1. Compact RICH detector Claudia Höhne, GSI Darmstadt

2. Claudia Höhne CBM collaboration meeting Dresden, September 20072 Status electron simulations (March '07) all relevant detectors (RICH, TRD, TOF) fully implemented in CbmRoot RICH → ring finding, fitting, fake rejection, track matching TRD → 3 different routines available for calculating e-  separation from statistical analysis of energy loss spectra (likelihood, neural net,  k n ) TOF analysis of electron ID performance (efficiency, purity) full electron ID used for physics analysis (low-mass dileptons, J/  ) → "proof of principle": got everything running with reasonable results

3. Claudia Höhne CBM collaboration meeting Dresden, September 20073 Improvements since March '07 → make use of available infrastructure and continue software development: systematic studies: limitations/ relevant parameters for ring finding: hit/ ring density, noise level, magnetic stray field → impact on RICH design electron ID for different identification cuts, usage of detectors,... develop user friendly software in CbmRoot for electron ID optimization of cuts simple usage for physics analysis develop event display of CBM detector apply latest developments to physics analysis, understand remaining background sources optimization of RICH layout minimum size for reasonable physics output? (costs!) maximum material budget which is tolerable for global tracking? → S. Lebedev → S. Das → S. Lebedev → S. Das → T. Galatyuk, A. Maevskaya,....

4. Claudia Höhne CBM collaboration meeting Dresden, September 20074 Compact RICH – motivation save money! → reduce size of RICH: restrict acceptance (reduce mirror size, photodetector size) reduce length L (→ overall size) Cherenkov radiation for electrons → choose different radiator (Cherenkov angle  ) in order to compensate for reduction in L... first steps will be presented

5. Claudia Höhne CBM collaboration meeting Dresden, September 20075 Radiator radiatorn  th p th  [GeV/c] thresh [nm] radiation length [m] handling? N2N2 1.000298415.6< 160304 CH 4 1.0004433.64.7~ 145650  CO 2 1.0004533.34.65~ 175183 CF 4 1.000488324.47< 120chemically aggressive N2ON2O1.00050931.44.37(toxic) CH 3 OH (methanol) 1.00054630.34.2flammable C 2 H 6 (ethane)1.00070626.63.71~ 160340 as the RICH detector should mainly serve for electron identification, the pion threshold for emission of Cherenkov light should be sufficiently high in momentum

6. Claudia Höhne CBM collaboration meeting Dresden, September 20076 Radiator (II) CO 2 should still allow sufficient e-  separation up to ~ 10 GeV/c ! increase of number of pion rings! p [GeV/c] momentum distribution of pions in RICH (standard) N2N2 CO 2

7. Claudia Höhne CBM collaboration meeting Dresden, September 20077 Radiator (III) radiatorn cc  th p th  [GeV/c] L [cm]NN R [cm] #  R [cm]  R [%] N2N2 1.0002981.4415.625022 *6.10.14 $ 2.3 CO 2 1.000451.7233.34.65176~22 & 5.3? * from simulation, H8500-03 photodetector # R ~ L tan  $ simulation: R = 6.16± 0.14 cm & keep appr. constant → L ~1/(sin  ) 2 → factor 0.66 from N 2 to CO 2 keeping approximately the same number of photons, the length can be reduced by 30% expected radius reduction ~ 13 % assuming the same total resolution (0.15cm) the relative resolution is still < 3%! ~30% reduction!

8. Claudia Höhne CBM collaboration meeting Dresden, September 20078 Radiator (IV) dispersion similar in both gases

9. Claudia Höhne CBM collaboration meeting Dresden, September 20079 Radiator (V) N 2 absorption edge ~ 150 nm CO 2 absorption edge ~ 175 nm absorption also starts appr. at the same wavelength

10. Claudia Höhne CBM collaboration meeting Dresden, September 200710 RICH layout standard RICHcompact RICH mirror tilted by 5° first approach: keep overall same concept for layout and only reduce length

11. Claudia Höhne CBM collaboration meeting Dresden, September 200711 RICH layout standard RICHcompact RICH gasN2N2 CO 2 radiator length2.5 m1.76 m full length of RICH *2.9 m2.1 m end of RICH4.5 m 3.7 m mirror position4.1 m3.36 m mirror radius4.5 m3 m mirror size2 x (5.7 x 2) m 2 ~ 22.8 m 2 2 x (4.2 x 1.4) m 2 ~ 11.8 m 2 photodetector size **2 x (3.2 x 1.4) m 2 ~ 9 m 2 2 x (2.4 x 0.78) m 2 ~ 3.7 m 2 # channels~ 200k~ 85k * start at 1.6 m behind target ** still reducable on (small) acceptance losses

12. Claudia Höhne CBM collaboration meeting Dresden, September 200712 Photodetector plane standard RICHcompact RICH distribution of Cherenkov photons for 1000 UrQMD events reduce at least to (3.2 x 1.2) m 2 → 7.7 m 2 in total (170k channels) can be reduced further (~15%) → 3.1 m 2 (72k channels) analysis: cut inner region with r < 140 cm analysis: cut inner region with r < 130 cm

13. Claudia Höhne CBM collaboration meeting Dresden, September 200713 Ring projection standard RICHcompact RICH ring projection in ¼ of photodetector plane for different ( ,  )  – 0, 20, 40, 60, 80 degrees  – 5, 10, 15, 20, 25, 30 degrees   x [cm] y [cm] → bended photodetector plane needed!... next step

14. Claudia Höhne CBM collaboration meeting Dresden, September 200714 Simulations simulation UrQMD, central Au+Au collisions, 25 AGeV + 5 embedded e ± each magnetic field: "ActiveField" standard setup, only RICH geometry replaced reconstruction all routines for RICH can deal with mirrors/ photodetector planes tilted by arbitrary angles around x-axis CbmRichHitProducer CbmRichProjectionProducer compact RICH: distorted rings in particular in outer part no radius correction yet available no fake ring rejection by additional ring quality checks reduces current performance but will be improved

15. Claudia Höhne CBM collaboration meeting Dresden, September 200715 Numbers... standard RICHcompact RICH rings/event9775... from e6854... from e (N STS ≥ 6)1413... from  2920.5 N PMT /e-ring *22 ± 4.6 central Au+Au collisions, 25 AGeV beam energy * Hamamatsu H8500-03 MAPMT... not joking ;-)

16. Claudia Höhne CBM collaboration meeting Dresden, September 200716 Electron acceptance standard RICHcompact RICH acceptance = tracks in RICH acceptance/ tracks in STS acceptance STS acceptance : N STS + N MVD ≥ 4, use prim. vertex tracks only RICH acceptance: track projected on photodetector p = 10 GeV/c p = 0.5 GeV/c y p = 10 GeV/c p = 0.5 GeV/c y

17. Claudia Höhne CBM collaboration meeting Dresden, September 200717 Elastic Net Ring Finder p [GeV/c] Ring reconstruction efficiency standard RICHcompact RICH Hough Transform p [GeV/c] → next slide

18. Claudia Höhne CBM collaboration meeting Dresden, September 200718 Ring finding – compact RICH Hough Transform: → losses in outer regions due to distortions! → will change with optimized geometry! → finally same performance as for standard RICH expected distorted rings in outer regions! for "good rings" 90% level reached as for standard RICH!

19. Claudia Höhne CBM collaboration meeting Dresden, September 200719 Radius vs momentum standard RICHcompact RICH electrons only broad radius distribution for compact RICH due to distortions! → to be improved by bended photodetector plane (and later software corrections)

20. Claudia Höhne CBM collaboration meeting Dresden, September 200720 Ring-track distance standard RICHcompact RICH no fake ring rejection routines yet!! distance distribution broader due to ring distortions (affects ring center fit)

21. Claudia Höhne CBM collaboration meeting Dresden, September 200721 RICH electron identification standard RICHcompact RICH fake rings!! (Def.: < 60% "true" hits) lower  threshold for Cherenkov radiation!

22. Claudia Höhne CBM collaboration meeting Dresden, September 200722 RICH + TOF + TRD electron identification standard RICHcompact RICH TRD: Neural Net Method, require output values to be > 0.8 TOF 2-dimensinal cut in m 2 vs p plane → similar performance except fake ring rejection! → in particular TRD copes up for (currently) reduced RICH performance! 96% purity of id.e 87% purity of id.e

23. Claudia Höhne CBM collaboration meeting Dresden, September 200723 Electron efficiency standard RICHcompact RICH efficiency for identifying electrons embedded in UrQMD events, normalized to RICH acceptance major improvement since spring! (was ~60% for full ID) p [GeV/c] efficiency loss due to ring finding with optimized photodetector plane same performance as for standard RICH expected!

24. Claudia Höhne CBM collaboration meeting Dresden, September 200724 Pion suppression standard RICHcompact RICH p [GeV/c] → factor 10 4  suppression at 80% e-efficiency! p [GeV/c] pions are fine! improve on fakes and e-efficiency!

25. Claudia Höhne CBM collaboration meeting Dresden, September 200725 need for redesign of RICH detector after we could prove the feasibility of low-mass dilepton and J/  physics with the "first guess" layout of RICH first steps towards a compact RICH detector presented: factor > 2 reduction in mirror size (to be adopted to photodetector) ~ factor 2.8 reduction in photodetector size... while to first extend keeping the physics performance! → RICH becomes affordable!! optimize further and finally come up with a mature RICH design !!! increase activities on RICH R&D in parallel! → activities started on mirror R&D and photodetector module design aiming finally for a small RICH prototype Summary (I)

26. Claudia Höhne CBM collaboration meeting Dresden, September 200726 Summary (II) being RICH is wonderful!

27. Claudia Höhne CBM collaboration meeting Dresden, September 200727 Radius versus momentum standard RICHcompact RICH new HT supresses rings with R < 5 cm → pion rings suppressed as expected bad resolution due to distorted rings...  particles from UrQMD only

28. Claudia Höhne CBM collaboration meeting Dresden, September 200728 Radius standard RICHcompact RICH radius for rings from primary electrons with 1 GeV < p < 6 GeV → should be gaussian! still distortions in! not gaussian! broad distribution of radii!

29. Claudia Höhne CBM collaboration meeting Dresden, September 200729 Distance (II) mirror tilted by 5° photodetector tilted by -19° → CbmRoot can deal with these cases! plot distance for ideal matching stronger ring distortions → increased distances

30. Claudia Höhne CBM collaboration meeting Dresden, September 200730 RICH identified e in TRD TRD: Neural Net Method, require output values to be > 0.8 standard RICHcompact RICH TRD copes up for reduced RICH performance!

31. Claudia Höhne CBM collaboration meeting Dresden, September 200731 standard RICHcompact RICH RICH identified e in TOF TOF 2-dimensinal cut in m 2 vs p plane

32. Claudia Höhne CBM collaboration meeting Dresden, September 200732 Identified electrons identified electrons/ event from UrQMD only "standard" includes ring radius corrections and fake ring rejection by neural net evaluation → comparable performance except fakes!! compactstandard all id. e6.59.1 true e3.667.28 true  1.31.1 true p0.180.17 fake rings1.520.56 purity56%80% RICH only compactstandard all id. e2.034.23 true e1.764.07 true  0.05 true p0.010.02 fake rings0.410.15 purity87%96% RICH + TRD + TOF

33. Claudia Höhne CBM collaboration meeting Dresden, September 200733 Appendix: compact Rich performance number of hits for fake rings → cut!

34. Claudia Höhne CBM collaboration meeting Dresden, September 200734 Appendix: compact RICH performance (II) momentum distribution of pions

35. Claudia Höhne CBM collaboration meeting Dresden, September 200735 Appendix: compact Rich performance (III) ring-track distance vs mometum true false