Coherent and Incoherent p 0 Photoproduction on Nuclei

CB Collaboration Meeting, Dubrovnik, 7 April 2008 Claire Tarbert, Univeristy of Edinburgh

Coherent and Incoherent 0 Photoproduction on Nuclei

Claire Tarbert, University of Edinburgh

Experiment spokesperson: Dan Watts


Outline

1. Status of Incoherent analysis/publication.

C-12 status

Other targets

2. Status of Coherent analysis/publication.

Pb-208: status – cross sections

Pb-208: extracting the matter radius

MAMI-B data:

March/April 2005

Ee = 883MeV

Pb-208, Ca-40, O-16, C-12


Incoherent A(0)A*

Tagg the final state by coincident detection of nuclear decay gammas.

Expect strong anisotropy in decay gamma angular distribution.

IncoherentNuclear0 Photoproduction on - 12C

+ data-- Geant3


IncoherentNuclear0 Photoproduction on - 12C

• Calculations by Takaki: DWIA + -hole model

• Calculations by Tryasuchev: IA + L-S coupling.

• Published in PRL – last week!


IncoherentNuclear0 Photoproduction – C-12


IncoherentNuclear0 Photoproduction – E dependence of C-12

Work in progress…..


IncoherentNuclear0 Photoproduction – Ca-40 and O-16

O-16Ca-40

sin)sin25.0)3sin(25.1( 2Calculation (J = 3- final state) :

[o]

• Calculation has been corrected for geometric acceptance of detectors.

• Need to investigate angular distribution of decay s more before normalising incoherent cross sections on Ca-40 and O-16.

• No calculations exist for Ca-40 or O-16.


• Presented finalised total and differential coherent cross sections as a function of pion angle on 208Pb, 40Ca, 16O, 12C in my thesis.

• See satisfactory agreement with previous data and theory calculations.

• At present working on extracting the matter form factor from final normalised cross sections.

Coherent A(0)A

Missing energy analysis to isolate coherent events.

CoherentNuclear0 Photoproduction


CoherentNuclear0 Photoproduction – E dependence

Pb-208

C-12O-16

Ca-40

+ CB data+ Glasgow TAPS data

Kamalov Calcs:PWIADWIAFull Calc (DREN)


CoherentNuclear0 Photoproduction – Pb-208

+ CB data+ Glasgow TAPS data-- DREN (Kamalov)


Have re- derived cross sections as a function of momentum transfer to the nucleus …..



Extracting the Matter Distribution – Pb-208

Without FSI cross section could be descibed by PWIA.

FSI has effect of: 1. Changing momentum of outgoing pion as it leaves the nucleus (shift in q).2. Loss of strength with another channel.



At least 2 possibilities:

1. Put different matter distributions into the Kamalov model parametrised as a series of Bessel functions. Then do a2

minimisation against the data.

2. Correct the data for the effects of FSI first => gives a PWIA cross section. Form factor can then be lifted out and r.m.s. matter radius extracted in a number of ways.


A simple model to correct for FSI

Vo = [M2+p’2]1/2 – [M2+p2]1/2 + [m

2 + p’2]1/2 – [m2 + p2]1/2

• Use complex potential from Kamalov model to approximate Vo in simple model.

• Use shift in the form factor minimum position between the PWIA and DREN calculations to approximate potential height.

M

m



+ V calculated using shift in 1st minimum position

+ V calculated using shift in 2nd minimum position

+ V calculated using shift in 3rd minimum position



Insert beautiful plot here showing that DREN calculations can be corrected back to PWIA.



E = (200-220)MeV

Cross section corrected for FSI using simple model.

Fitted with a Bessel function



No skin

0.1fm skin

* No correction for FSI

* Corrected for FSI

Position of first minimum

=> Non zero neutron skin


Summary

• Incoherent reaction

• Differential cross sections for C-12: PUBLISHED.• E dependence of C-12 cross sections: ANALYSIS BEING FINALISED.• In principle can do the same for O-16 and Ca-40: NEED CALCULATIONS.

• Coherent reaction

• Have finalised all cross sections as a function of theta.• Have finalised Pb-208 cross sections as a function of q.• Trying to extract matter radius.• Have first draft of paper within 2 months.……………………………….. IN PROGRESS.


End


Extracting the Matter Distribution – Still to do

• Improve resolution if diffraction minima.

• Fine tune FSI correction.

• Once have PWIA cross section convert to a F(q)

• Extract r.m.s. radius


Working on extracting matter form factor for Pb-208

Postdoc finishes in May 2008 – needs to be done by then!

A preliminary look…….

Comparison with Krusche TAPS data Comparison with Kamalov Calcs



Have derived cross sections as a function of momentum transfer to the nucleus …..



Pb

+ CB data+ Glasgow TAPS data-- DREN



Have derived cross sections as a function of momentum transfer to the nucleus …..


IncoherentNuclear0 Photoproduction – C-12



0.1fm increase in rms => 0.01fm-1 shift in 1st minimum position

Coherent and Incoherent p 0 Photoproduction on Nuclei

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