1. Status of Compton Analysis
Yelena Prok
PrimEx Collaboration meeting
February 25, 2007

2. Outline
Analysis Note posted before the last meeting; no comments received
->it must be perfect
Since the last meeting:
Study of integrated vs total cross section
Implementation of radiative corrections, Primex Note

3. Integrated (Partial) XS
Data with the beam energy in the range of 4.9<E<5.5 GeV covers the angular range of ~ degrees (due to our geometry).
When evaluating the total cross section, a large fraction of the final result comes from the extrapolation in the rest of the region
Is there any systematic uncertainty introduced by this extrapolation?
To answer this question we evaluate cross section, integrated over four regions of the photons’ scattering angle:
0.1 <  < 90
0.1 <  < 10
0.1 <  < 5
0.1 <  < 3

4. Generated kinematics 0.0 <  < 180 0.1 <  < 5.0
electron
photon
photon
electron
Scattering angle (deg)
Scattering angle (deg)

5. Efficiency

6. Integrated Cross Section, (Be target)
Experimental result relative to theory
is independent of which region is chosen

7. BornBorn+RC Cross section evaluation expt =N/ Yield, N
Efficiency, 
Theory, theory
expt =N/
theory,born
expt
In order to evaluate radiative corrections, need:
1. ’Radiated’ theory: theory,BORN  theory, BORN+RC
2. ’Radiated’ efficiency: 0  RC

8. Radiative Corrections
Virtual: possibility of emission and re-absorption of virtual photon by an electron during the scattering process
Double Compton scattering
Soft: secondary photon of energy k<<kmax, not accessible to the experiment
Hard: secondary photon of energy k>kmax, accessible to the experiment

9. Total (RC) Cross Section (1)
Integrate differential cross sections for 2 processes, ‘soft-virtual’ and ‘hard double’ scattering.
Corrections separated into 2 based on whether the energy of secondary emitted photon is greater or smaller than some parameter 2max << me
‘Soft-Virtual’ term, based on ref. [4] of PN 42, contains a term ‘ln(2max/me); integrated over the scattered photon’s polar angle
‘Double-hard’ term, according to ref. [5] of PN 42, 2max is a lower limit of integration over the energy of one of the scattered photons; integration is carried also over the 2 polar angles of the scattered photons, and azimuthal angle between their planes.
Result must be independent of the choice of 2max

10. Total correction wrt Born term (independent of the choice of 2max )

11. Total (RC) Cross Section
Used 2 independent
methods of numeric
integration to check
the values of total
cross section and
compare with NIST
Uncertainties:
NIST (5+ %)
Integration ( » 1 %)

12. Event Generators Utilizing BASES/SPRING package
created event generators
for 2-particle and 3-particle processes
Generated 2-particle and 3-particle events according to their total cross section ratio
Propagated events through the setup
using GEANT-3
Calculated ‘radiated’ efficiency

13. Generated Kinematics Born vs Born+SV vs Double Compton Scattering
electron
electron
photon
photon
Scattered energy (GeV)
Scattering angle (deg)

14. Generated Occupancy on HyCal
Born
Born+SV
Double Compton
Y(cm)
X (cm)
Cut: 2 particles outside of the central hole

15. Generated Occupancy on Hycal
Born
Born+SV
Double Compton
Y(cm)
Y(cm)
Cut: 2 particles outside of the central hole

16. Clusters on Calorimeter
Born +SV event
Double Compton event

17. ‘Radiated’ Efficiency
Carbon Target
Born
Born+SV+DC
‘Radiated’ efficiency is ~ 5% smaller (needs more checks)

18. Radiatively Corrected Cross Section
~ 1 % agreement between the data and theory
(more checks are needed)

19. Done To Do New flux/binning scheme
Total, integrated, and differential cross sections are evaluated at the Born level for all carbon and beryllium data for 4.9<E<5.5 GeV beam
Mechanism for implementation of radiative corrections has been developed and is documented in Primex Note 42
Initial evaluation of radiatively corrected cross section with the carbon target shows very good agreement with theory (~1 %)
New flux/binning scheme
More work on RC (also for the Be target)
Systematic Errors
Low energy data set