1. Crystal Ball Collaboration Meeting, Basel, October 2006 Claire Tarbert, Univeristy of Edinburgh Coherent  0 Photoproduction on Nuclei Claire Tarbert, University of Edinburgh Spokesperson: Dan Watts

2. Crystal Ball Collaboration Meeting, Basel, October 2006 Claire Tarbert, Univeristy of Edinburgh Coherent  0 Photoproduction Takes place with ~same probability on n and p. Reaction amplitudes from all nucleons add coherently.  Cross section contains information on matter distribution F 2 m (q) is Fourier Transform of Matter Density as a function of radius.  r.m.s matter radius CoherentA(  0 )A IncoherentA(  0 )A*  0 Photoproduction

3. Crystal Ball Collaboration Meeting, Basel, October 2006 Claire Tarbert, Univeristy of Edinburgh Nuclear Matter Radii Charge radii (distribution of protons) well known from electron scattering etc. Matter radii (protons and neutrons) less well known. Theory predicts a neutron skin for n-rich nuclei ( 208 Pb ~0.1 – 0.3 fm) Traditionally use strong probes to probe matter radius e.g. p, a scattering Encounter problems with model dependency – initial and final state interactions. Elastic Electron Scattering Nuclear Charge Radii Matter radii are important as: A test of Nuclear Theories A constraint for Atomic Parity Non-Conservation A constraint on the properties of Neutron Stars

4. Crystal Ball Collaboration Meeting, Basel, October 2006 Claire Tarbert, Univeristy of Edinburgh Crab Pulsar Skin thickness on 208 Pb gives info about compressibility of matter. Calibrates symmetry energy as a function of density at low densities. Large neutron skin  large crust on neutron star. 208 Pb and Neutron Stars 208 Pb Neutron Skin Possible Equations of State for Neutron Stars

5. Crystal Ball Collaboration Meeting, Basel, October 2006 Claire Tarbert, Univeristy of Edinburgh 1.Calibration of Crystal Ball using low energy  0 s. 2.Particle identification. 3.Select  0 s. 4.Separation of Coherent/Incoherent events. - Pion Missing Energy Analysis Framework  E  = E  (  1,  2 ) – E  (E  ) E  (  1,  2 ) = detected pion energy (cm) E  (E  ) = calculated pion energy (cm) Incoherent  0 s always less energetic than coherent equivalent. Nuclear decay  s Nuclear decay  s.

6. Crystal Ball Collaboration Meeting, Basel, October 2006 Claire Tarbert, Univeristy of Edinburgh Analysis Framework Angular distribution of photons Sharp drop off in no of detected photons in region of phase space covered by TAPS. See similar distribution for protons. Now only use TAPS to veto charged particles.

7. Crystal Ball Collaboration Meeting, Basel, October 2006 Claire Tarbert, Univeristy of Edinburgh Fits to  E 

8. Crystal Ball Collaboration Meeting, Basel, October 2006 Claire Tarbert, Univeristy of Edinburgh Fits to  E  Crystal Ball TAPS 2001 data  (MeV)  (MeV) Completed first iteration of fits to pion missing energy.   = (30-32) o

9. Crystal Ball Collaboration Meeting, Basel, October 2006 Claire Tarbert, Univeristy of Edinburgh “Cross Sections” 208 Pb Still to include: Better fits. Simulated detection efficency (flat detection efficiency assumed at the moment). Correction for cut on  0 invariant mass.

10. Crystal Ball Collaboration Meeting, Basel, October 2006 Claire Tarbert, Univeristy of Edinburgh “Cross Sections” 208 Pb

11. Crystal Ball Collaboration Meeting, Basel, October 2006 Claire Tarbert, Univeristy of Edinburgh Diffraction from a circular disc:  r m ~ 5.85fm Comparison to Theory + Data -- DREN Compare one energy bin to DREN calculation –  r m ~ 5.78fm (cf r c = 5.45fm) DREN calculation by Kamalov  r m – r c ~ 0.33fm

12. Crystal Ball Collaboration Meeting, Basel, October 2006 Claire Tarbert, Univeristy of Edinburgh Finalise coherent cross sections improve fits to  E  finalise calibrations finish  0 detection efficiency simulations Extract matter form factor via comparison to theory Continue analysis of Incoherent p0 photoproduction using detection of nuclear decay  s Conclusion To do

13. Crystal Ball Collaboration Meeting, Basel, October 2006 Claire Tarbert, Univeristy of Edinburgh Comparison to Theory 208 Pb Theoretical Calculations by S.Kamalov --- PWIA --- DWIA --- DREN

14. Crystal Ball Collaboration Meeting, Basel, October 2006 Claire Tarbert, Univeristy of Edinburgh Just in case 40 Ca References: APNC -

15. Crystal Ball Collaboration Meeting, Basel, October 2006 Claire Tarbert, Univeristy of Edinburgh Preliminary Analysis Coherent  0 Photoproduction Theoretical Calculations: PWIA (Plane Wave Impulse Approx ) DWIA (Distorted Wave Impulse Approx) DREN (Delta Resonance Energy Model) DWIA, DREN take into account FSI. Good agreement with theory. Same quality of data for all targets. F 2 m (q) is same for all E  bins, but E  increases  can fit to at least 40 spectra for each target to extract form factor and pion distortion parameters. 208 Pb