Calorimetry for Deeply Virtual Compton Scattering in Hall A

1. Calorimetry for Deeply Virtual Compton Scattering in Hall A Alexandre Camsonne Hall A Jefferson Laboratory Workshop on General Purpose High Resolution Radiation Hard Electromagnetic Calorimeter at JLab October 31st 2008

2. Measurement • Experimental technique • Background • Analysis • New experiment • Requirements summary Outline

3. Deeply Virtual Compton Scattering + + DVCS Bethe and Heitler Workshop on Calorimetry October 31, 2008

4. Deeply Virtual Compton Scattering in Hall A • High resolution and high precision on a limited kinematic range • Study of scaling with fixed xbj and variation in Q2 • High resolution calorimeter • Focus on cross section measurement • Ensure exclusivity relying on calorimeter • High luminosity Workshop on Calorimetry October 31, 2008

5. HRS g PbF2 electron g* p Specificity of the experiment qg*g Central angle up to 14 degrees electron Workshop on Calorimetry October 31, 2008

6. Background issues Workshop on Calorimetry October 31, 2008

7. p0 contamination • Symmetric decay: minimum angle in lab of 4.4° at max po energy • Asymmetric decay: sometimes one high energy cluster can be misindentified for a DVCS event • Interesting : study of Deep Exclusive p0 production could access to another linear combination of GPDs Workshop on Calorimetry October 31, 2008

8. Experimental setup Workshop on Calorimetry October 31, 2008

9. Cross sections measurement Electron helicity dependent cross sections of photon electroproduction Workshop on Calorimetry October 31, 2008

10. Background reduction High luminosity running possible by • reducing secondary background source 15 cm Liquid H2 target 5 cm 110 cm beam dump PbF2 • Scattering chamber 1 cm Al as shielding Workshop on Calorimetry October 31, 2008

11. Data analysis p0 subtraction done using the p0 sample recorded in the calorimeter Subtracted data fits exactly the simulation and the shape of the exclusive events: good understanding of the detectors Exclusivity in two arms Cut im Mx2 Workshop on Calorimetry October 31, 2008

12. nDVCS – deuterium Data analysis Workshop on Calorimetry October 31, 2008

13. π0 electroproduction Invariant mass of 2 photons in the calorimeter Sigma = 9.5 MeV gg π0 Missing mass2 of epeπ0x Sigma = 0.160 GeV2 2π production threshold Separation of photons for 3 GeV π0 : 4.4 degrees = 8.4 cm at 110 cm

14. New experimental setup • Double arm experiment • Increase acceptance • Increase in luminosity • Calorimeter • Increased size of the calorimeter from 132 to 208 blocks for larger acceptance in t • 11x12 blocks = 33 cm x 36 cm = = 30 mrd x 32 mrd= 98 msrd to 13x16 blocks = 39 cm x 48 cm = = 32.5 mrd x 40 mrd = 120 msrd Covers full acceptance of HRS at 110 cm from target • Improved trigger for optimal p0 detection • Data transfer improvement to accommodate lower threshold Workshop on Calorimetry October 31, 2008

15. Kinematics 6 GeV Workshop on Calorimetry October 31, 2008

16. Kinematics 12 GeV Workshop on Calorimetry October 31, 2008

17. Radiation hardness Curing planned every two weeks for new experiments when more than 20 % attenuation Workshop on Calorimetry October 31, 2008

18. Requirements summary • Lead fluoride performance were sufficient • Energy resolution • 2.4% at 4.2 GeV • 2 % + 3.2 %*E^1/2 , DVCS photons 2 to 3 GeV • Position resolution of 3 mm • 120 msrd = 32 mrd x 40.5 mrd • Radiation Hardness to preserve resolution : around 20% change for 750 kRad. • 2000 kRad for 6 GeV experiment, 8400 kRad for 12 GeV • Curing of blocks about every 2 weeks • Cerenkov to reduce hadronic background and fast to reject background ( coincidence time 0.6 ns ) • Reach forward angles around centered around 14 degrees Workshop on Calorimetry October 31, 2008