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 31 st 2008

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

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

4. Workshop on Calorimetry October 31, 2008 High resolution and high precision on a limited kinematic range Study of scaling with fixed x bj and variation in Q 2 –High resolution calorimeter –Focus on cross section measurement –Ensure exclusivity relying on calorimeter –High luminosity Deeply Virtual Compton Scattering in Hall A

5. Workshop on Calorimetry October 31, 2008 Specificity of the experiment electron HRS PbF2 electron   p   Central angle up to 14 degrees

6. Workshop on Calorimetry October 31, 2008 Background issues

7. Workshop on Calorimetry October 31, 2008  0 contamination Symmetric decay: minimum angle in lab of 4.4° at max  o energy Asymmetric decay: sometimes one high energy cluster can be misindentified for a DVCS event Interesting : study of Deep Exclusive  0 production could access to another linear combination of GPDs

8. Workshop on Calorimetry October 31, 2008 Experimental setup

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

10. Workshop on Calorimetry October 31, 2008 Background reduction Scattering chamber 1 cm Al as shielding 15 cm 5 cm beam dump Liquid H 2 target 110 cm High luminosity running possible by reducing secondary background source PbF 2

11. Workshop on Calorimetry October 31, 2008 Data analysis  0 subtraction done using the  0 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 Mx 2

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

13. π 0 electroproduction Invariant mass of 2 photons in the calorimeter Missing mass 2 of ep  eπ 0 x 2π production threshold Sigma = 0.160 GeV 2 Sigma = 9.5 MeV   π 0 Separation of photons for 3 GeV π 0 : 4.4 degrees = 8.4 cm at 110 cm

14. Workshop on Calorimetry October 31, 2008 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  0 detection –Data transfer improvement to accommodate lower threshold

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

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

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

18. Workshop on Calorimetry October 31, 2008 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