1 Geometry layout studies of the RICH detector in the CBM experiment Elena Belolaptikova Dr. Claudia Hoehne Moscow State Institute of Radioengineering, Electronics and Automation (TU) GSI, Darmstadt

2 Outline Studies of the RICH material budget Compact RICH design Summary

3 Studies of additional material budget in the CBM RICH detector

4 Motivation Study the influence of the RICH material budget to the STS, TRD and global (STS+TRD) track reconstruction. Thick mirror  easy and cheap construction.

5 The simulation UrQMD events, Au-Au central collisions at 25 AGeV Additionally 50 electrons were embedded in each event; Detailed simulations have been performed in order to study the material of the RICH mirrors.  The standard RICH geometry was tested with different mirror thicknesses – 3 mm, 6 mm and 10 mm;  3 mm (idealistic);  6 mm (realistic);  10 mm (safety factor)  The mirror support structure was simulated.  The L1 STS track reconstruction algorithm was used;  Two different methods were used for TRD track reconstruction: LIT and L1.

6 The support structure for the mirrors  material – Al;  distance between tubes – 40 cm The first version  radius – 3 cm;  thickness – 5 mm; The second version  radius – 1.5 cm;  thickness – 2 mm; (proposal of E. Vznuzdaev, PNPI St. Petersburg) The support structure

7 TRD track finding efficiency for electrons Without support structure With support structure

8 Track finding results STS tracking efficiency doesn’t depend on the presence of the grid support structure. For all tested RICH geometries efficiency for all tracks is about 82%, and for electron tracks – 87%. The TRD track finding efficiency drops down on 2-2.5% with increasing mirror thickness Difference between presence of the first version of the support structure and its absence is roughly 1.5 – 2.5 %. For the second version – less than 1%.

9 Summary table for the TRD track finding No support structureWith support structure 3 mm6 mm10 mm3 mm6 mm10 mm LITL1LITL1LITL1LITL1LITL1LITL1 All, % Electrons,% Ghosts, #/ev Mismatches, % Designation of the summary table: All – TRD tracks with 12 hits; Electrons – embedded primary electrons in UrQMD; Ghost – wrongly found tracks; Mismatch – wrong matches with STS tracks. realisticidealistic

10 Compact RICH design

11 Motivation CBM RICH is an expensive detector. In order to save money the optimization of size and geometry is needed. The most important and expensive component is the photodetector. The dimensions of this part should be minimized.

12 Comparison of large and compact RICH LargeCompact radiator gas N2N2CO2 reflective index pth [GeV/c] radiator length [m] full length [m] mirror radius [m] 4.53 mirror size [m 2 ] photodetector size [m 2 ] No. of channels 200k55k The length of the compact RICH radiator was calculated in order to keep mean number of hits in electron ring equals to 22. This is a requirement of the ring reconstruction algorithm.

13 The compact RICH layout optimization A design of the compact RICH detector was implemented; The detector layout was not optimized – rings have strong distortions and elliptical shapes in the PMT plane  reduction of the ring reconstruction efficiency and increase in ring radius resolution  bad electron identification performance. Optimization of the photodetector and mirrors positions is needed.

14 Optimization parameters The following parameters are chosen to be optimized:  RICH detector acceptance;  A, B and B/A ratio;  Hit and ring density;  Electron ring distribution on the PMT plane.  Number of hits; Special routines for the calculation and visual representation of the parameters were implemented. The RICH event display was used to visualize hits and rings in the PMT plane. A B

15 The Compact RICH Different compact RICH geometries were implemented, simulated and investigated to find the best one. Analyses of these geometries were done by the parameters mentioned above. The most appropriate geometry was chosen with the best correlation of the selected parameters.

16 Chosen compact RICH geometry PMT plane (divided into 4 panels)  rotation around x-axis: 5°  rotation around y-axis: - 5°  z position mm  y position - ±1275 mm  ∆y = ±300 mm Mirror tilted by -1° around x-axis

17 Standard vs. Compact RICH Hits distribution PMT area = 9 m 2 PMT area = 2.4 m 2 Number of hits in primary electron ring.

18 Standard vs. Compact RICH Acceptance Acceptance for primary electrons in dependence on momentum. ― electrons which have RICH ring with >=5 hits Mean acceptance = 88.88% Mean acceptance = 83.86% Parameters of BoxGenerator are following: Pt (0., 3.) Phi (0., 360.) Theta (2.5, 25.)

19 Standard vs. Compact RICH, Distributions of A, B and B/A compact RICH standard RICH A B

20 Standard vs. Compact RICH, Electron ring distributions on the PMT plane Standard Compact (selected region shown)

21 Standard vs. Compact RICH, Ring reconstruction efficiency. Au-Au at 25 AGeV UrQMD + 5 e- and 5 e+ in each event Mean efficiency = 95.04% Standard RICH Compact RICH Fakes/event = 1.50 Mean efficiency = 90.63% Fakes/event = 3.55 ― electrons which have RICH ring with >=5 hits and track projection on PMT plane

22 Summary RICH geometries with different mirror thicknesses were simulated. The mirror support structure was implemented. Having only changes on few percent level in the track finding efficiency reassure for planning a “standard” RICH mirror of 6 mm glass thickness and aluminum support. This will save money and efforts. RICH geometry testing routines were implemented and different compact RICH geometries were simulated and investigated. Better positions of PMT and mirrors were found. The best compact RICH geometry was tested with UrQMD events. Obtained results are very promising.

23 Thanks for your attention!