1. Monitoring Energy Gains Using the Double and Single Arm Compton Processes Yelena Prok PrimEx Collaboration Meeting March 18, 2006

2. Objectives 10/0911/22 first calibration second calibration Compton runs Check the quality of calibration Monitor gain drift with time Comparison with LMS monitoring Obtain short term gain variation Production runs throughout

3. Double Arm Compton Runs Carbon target, beam energies of 4.9<E<5.5 GeV and 2.0<E<3.1 GeV 7 groups of runs, in chronological order Data taken on the following dates : 1.Oct 10, 2004 2.Oct 19, 2004 3.Nov 2, 2004 4.Nov 3, 2004 5.Nov 9, 2004 6.Nov 14, 2004 7.Nov 19, 2004 Radiation Incident Run 5050 1356724 Calibration constants change in the database

4. Calibration Procedure “ Expected” energy of the photons/electrons can be calculated from the Compton kinematics: E  (el) =E beam /[1+2E beam /m e *sin 2 (   (el) /2)] For each HyCal module, divide the measured cluster energy by the “expected” value: Gain_Corr is defined: E HyCal /E  (el) Module 1498 Using photons Gain_Corr = 1.038  » 3.8 %

5. Calibration by Iteration After the gain correction factors (g i ) are found for the central modules of clusters, the corrections are applied, and the procedure is repeated: New g i =[  i cluster members E i /g i ]/E c To check the effect of this procedure, the quantity (e 1 +e 2 )/ebeam is plotted, before and after the application of gain correction factors Results converge after 3-4 iterations Group 3 before after

6. What is new: calibration by matrix inversion Gain correction factors are found simultaneously by solving a system of linear equations Resulting gains are plotted Vs the module number for 6 groups of runs. Blue: (iteration) Pink: (matrix inversion) The two methods are compatible.

7. What is new : Calibration at low energies, 2.1<E<3.1 GeV ~150 modules have 2 types of gains: obtained with 4.9<Ebeam<5.5 GeV and 2.1<Ebeam<3.1 GeV The difference between two types of gains is plotted on the right. Gains obtained with the low E tend to be ~1-3 % higher. Application of the energy non- linearity correction brings the two types of gains closer together After showing that the two types are compatible, can combine data at all energies to evaluate one final gain value No corr. Mean=0.006 With corr. Mean=0.0007

8. More Results Group 2 Group 4 Group 5 Group 7

9. Geometric Coverage Problem with coordinate reconstruction at x>16 cm All energiesHigh energies How different are these gains From the “snake” gains

10. Double Arm Compton Gains: What we learned so far: ~600 modules can be calibrated using dedicated Compton runs Energy resolution in Compton runs is improved by 6-70% For short term changes need to utilize Single Arm Compton events in the production data Red: ”snake” gains<Compton gains Blue: ”snake” gains>Compton gains

11. Double Arm Compton Gains: What is the effect on the production data ? 12 C production runs 5159-5170 Events with 2 clusters are selected, where 0.095<M<0.3 GeV, and |x,y|< 30 cm Plot (e 1 +e 2 )/ebeam, fit a gaussian Compton gains improve energy resolution  0.188  0.172 Snake gains Compton gains

12. Double Arm Compton gains: What is the effect on the production data ? Lead production runs 5080-5195 Same procedure as for carbon Resolution is improved  0.0212  0.0159 Snake gains Compton gains

13. Double Arm Compton Gains: Potential Problems The procedure is very sensitive to the knowledge of coordinates Any uncertainty in the distance between the target and calorimeter will influence the results Uncertainty in the beam position will influence the results If the magnetic field had any effect on the energy gains, they might not be exactly correct for the production data

14. Single Arm Compton Data Look for Compton events in the production data Choose events with one cluster only, require that cluster to be neutral (according to VETO), and with E>0.5 GeV Build a distribution of E cluster /E compton (Ebeam, x,y,z) for every module individually Fit the distribution

15. Single Arm Compton: Production on Carbon 12 C production runs 5159- 5179, ~ 24 hrs of data ~ 300 modules have sufficient statistics Compton peak is clearly visible, but the background changes depending on the position of the module ! makes it difficult to fit the background A simple gaussian does a better job of locating the peak Change from Double Compton Arm is small, 1-2 %,  ~ 4 %

16. Single Arm Compton: Geometric Coverage ~ 300 modules Difference between the “snake” and single arm compton gains! pattern following closely the one from double arm comparison Difference between the double arm and single arm is small

17. Single Arm Compton: Change in resolution ? Dcomp gains  0.1723 Dcomp+Scomp gains  0.01735 Resolution is practically unchanged

18. Single Arm Compton: Production on Lead  Runs 5080-5100, ~ 24 hrs of data taking  Finding a Compton peak in the lead target is more problematic. Perhaps, need more statistics

19. Summary  Double Arm Compton Calibration is complete  Two methods of calibration and two ranges of beam energy produce consistent results  This calibration results in significant improvement of energy resolution  The procedure is sensitive to coordinate reconstruction and accuracy: there are problems with coordinate reconstruction for |x,y|>16 cm, also initial beam offset would influence the result  Single Arm Compton needs to be investigated further; it can be used to obtain gains on a short term basis, and to understand the LMS behavior

20. Comparison with LMS Gain correction factors for the five selected modules with x<0 are plotted vs group number, along with the LMS gains for these modules The two gains follow the same pattern More work needs to be done to understand how to use the LMS gains along with the gain correction factors LMS gainsGain_corr LMS_gain*Gain_corr Modules more spread out

21. Conclusions/Outlook What we learned Gains drift with time We are sensitive to the beam position Gain correction factors found using the Compton data are compatible with LMS patterns Radiation incident has caused a dramatic change in the gain factors in some modules This calibration method has resulted in the energy resolution theoretically expected for the detector What remains to be done Include low energy events to increase the number of modules that can be analyzed Need to have beam position information from the beam line devices Check the linearity of energy response Understand how to use the LMS data Check results with the matrix inversion method Single arm Compton?