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P. Lecoq, E. Auffray , S. Gundacker CERN, Geneva, Switzerland

Ultimate Time Resolution in Scintillator -based detectors for Calorimetry and Time-of-Flight PET. P. Lecoq, E. Auffray , S. Gundacker CERN, Geneva, Switzerland. This work is supported under the ERC Grant Agreement N°338953–TICAL. Why fast timing in HEP?. TOF for Particle ID

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P. Lecoq, E. Auffray , S. Gundacker CERN, Geneva, Switzerland

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  1. Ultimate Time Resolution in Scintillator-based detectors for Calorimetry and Time-of-Flight PET P. Lecoq, E. Auffray, S. Gundacker CERN, Geneva, Switzerland This workissupportedunder the ERC Grant Agreement N°338953–TICAL

  2. Whyfast timing in HEP? • TOF for • Particle ID • Pileupmitigation athighluminositycolliders • Improve pattern recognition in Cerenkov detectors • Cerenkov/Scintillation differentiation (Dual Readout Cal) • Bringadditional information on the showerdevelopment in a segmentedcalorimeter • Current state of the art for TOF in Alice expt: 75ps • Major advances in detector/enabling technologies • Fast and high light yieldscintillators • SiPMs, MCPs • Fastlow noise FE electronics (NINO) • A 4D imaging HHCAL iswithinreach

  3. Whyfast timing in PET? • TOF for rejecting background events (event collimation) • Requires200ps TOF resolution for a few cm ROI (EndoTOFPET-US FP7 project) • TOF for improving image S/N • Requires100ps TOF resolution for x5 S/N improvement, whichbrings a potentialsensitivity gain (dosereduction) • TOF for direct 3D information • Requires20ps TOF resolution for 3mm resolutionalong LOR • TOF for restoring image quality for limited angle tomography

  4. State of th Art: CTR with NINO chip (Time over Threshold)

  5. Influence of crystallength on CTR S. Gundackeret.al., NIMA, dx.doi.org/10.1016/j.nima.2013.11.025

  6. State of the art: EndoTOFPET system performance • CTR distribution of 168 Modules (4x4 cells each) , 2688 LORs • The bias voltage applied to each module is fixed to 2.5 Volt over breakdown Voltage. • Same threshold and temp for all channels To be compared to ≈ 550(350) ps on commercial systems 4x4 cells 3.5x3.5x15mm3crystals 80mm 3M ESR gap DiscreteSilicon-through-via (TPV) MPPC array Hamamatsu (S12643-050CN) 3x3mm2, 0.6mm gap NINO ASIC 239 ps

  7. The detectionchain Crystal SiPM electronics Dt q2 g tkthpe = Dt + tk’ ph + ttransit + tSPTR + tTDC Scintillation process Transit time jitter Single photon time spread TDC conversion time Conversion depth Unwanted pulses 1 DCR, cross talk Afterpulses Randomdeletion 1 Absorption Self-absorption Randomdeletion 2 SiPM PDE Unwanted pulses 2 DCR

  8. Modeling the whole chain SiPM S. Gundacker Thesis, CERN, Feb2014

  9. Analog vs Digital approachCramer-Raolowerbound • Under investigation • in the frame of the FP7 EndoTOFPET-USproject • with the Philips digital evaluation kit recentlyordered S. Gundacker Thesis, CERN, Feb2014

  10. Parameters of interest to improve timing resolution Parameters for LSO: Ce, Ca and Hamamatsu S10931-050P MPPC Rise time influence limited by SPTR (66ps) CTR improveslike SQRT (photon time density)

  11. Factorsinfluencingscintillator time resolution Besides all factorsrelated to photodetection and readoutelectronics the scintillatorcontributes to the time resolutionthrough: • The scintillation mechanism • Light yield, • Rise time, • Decay time P. Lecoq et al, IEEE Trans. Nucl. Sci. 57 (2010) 2411-2416 • The light transport in the crystal • Time spreadrelated to different light propagation modes • The light extraction efficiency (LYLO) • Impact on photostatistics • Weights the distribution of light propagation modes

  12. Influence of prompt photons 2x2x3mm3LSO:Ce, Ca with 70ps rise time and an arbitrarynumber of prompt photons generated

  13. Light generation in scintillators 5d Rare Earth 4f

  14. Hot intraband luminescence • Wideemissionspectrumfrom UV to IR • Ultrafastemission in the ps range • Independant of temperature • Independant of defects • Absolute Quantum Yield Whn/Wphonon = 10-8/(10-11-10-12) ≈ 10-3 to 10-4 ph/eh pair • Higheryield if structures or dips in CB? Interesting to look at CeF3 More details in SCINT2013 paper TNS-00194-2013 M. Korzhik, P. Lecoq, A. Vasil’ev

  15. Photonpropagation time spread Photodetector q2 x g L with q1 0 q2qc Dtmax= 71 ps for x = L Dtmax= 384 ps for x = 0 For L = 20mm LSO (n = 1.82) ngrease= 1.41 qc = 50.8°

  16. Photoniccrystals Nanostructured interface allowing to couple light propagation modes inside and outside the crystal Crystal- air interface with PhC grating: Crystal air θ>θc θ>θc Total Reflection at the interface θ>θc Extracted Mode

  17. Photoniccrystalsincrease the light extraction efficiency • Use large LYSO crystal: 10x10mm2 to avoidedgeeffects • 6 different patches (2.6mm x 1.2mm) and 1 (1.2mm x 0.3mm) of differentPhC patterns 0° 45° A. Knapitsch et al, “Photonic crystals: A novel approach to enhance the light output of scintillation based detectors, NIM A268, pp.385-388, 2011

  18. Photoniccrystalscompress the light propagation modes Extract more photons at first incidence with PhC = better timing Regular LYSO a) b)

  19. Conclusions • Standard scintillation mechanisms are unlikely to giveaccess to the 10ps range • A number of transientphenomenacouldgeneratepsmeasurablesignals • Photoniccrystalsimprovescintillator timing resolution by twomeans: • By increasing the light output and thereforedecreasing the photostatisticsjitter • By redistributing the light in the fastest propagation modes in the crystal

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