1. Development of FARICH-detector for the ALICE experiment at CERN A.I.Berlev, T.L.Karavicheva, E.V.Karpechev, Yu.V.Kupchinskiy, A.B.Kurepin, A.N.Kurepin, A.I.Maevskaya, Yu.V.Musienko, V.I.Razin, A.I.Reshetin, D.A.Finogeev Institute for Nuclear Research of the Russian Academy of Sciences, Moscow, Russia A.F.Danilyuk, V.L.Kirillov Boreskov Institute of Catalysis S.A.Kononov, E.A.Kravchenko, A.P.Onuchin Budker Institute of Nuclear Physics, Novosibirsk, Russia Feb.27 – March5, 2008 Development of FARICH-detector for the ALICE experiment at CERN Andrey Reshetin INSTR08, Novosibirsk, RUSSIA (slide 1) Institute for Nuclear Research, Moscow

2. Outline ☻ ALICE HMPID-system upgrade ☻ FARICH (Focusing Aerogel RICH) concept ☻ Simulation of a multi-layer aerogel radiator for FARICH-detector ☻ Design project of FARICH-detector with MRS APDs ☻ MRS APD properties (CPTA, Moscow) ☻ Winston-cone holes for light-collection ☻ Cooling system for MRS APD ☻ Schedule for the FARICH beam test at CERN Feb.27 – March5, 2008 Development of FARICH-detector for the ALICE experiment at CERN Andrey Reshetin INSTR08, Novosibirsk, RUSSIA (slide 2) Institute for Nuclear Research, Moscow

3. ALICE HMPID-system upgrade 2 m Each of 7 HMPID modules (42 windows): - has sizes of about 1.5 x 1.0 m - covered azimuth angle Δθ ≈ 18 degrees Each HMPID window covers Δθ ≈ 6 degrees (solid angle ΔΩ ≈ 10 msr) There are free modules (windows) for upgrade with Very High Momentum PID-system Free modules (windows) for VHMPID upgrade Ref: D.Cozza et al. (HMPID Collaboration) NIM A 502 (2003) 101-107. Feb.27 – March5, 2008 Development of FARICH-detector for the ALICE experiment at CERN Andrey Reshetin INSTR08, Novosibirsk, RUSSIA (slide 3) Institute for Nuclear Research, Moscow

4. ALICE HMPID-system upgrade ALICE HMPID-system uses the proximity type geometry without focusing, consists of: - container with liquid C6F14 radiator (n = 1.26) and quartz window - photosensitive detector on the basis of MWPC with CsI-photocathode plane segmented into the pad readout structure (sizes of the pad are 8 x 8.4 mm) Rings measured during the HMPID beam test run ALICE HMPID-system performances (Results of HMPID beam test runs at CERN): ● On an average 16 pe / ring per event track ● Single photon resolution – about 12 mrad ● Cherenkov angle resolution – about 3 mrad ● Particle identification: π/K separation in the momentum range from 1 to 3 GeV/c K/p separation in the momentum range from 1.5 to 5 GeV/c Feb.27 – March5, 2008 Development of FARICH-detector for the ALICE experiment at CERN Andrey Reshetin INSTR08, Novosibirsk, RUSSIA (slide 4) Institute for Nuclear Research, Moscow

5. An important experimental direction of the study in physics of heavy ion collisions is the measurement of the yield of high-Pt particles. The main problem is to study the dominant mechanism of parton energy loss in compressed nuclear matter. “Jet quenching effect” by RHIC PHENIX Collaboration (K.Adcox et al., Phys.Rev.Lett. 88 (2002) 022301 ) gives the indication on a different loss of energy by partons and gluons in nuclear matter. Data by RHIC STAR Collaboration (C.Adler et al. Phys.Rev.Lett. 89 (2002) 202301) show the effect of supression of high-Pt particles up to a momentum ≥ 10 GeV/c (!) ALICE HMPID-system upgrade Physical requirements to characteristics of the VeryHMPID system π/K separation in the momentum range from 3 to 10 GeV/c K/p separation in the momentum range from 5 to 14 GeV/c INSTR08, Novosibirsk, Russia (Feb.27 – March5) (slide 5) Andrey Reshetin, INR, Moscow

6. TIC detector ALICE HMPID-system upgrade FARICH detector There are 2 options for ALICE Very-HMPID-system: 1. Focusing Aerogel RICH (FARICH) detector and 2. Threshold Imaging Cherenkov (TIC) detector A.Braem et al. Nucl. Instr. And Meth. A 409 (1998) 426 INSTR08, Novosibirsk, Russia (Feb.27 – March5) (slide 6) Andrey Reshetin, INR, Moscow

7. FARICH concept First references on this concept: Belle group: 1. P.Krizan, Aerogel RICH, talk given at Super B Factory Workshop in Honolulu, Hawaii 19-22 January 2004, http://www.phys.hawaii.edu/superb04 2. S.Nishida, et al., Studies of a proximity focusing aerogel RICH for the Belle upgrade, Proceedings of the IEEE Nuclear Science Symposium Rome, Italy, October 17- 22, 2004. 3. T.Iijima, S.Korpar et al., Nucl. Instr. and Meth. A548 (2005) 383. 4. S.Korpar et al., Nucl. Instr. and Meth. A553 (2005) 64-69 Novosibirsk group: started discussions of the use of a multy-layer aerogel – April 2003, Alexander Danilyuk – production of 4-layered aerogel May 2004 A.Yu. Barnyakov et al., Nucl. Instr. and Meth. A553 (2005) 70. Charged particle Aerogel n 1 n 2 Photon detector The main goal of the FARICH concept is - to increase the number of photons by using thicker radiator; - to focus Cherenkov cones on the detector sensitive plane without degrading the angle resolution. The FARICH proximity focusing type geometry was proposed. - the use of several layers of aerogel with gradually increasing refractive indices, n3 > n2 > n1 allows to focus Cherenkov cones of the same radius; - refractive indices are determined by different proximity gaps. INSTR08, Novosibirsk, Russia (Feb.27 – March5) (slide 7) Andrey Reshetin, INR, Moscow

8. Simulation of a multi-layer aerogel radiator for FARICH-detector GEANT4 package was used to estimate the performance of the FARICH-detector Input conditions and parameters for optimization of aerogel radiators: - photo-sensor array of MRS APDs with 100% geometrical efficiency; - the measured APD photon detection efficiency (PDE, [%]) as function of the light wavelength; - MRS APD with/without WLS-paint on the entrance window; - the distance between the layer No.2 and the focus plane: D = 500 mm (see Fig.) The following aerogel parameters were considered: ● scattering length λ(sc) = 5 cm at light wavelength 400 nm; ● absorption length λ(abs) = 400 cm “ “ 400 nm; ● total radiator thickness T ≤ 50 mm; We investigated the response of silica aerogel radiators made of 2 to 4 layers to kaons of momentum P = 10 GeV/c. Pion/kaon and kaon/proton separation power values for momenta 10 GeV/c and 14 GeV/c, respectively, have been calculated. INSTR08, Novosibirsk, Russia (Feb.27 – March5) (slide 8) Andrey Reshetin, INR, Moscow

9. Simulation of a multi-layer aerogel radiator for FARICH-detector The simulated dependences of the angle resolution per track σ and number of photoelectrons N pe on a total aerogel thickness T [mm] are shown in Figures Conclusion: at total aerogel thickness up to 30-35mm the angle resolution is almost same for 2-, 3- and 4- aerogel layers (difference: 10-15 %). INSTR08, Novosibirsk, Russia (Feb.27 – March5) (slide 9) Andrey Reshetin, INR, Moscow

10. Simulation of a multi-layer aerogel radiator for FARICH-detector Results of the simulation for momentum 10 GeV/c where: r is the average radius of the Cherenkov ring; σr, 1 pe is the mean deviation of the Cherenkov radius (for single photon). S is the ring area; Npe is the number of detected photoelectrons; σӨ is Cherenkov angle resolution in mrad; π/K sep is the pion/kaon separation power in number of standard deviations for momentum 10 GeV/c. INSTR08, Novosibirsk, Russia (Feb.27 – March5) (slide 10) Andrey Reshetin, INR, Moscow

11. Design project of FARICH- Prototype with MRS APDs CONSTRUCTIONAL and FUNCTIONAL PARTS of the FARICH PROTOTYPE The FARICH Prototype consists of 1. Light-isolating box 2. Thin carbon entrance window for the beam 3. Radiator of Cherenkov photons (2-layer silica aerogel) on the support frame 4. Light-collecting plane with the matrix of Winston-cone holes 5. Photosensitive coordinate matrix with MRS APDs 6. Plate with LV-supply dividers and front-end electronics INSTR08, Novosibirsk, Russia (Feb.27 – March5) (slide 11) Andrey Reshetin, INR, Moscow

12. Design project of FARICH-prototype with MRS APDs MRS APD produced by CPTA Light-collecting Cell (Winston-cone hole) Diam. 3 mm ↓ Diam. 1.1 mm Sensitive area: ≈ 1 mm2 600 pixels FARICH-Prototype is developing in frameworks of INTAS-CERN Research Project No. 05-103-7544: “Development of a Cherenkov detector to extend the PID Capability of ALICE beyond 5 GeV/c” Proposal has been submitted to INTAS in September, 2005 and this Development is the INTAS property. We would like to thank the Belle group for very useful test results obtained in the similar Project. (!) ↓ ↓ ↓ ↓ ↓ Belle group: 1. S.Korpar et al., Silicon photomultiplier as a position sensitive detector of cherenkov photons. “RICH2007”, Trieste, Italy, October 15-20, 2007. 2. T.Iijima et al., Geiger-mode APD as a RICH Photodetector. International Workshop on New Photo-Detectors (PD07) June 28, 2007 INSTR08, Novosibirsk, Russia (Feb.27 – March5) (slide 12) Andrey Reshetin, INR, Moscow

13. Design project of FARICH-prototype with MRS APDs R(max) = 165 mm R(min) = 133 mm Results of simulation for 2 aerogel layers: n1 = 1.050 ; n2 = 1.047 (T1 = 17.2 mm, T2 = 17.8 mm) K-mesons with momentum 10 GeV/c: r = 157 mm (σ = 2.0 mm for 1 pe) Protons with momentum 5 GeV/c: r = 135 mm β = 1.0 r (limit) = 160 mm Aerogel thickness (2 layers) T = 35.6 mm N(pe) = pe / ring (per event track) Angle res. for K-mesons 10 GeV/c σ=0.61 mrad π/K separation 5.8 σ Taking into account simulation results the design Geometry for the Prototype Photosensitive Matrix has been chosen: Photosensitive ring is divided by 4 sectors: R(min)=133 mm, R(max)=165 mm, S=120 cm2 Total amount of MRS APDs: 900 - on the Ring, 25 – in centre Geometrical efficiency: about 50% (APD cell sizes) and about 47% (ring sector sizes) We will have the total amount of photoelectrons: pe / ring per event track for Prototype Matrix and pe / ring for full scale Matrix w Prototype Photosensitive Matrix INSTR08, Novosibirsk, Russia (Feb.27 – March5) (slide 13) Andrey Reshetin, INR, Moscow

14. MRS APD performances (CPTA, Moscow) Measurements of MRS APD performances were carried out by Yu.Musienko on test benches at CERN APD Lab and D.Finogeev and Yu.Kupchinskiy at INR, Moscow As example the dependence of the photon detection efficiency PDE on a light wavelength for MRS APDs of different types is shown. We plan to use “50V-APD” for our FARICH Prototype INSTR08, Novosibirsk, Russia (Feb.27 – March5) (slide 14) Andrey Reshetin, INR, Moscow

15. MRS APD performances (CPTA, Moscow) For tests, the entrance windows of a few APDs was covered by a special wave length shifter film (paint) developed by Photonique SA (Geneva). Dependences of the PDE on a light wavelength for MRS “50V-APDs” and the “50V-APDs” + WLS-paint are shown. As result the WLS-film increases the PDE of about two times at 450 nm and about ten times in the range 300-400 nm. INSTR08, Novosibirsk, Russia (Feb.27 – March5) (slide 15) Andrey Reshetin, INR, Moscow

16. MRS APD performances (CPTA, Moscow) 0.6 mrad 0.9 mrad Nevertheless the simulation results show that angle resolution for MRS APD with WLS is degraded: to 0.9 mrad as compared 0.6 mrad for APD without WLS The reason: a big dispersion of the reflective index in aerogel n = f(λ) for a blue light (?) Or a big forward scattering for a blue light (?) INSTR08, Novosibirsk, Russia (Feb.27 – March5) (slide 16) Andrey Reshetin, INR, Moscow

17. Dependences of the Dark current, Gain and PDE (410 nm) on Bias [V] for “50V - MRS APD” with WLS-paint produced by CPTA (Moscow). For the set of 925 MRS APD we use optimal Bias in a range of about 50-51 V 474849505152474849505152474849505152 MRS APD performances (CPTA, Moscow) Dark current [mkA] APD Gain (x10^6) PDE (410 nm) [%] INSTR08, Novosibirsk, Russia (Feb.27 – March5) (slide 17) Andrey Reshetin, INR, Moscow

18. Winston-cone holes for light-collection Winston-cone hole: Diam. 3 mm → Diam. 1.1 mm For testing the prototype Winston-cone holes with parabolic inner surface in aluminium and stainless steel plates have been produced. Winston-holes in aluminium plate had 4 types of the treatment of an inner surface: - treatment with special (14 class) polishing - treatment with polishing of a tool edge; - pressure method; - pressure method with polishing. Winston-holes in stainless plate were polished by 4 different methods of electric-plasma polishing. parabolic inner surface INSTR08, Novosibirsk, Russia (Feb.27 – March5) (slide 18) Andrey Reshetin, INR, Moscow

19. Winston-cone holes for light-collection For APD without Winston- cone light collection (open version) the mean value of amplitude spectrum is in 120 ch. = 600 ch – for stainless steel Winston-cone holes Pedestal: = 40 ch. Experimental geometrical factor: ≈ 7.0 +/_ 0.36 Calculated geometrical factor: ≈ 7.44 Estimation of light collection efficiency: ≈ 94 +/_ 5% Relative dependence of the light collection efficiency on Winston- cone holes of different types INSTR08, Novosibirsk, Russia (Feb.27 – March5) (slide 19) Andrey Reshetin, INR, Moscow

20. Cooling system for MRS APD Lay-out of the Cooling system is presented in Fig.1 1. Copper plate 2. Heat Exchanger: Peltier module (131 W) 3. Cooler: Water radiator 4. MRS APD 5. Thermo-pair sensor The temperature T min = - 17 ºC around the CPTA APD position was achieved Fig.1 Water micro-tubes 2 1 3 45 INSTR08, Novosibirsk, Russia (Feb.27 – March5) (slide 20) Andrey Reshetin, INR, Moscow

21. Cooling system: heat exchanger and cooler 1. Heat Exchanger: Peltier Module “Drift 1.05” Work performances: Power = 131.0 W Sizes: 40×40×3.5 mm Voltage = 24.6 V Current = 8.6 A ∆T = 70 ºC 2. Cooler a) air cooler b) water cooler Results of CPTA APD cooling (APD coupled with copper plate ∆h = 1 mm) 0.08-17water option 0.20+8air option 1.66+22room Dark noise [MHz]T ºC Cooling system for MRS APD At -17 C Dark noise can be decreased in about 20 times (until 0.08 MHz) (!) INSTR08, Novosibirsk, Russia (Feb.27 – March5) (slide 21) Andrey Reshetin, INR, Moscow

22. Schedule for the FARICH beam test at CERN Beam channel – ALICE test beam channel T10 Beam particles – negative pions (electrons) Momentum range - 2 ÷ 10 GeV/c Beam intensity - 200-500 particles/spill Beam time – October-November, 2008 20 shifts INSTR08, Novosibirsk, Russia (Feb.27 – March5) (slide 22) Andrey Reshetin, INR, Moscow