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Performance of the PWO Crystals of the CMS electromagnetic calorimeter

Performance of the PWO Crystals of the CMS electromagnetic calorimeter. Francesca Cavallari INFN Rome (on behalf of the ECAL CMS collaboration). Outline. Introduction The choice of the PWO The production Crystal properties Radiation Hardness Test-beam results. Introduction.

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Performance of the PWO Crystals of the CMS electromagnetic calorimeter

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  1. Performance of the PWO Crystals of the CMS electromagnetic calorimeter Francesca Cavallari INFN Rome (on behalf of the ECAL CMS collaboration)

  2. Outline • Introduction • The choice of the PWO • The production • Crystal properties • Radiation Hardness • Test-beam results

  3. Introduction

  4. The choice of the PWO The LHC is a very demanding environment for the detectors: Requirements: ECAL characteristics: Crystal calorimeter • High resolution for high energy e/ • LHC bunch separation 25 ns 80% of the PWO light is collected in 25ns • LHC Luminosity 1034cm-2s-1 PWO is radiation tolerant and with R&D is acceptable for LHC • High granularity • Detector must be compact PWO has Xo=0.89 cm RM=2.2 cm Photon sensors: solid state devices (barrel) and VPT in Endcaps • Magnetic field in CMS is 4T • Cost must be limited PWO is not so expensive (1.6 $/cm3 ) and easy to produce in big quantities Ushower = R2M Xo=13.5cm3 => PWO cost = 21.6 $/Ushower

  5. The choice of the PWO PWO Disadvantages: • PWO Light Yield is rather low: ~10 pe/MeV • (with PMT and tyvek wrapping at 18 C) • so photon sensors with some amplification are needed • (APD in the barrel, VPT in the Endcap) • Low S/N ratio and complex electronic • PWO LY T coefficient is –2%/C • A good temperature • stabilization is required

  6. Theoretical transmission 100 '98 crystal Transmission (%) 80 60 '95 crystal 40 20 1998 1995 0 Wavelength (nm) 300 350 400 450 500 550 600 650 700 The choice of the PWO • 1992 : first expression of interest • 1994 : choice of PWO for CMS-ECAL • 1994-1998 : R&D phase • 1998-2000 : Pre-Production of 6000 crystals • 2001 : Start of the Production

  7. 50 Dimensions Transmission 40 Light Yield Decay time 30 Slope/Rad.hardness 20 10 0 set-98 set-00 set-99 dic-00 dic-98 dic-99 giu-99 giu-00 mar-00 mar-99 The production CMS PWO Barrel production crystals are made by Bogoroditsk BTCP with the Czochralski method • Improve the quality • Homogeneity of parameters • Success to: • Increase the yield • Increase the production rate

  8. Barrel 1996 preprod. Endcap 1999 32 mm 44 mm Barrel End 2000 65 mm The production

  9. The production: new developments 4 Barrel crystals … or 2 Endcap crystals 85 mm 85 mm Still R&D…

  10. LY@8X0 500 400 LY(x) 300 200 100 1400 0 1200 LY@8X0 LY@8X0 (pe/MeV) 0 1 3 6 9 10 11 12 13 14 16 2 4 5 7 8 15 1000 800 600 400 200 0 1 4 8 10 11 12 14 16 0 2 3 5 6 7 9 13 15 LY@8X0 (pe/MeV) Crystal properties: LY Batch 1 to 7 • LY@8X0 8 pe/MeV at 18°C • LY(100ns)/LY(1ms) > 90% • -0.35 %/X0 FNUF  +0.35 %/X Batch 8 to 14 Check quality and guarantee the resolution of the calorimeter

  11. Crystal properties: LY uniformity FNUF=1/LY dLY/dx (3.5-11.5 cm) • all polished • Ra=0.34 m • Ra=0.24 m Depolishing 1 lateral face causes LY loss but gives required LY uniformity

  12. (crystals all polished) Lab measurement Crystal properties: LY uniformity Test beam data Resolution calculated on a single crystal

  13. 350 LY@8X0 FNUF 300 500 250 200 400 150 300 100 50 200 0 -1.5 -1 -0.5 0 0.5 1 1.5 2 NuF Front (%/Xo) 100 1400 1200 FNUF 0 1200 LY@8X0 LY@8X0 (pe/MeV) 0 1 3 6 9 10 11 12 13 14 16 2 4 5 7 8 15 1000 1000 800 800 600 600 400 400 200 200 0 0 1 4 8 10 11 12 14 16 0 2 3 5 6 7 9 13 15 -1.5 -1 -0.5 0 0.5 1 1.5 2 LY@8X0 (pe/MeV) NuF Front (%/Xo) Crystal properties: LY uniformity Batch 1 to 7 <Ra> depolished face +0.2 Batch 8 to 14 <Ra> depolished face +0.39

  14. NO XTAL defects TT LT LT TT homogeneity of dopant Good trans. at emis. Peak => LY Rad-hardness Crystal properties: Transmission T=p2·exp(-(p3)/w- exp((p0-w)·p1)) • LT360nm 25% • LT420nm 55% • LT620nm 65% • LTslopeinflection > 3%/nm •  dlTT=50% 3nm

  15. batch 1 10 Mean: 61.88% StDev. : 7.5% 8 100 6 Number of crystals Longitudinal Transmission (%) 90 4 80 batch 8 2 70 60 250 0 75 30 35 40 45 50 55 60 65 70 80 Mean: 69.01% Transmission at 420nm (%) 50 200 StDev. : 1.59% 40 Wavelength (nm) 150 30 1400 6000 crystals 100 20 1200 10 50 batch 14 1000 150 55% 0 Mean: 70.07% 800 0 700 300 350 400 450 500 550 600 650 30 40 50 55 60 75 80 35 45 65 70 no.of Xtals Transmission at 420nm (%) StDev. : 1.46% 600 100 400 200 50 0 30 35 40 45 50 55 60 65 70 75 80 Transmission at 420nm (%) 0 30 35 40 45 50 55 60 65 70 75 80 Transmission at 420nm (%) 11.04.01 Crystal properties: Transmission

  16. Total dose after 10 years of running (5x105 pb-1) [cm] EE [Gy] EB EE 0.15 Dose rates [Gy/h] in ECAL at luminosity L=1034cm-2s-1 Radiation environment in CMS Total dose in the barrel after 10 years at the LHC is ˜2*103Gy EB Dose rate at high L in the Barrel is 0.15 – 0.3 Gy/h in the Endcaps 0.3-15 Gy/h

  17. 8 0 Front irrad., 1.5Gy, 0.15Gy/h 7 0 6 0 5 0 T(%) LYloss=(LY0-LYirr)/LY0 (%) 4 0 i n i t i a l 3 0 LYirr/LY0 (%) a f t e r i r r a d i a t i o n 2 0 1 0 0 3 0 0 3 5 0 4 0 0 4 5 0 5 0 0 5 5 0 6 0 0 6 5 0 7 0 0 w a v e l e n g t h ( n m ) 2) Saturation level Crystal Radiation Hardness • Scintillation mechanism not • affected but Transparency loss

  18. N = 32 Xtals StDev : 1.21%Mean: 3.39% batch 1 10 Front irrad., 1.5Gy, 0.15Gy/h 8 100 6 4 Statistics on 368 crystals Mean : 2.45 % StDev : 1.06% 80 LY loss (%) 2 20 60 0 N = 33Xtals batch 8 16 StDev : 0.9%Mean: 1.92% 40 0 0 0 1 1 1 2 2 2 3 3 3 4 4 4 5 5 5 6 6 6 7 7 7 8 8 8 9 9 9 10 10 10 12 Rejected for LTslope < 1.5%/m Rejected for LT@350nm < 10% 8 20 20 4 StDev : 1.21%Mean: 0.92% N = 19Xtals 0 16 0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 LY loss (%) 12 batch 14 8 LY loss (%) 4 0 LY loss (%) Irradiation tests LYloss=(LY0-LYirr)/LY0 (%)

  19. Barrel crystal Endcap crystal =1.7 =1.7 =2.3 =3.0 =2.3 =3.0 Irradiation tests Saturation levels

  20. ACCOR Dark room temperature : 20±0.5°C rel. humidity: 50±10% ACCOCE Capacity: 35 crystals/run 1 run time: approx. 10 hours Crystal Quality Control All the relevant Crystal characteristics are controlled by two automatic machines (ACCOCE and ACCOR) before assembly.

  21. crystal LY Electronic calibration with test-pulse APD gain (ACCOS) (CAPUCINE/ETTE) (LYON) Test-beam data LAB measurements Detector Calibration with Lab measurements The quality of the lab measurements is so high that we can predict the crystal intercalibration in CMS at ~ 5%

  22. Test-beamperformance The careful control of crystal properties shows that a very good resolution can be obtained • 280 GeV electrons • 1999 prototype • 30 preprod. crystals • Charge ADC Resolution as a function of energy

  23. Conclusions • The CMS PWO prod. crystals are now well suited for CMS • Several years of R&D have led to satisfactory and homogeneous properties of the crystals • All relevant info about radiation hardness and calorimeter resolution can be measured in the lab. Before assembly • BCTP has successfully produced new crystals from large ingots • New development under way to increase further the rate

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