Prototypes of high rate MRPC for CBM TOF Jingbo Wang Department of Engineering Physics, Tsinghua University, Beijing, China RPC-2010-Darmstadt, Germany

Outline CBM TOF requirement Low resistive silicate glass Pad readout MRPCs  Chamber Structure  Test setup  Test results Strip readout MRPCs  Chamber Structure  Test setup  Test results A prototype for CBM TOF 2/27

1. CBM TOF requirement Overall time resolution σ T = 80 ps. Space resolution ≤ 5 mm × 5 mm. Efficiency > 95 %. Pile-up < 5%. Rate capability > 20 kHz/cm 2. Multi-hit capability (low cross-talk). Compact and low consuming electronics (~ electronic channels). 3/27 20 kHz/cm 2

2. Low resistive silicate glass 4/27 Using electrodes made of semi- conductive glass is an innovative way of improving the rate capability of Resistive Plate Chambers. The accumulated charge was 1 C/cm 2, roughly corresponding to the CBM life-time over 5 year operation at the maximum counting rate. T = 28 C° HV = 1kV 3-4×10 10 Ωcm

3. Pad readout MRPCs Chamber structure Test setup HV scan Rate scan 5/27

Structure: MRPC#1_6-gap mm  Parameters Gap number: 6 Glass type: silicate Gap width: 0.22mm Glass thickness: 0.7mm Gas mixture: Freon/iso-butane/SF6 96.5%/3%/0.5% Almost the same as the standard STAR module Low-resistive silicate glass with a bulk resistivity of 3~4×10 10 Ωcm

Structure: MRPC#2_10-gap 7/27 30mm 31.5mm Negative HV Positive HV MRPC#2 has a similar structure and working conditions than MRPC#1 but with different dimensions of the pick-up pads. Such a structure provides higher signal amplitudes and smaller fluctuations, which are expected to improve the detection efficiency as well as the time resolution.

Test setup 8/27 Tests were performed at GSI-Darmstadt under uniform irradiation by secondary particles stemming from proton reactions at 2.5 GeV. The higher rates can be obtained by moving the RPCs up closer to the main beam. 2.5GeV

Counting rate 9/27 PMT rate: 0.8~20 kHz/cm 2 MRPC rate: 2~30 kHz/cm 2 Mean rate: 1.4~25 kHz/cm 2 Top View The beam comes in spills. We take the mean of the PMT and MRPC measurements as a sound reference for rate estimates.

Time difference 10/27 Time diff =T MRPC#1 -T MRPC#2

Charge distribution of MRPC#2 11/27 MRPC#2: 10-gap With rate increasing, the average charge decreases, which leads to a relativity lower efficiency.

HV scan at 800Hz/cm 2 12/27 MRPC#1: 6-gapMRPC#2: 10-gap The efficiency reaches above 90% and the time resolution remains below 90ps once at the efficiency plateau. By means of using more gas gaps, the 10-gap RPC shows a better performance.

Rate scan 13/27 90% 76% 110ps 85ps MRPC#1: 6-gap MRPC#2: 10-gap The efficiencies and time resolutions deteriorate with the counting rate. MRPC#2 yields much better results: 90% efficiency, 85ps resolution.

4. Strip readout MRPCs 14/27 Chamber structure  MRPC#3: silicate glass  MRPC#4: common glass Test setup HV scan Position scan Analysis with particle tracking

Structure: MRPC#3 & MRPC#4 15/27 1.5mm 5mm Diameter:1.5mm Hole size:0.5mm Width:0.508mm Top and bottom layers 240mm 22mm 3mm Guarding line Glass type: silicate / common HV electrode: colloidal graphite Number of gaps: 10 Gap width: 0.25mm Glass thickness: 0.7mm Gas mixture: Freon/iso-butane/SF6 96.5%/3%/0.5% colloidal graphite

Test Setup Main beam Target  10 m PM12 PM34 Tsinghua RPC PM5 Silicon 16/27 MRPC#3 ： silicate glass MRPC#4: common glass

HV scan 17/27 T diff =T MRPC#3 -T MRPC#4, σ MRPC#3 ≈ σ MRPC#4 ≈ σ diff / sqrt(2)

Position Scan 18/ Rpcy "or" eff strip1 strip2 strip3 "and" eff Efficiency(%) Rpcy(mm) MRPC#3 MRPC#4

19/27 T1T2 DeltaT=(T2-T1)/2 Position resolution Using the tracking, we get the signal propagation velocity: ~ 54ps/cm Position resolution: ~ 1 cm

Efficiency correction with tracking 20/27 2×4 (cm 2 ) 1×2 (cm 2 ) Efficiency: 95% 97% MRPC#3MRPC#4

Crosstalk: MRPC#3_silicate 21/ Rpcy (cm) 20% 10% Crosstalk_1=counts(T2>0 && T1>0) / counts(trigger)

Crosstalk: MRPC#4_common 22/ Rpcy (cm) 2% Crosstalk_1=counts(T2>0 && T1>0) / counts(trigger)

5. A prototype for CBM TOF 23/27 Chamber structure Cosmic ray test system HV scan

Structure: MRPC#5 24/27 2 cm 13 cm Glass type: silicate HV electrode: graphite Number of gaps: 10 Gap width: 0.25 mm Glass thickness: 0.7 mm Pad dimension: 2*2 cm 2 Gas mixture: Freon/iso-butane/SF6 96%/3%/1% For the inner region of the CBM TOF wall

Cosmic ray test 25/27 Cosmic ray

HV scan 26/27 Beam test is needed! 96% ~75ps

Summary  CBM TOF requirement: 20kHz/cm 2  Low resistive silicate glass: 3-4×10 10 Ωcm  MRPC#2: 10-gap, pad readout, silicate glass HV scan at 800 Hz/cm 2 Efficiency>95%, Time resolution: <70ps Rate capability: 25 kHz/cm 2 Efficiency: ~90%, Time resolution: ~85ps  MRPC#3: 10-gap, strip readout, silicate glass Efficiency: ~97%, Time resolution: ~75ps Crosstalk: 20%, 10%? (further study is needed)  MRPC#5: 10-gap, 12 pads, silicate glass Efficiency: ~96%, Time resolution: ~75ps  Beam test is needed in the future! 27/27

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