Coherent p 0 Photoproduction

Collaboration Meeting, 28 March 2006, Glasgow Claire Tarbert

Coherent 0 Photoproduction

Claire Tarbert, University of Edinburgh

Collaboration Meeting, 28 March 2006, Glasgow Claire Tarbert

Coherent0 Photoproduction

Coherent A(0)A

IncoherentA(0)A*

208Pb

Theoretical Calculations (Kamalov):

PWIA (Plane Wave Impulse Approx ) DWIA (Distorted Wave Impulse Approx) DREN (Delta Resonance Energy Model)

Good agreement with theory.

Collaboration Meeting, 28 March 2006, Glasgow Claire Tarbert

Coherent0 Photoproduction

Pion Missing EnergyDecay Gammas (16O)

Energy (MeV)

Pion Missing Energy:

E = E(1,2) – E(E)

E(1,2) = pion energy calculated from energy and angle of decay photonsE(E) = pion energy calculated from incident photon assuming a coherent reaction

Collaboration Meeting, 28 March 2006, Glasgow Claire Tarbert

Crystal Ball Energy Calibration

Traditionally calibration of CB uses 2 body 0 decay kinematics:p p

Instead try using kinematics of 0 decay from 12C: 0

i.e. for each crystal plot M when it is the central element of one of two clusters making a 0

Constraints:

Limit E < 180 MeV i.e. just above threshold ratio of light collection/shower loss remains ~constant low energy 0s i.e. photon opening angle is large

80% of cluster energy in central crystal Correction for cluster ~ correction for central crystal I E1 – E2 I < 0.25( E1 + E2 ) Same correction applies to both 0 photons

M2 = 2E1E2(1 - cos)

Collaboration Meeting, 28 March 2006, Glasgow Claire Tarbert

Crystal Ball Energy Calibration

Result:

Correction factor for MeV/Chn values for each crystal.

Correction Factor = m / M

Collaboration Meeting, 28 March 2006, Glasgow Claire Tarbert

Crystal Ball Energy Calibration

p p0 Calibration(January 2005)

Using low E 0s from 12C(March/April 2005)

Collaboration Meeting, 28 March 2006, Glasgow Claire Tarbert

Linearity of Energy CalibrationSeparate into bins according to E1 and E2 (0 decay photon energies)e.g. 200 < E1 < 210 MeV && 40 < E2 < 60 MeV, 200 < E1 < 210 MeV && 60 < E2 < 80 MeV,

200 < E1 < 210 MeV && 80 < E2 < 100 MeV etc…

Collaboration Meeting, 28 March 2006, Glasgow Claire Tarbert

Linearity of Crystal Ball Energy Calibration

Tabulated values plotted

Collaboration Meeting, 28 March 2006, Glasgow Claire Tarbert

Linearity of Crystal Ball Energy Calibration

Collaboration Meeting, 28 March 2006, Glasgow Claire Tarbert

Linearity of Crystal Ball Energy Calibration

Fit to plots:

aE3 + bE2 + CE + d

(Fit to average of data… will improve fit!!)

i.e. M = aE3 + bE2 + CE + d

To correct photon cluster energy:

Etrue = Edet ( mo / M )2

Collaboration Meeting, 28 March 2006, Glasgow Claire Tarbert

Linearity of Crystal Ball Energy Calibration

Reran WITHCorrection Factor

Without correction fornon linearity

(Only 1/3 of data)

Collaboration Meeting, 28 March 2006, Glasgow Claire Tarbert

Low Energy Calibration of Crystal Ball

• Use 4.43MeV decay s from 12C.• Select events where decay fires single crystal.• new MeV/Chn values for low energies.

Collaboration Meeting, 28 March 2006, Glasgow Claire Tarbert

Low Energy Calibration of Crystal Ball

Comparison to AmBe calibration

Collaboration Meeting, 28 March 2006, Glasgow Claire Tarbert

Low Energy Walk Correction of Crystal Ball

Collaboration Meeting, 28 March 2006, Glasgow Claire Tarbert

Low Energy Walk Correction of Crystal Ball

With Low Energy Walk Correction

Collaboration Meeting, 28 March 2006, Glasgow Claire Tarbert

Preliminary look at Incoherent 0 Photoproduction

12C

•Contains information on overlap of wavefunction between ground and excited state i.e. Matter Transition Form Factor.

•Interesting minimum at high energies?

Cro

ss

se

cti

on

(A

rb.

Un

its

)

Cro

ss

se

cti

on

(A

rb.

Un

its

)

+ Coherent+ Incoherent

Collaboration Meeting, 28 March 2006, Glasgow Claire Tarbert

Conclusion

• Solid target CB energy calibration almost finalisedCoherent Photoproduction cross

sections hopefully available soon.

• Interesting hints from incoherent channels.

Collaboration Meeting, 28 March 2006, Glasgow Claire Tarbert

Preliminary decay gammas from nucleon knockout

12C(,ppp)9Li

Q value

Low energyclusters from shaded region

2.69 MeV

E=400-500 MeV

i=1

3

• Also look at pp, 4p, 5p … knockout

Missing Energy (MeV) = E–Tpi –Trec

Energy of cluster (MeV)