1. Chamber R&D for CBM Muon Tracker Anand Kumar Dubey VECC, Kolkata

2. Muon detector requirements: Main issues:  The first plane(s) has a high density of tracks -- detector should be able to cope up with high rate. ~ 10 MHz/cm 2  good position resolution  Should be radiation resistant  Large area detector – modular arrangement  Should be cost effective Use of detectors based on micropattern technology --- GEMs, THGEMs and Micromegas

3. Gas Electron Multiplier (GEM) and its working principle Active medium is a gas mixture. electron multiplication takes place in holes of two copper foils separated by kapton Amplification may use 2 or 3 stages. – Maximum size ~30 x ~30 cm 2 – Cost ~$ 700 (made at CERN) 70  m 140  m --- a 50 micron polyimide foil with a 5 micron Cu layer deposited on both sides of polyimide

4. Multi GEM configurations.. We have assembled and tested both --- double and triple GEM.

5. Double GEM stack under test (at VECC) Gas Inlet Gas mixture: Ar/CO2 – 70/ Readout : single pad 1cm x 1cm

6. 3GEM: Test with Fe-55 (at VECC) Gas mixture: Ar/CO2-70/30 Readout pad: 8mm x 3.5 mm Only one pad connected readymade stretched and framed GEM foils from CERN

7. 3GEM: Test with Fe-55 3GEM: Gain vs. Vgem

8. Testing of GEM chambers @GSI First beam test September 28-30, 2008, SIS 18 6 hours of beamtime we had carried two chambers –2GEM and 3GEM chambers Testing with proposed FEE for CBM -- first successful test with n-XYTER readout chip(64 channels connected) Testing of the chambers with real DAQ Response to 3.5 GeV protons. --- Obtained MIP spectra, saw the beam spot --- cluster spread….granularity test could not be done as only alternate channels were bonded. Second beam test Aug 29-September 8 th, 2009, SIS 18 --- Carried two triple GEM chambers the difference being that one of the chambers had a larger induction gap than the other.

9. Schematic of Chamber assembly for beam test at GSI GEMS 1 2 3 Drift plane (inner side copper plated) 12 x cm 12 cm x 10 mm Readout PCB 5 CERN made GEM foils obtained from Area: 10cm x 10cm One triple GEM One double GEM Assembled at VECC Double GEM chamber: Drift gap: 7mm Inductive gap: 1.5mm Transfer gap: 1mm Triple GEM chamber: Drift gap: 6.5 mm Inductive gap = 1.5mm Transfer gap = 1mm

10. Detector fabrication at VECC for Sep08 beam test Readout : 256 Pads with staggered layout each pad 8 mm x 3.5 mm 10 ohm Resistors for protection Outer side of the readout PCB

11. 3 days beam time (2hrs/day) 1 st Day: Triple GEM Beam seen, MIP peak visible > 2700V 2 nd day: Triple GEM Voltage and DAQ threshold scan Tried to optimise voltages 3 rd day: Double GEM 3 voltages, same threshold one run with high intensity beam 3 small runs with new connector

12. Sr-90 tests with nXYTER+3GEM HV 3050V HV 2950V HV 3150V

13. Testbeam-2008: chambers mounted in the BEAM AREA

14. Test beam- 2008 Beam Region fired Only alternate channels hit BEAM SPOT 3-GEM 2-GEM High intensity run

15. The readout PCB only alternate channels connected to nXYTER. beam

16. MPV increases slowly with HV (note: only alternate channels fired) No of cells : mostly 1-1.5 Triple GEM: Variation of MIP MPV and no of cells V_gem=320 2800V(Vgem~320) 3100V (Vgem~350)

17. Relative detected fraction Fraction =1 at 3100V Do we see plateau at 3000V? Saturated fraction Increases with HV up to ~22%. (the dynamic range of n-xyter is 20 fC) Triple GEM Saturation fraction

18. Observations from test beam08 experience: Both triple and double GEM gives MIP peak and Sr90 spectra Triple GEM: MIP peak and detection eff increases with HV Eff plateau at 3000V? Number of cells/cluster increases slowly Gain ~ 10^3 Saturation goes up with HV but slowly Double GEM: MIP peak seen >2900V(delta_V ~ 347 V) No of cells ~ 1.5 detection eff, MIP peak position, cluster-size does not change drastically for higher beam intensity -- not everything fine with the AUX signal. so could not perform the efficiency studies. -- Moreover, with alternate channels connected, cluster size and efficiency studies not possible with nXYTER..

19. Questions remaining from last test beam Absolute efficiency and HV dependence Beam intensity dependence Absolute gain estimate Uniformity over small zone New questions: Pad multiplicity/cluster size Position resolution Required dynamic range before saturation Induction gap (does it increase cluster size?)

20. Readout Board for Test beam Aug-Sep 09 Inside view Outside view Two triple GEM chambers were fabricated : det 01 – with two different pad sizes(shown above) det02 -- same size pads but with larger induction gap

21. Test with Fe-55 before shipping to GSI det01 Tests done using standard NIM electronics at VECC

22. Main Features: --- more number of days as compared to last test beam --- A new fully connected nXYTER board --- An X--Y movement facility was provided exclusively for the GEM ch. --- A better trigger arrangement for efficiency studies. --- STS, RICH + Panda (parasitic run with Panda) Summary of data taken: 2 ROCs connected to one half of each detector small cell size in det1 and large cell size in det 2 one day data: Both large pad sizes --- First Day – Problem with SY1527 calibration --- Movement in both X and Y (Beam spot moved and went away) Aux signals: 2 days data where Aux from different detectors can be correlated (can be used for position resolution) One day data for good AUX (crucial for eff) Trigger data: One run for 10 minutes Test beam Aug-Sep: 2009

23. Fe-55 spectra with full readout DeltaV (GEM) ADC Test with Fe55 + nXYTER using 3GEM ADC Readout for Pad#20

24. actual pad readout plane the beam profile on Respective planes Protons of 2.3 Gev/c

25. 459 2109.61 6.82203 462 2094.02 5.62808 466 2105.38 7.27812 470 2104.08 5.26833 474 2128.5 4.3662 478 2137.73 4.57708 482 2139.69 5.05639 497 2143.44 4.50543 513 2145.04 4.44678 HV nXYTER (I uA) mean ADC rms -- one can look at all 128 pads -- GEM bias voltage doesn’t affect the baseline the change maybe about 1-2 % This nothing as compared to the drift due to temperature ! Any plan of controlling this in future revisions ? 459 2217.08 6.69564 462 2201.52 5.48452 466 2213.07 7.14234 470 2211.54 5.27438 474 2235.52 4.32994 478 2245.7 4.54713 482 2247.27 5.02932 497 2250.96 4.41502 513_vth50 32 2252.64 4.32795 HV nXYTER (I uA) mean ADC rms nXYTER Baseline(position of zero signal) study using triggered mode data (no source/beam) Pad # 20 Pad # 32

26. Time difference between aux and GEM ROC Offset + Drift time(~160 ns) -- why this large spread ?? Procedure: Select fired GEM cells in 900-1200 nsec after last Aux. All Aux channels: eff:10% Aux-Channel=2 (4 fold) eff = 71% ---- copied from Sauli’s slides

27. BEAM SPOT ON TWO CHAMBERS Cell size: 1.6mm x 16mm Cell size: 3.5mm x 8mm

28. MIP distribution of hit cell Correlation between GEM1 and GEM2 Position of spots (cell units) from 2 detectors Shown (well-correlated)

29. ADC distribution of main cell and variation with HV 4 fold increase in ADC for a deltaV(GEM) increase by 50V

30. PAD multiplicity Two back to back detectors similar pad multiplicity.. No effect of increased induction gap? (Last day’s data, det2 had low eff, went bad after 3500V) Depends on beam profile, needs correlating with beam tracker (Same granularity but different induction gap) -- no effect of induction gap on the cluster size

31. Efficiency of detector 1 (large pad size) Only aux2 taken, all aux gives low eff (23%). Time window: 900-1200 nsec Detector2 (5 th sept data) goes upto 71% Maybe we need 5-fold coincidence Above>3600V, nXYTER saturates, needs larger dyn range

33. Fe55 -- Cluster ADC 2 ring cut Mean ~ 1700 All pads Mean ~ 3900 After subtraction from the baseline

34. GEM Signal from a fast preamp Rms ~ 40 ns

36. Cosmic Ray test setup at VECC

37. Further analysis and issues: Correlation with beam counter for position resolution. Pad to pad variation Absolute gain study from Fe-55 data Puzzle : Low efficiency (Gain high, large eff expected, better beam defn? Wider (and grass) time spectra Plan: Efficiency at lab with Fe-55 and cosmic ray Test cross-talks if any Build rectangular pads – to avoid mapping confusions Problem with 2-hour beam time?? --- efficiency studies by Bipasha

38.  Efficiency of charged particle detection : --- will be done using cosmics. We have the setup ready at VECC and with Ortec -142IH (charge sensitive preamp) we could get some efficiency numbers. --- we need a fast preamp : Christian gave us one. It worked fine for some days before developing some snag. Which fast preamp to use – any suggestions ?? Problem with Chamber : resolve the butterfly problem: (1) use nXYTER and test it with Fe55 source – if the butterfly is obtained, then something wrong with the detector. -- some cross talk is appearing somewhere. We have to think which is an easy way. (2) det02 – in case det01 is not found O.K.  Cluster size distribution: in lab can be determined using Fe55+nXYTER Issues to resolve

39. Thanks For Your Attention

40. BACKUPS

41. Analysis so-far (very preliminary and work in progress): Took Volker’s rootified file Event == +- 100nsec time window Beam info from aux ROC==0,1 for STS, ==2 for GEM Looked at fired channels every event Offset is taken = 2000 Could not understand AUX so far !!

42. 0.1 mm 0.5 mm A closer view of THGEM holes 1.2 mm The position of the rim is not concentric with the G10 holes and the gap is too little at some places. “eccentricity” problems

44. Detector Biasing Scheme ---- symmetric mode of biasing scheme, (i.e. same voltage across each GEM) Readout from 1 cm 2 pad

45. Suitable Options : Micropattern gas detectors: GEM (Gas Electron Multiplier) MICROMEGAS more recently THGEM 1. Lab tests with Double and Triple GEMs 2. results from Sep08 beamtest 3. Working with nXYTER 4. results/some questions from nXYTER tests at VECC 5. R&D with THGEMs

46. A)Back to back B) same side FEB Structural support Chamber frames Active chamber area FEB How do we mount the chambers??

47. ch#32 HV=3100 ch#32 HV=3000 Fe55 Some puzzling peaks !! Under investigation Double GEM with nXYTER(Rev B) SATURATION ch#32 HV=3050