1. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 1 CMS: Electromagnetic calorimetry and e/gamma performance G. Dissertori ETH Zürich LHC Symposium, FNAL, Chicago May 1, 2002 on behalf of the CMS ECAL collaboration

2. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 2 Contents n Setting of the stage n Construction status u Crystals, APDs, VPTs n The new electronics layout n Results from the 2002 test beam n e/gamma performance u Calibration, reconstruction n Preshower n Summary

3. The setting of the stage

4. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 4 The CMS electromagnetic calorimeter n Choice of crystals:  Excellent energy resolution u Structural compactness u Tower structure facilitates event reconstruction (cluster algorithms) n Choice of PbWO 4 : u LHC rate (25 ns) u Radiation hardness u Longitudinal containment (X 0 ) n Choice of Photodetectors (APD, VPT) u |B|=4 T u Intrinsic gain (low light yield) u Radiation level |  | < 1.48 61.2k crystals ~22x23x230 mm 3 (17 types) 25.8 X 0 25 X 0 14.6k crystals Preshower, 3 X 0 (Pb/Si)

5. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 5 Focus on energy resolution If you want precision, you have to take a lot of care... u Longit. and lateral shower containment u Light production, collection uniformity u Nuclear counter effect u Stability of PD gain u Channel to channel intercalibration u Electronic noise u Temperature stability and uniformity u Radiation damage u Pileup u... High Lumi (ECAL TDR)  /E total a = stochastic, 2.7% b = calib, LY non-unif., 5 ‰ c = noise, < 200 MeV Low Lumi

6. Production status

7. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 7 Crystals production Barrel1996 32 mm 44 mm 65 mm Endcap1999 Barrel end 2000 4 Barrel 2 Endcap 2003 85 mm Technological steps in Bogoroditsk Longitudinal wire cut after annealing, ok Difficult longitudinal cut before annealing (because of oven size) u Growing of large ingots well mastered u All 138 ovens upgraded for 85 mm ingot production u Fine-tuning of cutting technology going on see also talk by M. Della Negra

8. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 8 Status: u Same quality obtained with new tech. u Barrel u Barrel : overall 16300 crystals received u Further 3000 crystals expected for Q2 03 u Endcap u Endcap : First batch of 100 pre-production crystals studied, waiting for 2. batch u Super Module production u Super Module production: Bare/Dressed scheme Crystal production: Status

9. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 9 Status: u APDs optimized with extensive R&D programme u Strict Q&A applied, want 99.9% reliability u Production (Hamamatsu) well under way, already > 50 % finished Avalanche Photo Diodes Si 3 N 4, SiO 2, contact p ++ photon conversion p e - acceleration n e - multiplication n - e - drift n ++ e - collection contact Two APDs per capsule Issues: u Contributions to all resolution terms (C, I dark, excess noise factor, gain stability) u Nuclear counter effect u Radiation hardness Internal gain=50 for V=380 V

10. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 10 Status:  All VPTs are measured at 0 < B < 1.8 T and -30 0 <  < 30 0 at RAL  Sample VPTs checked at B=4T and  =15 0 at Brunel, in addition faceplate irradiation u Measured performance matches EE design objectives, but ‘sorting’ might be needed to accommodate a spread in anode response u Production well under way >25% delivered Vacuum Photo Triodes (Endcaps) Single stage photomultiplier tube  = 26.5 mm MESH ANODE Gain 8-10 at B=4T, QE ≈ 20% at 420 nm

11. ECAL electronics

12. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 12 Read out chain Energy  Light  Current  Voltage  Bits  Light PbWO 4 Crystal PbWO 4 Crystal APD VPT APD VPT Floating-Point Preamplifier 4 gain ranges analog gain selection Floating-Point Preamplifier 4 gain ranges analog gain selection Fiber Readout Fiber Readout ADC12-bit 40 MHz ADC12-bit 40 MHz ADC Pipeline  To DAQ Digital Trigger Sum To Trigger Upper-Level Readout ≈ 1000 boards, in counting room one optical link per crystal 800 Mbit/s Curren t VoltageVoltage BitsBits Light Very Front End Board, 1/5 chan n On-detector Light-to-Light readout n All radiation hard n High dynamic range (50 MeV  2 TeV) Problems : Severe cost overrun for data links High cost of ULR In addition : FPPA, noise excess Decision in spring 2002 : Review the ECAL architecture (and resubmit the FPPA) Aim : Reduce cost, maintain functionality Very difficult undertaking, in view of the time scales Problems : Severe cost overrun for data links High cost of ULR In addition : FPPA, noise excess Decision in spring 2002 : Review the ECAL architecture (and resubmit the FPPA) Aim : Reduce cost, maintain functionality Very difficult undertaking, in view of the time scales

13. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 13 Pipeline  To DAQ Digital Trigger Sum To Trigger Upper-Level Readout ≈ 1000 boards, in counting room one optical link per crystal 800 Mbit/s Curren t VoltageVoltage BitsBits Light Read out chain / NEW PbWO 4 Crystal PbWO 4 Crystal APD VPT APD VPT Floating-Point Preamplifier new version 2001 4 gain ranges analog gain selection Floating-Point Preamplifier new version 2001 4 gain ranges analog gain selection ADC12-bit 40 MHz ADC12-bit 40 MHz ADC Very Front End Board, 1/5 chan n On-detector Light-to-Light readout n All radiation hard n High dynamic range (50 MeV  2 TeV) see also talk by M. Della Negra Fiber Readout Fiber Readout Pipeline  To ULR Digital Trigger Sum To Trigger Upper-Level Readout ≈ 220 boards, in counting room Upper-Level Readout ≈ 220 boards, in counting room three optical links per Trigger Tower 25 xtals 800 Mbit/s TriggerTrigger Front End Board, 1/25 channels, 1/25 channels, FENIX chip

14. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 14 Alternative solution Crystals and APD 5 x VFE board FE board n Goal  Replace FPPA (Harris) + ADC (ADI) with new chips in 0.25  m techn. l FPPA considered to be main risk factor u MGPA : 3 parallel ampl, i.e. 3 gains u ADC : 4 parallel 12-bit ADCs u + digital gain selection n Features u All on-detector electronics in same technology, with details known to us u Facilitates LV supply u Reduction of power consumption u Cost reduction n Situation u Chips submitted u Will be studied asap, in lab, if possible, in beam u Decision in summer.... !! MGPA : Multi-Gain Pre-Amplifier new ADC in 0.25  m technology see also talk by M. Della Negra

15. Test beam results M0’, 2002

16. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 16 M0’ in 2002 n M0’ u First complete barrel system test u Uniform construction procedure u 100 channels of a module type 2 l “Old” electronics, noisy FPPA l Final Laser monitoring l Services (Cooling, HV, LV, DCS) n H4 test beam area u Scanning table with automatic positioning of crystals in front of beam (electrons, pions) u Online monitoring (laser, beam data) module on scanning table 100 channels, VFE cards

17. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 17 Objectives n Large scale system test u VFE, HV, LV, DAQ, DCS u Cooling for a large number of channels n Step towards ECAL calibration u System readiness for testbeam in 2003 and calibration in 2004 l DAQ and online software l Moving table l Understand laser monitoring system l Stability checks (laser, temperature) l Preparation for offline analysis n Crystal behaviour under irradiation u Compare laser with beam response, many crystals u Universality n Calibration u Compare lab measurements with beam data

18. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 18 Cooling system Why is temperature stability so important? u Strong dependence of crystal light yield with T, -2%/ 0 C at 18 0 C u Strong temperature dependence of APD gain, dM/dT = -2.4%/ 0 C Thus the requirements are: n Long term stability of xtals and APDs < 0.1 0 C 0.06°C 2 months temperature measured on APDs

19. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 19 Laser monitoring Why is the laser monitoring so important? Light transmission Thus the idea is: n Inject laser light to monitor crystal transparency n Follow signals from beam and laser n Determine slope laser vs. beam n Check universality  laser  particle Signal/Signal 0 t t0t0  particle vs  laser ? 5-10% excellent stability of the laser system achieved, stable at the 0.1% level ! Laser PN diodes Crystals

20. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 20 Laser monitoring signal from Laser signal from Beam (e - )   slope :  = 1.55 Dispersion of  for 19 crystals  Use of same coefficient for all crystals possible ! all crystals possible !  /  = 6.3 % on top of a 5 -10 % effect  /  = 6.3 % on top of a 5 -10 % effect

21. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 21 Calibration n Idea: u Obtain preliminary crystal intercalibration from light yield measurements (and comparison to reference crystal) in the LAB u Previously expected: 6% achievable, as starting point for calibration u Put crystals in test beam and check intercalibration LAB - BEAM u Then compare LAB - BEAM Comparison of Light Yield LY (LAB - BEAM)/BEAM n Result: 4.5 % ! u Possible to infer intercalibration coefficient from LAB measurements at a precision of 4.5 % !... good starting point... 97 crystals : RMS = 4.57 % Sigma = 4.40 % 97 crystals : RMS = 4.57 % Sigma = 4.40 %

22. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 22 Test beam: Conclusions n Learned a lot, still a lot to learn n Important achievements: u Stability of cooling system and laser monitoring system u Behaviour of APDs, HV, LV, VFE electronics u Universality of irradiation behaviour u Intercalibration from LAB measurements n To be improved/changed/foreseen for 2003, 2004: u Final electronics (noise level, auto-gain switching) u Test larger system (up to 400 channels in 2003) u Quick online/offline analysis of incoming data

23. e/gamma performance (calibration and reconstruction) for trigger issues, see talk by C. Seez

24. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 24 Calibration steps n In-situ calibration: at low Lumi  A) Fast intercalibration using  - symmetry, ≈2% few hours  B) Use Z  e + e - for intercalib in  and absolute E scale few days  C) When tracker fully operational : E/p from W  e  few months u Final goal : 0.5 % n In-situ calibration: at low Lumi  A) Fast intercalibration using  - symmetry, ≈2% few hours  B) Use Z  e + e - for intercalib in  and absolute E scale few days  C) When tracker fully operational : E/p from W  e  few months u Final goal : 0.5 % n Laser monitoring: u Correct for variations in crystal transparency due to irradiation n Laser monitoring: u Correct for variations in crystal transparency due to irradiation intercalibration goes directly into constant term (most of the energy in a single crystal) n Precalibration: u Lab measurements, < 5% u Test beam, < 2% but only a fraction of ECAL will be calibrated n Precalibration: u Lab measurements, < 5% u Test beam, < 2% but only a fraction of ECAL will be calibrated

25. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 25 n Idea:  Total transverse energy deposited from a large number of events is the same for all crystals at fixed   Correct ∑E T in a xtal to  ∑E T  in a ring  Reduce number of calibration constants from 60k (in barrel) to 170 (  -rings in barrel)  -symmetry calibration n Limitations:   symmetry not exact: tracker material not homogeneous u With increased knowledge of the tracker material : precision down to 1% in the whole barrel region  Worries: non-Gaussian noise (spikes), large lever arm of extrapolation to high energies n Rates: u If 1kHz of L1 bandwidth assigned, handled by HLT farm: u 1 kHz = 3.6M evts/hour. For L=10 33 this corresponds to 6M minimum-bias crossings/h n Future: u Look at jet triggers u High tresholds to avoid trigger bias n Idea:  Total transverse energy deposited from a large number of events is the same for all crystals at fixed  u Correct ∑E T in a xtal to  ∑E T  in a ring  Thus: reduce number of calibration constants from 60k (in barrel) to 170 (  -rings in barrel) Barrel precision with 18M evts, ignoring  inhomogeneity tracker forward works also for Endcap

26. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 26 Electron reconstruction e  single electrons, p t > 28 GeV only single clusters super-clusters n Main difficulty : tracker material  bremsstrahlung  E breams /E  = 43.6 %, P t = 35 GeV, |  | < 1.5 n Recover by reconstructing clusters of clusters ( super-clusters ) Essential for Z  ee and W  e reconstruction, find compromise between statistics and little bremsstrahlung-loss

27. Preshower

28. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 28 CMS Preshower – Overview Idea of Preshower: Single incident photon Two closely-spaced incident photons from the decay of a  0 Shower profile measured by 2mm-pitch silicon strip sensors

29. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 29 CMS Preshower – Current highlights Active part of the Preshower are 4300 “micromodules” based on 6.3x6.3cm 2 silicon sensors, with 32 strips, equipped with high dynamic range analogue readout (PACE3) 25% of sensors have been produced (in Russia). Remainder will be produced in Russia, India and Taiwan this year Front-end electronics (0.25  m “PACE3” and “K-chip”) submitted in March. Will be tested in Summer 2003 Micromodules are assembled into “Ladders” Ladders are arranged to cover fiducial area Large mechanical pieces being fabricated in 2003 Full-scale production of micromodules on schedule to start in mid-2004

30. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 30 Summary n Construction of the CMS ECAL is progressing well u Improved technology for crystal production (larger ingots) u > 50% of APDs, > 25% of VPTs already there n Major re-design of the electronics readout scheme u Remarkable progress in the project, under high pressure with little time  In summer decision if 0.25  m solution instead of FPPA n Test beam in 2002 u Several essential tests carried out (temperature stability, laser monitoring, precision of the lab intercalibration < 5%) n Calibration and reconstruction  Method identified which allows to achieve in-situ a quick intercalibration in  using minimum bias events u Knowledge of tracker material and bremsstrahlung-recovery essential for good reconstruction

31. G. Dissertori ETH Zürich May 1, 2003 LHCS03, CMS ECAL 31 Acknowledgements n Many thanks to all those who helped me for the preparation of this presentation D. Barney, P. Bloch, J. Cogan, M. Dejardin, M. Diemoz, S. Gascon- Shotkin, P. Lecomte, P. Lecoq, A.v.Lysebetten, F. Nessi-Tedaldi, M. Paganoni, R. Paramatti, C. Seez,... n Thanks to the organizers of the symposium