Compact RICH detector Claudia Höhne, GSI Darmstadt

Claudia Höhne CBM collaboration meeting Dresden, September 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

Claudia Höhne CBM collaboration meeting Dresden, September 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,....

Claudia Höhne CBM collaboration meeting Dresden, September 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

Claudia Höhne CBM collaboration meeting Dresden, September Radiator radiatorn  th p th  [GeV/c] thresh [nm] radiation length [m] handling? N2N < CH ~  CO ~ CF < 120chemically aggressive N2ON2O (toxic) CH 3 OH (methanol) flammable C 2 H 6 (ethane) ~ as the RICH detector should mainly serve for electron identification, the pion threshold for emission of Cherenkov light should be sufficiently high in momentum

Claudia Höhne CBM collaboration meeting Dresden, September 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

Claudia Höhne CBM collaboration meeting Dresden, September Radiator (III) radiatorn cc  th p th  [GeV/c] L [cm]NN R [cm] #  R [cm]  R [%] N2N * $ 2.3 CO ~22 & 5.3? * from simulation, H 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!

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

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

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

Claudia Höhne CBM collaboration meeting Dresden, September 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

Claudia Höhne CBM collaboration meeting Dresden, September 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

Claudia Höhne CBM collaboration meeting Dresden, September 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

Claudia Höhne CBM collaboration meeting Dresden, September 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

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

Claudia Höhne CBM collaboration meeting Dresden, September 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

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

Claudia Höhne CBM collaboration meeting Dresden, September 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!

Claudia Höhne CBM collaboration meeting Dresden, September 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)

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

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

Claudia Höhne CBM collaboration meeting Dresden, September 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

Claudia Höhne CBM collaboration meeting Dresden, September 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!

Claudia Höhne CBM collaboration meeting Dresden, September 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!

Claudia Höhne CBM collaboration meeting Dresden, September 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)

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

Claudia Höhne CBM collaboration meeting Dresden, September 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

Claudia Höhne CBM collaboration meeting Dresden, September 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!

Claudia Höhne CBM collaboration meeting Dresden, September 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

Claudia Höhne CBM collaboration meeting Dresden, September 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!

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

Claudia Höhne CBM collaboration meeting Dresden, September 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. e true e true  true p fake rings purity56%80% RICH only compactstandard all id. e true e true  0.05 true p fake rings purity87%96% RICH + TRD + TOF

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

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

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