1Daya Bay collaboration meeting, IHEP, Beijing, Aug. 1-3, 2007

Test OPERA gas mixture on IHEP RPC w/ 8m long strip

C. Lu

Princeton University

2Daya 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 plateau Single’s rate

Notice very low HV used, plateau starts at 5400V! Also good plateau length!

Very low single’s rate, 17Hz/m2, 100 times lower than what we expect for Daya Bay RPC!!

Larger amount of Ar, less R134A, save gas cost.

3Daya 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

4Daya Bay collaboration meeting, IHEP, Beijing, Aug. 1-3, 2007

… Test on IHEP RPC

Efficiency plateau curve: Dark current:

5Daya Bay collaboration meeting, IHEP, Beijing, Aug. 1-3, 2007

Streamer induced signal after the buffer

HV = 5800V, 100mV/div, 80ns/div

6Daya Bay collaboration meeting, IHEP, Beijing, Aug. 1-3, 2007

…Streamer induced signal after the buffer

HV = 6200V, 100mV/div, 80ns/div

7Daya 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/m2 (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 ....

8Daya 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?

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