1. 1 Daya Bay collaboration meeting, IHEP, Beijing, Aug. 1-3, 2007 Test OPERA gas mixture on IHEP RPC w/ 8m long strip C. Lu Princeton University

2. 2 Daya Bay collaboration meeting, IHEP, Beijing, Aug. 1-3, 2007 Why OPERA RPC gas mixture? OPERA RPC gas mixture: Ar/R134A/Isobutane/SF6 (75.4/20/4/0.6) Their test results: Efficiency plateauSingle’s rate Notice very low HV used, plateau starts at 5400V! Also good plateau length! Very low single’s rate, 17Hz/m 2, 100 times lower than what we expect for Daya Bay RPC!! Larger amount of Ar, less R134A, save gas cost.

3. 3 Daya Bay collaboration meeting, IHEP, Beijing, Aug. 1-3, 2007 Test on IHEP RPC with 8m long strip readout ADC peak spectrum, calibration curve: V(mV)=0.181*ADC(ch)+9.88

4. 4 Daya Bay collaboration meeting, IHEP, Beijing, Aug. 1-3, 2007 … Test on IHEP RPC Efficiency plateau curve:Dark current:

5. 5 Daya Bay collaboration meeting, IHEP, Beijing, Aug. 1-3, 2007 Streamer induced signal after the buffer HV = 5800V, 100mV/div, 80ns/div

6. 6 Daya Bay collaboration meeting, IHEP, Beijing, Aug. 1-3, 2007 …Streamer induced signal after the buffer HV = 6200V, 100mV/div, 80ns/div

7. 7 Daya Bay collaboration meeting, IHEP, Beijing, Aug. 1-3, 2007 More R&D on OPERA gas mixture The single's rate of OPERA RPC underground is remarkably low: 17Hz/m 2 ( NIM A572(2007)177 ), that means the intrinsic noise rate is extremely low, it is almost 2 orders of magnitude lower than the ordinary RPC performance. Private communication with Alberto Garfanini of OPERA RPC group confirms the condition for them to get such low noise rate: Trigger threshold is 40mV; The rate is obtained with self-triggering scheme, w/o any other triggers, thus reveals the intrinsic noise rate of the RPC. Gas mixture used is a premixture of Ar/C2H2F4/iso-C4H10/SF6 (75.4/20/4/0.6%); Gas flow rate is 5 volume changes/day; Alberto mentioned that with this gas mixture the after pulses are a bit higher, probability is a factor of two respect to our previous mixture 48/48/4 - babar, Santonico....

8. 8 Daya Bay collaboration meeting, IHEP, Beijing, Aug. 1-3, 2007 … More R&D on OPERA gas mixture Flow rate influence on the single’s rate; After pulse study, how serious it will affect the random noise rate?