Chamber R&D for CBM Muon Tracker

Anand Kumar Dubey VECC, Kolkata

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/cm2

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

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 cm2

– Cost ~$ 700 (made at CERN)

70m

140m

--- a 50 micron polyimide foil with a 5 micron Cu layer deposited on both sides of polyimide

Multi GEM configurations..

We have assembled and tested both --- double and triple GEM.

Double GEM stack under test (at VECC) Gas Inlet

Gas mixture: Ar/CO2 – 70/

Readout : single pad 1cm x 1cm

3GEM: Test with Fe-55 (at VECC)

Gas mixture: Ar/CO2-70/30Readout pad: 8mm x 3.5 mm

Only one pad connected

readymade stretched and framed GEM foils from CERN

3GEM: Test with Fe-55

3GEM: Gain vs. Vgem

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 8th , 2009, SIS 18 --- Carried two triple GEM chambers the difference being that one of the chambers had a larger induction gap than the other.

Schematic of Chamber assembly for beam test at GSI

GEMS1 2 3

Drift plane (inner side copper plated)

12 x cm 12 cm x 10 mm

Readout PCB

5 CERN made GEM foils obtained fromArea: 10cm x 10cm

One triple GEMOne double GEMAssembled at VECC

Double GEM chamber:Drift gap: 7mmInductive gap: 1.5mmTransfer gap: 1mm

Triple GEM chamber:Drift gap: 6.5 mmInductive gap = 1.5mmTransfer gap = 1mm

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

3 days beam time (2hrs/day)

1st Day:• Triple GEM• Beam seen, MIP peak visible > 2700V

2nd day: Triple GEM• Voltage and DAQ threshold scan• Tried to optimise voltages

3rd day: Double GEM• 3 voltages, same threshold• one run with high intensity beam• 3 small runs with new connector

Sr-90 tests with nXYTER+3GEM

HV 3050V

HV 2950V

HV 3150V

Testbeam-2008: chambers mounted in the BEAM AREA

Test beam- 2008 Beam Region fired

Only alternate channels hit

BEAM SPOT

3-GEM

2-GEMHigh intensity run

The readout PCB

only alternate channels connected to nXYTER.

beam

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)

Relative detected fractionFraction =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

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.

.

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 sizePosition resolutionRequired dynamic range before saturation

Induction gap (does it increase cluster size?)

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

Test with Fe-55 before shipping to GSIdet01

Tests done using standard NIM electronics at VECC

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

Fe-55 spectra with full readout

DeltaV (GEM)ADC

Test with Fe55 + nXYTER using 3GEM

ADC

AD

C

Readout for Pad#20

actual pad readout plane

the beam profile on

Respective planes

Protons of 2.3 Gev/c

459 2109.61 6.82203462 2094.02 5.62808466 2105.38 7.27812470 2104.08 5.26833474 2128.5 4.3662478 2137.73 4.57708482 2139.69 5.05639497 2143.44 4.50543513 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 6.69564462 2201.52 5.48452466 2213.07 7.14234470 2211.54 5.27438474 2235.52 4.32994478 2245.7 4.54713482 2247.27 5.02932497 2250.96 4.41502513_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

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

BEAM SPOT ON TWO CHAMBERS

Cell size: 1.6mm x 16mm

Cell size: 3.5mm x 8mm

MIP distribution of hit cell

Correlation between GEM1 and GEM2

Position of spots (cell units) from 2 detectors Shown (well-correlated)

ADC distribution of main cell and variation with HV

4 fold increase in ADC for a deltaV(GEM) increase by 50V

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

Efficiency of detector 1 (large pad size)

Only aux2 taken, all aux gives low eff (23%).

Time window: 900-1200 nsec

Detector2 (5th sept data) goes upto 71%

• Maybe we need 5-fold coincidence• Above>3600V, nXYTER saturates, needs larger dyn range

Fe55 -- Cluster ADC

2 ring cutMean ~ 1700

All padsMean ~ 3900

After subtraction from the baseline

GEM Signal from a fast preamp

Rms ~ 40 ns

Cosmic Ray test setup at VECC

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

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

Thanks For Your Attention

BACKUPS

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 !!

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

Detector Biasing Scheme---- symmetric mode of biasing scheme, (i.e. same voltage across each GEM)

Readout from 1 cm2 pad

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

A) Back to back B) same side FEB

Structural support Chamber frames Active chamber area FEB

How do we mount the chambers??

ch#32HV=3100

ch#32HV=3000

Fe55

Fe55

Some puzzling peaks !!

Under investigation

Double GEM with nXYTER(Rev B)

SATURATION

ch#32HV=3050