Highly Granular Scintillator-based Calorimetry with Novel Photodetectors

1. ICHEP’04 Beijing Highly Granular Scintillator-based Calorimetry with Novel Photodetectors for Future Linear Collider Michael Danilov ITEP(Moscow) Representing CALICE Collaboration

2. LC Physics goals require DEJ/√EJ~30% This can be achieved with Particle Flow Method (PFM): Use calorimeter only for measurement of K,n, and g Substitute charged track showers with measurements in tracker LC detector architecture is based on PFM, which is tested mainly with MC Experimental tests of PFM are extremely important We are building now a prototype of scintillator tile calorimeter to test PFM

3. Particle Flow Method • Ejet = Echarged + Ephotons + E neutr.hadr. • 100% 65% 25% 10% • 2Ejet = 2Echarg. + 2Ephot + 2Eneutr + 2Confusion • 2Confusion - Dominant contribution • Shower separation and reconstruction are the main optimization parameters

5. 3x3 cm2 granularity is highly desirable for shower separation. Is it possible? YES – with a novel photo detector Silicon Photomultiplier developed in Russia

6. SiPM main characteristics • Pixel size ~20-30mm • Electrical inter-pixel cross-talk minimized by: • decoupling quenching resistor for each pixel • boundaries between pixels to decouple them •  reduction of sensitive area • and geometrical efficiency • Optical inter-pixel cross -talk: • due to photons from Geiger discharge initiated by one electron and collected on adjacent pixel • Working point: VBias = Vbreakdown + DV ~ 50-60 V • DV ~ 3V above breakdown voltage • Each pixel behaves as a Geiger counter with • Qpixel = DV Cpixel • with Cpixel~50fmF  Qpixel~150fmC=106e • Dynamic range ~ number of pixels (1024) •  saturation 42m 20m pixel h Resistor Rn=400 k Al R 50 Depletion Region 2 m Substrate Ubias

7. SiPM Spectral Efficiency • Depletion region is very small ~ 2mm • strong electric field (2-3) 105 V/cm • carrier drift velocity ~107 cm/s • very short Geiger discharge development < 500 ps • pixel recovery time = (Cpixel Rpixel) ~ 20 ns • Photon detection efficiency (PDE): • - for SiPM the QE (~90%) is multiplied by Geiger efficiency (~60%) and by geometrical efficiency(sensitive/total area ~30%) • highest efficiency for green light •  important when using with WLS fibers • Temperature and voltage dependence: • -1 oC  +4.2% in Gain * PDE*Xtalk • +0.1 V  +4.5% in Gain * PDE*Xtalk WLS fiber emission

8. 20 40 one pixel gain (exp. data) one pixel gain (linear fit) , % =565nm) detection efficiency ( l e 15 30 5 10 20 One pixel gain M, 10 Efficiencyof light registration 5 10 operating voltage 0 0 0 1 2 3 4 5 6 , V Overvoltage U=U-U D U =48V breakdown breakdown Photon detection efficiency  = QEgeom

9. : ,pixels SiPM signal saturation due to finite number of SiPM pixels Average number of photoelectrons for central tiles for 6 GeV Very fast pixel recovery time ~ 20ns For large signals each pixel fires about 2 times during pulse from tile

10. SiPM Noise random trigger noise rate vs. threshold 1p.e. 2p.e. Ped. 3p.e. 1p.e. noise rate ~2MHz. threshold 3.5p.e. ~10kHz threshold 6p.e. ~1kHz Optimization of operating voltage is subject of R&D at the moment.

11. Experience with a small (108ch) prototype (MINICAL) Moscow Hamburg SiPM Tile with SiPM cassette 3x3 tiles

12. Light Yield from Minical tiles (5x5x0.5cm3) Using triggered Sr source and LED at ITEP LED b N pixel Using electron beam at DESY (SiPM signals without amplification) Good reproducibility after transportation from Moscow to Hamburg

13. Y11 MC 1mm fiber, Vladimir Scintillator, mated sides, 3M foil on top and bottom Reduction in light yield near tile edges is due to finite size of a b source Light yield drop between tiles acceptable (Calorimeter geometry is not projective) Cross-talk between tiles ~2% - acceptable Light Collection Uniformity, Light collection efficiency 5x5x0,5cm3 mm Sufficient uniformity for a hadron calorimeter even for large tiles Acceptable cross-talk between tiles of ~2% per side Sufficient light yield of 17, 28, 21 pixels/mip for 12x12, 6x6, and 3x3 cm2 tiles (quarter of a circle fiber in case of 3x3 cm2 tile)

14. Shower Shape 3 GeV e+ Black – data Yellow -MC After single tile calibration and smearing MC describes well shower shape

15. Energy Resolution Measurement of electron energy with HADRON CALORIMETER resolution modest • Very good agreement between PM and SiPM on the whole range 1 - 6 GeV • Low sensitivity to constant term due to limited energy range • MC tuning still in progress include more effects: -beam energy spread -steal thickness tolerances Preliminary • SiPM • PM • MC (SiPM)

16. SiPM Beam position NON-LINEARITY and ENERGY RESOLUTION for DIFFERENT BEAM POSITIONS For all cases the same fit function is used ! Energy resolution With universal SiPM calibration curve there is no differences in response for different beam positions (different SiPM saturation)

17. Cassette, Absorber and Support Structure Cassette contains 220 tiles with SiPM and electronics There are 40 cassettes between 2cm iron absorber Altogether about 8000 tiles of 3x3, 6x6 and 12x12 cm2 with SiPM and individual readout

18. CONCLUSIONS Particle Flow Method requires high granularity especially longitudinally Scintillator tiles with WLS fiber light collection and SiPM mounted directly on tiles can be used to build highly segmented hadronic calorimeter, which can be used in analog or semidigital mode Tests of 108 channel prototype (MINICAL) demonstrated effectiveness and robustness of this technique Eight thousand channel calorimeter prototype with tiles in the core as small as 3x3 cm2 is being constructed now. It will be ready for tests next year. Hcal prototype together with Ecal prototype will allow to to test experimentally the Particle Flow Method

19. Backup Slides

20. SiPM

21. SiPMs will be tested and calibrated with LED before installation into tiles (noise, amplification, efficiency, response curve, x-talk) PC driven generator LED driver Remote control 16 channel power supply Steering program DATA BASE ……. gate Tested SiPM .. X~100 16 ch 12 bit ADC 16 ch amp 16 ch 12 bit ADC Scheme of test bench for SiPM selection at ITEP

22. Tiles will be tested with a triggered β source and LED before installation into cassette Test bench for tile tests at ITEP 16 ch 12 bit ADC 16 chan amps gate 16 ch remote control power supply Steering program b -source 16 sci tile plane step motor trigger counter DATA BASE movable frame discriminator

23. Emission Spectrum of Y11 WLS Fiber Measured at distances 10cm, 30cm, 100cm and 300cm from source.

24. Longitudinal segmentation more important

25. Separation can be further improved by optimization of algorithm

27. Comparison of the SiPM characteristics in magnetic field of B=0Tand B=4T (very prelimenary, DESY March 2004) LED signal ~150 pixels A=f(G, , x) No Magnetic Field dependence at 1% level (Experimental data accuracy)

28. Long term stability of SiPM • 20 SiPMs worked during 1500 hours • Parameters under control: • One pixel gain • Efficiency of light registration • Cross-talk • Dark rate • Dark current • Saturation curve • Breakdown voltage No changes within experimental errors 5 SiPM were tested 24 hours at increased temperatures of 30, 40, 50, 60, 70, 80, and 90 degrees No changes within experimental accuracy