring of 7Be activity
• ?precision determination of Number of 7Be
  atoms sputtering
• Clean cryopumped vacuum system multiple LN2
  cold traps
• ?no carbon built up, as evidenced by
  repeated 7Be(?,?)11C measurements
• Direct measurement of 8B backscattering losses
• ?this potentially important aspect is shown
  to be small in this work
• Measurement of all important sources of
  systematic error

9
Experiments

• Exp. 1 Jan/Feb 2001
• A.R. Junghans et al., PRL88 (2002) 041101
• Exp. 2 Feb 2002
• Limited test measurement,
• Test of solid angle determination
• 1 MeV lt Ep lt 2.8 MeV
• Exp. 3 May-Aug 2002
• Complete measurement with independent
  normalization down to lower Ep 116 keV.

• 100mCi target
• 450mm2 detector
• close geometry
• solid angle from 7Li(d,p) ratio

• 100mCi target
• 450mm2 detector
• very close geometry

• 300mCi target
• 150mm2 450mm2 detector
• far geometry
• solid angle from ?-source

10
Principle of the measurement

• Independent of

• Y?(Ep) Yield of ? particles from 8B decay
• ?(8B) inverse counting cycle efficiency
• ?p integrated beam flux
• N7Be(t) number of target atoms
• ? solid angle of counting detector

11
Beam and target uniformity

• Aperture flux ratios are unity for a homogeneous
  beam flux.
• Yield normalized to integrated beam flux is
  constant, when product of beam and target density
  is uniform.

Exp. 1
12
HPGe efficiency calibration

• Absolute efficiency calibrated in situ, Ge
  detector on lid of chamber.
• 54Mn, 125Sb, 133Ba, 134Cs, 137Cs (0.8, 1?).
  Fit ?2/dof 1.2
• Relative activity with independent 137Cs source
  (0.4, 1?) agrees to better than 1
• ?(478keV) (4.62 0.02) 10-7
• separate tabletop 7Be activity determination
  agrees with in situ measurements with 1.5.

13
Absolute target activity

• Collimated Ge detector
• - in situ 7Be activity monitoring
• ?7 activity loss due to sputtering
• Absolute activity determined to 2

14
Target energy thickness

• Sharp resonance in 7Be(?,?)11C at E?1.376 MeV
• Target profile changed through unrastered beam
  incident on target
• (?,?) profiles determine target thickness
  distribution - used for energy-averaging the
  (p,?) cross section
• Mean alpha energy loss in the target 44 1 keV
• 60 atomic purity of the metallic 7Be target!!!

Exp. 3
15
7Be(p,?)8B spectrum of ? particles
Exp. 3
450mm2,Ep305 keV
450mm2,Ep150 keV
150mm2,Ep305 keV
150mm2,Ep1000 keV

• Noise caused by high ? flux from 7Be target.
• Lower threshold in thin 150 mm2 20? detector vs.
  450 mm2 33? detector
• Cutoff correction reduced to lt 1 below M1
  resonance
• Fitted TRIM MC simulation describes the spectra

16
8B backscatter setup

• Target mounted in a fixed position in beam
• backscattered 8B caught on catcher plates on both
  ends of arm
• Measurement at Ep 724 keV and 1379 keV where ?
  is large
• First experiment to measure this effect

17
8B backscattering correction

• 8B backscatter probability is small in this work
• Be/Mo admixture (solid line) describes the data
  well in TRIM simulations
• Best fit includes a small amount of Carbon

18
Cross section of 7Be(p,?)8B
Exp. 1

• ?(E) fit Descouvemont Baye cluster model
  Breit-Wigner term fors the resonance
• Averaging over the energy loss of the beam in the
  target
• mean proton energy in the target ?
• c.m. resonance parameters
• E0 629.8 0.3 keV
• ?p 35.7 0.6 keV
• ?? 2.62 0.03 ?10-2 eV

19
Astrophysical S17 factor

• Exp.1 S17(0) 22.3 0.7 eV barn
• S17 fit including M1-resonance and the cluster
  model of
• P. Descouvemont and D. Baye (1994)
• Exp. 3 Measurement down to
• S17(0) 22.1 0.6 eV barn

20
Comparison of direct measurements

• Kavanagh, Parker, Filippone renormalized with
  ?(7Li(d,p)) 152 6 mbarn
• Point to point scatter of data strongly reduced
  in this work
• Old Parker, Kavanagh systematically higher

21
Extrapolation to S17(0)

• Most models do not describe well the data up to
  Ecm1200 keV
• Nuclear Structure more complicated at higher
  energies
• Best fit to our data with Descouvemont Baye
  model
• Deduce S17(0) from fit of 12 models to low energy
  data
• Ecmlt 365 keV
• Standard deviation ? 0.6 eV barn for both S(20)
  and S(0)

Exp. 1
Exp. 3
22
S17(0) from direct measurements

• Fits to Filippone and more modern experiments
• Fit range Ecmlt 1200 keV ?2/dof 2.1
• Fit range Ecmlt 425 keV
• ?2/dof 1.2 (P 30).
• Weighted average
• S17(0) 21.4 0.5(exp.)
• 0.6(theo.) eV barn
• (1? error)

23
Coulomb dissociation

• Coulomb breakup allows to investigate the inverse
  reaction to radiative capture (principle of
  detailed balance)
• Breakup reactions with small Q-values
• Kinematic Enhancement of the virtual photon
  spectrum

b lt r208Pb r8B Onset of nuclear interactions
F. Schümann, PhD thesis U Bochum
2002 Nucl-ex/0304011v1
24
S-factor from Coulomb Dissociation

• Measurement of CD cross section as a function of
  relative energy
• MC Simulation of geometric efficiency and
  experimental resolution
• Must know virtual photon spectrum, and multipole
  decomposition of cross section
• Convolution of experimental efficiency with
  theoretical cross section and fit to data to
  obtain inferred 7Be(p,?)8B S-factor
• Systematic Uncertainties
• Size of E2 contribution to breakup and
  interference with E1
• Higher order electromagnetic transitions
• Nuclear absorption and diffraction
• Coulomb reacceleration effects

Iwasa et al., Phys. Rev. Lett. 83 (1999) 2910
Davids et al., Phys. Rev. Lett. 86 (2001) 2750
25
S17(E) from C.D. vs. Direct 7Be(p,?)8B

• Upper panel All CD data normalized to the mean
  S17(0) 19.3?0.7 eV barn
• (from DB fits with Ecmlt 425 keV)
• Comparison of CD data and DB curve
• Slope is systematically different between CD and
  direct experiments!!
• Lower panel
• Direct and CD S(E) agree at high energy,
• CD is lower at low energies.
• Blue points and curve Junghans data, plus DB
  fit.

26
Impact of S17 on solar neutrino physics
Global Fit to all solar neutrino data KAMLAND
Bahcall et al. hep-ph/0212147 v3
Standard Solar Model (Bahcall et al.)
2.67
19
S17 eV barn ?
?SSM 5.05 0.91 x 106/cm2/s new S17 21.4
0.8 eV barn ? ?SSM 5.66 0.82
-1.33
fB,total ?fB,total(1?) Not incl.?S17 fB,total ?fB,total(1?) incl. ?S17
7.1.10-5 4.5.10-1 1.00 0.092 0.892 0.152
1.5.10-4 4.3.10-1 0.88 0.015 0.785 0.114
2
tan
Q
SSM with new S17 favors lower ?m2
(3?)/3
27
Limit on active-sterile admixture
?m2 7.1 x 10-5 (eV)2 1.5 x 10-4
Solar ? plus Kamland Bahcall et
al. hep-ph/0212147 v3
Arrows indicate the 2? limit from SSM with new
S17 (limit has increased as a result of new S17)
28
Conclusions

• New Seattle/Triumf experiment confirms our
  published S17(0) to within 1. Our final value
  
• S17(0) 22.1 0.6(exp) 0.6(theo) eV barn
• Weighted average from all modern direct
  experiments below
• Ecm 425 keV
• S17(0) 21.4 0.5(exp) 0.6(theo) eV barn
  ( 4 overall error)
• Theoretical extrapolation uncertainty needs
  improvement!!!
• S17 inferred from Coulomb dissociation disagrees
  with direct S17 values, both energy dependence
  and absolute values, currently not understood
• S17 is an important parameter for neutrino
  physics oscillation parameters, active/sterile
  admixture, CPT violation
• A.R. Junghans et al., PRL 88 (2002) 041101-1