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

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

Integrated (Partial) XS Data with the beam energy in the range of 4.9<E<5.5 GeV covers the angular range of ~ 0.2-3.0 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

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

Efficiency

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

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

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

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

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

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 %)

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

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

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

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

Clusters on Calorimeter Born +SV event Double Compton event

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

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

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