Structure of 8 B through 7 Be+p scattering 1 Jake Livesay, 2 DW Bardayan, 2 JC Blackmon, 3 KY Chae, 4 AE Champagne, 5 C Deibel, 4 RP Fitzgerald, 1 U Greife, 6 KL Jones, 6 MS Johnson, 7 RL Kozub, 3 Z Ma, 7 CD Nesaraja, 6 SD Pain, 1 F Sarazin, 7 JF Shriner Jr., 4 DW Stracener, 2 MS Smith, 6 JS Thomas, 4 DW Visser, 5 C Wrede ORNL Workshop 1 Colorado School of Mines 2 Oak Ridge National Laboratory 3 University of Tennessee at Knoxville 4 University of North Carolina 5 Yale University 6 Rutgers University 7 Tennessee Tech University 10/5/2015

Outline of Talk Motivation Previous Measurements Making 7 Be (TUNL) Experimental Setup (HRIBF) Normalization Preliminary Results Future Work

Predicted Positive Parity States Positive Parity States come from coupling of proton and neutron in p shells 3/ /2 - → 0 +,1 +,2 +,3 + There are other predicted levels which have yet to be observed

Basic shell Model Prediction 7 Be ground state is 3/2 - due to the unpaired 3/2 - neutron – a very proton rich nucleus protonneutron s 1/2 p 3/2 p 1/2 7 Be+ (l=0) p 3/2 proton is an elastic scattering reaction with expected positive parity states: 0 +,1 +,2 +,3 + 7 Be+ (l=1) p 1/2 proton is an inelastic scattering reaction with expected positive parity states: 0 +,1 +,2 +

7 Be(p,  ) 8 B extrapolation Uncertainty in shape of d  /d  and 7 Be(p,  ) extrapolation to solar energies dominated by s-wave scattering lengths P. Descouvemont, PRC 70 (2004) 7 Be+p: a 01 = 25  9 fm, a 02 = -7  3 fm 7 Li+n: a 01 = 0.87  0.07 fm, a 02 =  0.05 fm Junghans et al. (2003) C. Angulo et al., NPA 716 (2003) 7 Be(p,p) 7 Be CRC-Louvain-le-Neuve ~ 5% uncertainty in S 17 (0)

Previous Measurements of 7 Be(p,p) 2 - at 3.5 MeV Rogachev et al, PRC 2002 Agrees with literature value for 3 + Doesn’t locate other positive parity states in region Two measurements nearly overlap in energy 3 + at 2.32 MeV 1 + at 1.3 MeV – ruled out

Li metal 12 MeV protons ~ 10 mA 7 Li(p,n) 7 Be 7 Be beam production 0.2 Ci 0.12 Ci 2* Be/s

Thick Target 14 MeV beam of 7 Be 4.3 mg/cm 2 CH 2 7Be(p,p)7Be Setup 7 Be Thin Target 17 bombarding energies 100  g/cm 2 CH 2 target E cm = 0.4 to 3.3 MeV θ 1cm =80-128, θ 2cm = , θ total = Normalization to 7 Be+Au scattering and to 7 Be+ 12 C 7 Be and protons

Silicon Detector Array 16 Strips per detector 40 keV energy resolution 128 channels of electronics keV keV

 cm (degrees) d  /d  (mb/sr) 12 C( 7 Be, 7 Be) 12 C E cm = 2.5 MeV Rutherford Livesay et al. DWUCK5 Livesay et al E (MeV) SIDAR strip 7 Be+Au & 7 Be+ 12 C Scattering (d  /d  Rutherford  lab (degrees) 12 C( 7 Be, 7 Be) 12 C E cm = 9.5 MeV 7 Be+p beam current determined by fitting 7 Be + 12 C cross section

Spectra without Inelastic Peak (7 MeV) Protons elastically scattered from 7Be 7Be scattered from 12C 7Be+12C 7Be+p

Spectra with Inelastic Scattering Elastic 7Be+p Inelastic 7Be+p α Elastic 7Be+12C Some background is due to knocked-out C from the target

Thick Target Method 7 Be p E p = E beam –ΔE beam -ΔE p 7 Be p’ E p’ = E beam –ΔE beam’ -ΔE p’ -E excited state ΔE beam’ - ΔE p’ - E exc = ΔE beam - ΔE p Many positions in target can produce equal elastic and inelastic energies Energy loss in thin target is much less than excited state energy

E cm (keV) Thick-target excitation function Counts/channel 1+1+ Front of target protons above this energy forbidden by beam energy  Background 7Be+12C Thick target good for comparison to previous measurement – but difficult to analyze and not as informative as thin target Counts/channel

Inelastic Scattering Inelastic locus behaves kinematically like protons – Shape Inelastic locus is of correct energy (elastic proton energy less 7Be FES energy) - Separation ΔEΔE

Inelastic Prediction General behavior of inelastic prediction consistent with data

Simultaneous Fit of Elastic and Inelastic Fitting must be done simultaneously for many dimensions This requires a single set of resonance parameters for whole data set Consequence is that total χ 2 must be considered

Thin-target data Example of p and p` at one angle Possible positive parity resonance observed in inelastic channel  Not the known 3 +  3 +  f-wave in inelastic E cm ~ 2.3 MeV Possible: J  =0 +, 1 +, 2 + Accurate absolute normalization should allow accurate determination of scattering lengths Resonance is too high in energy to significantly affect S(0), but may explain some of the higher energy behavior E cm (MeV) Inelastic  cm =124  d  /d  (mb/sr) Elastic  cm =128 

Minimization versus Grid Search Grid Search 1.+Allows for arbitrarily precise parameter search 2.-Eats up computer time Minimization 1.-Favors nearest minima (would be plus for well-known landscape) 2.+Converges quickly based on local curvature χ2χ2 parameter i parameter j Minimization tends toward broad minima – not necessarily the deepest. This is a well known weakness of purely minimizing routines. Combined Grid-Powell Technique may lift this weakness – but add considerable CPU time Minimization versus Grid Search χ2χ2 parameter i parameter j

Current Analysis Multi Calculations being performed with large parameter space – grid search Search requires iteration over assignments of J π, energies and widths Grid search gets quickly out of hand #calculations = #steps (#parameters) 5steps (12 parameters) ≈ Calculations x 11 x 12 x 13.. x 1n x 11 x x 2n x x n1 x n2 x n3... x nn.

Future Work Determine Resonance Parameters of states in the region of 1 to 4 MeV and sensitivity to each parameter Another 7 Be(p,p) experiment would help to flesh out the cross section above 3.5 MeV Determine scattering lengths from low energy data.

SIDAR Lampshade Configuration Increased solid-angle coverage Can be configured for ΔE-E telescopes Extends angular coverage to more ‘backward’ angles