RPCs in a NuMI Environment

1. RPCs in a NuMI Environment • Introduction to RPCs • Principles of operation • Case Studies • Comments on RPCs @ NuMI ND Caveat: I am not an RPC expert!

2. Resistive plate HV Gas What is an RPC? readout • Resistive Plate Counter • HV/Gas device using resistive plates as electrode • Capacitive readout • Streamer or avalanche mode Gaps are typically O(mm) • Key features: • High bulk resistivity: self quenching through charge depletion • HV distribution surface: high enough surface resisitivity to prevent signal shielding (e.g., ink) • Capacitive readout: HV blocking not needed

3. Resistive plate Resistive plate Resistive plate HV HV HV Principles of Operation Charge depletion induces signal. Charge depletion fixed by geometry, resistivity, gas. Dielectric ++++++++++++++++ +++++ +++++ +++++ + + +++++ Streamer forms, depletes charge over O(1-10mm2). Field drop quenches streamer Region recharges on scale of up to sec due to bulk resistivity O(1011Wcm) Ionization leads to avalanche kV/mm Gas --------------- ----- ----- ----- - - ----

4. Flavors of RPC • Insulator type • Bakelite treated with linseed oil • Glass (can be coated with fancy chemicals (CsI) for special performance) • “Standard” RPCs: Variations of Insulator ~108-1012Wcm • Rates from kHz/cm2 down to few Hz • Signal mode • Avalanche: smaller signal, faster recovery • Streamer: large signal, longer recovery. • Readout • Coarse: single strips wider than streamer • Fine: use charge weighting on small strips to get s~100mm

5. RPC Sampler (according to Web searching…)

6. Case Study: Belle • Belle KLM system • Glass RPCs • Very low rate • Well behaved at first • … problems developed • High dark current, low efficiency • Traced to water vapor • Solved by replacing tubing • Good behavior since, e > 97% See Rice U. seminar by D. Marlow

7. Another Case Study: BaBar • IFR (KL, m) • Initial behavior excellent • Low dark current, >95% efficiency • Period of rapid efficiency decrease • Coincided with higher than desired temperatures in RPCs • Lower temperature lower rate of decrease • Uncured linseed oil “stalagmites” • Various solutions temporarily improved situation in tests, but problem remains

8. Low Z Calorimeter • NuMI off-axis detector • ne appearance – low Z fine grained calorimeter • Electron ID without pulse height info • Low rate, O(100000) m2 of detector • Cheap and simple • Particle board + RPCs are 1 option under consideration Hits/plane nm CC Hits/plane ne CC

9. Local Experience • RPC studies for Off-Axis detector • Valeri Makeev, Alexander Terekhov, Vladimir • Working towards cosmic ray background study for ne appearance • Investigations • 30cm x 30cm test chamber • Extra Belle type RPCs (2.2m x 2.7m) Test RPC: Beefy pulse

10. RPC Efficiencies • Single gap efficiency > 94% • About 2% inefficiency due to spacers From Valeri Makeev Test chamber Belle chamber

11. RPC @ NuMI ND • ND for Off-axis: • 3cm strips • Hit Timing information only • RPC Cost estimate (not mine) based on Belle: O($110/m2) • Coarse tracking • Use interleaved with another technology for <10ns timing? • What about better position resolution? • Charge weighting: requires vastly smaller segmentation and ADCs • Would no longer a plausible inexpensive option. • Tracking in high multiplicity region? • If need pulseheight info, then streamer mode won’t work.

12. NuMI ND Rates • Rate per se not an issue • Overlap between events of 1mm dead region not an issue • Time resolution more than sufficient • Streamer region dead for 100 ms, but strips are only dead for readout timescale 3cm readout strip Streamer zones dead for entire spill These two hits can be with O(100ns) of each other with no deadtime

13. Conclusions • Rate • RPCs can handle the rate for simple tracking, at low production cost • Bell experience • “Satisfactory” and even “quite good” • A lot of R&D in the last decade • Alchemy • “Surface physics”, Complicated Organic chemistry • Sense of unknown technical risk • Maybe small ND would be good trial?