1. Test results of Multi-gap RPC Test Chambers for a Digital HCAL  Geometrical design  Test setup  Signal: avalanche mode and streamer mode  Comparison of different chamber configurations  Efficiency of MIP signal, noise level  Plan for further tests Lei Xia Argonne National Laboratory

2. Geometrical design: things to consider  Chamber as thin as possible (~1cm or less)  High efficiency (~90% or better)  Small inactive region  Last long enough time (20 years or longer)  Low cost (large area)  Will only address some of them at this point…

3. Geometrical design: basic parameters  Chamber size: 8 x 8 inch  Three layers of thin glass sheets with 0.85mm thickness  Two 0.64mm gas gaps, using nylon fishing lines as spacers (use multi- gap design to get better long-term stability, higher efficiency, lower cross talk…)  Glass, fishing lines and gas tubes hold by specially designed ‘channels’, made by high density polyethylene

4. Geometrical design: basic parameters  Resistive layer: graphite spray (Dry Graphite Lube)  Control of block resistivity over a large range (~10kΩ- 1MΩ)  1 spray layer: ~900kΩ/ □  2 layers: ~350kΩ/ □  ~5 layers: ~50kΩ/ □  Signal readout pad 7.2 x 7.2 inch at the center  Overall thickness ~ 5mm Spacers (fishing line) hole for gas tube Chamber with all gas tubes

5. Signal: test set up  Trigger: cosmic ‘telescope’ with 4 layers of scintillators (signal rate ~1Hz)  Electronics: ‘RABBIT’ system  Gives total charge of the signal  Capable of multi-channel readout  However, the integration time is too long (up to ~  s) which brings in extra noise  Alternative: amplifier, shaper, and discriminator

6. Signal: avalanche mode  Gas: Freon/Argon/IsoButane at 62:30:8  High Voltage: below 7.4 KV  Total charge of the signal increase with HV  Gives ~0.2pc/avalanche at 7.4 KV  Want to stay with this mode for long term run

7. Signal: streamer mode  Gas: Freon/Argon/IsoButane at 62:30:8  High Voltage: 7.5 KV or above  Multi-streamer may occur  Gives ~10pc/streamer at 8.0 KV

8. Signal: comparison of different chamber setup  Signal pad on electron drifting direction  Signal pad on ion drifting direction Seems they work equally well concerning signal, but may give difference on cross talk between pads…

9. Efficiency: using RABBIT system  Threshold at 6925 ADC counts  Efficiency better than 90% for HV > 7.3 KV  Fraction of steamers is small for HV < 7.5 KV  Noise rate increase with HV (from ~1kHz at 6.5KV to ~4kHz at 8KV), but remember the long gate of the RABBIT system, as well as the noisy environment of our lab (will have a Faraday cage for further test)

10. Efficiency: as a function of discriminator threshold  Use x1000 amplifier and shaper before sending the signal to the discriminator  HV = 7.4 KV, which gives the largest avalanche signal without streamers  Efficiency better than 90% for discriminator threshold lower than ~100mV  Noise rate is reasonable (this is the actual noise rate!) for threshold higher than ~40mV, can be further reduced

11. Efficiency: as a function of HV  Amplifier + shaper + discriminator setup.  Discriminator threshold at 42.8 mV  Efficiency better than 90% for HV > 7.0 KV  Fraction of streamers is small for HV < 7.5 KV  Noise rate increase with HV, reasonable rate for HV < 7.6KV, may be reduced

12. Things we know about…  Acquired expertise with construction of RPC’s  We studied signals both in avalanche and streamer mode  Efficiency of the chamber meet the requirement of a digital HCAL. In addition, quite large parameter space will give good efficiency.  Noise rate under control (room for improvement)

13. Plan for further tests  Go to multiple pad chamber and study the cross talk between small signal pads (new chamber built, readout for multi-pad configuration ready)  Chamber lifetime study (avalanche, streamer)  Fully studies of application of resistive layers  Further study of different chamber geometry  Number of gas-gaps  Thickness of glass  Rate capability