1. Peter Shanahan – Fermilab Neutrino Scattering Experiment meeting March 14, 2003 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. Peter Shanahan – Fermilab Neutrino Scattering Experiment meeting March 14, 2003 2 What is an RPC? Resistive Plate Counter HV/Gas device using resistive plates as electrode Capacitive readout Streamer or avalanche mode Gas HV Resistive plate 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 readout

3. Peter Shanahan – Fermilab Neutrino Scattering Experiment meeting March 14, 2003 3 Principles of Operation Gas HV Resistive plate ++++++++++++++++  kV/mm Ionization leads to avalanche HV Resistive plate +++++  Streamer forms, depletes charge over O(1-10mm 2 ). Field drop quenches streamer Charge depletion induces signal. Charge depletion fixed by geometry, resistivity, gas. HV Resistive plate +++++ + + +++++  Region recharges on scale of up to sec due to bulk resistivity O(10 11  cm) Dielectric

4. Peter Shanahan – Fermilab Neutrino Scattering Experiment meeting March 14, 2003 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 ~10 8 -10 12  cm –Rates from kHz/cm 2 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  ~100  m

5. Peter Shanahan – Fermilab Neutrino Scattering Experiment meeting March 14, 2003 5 RPC Sampler (according to Web searching…) TimeframeExperimentUseMaterialRateGapReadout NowBaBar IFR (K L,  ) Bakelitelow2mm Belle  Glasslow2mm 5cm strip,  (t)~ns PlannedCMS??Bakelitehigher Monolith(?) Tracking/ Calorimetry Glasslow Atlas?MuonBakelitehigher2mm 1cm x 1 ns resolution Possible NuMI Off-Axis Tracking/ Calorimetry Glass?low Medical Imaging coincidence Glass/special coatings highmicro INO ?(India) (a la Monolith)

6. Peter Shanahan – Fermilab Neutrino Scattering Experiment meeting March 14, 2003 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,  > 97% See Rice U. seminar by D. Marlow

7. Peter Shanahan – Fermilab Neutrino Scattering Experiment meeting March 14, 2003 7 Another Case Study: BaBar IFR (K L,  ) 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. Peter Shanahan – Fermilab Neutrino Scattering Experiment meeting March 14, 2003 8 Low Z Calorimeter NuMI off-axis detector – e appearance – low Z fine grained calorimeter –Electron ID without pulse height info –Low rate, O(100000) m 2 of detector Cheap and simple –Particle board + RPCs are 1 option under consideration Hits/plane  CC Hits/plane e CC

9. Peter Shanahan – Fermilab Neutrino Scattering Experiment meeting March 14, 2003 9 Local Experience RPC studies for Off-Axis detector –Valeri Makeev, Alexander Terekhov, Vladimir –Working towards cosmic ray background study for e appearance Investigations –30cm x 30cm test chamber –Extra Belle type RPCs (2.2m x 2.7m) Test RPC: Beefy pulse

10. Peter Shanahan – Fermilab Neutrino Scattering Experiment meeting March 14, 2003 10 RPC Efficiencies Test chamber Belle chamber Single gap efficiency > 94% About 2% inefficiency due to spacers From Valeri Makeev

11. Peter Shanahan – Fermilab Neutrino Scattering Experiment meeting March 14, 2003 11 RPC @ NuMI ND ND for Off-axis: –3cm strips –Hit Timing information only RPC Cost estimate (not mine) based on Belle: O($110/m 2 ) 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. Peter Shanahan – Fermilab Neutrino Scattering Experiment meeting March 14, 2003 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 These two hits can be with O(100ns) of each other with no deadtime 3cm readout strip Streamer zones dead for entire spill

13. Peter Shanahan – Fermilab Neutrino Scattering Experiment meeting March 14, 2003 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?