1. Towards an RPC-based HCAL Design Stephen R. Magill Argonne National Laboratory Digital HCAL for an E-Flow Calorimeter Use of RPCs for DHCAL RPC Design Choices, Issues Readout Electronics Time Scales

2. Summary of Recent Mini-Workshop on RPCs for a LC HCAL Participants : G. Drake, V. Guarino, S. Kuhlmann, S. Magill, B. Musgrave, J. Repond, D. Underwood, B. Wicklund Argonne National Laboratory J. Butler, M. Narain Boston University E. Blucher, M. Oreglia University of Chicago Topics : RPC Parameters Design Choices/Optimizations Issues/Concerns for R&D Mechanical/Electronics R&D Time Scales Organized by J. Repond at ANL – November 1

3. Digital HCAL for an E-Flow Calorimeter Charged particles ~ 62% of jet energy -> Tracker  /p T ~ 5 X 10 -5 p T 190 MeV energy resolution to 100 GeV Jet Photons ~ 25% of jet energy -> ECAL  /E ~ 15-20%/  E : ~900 MeV to energy resolution Neutral Hadrons ~ 13% of jet energy -> HCAL  /E < 80%/  E W, ZW, Z 30%/  M 75%/  M Can explore EWSB thru the interactions : e + e - -> WW and e + e - -> ZZ -> Requires Z,W ID from dijets -> Can’t use (traditional) constrained fits

4. Compare to digital  K L 0 Analysis – Analog Readout  /mean ~ 26% E average ~ 13 GeV

5. Average : ~43 MeV/hit Analog EM + Digital HAD x calibration Slope = 23 hits/GeV K L 0 Analysis - Digital Readout  /mean ~ 24%  Digital   Analog

6. Generic design HV Gas Pick-up pad(s) Graphite Mylar Resistive Plates: Glass or Bakelite Advantages: Thin layer (≤ 10 mm) High single particle efficiencies (> 95%) Flexible geometrical design Flexible pad readout segmentation Printed circuit Simple Front-End readout Reliable Underlying physics mostly understood see http://www.coimbra.lip.pt/~rpc2001/talks.html Cheap Use of RPCs for Digital HCAL

7. Resistive plates Glass cheap, simple Bakelite needs to be coated with linseed oil source of major problem with BaBar chambers Geometry Glass thickness Several thicknesses on hand Gas gap thickness Smaller → reduced HV Multiple gaps Smaller gaps → improved long-term stability Higher efficiency Completely different design Preferred HARP Experiment at CERN: TOF Preferred Particle Design Choices

8. Operation Avalanche mode Faster (~10kHz) Lower HV Smaller signal (~1pC) Needs pre-amplifier Better long-term prognosis No multiple streamers Streamer mode Slower (~1kHz) Higher HV Large signals (~100pC) Sharp signal Multiple streamers Cosmic ray tests at ANL Charge [pC] High Voltage [kV] Preferred Gas Mixture Freon/Argon/IsoButane 62:30:8 Used by Belle (does not suppress streamers) Freon/IsoButane/SulfurHexafluoride 90:5:5 Used by HARP (suppresses streamers) Many more…

9. Safety with HV Using up to 10kV Can be reduced with smaller gaps by operation in avalanche mode Cross talk between pads Significant charge on neighboring pad Reduced with higher resistivity graphite layer 40kΩ/□ → 200kΩ/□ → 1M Ω/ ٱ pad – ground plane distance dependence Signal shape very different Easy to discriminate: cross talk at 1- 4% level Long term operation Significant experience elsewhere (L3) Reason for choosing avalanche mode/multiple gaps Overall Thickness Most likely will need  10 mm Calibration Will be needed? Pad structure Issues and Concerns

10. Assume L LC = 0.5x10 34 cm -2 s -1 = 0.5x10 -2 pb -1 s -1 σ 1 γ (500 GeV) = 4 pb → N/s = 0.02 σ 2 γ→ee (800 GeV) = 34 mb → N/s = 170x10 6 σ 2 γ→μμ (800 GeV) = 473 nb → N/s = 2400 σ 2 γ → h (800 GeV) = 189 nb → N/s = 945 From V M Budnev et al. Phys. Lett. 15(1974) 181-282 Easy Not our problem Should be ok Recharging time of RPCs : Avalanche mode ~10 4 Hz Streamer mode ~10 3 Hz Rate Estimations Particle rates from PYTHIA Beam pipe 24.1 % = 15.7 GeV Endcaps 75.8 % = 1.53 GeV Rate/endcap = 613 Hz 283 Hz (E> 1GeV) Barrel 0.06 % = 5.0 GeV

11. A Readout Electronics System for RPCs General Concepts Each Channel has a Discriminator – a 1-Bit ADC Timestamp Each Hit Store Timestamps in Local Buffers, Read Out Periodically No Trigger System  Read Out Timestamps into Trigger Processor  Use Timestamps to Construct Hits  Works Well for Low Event Rates and Low Noise Rates  Like MINOS DAQ

12. Custom Front-End IC Essential Functions : Low-Noise Preamp (Needed for Avalanche Mode) Discriminator Timestamp Circuitry Holding Buffer Readout For Testbeam (~400K Channels) – Will Probably Need Dedicated Run (~$100K, 3-6 Months, Packaging, Wafer Testing...)  Like CDF SVX Detector! For Production (~50M Channels) – Cost of Custom IC Design & Fab Will Be Worth It  << $1 /Channel for Chip

13. Front-End PCB Design Top View – highly-integrated approach Cross-sectional view of multi-layer PCB

14. Back-End Readout Essential Functions : Receive Serial Data Streams from Front Ends Concentrate Data Form "Time Frames“ (~1 Sec for MINOS) Send Data to Trigger Processor Realization : Use VME Crates for Infrastructure Data Concentrators Receive Serial data streams from Front Ends Data Concentrators Also Provide Clock & Control

15. Until September of 2004 Finalize prototype design Construct 40 layers of 1m 2 corresponding to an 1 m 3 HCAL section Build gas mixing/distribution system Select/purchase HV/LV power supplies Next 6 months Build chambers: explore different designs R&D with resistive layer Initiate design of prototype chambers Design and build readout pads (multilayer boards) Design and build readout system for O (100 channels) Design custom readout chip Prototype R&D Evaluate various designs with respect to : Efficiency Noise rate Rate capability? Cross-talk Evaluate in CERN test beam : Viability of design Validation of MC Comparison with analog HCAL Time Scales