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The CLEO CsI Calorimeter

The CLEO CsI Calorimeter 15 Years of Physics with Photons h c ( 1 P 1 charmonium) Discovery M(  c ) (GeV)  c Inclusive  c reconstructed M(  0 -recoil) (2S) 0 h c  0 ( c ) >5.5  significance M(h c )=3524.4 0.60.4 MeV (consistent w/spin-wtd  cJ avg) Requirements

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The CLEO CsI Calorimeter

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  1. The CLEO CsI Calorimeter 15 Years of Physics with Photons CsI to CMS. B. Heltsley. April 2005

  2. hc (1P1 charmonium) Discovery M(c) (GeV) cInclusive c reconstructed M(0-recoil) (2S)0 hc0(c) >5.5 significance M(hc)=3524.40.60.4 MeV (consistent w/spin-wtd cJ avg) CsI to CMS. B. Heltsley. April 2005

  3. Requirements • Early 80’s detector landscape • Good tracking + poor calorimetry • Mark III, CLEO I, Argus • Poor tracking + good calorimetry • Crystal Ball, CUSB • CLEO II: have both! • EMCal must fit outside ~1m radius tracking chamber • Magnet coil outside EMCal, so EMCal must be compact, work inside B-field CsI to CMS. B. Heltsley. April 2005

  4. CsI(Tl) Properties Light Output E/E (%) CsI to CMS. B. Heltsley. April 2005

  5. Hermetic Coverage CsI to CMS. B. Heltsley. April 2005

  6. CLEO III/c Layout 48 rings, 128 per ring RICH 820/endcap Drift Chamber 7800 crystals overall CsI to CMS. B. Heltsley. April 2005

  7. Calibrations • Electronic channel level • Pedestals & Gains on each of 3 ranges • Crystal level: conversion factor • Shower level: Energy Scale CsI to CMS. B. Heltsley. April 2005

  8. Bhabha Calibration e+e- E/E = 1.4% @5 GeV Eshower/Ebeam • Assume linearity of light  energy • Obtain a single constant per crystal: gives relative gain • Select e+e- evts: each e has ~Ebeam • Minimize shower energy resolution • 78007800 sparse matrix equation (non-zero near diagonal) • Once determined, why should they change? CsI to CMS. B. Heltsley. April 2005

  9. Light Collection Degradation Crystals migrate from the top band to the bottom band, then stabilize. Cause: lucite-CsI glue joint opens up. CsI to CMS. B. Heltsley. April 2005

  10. Absolute Energy Scale • 0 •  • +- • (2S)cJ Fit huge combinatoric background & subtract E CsI to CMS. B. Heltsley. April 2005

  11. Current CLEO SCal CsI to CMS. B. Heltsley. April 2005

  12. Performance Energy resolution Angular resolution M (GeV) CsI to CMS. B. Heltsley. April 2005

  13. Non-photon rejection • Energy deposited near tracks easy to reject on that basis • Nuclear int’ns cause “splitoffs” separated from central shower matched to track • Splitoffs cause bgd for 0,  • Splitoffs make “neutrino reconstruction” (missing energy) more challenging • Several algorithms developed for rejection • Based on lateral shower profile- collimated or not? • Proximity to track entry points • Energy CsI to CMS. B. Heltsley. April 2005

  14. Lepton ID Example:(2S)+- J/, J/l+l- • e deposits ~all energy •  deposits ~220 MeV (min. i.) with Landau tail • Form “E/p” variable: shower energy/momentum • Peak near ~1 for e • Only small tail from  at high E/p •  peak near small E/p MC Data CsI to CMS. B. Heltsley. April 2005

  15. Example: (2S)00 J/, J/l+l- Very clean, well-modeled 000 CsI to CMS. B. Heltsley. April 2005

  16. Conclusions • W/careful design, a CsI(Tl) EMCal offers excellent resolution in energy (1.5-8%) & angle (3-15mr) for E=0.05-5 GeV • Long term stability demonstrated (glue joints!) • Preserve energy resolution w/careful summing; angular resolution w/MC corrections to c.o.g. • Scale calibration a challenge, but can achieve <0.5% accuracy above 50 MeV with some work • Shower shape, track-shower matching both useful for isolation & splitoff rejection • Payoff in PHYSICS: -lines, 0 & , e & , -reconstruction CsI to CMS. B. Heltsley. April 2005

  17. Crystal Testing CsI to CMS. B. Heltsley. April 2005

  18. Readout • 4 diodes/crystal • Local preamps, 4 crystals/card • Externally summed • Shaped • Digitized (3 scales to preserve dynamic range) • Sparsified • To tape • Disabled diode compensation • CLEO has 4 diodes/crystal, can disable & compensate via downloadable settings to crates • Output gets amplified up accordingly • After 15 yrs, CLEO has 251/7784 crystals w/1 diodes off because they died or became noisy • 240 (1 disabled), 11 (2 disabled), 0 (3 or 4 disabled) CsI to CMS. B. Heltsley. April 2005

  19. Dead Diodes • Disabled diode compensation • CLEO has 4 diodes/crystal, can disable & compensate via downloadable settings to crates • Output gets amplified up accordingly • After 15 yrs, CLEO has 251/7784 crystals w/1 diodes off because they died or became noisy • 240 (1 disabled), 11 (2 disabled), 0 (3 or 4 disabled) CsI to CMS. B. Heltsley. April 2005

  20. How many to sum? Optimize additional energy vs additional noise. CsI to CMS. B. Heltsley. April 2005

  21. Position/angle determination • Correction to centroid: • ~0 at ctr • ~0 at boundaries • not symmetric due to 50-mrad tilt away from vertex-pointing & staggering of front faces • smaller effect at larger energy because shower spreads more, which helps centroid accuracy • peak correction typically 5-10 mm CsI to CMS. B. Heltsley. April 2005

  22. Shower Energy Scale • Which do you want? •  energy peaks at right place • 0 mass peaks at right place • You can’t have both, because • Line shape has low-side tail (leakage!) • W/correct  energy,  mass peaks LOWER than M(0) • CLEO chose  energy peak to be accurate, allowing 0 constrained fit to fix the bias CsI to CMS. B. Heltsley. April 2005

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