# Presentation: 504270

## 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!*

## What is an RPC?

- 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

- readout

## Principles of Operation

- Gas

- ++++++++++++++++

- 

- kV/mm

- Ionization leads to avalanche

- +++++          +++++

- 

- Streamer forms, depletes charge over O(1-10mm2). Field drop quenches streamer

- Charge depletion induces signal.  Charge depletion fixed by geometry, resistivity, gas.

- +++++  +   +   +++++

- 

- Region recharges on scale of up to *sec* due to bulk resistivity O(1011cm)

- Dielectric

## 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 ~108-1012cm
- 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 ~100m

**Notes:**
Verify rates, resistivities, coatings

## RPC Sampler (according to Web searching...)

| Timeframe | Experiment | Use |  | Material | Rate | Gap | Readout |
| --- | --- | --- | --- | --- | --- | --- | --- |
| Now | BaBar | IFR (KL, ) |  | Bakelite | low | 2mm |  |
|  | Belle |  |  | Glass | low | 2mm | 5cm strip, (t)~ns |
| Planned | CMS? | ? |  | Bakelite | higher |  |  |
|  | Monolith(?) | Tracking/
Calorimetry |  | Glass | low |  |  |
|  | Atlas? | Muon |  | Bakelite | higher | 2mm | 1cm x 1 ns resolution |
| Possible | NuMI 
Off-Axis | Tracking/
Calorimetry |  | Glass? | low |  |  |
|  | Medical Imaging | coincidence |  | Glass/special coatings | high |  | micro |
|  | INO ?(India) | (a la Monolith) |  |  |  |  |  |

## 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

**Notes:**
Check numbers of each type – need design parameter book

## Another Case Study: BaBar

- IFR (KL, )
- 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

## Low Z Calorimeter

- NuMI off-axis detector
-  e 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  CC

- Hits/plane e CC

## 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

## RPC Efficiencies

- Test chamber

- Belle chamber

-  Single gap efficiency > 94%
-  About 2% inefficiency due to spacers

- From Valeri Makeev

## 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.

## 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

## 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?