Angular resolution of LAT

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

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

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

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. 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.  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

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

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. 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 sectors 48 sectors

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. 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