1. Angular resolution of LAT Agnieszka Kowal University of Science and Technology, Cracow TESLA Workshop on Forward Calorimetry Cracow, 10 October 2003

2. 2 Agenda LAT geometry angle reconstruction method different reconstruction schemes results from each reconstruction approach resolution in  and  summary and outlook

3. 3 Detector Layout rightside longitudinal cross section view of the detector LAT distance from the IP 305-325 cm LAT radial dimensions 8-28 cm angular coverage 26.2<  <82 mrad 0<  <360 deg

4. 4 Simulated LAT Structure  Si/W calorimeter  8/16/20/32/64/128 concentrical cylinders (in r)  30 rings (in z)  24/48 sectors (in  )  analyzed angular range:  30<  <78 mrad  0<  <360 deg

5. 5 Angle reconstruction method average over all LAT cells polar angle reconstruction azimuthal angle reconstruction

6. 6 Angle reconstruction schemes  reconstruction from all rings (all readout channels) from alternate rings with different # of cylinders (to improve linearity) from odd rings only (reduction of readout channels)  reconstruction as above for 24 or 48 sectors 8/32 cylinders in odd/even rings

7. 7  reconstruction from all rings „oscillations” around linear dependence due to detector granularity fade for 32 cylinders and more resolution in  about 0.2 mrad

8. 8  reconstruction from alternate rings with 8 and 32 cylinders compared with  reconstruction from all rings with 20 cylinders (same number of readout channels) linearity „oscillations” still present resolution worse than expected cyl. #  [mrad] RMS [mrad] 8/32-0.270.63 20-0.270.30

9. 9  reconstruction from odd rings good linearity for 32 or more cylinders problems with  resolution unexpected events outside the  peak spoil the resolution these events cut out „mechanically”

10. 10 LAT resolution in  as a function of the # of cylinders  obtained from all and odd rings are in agreement  RMS value constant for 32 or more cylinders  bias is smaller with 48 sectors 24 sectors48 sectors

11. 11  reconstruction for 24 and 48 sectors linearity „oscillations” due to detector granularity smaller for 48 sectors good resolution as expected same problems with  resolution for odd ring readout as for 

12. 12 LAT resolution in  as a function of the # of cylinders  obtained from all and odd rings are in agreement no dependence of the RMS on the # of cylinders  resolution better with 48 sectors 24 sectors48 sectors

13. 13 Summary angular resolution (mean and RMS) constant in  and  for 32 and more cylinders in LAT better resolution in  and  for 48 sectors good reconstruction linearity readout from odd rings only would allow reduction of readout channels with no effect on the resolution closer look needed at the few events outside the  and  peaks for odd ring readout best choice: 32 cylinders (odd ring readout) and 48 sectors – 23040 readout channels

14. 14 Outlook the obtained resolution in  is far from the assumed 1  rad increased statistics would improve the RMS both for  and  the bias of  is probably a matter of the applied reconstruction algorithm more work and carefull checks must be done