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A potential cost saver for the CMS GEM upgrade: GEM readout with zigzag strips Marcus Hohlmann Florida Institute of Technology CMS GEM Workshop III, April.

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Presentation on theme: "A potential cost saver for the CMS GEM upgrade: GEM readout with zigzag strips Marcus Hohlmann Florida Institute of Technology CMS GEM Workshop III, April."— Presentation transcript:

1 A potential cost saver for the CMS GEM upgrade: GEM readout with zigzag strips Marcus Hohlmann Florida Institute of Technology CMS GEM Workshop III, April 20, 2012

2 Motivation Cost is one of the biggest current issues for the CMS GEM upgrade project The single-largest budget item in the current GEM budget estimate is electronics: ~3M out of 6.4M total (TP CMS IN 2012/001) Clearly, we should seriously look for ways to reduce the electronics cost if possible –One potential real cost saver would be the significant reduction of readout channels  Can a zigzag strip readout help with that? 4/20/2012 GEM Workshop III - M. Hohlmann 2

3 Previous BNL 4/20/2012 GEM Workshop III - M. Hohlmann Zigzag strips: Charge sharing among adjacent strips allows quite sensitive position-interpolation in x-direction We are sacrificing the measurement of the 2 nd coord. (y) to gain precision in the 1 st coord. (x) CMS GE x/1 detectors are currently intended for 1D-coordinate measurements, so the zigzag approach is applicable to these detectors x (measured coordinate) Previous exp. studies show <100 µm resolution with 2 mm strip pitch is possible: y 3 Concept: ava- lanche BNL

4 Zigzag strips vs. straight strips 4/20/2012 GEM Workshop III - M. Hohlmann 4 Can reduce # of readout channels (and electronics cost) by 70% of current design Improve resolution by factor 3-4 Pitch [mm]Typical Resolution [µm] Zigzag strips & analog r/o2.080 Straight strips & VFAT (current design, short end) Improvement factor w/ zigzag strips A “figure of merit”: 3.33 × 3.75 = 12.5 ~ Potential for order of magnitude improvement over current design  Well worth a try! &

5 Zigzag r/o PCB (10cm × 10cm) 4/20/2012 APV25 Hybrid (using only 38% of 128 ch.) + SRS Readout Board for std. CERN 10cm×10cm Triple-GEM Detector 2 sets of 10cm zigzag strips with different zigzag pitch (along strip) BNL/FIT/Stony Brook Collaboration 24 fine zigzag strips 24 coarse zigzag strips LEMO footpads GEM Workshop III - M. Hohlmann 5 PCB with solder finish CAD Design by C. Pancake, Stony Brook 2 mm 0.5 mm 1 mm Solid ground plane on the back side.

6 2 nd batch: Gold plating finish 4/20/2012 GEM Workshop III - M. Hohlmann 6 Ordered second batch with gold plating finish because hot-air solder leveling (HASL) finish shows non-uniform surfaces: HASL Au plated Much higher surface quality

7 WHAT ABOUT NOISE? 4/20/2012 GEM Workshop III - M. Hohlmann 7  First commissioning step addressed noise question: Measure pedestals and compare with regular straight strips Does the noise increase substantially due to the increased strip area and capacitance?

8 Pedestal Distributions 4/20/2012 Readout Board with 10cm long zigzag strips covered with one GEM foil placed 2 mm above induction plane: ADC channel # ev. per ch. ADC channel # ev. per ch. APV ch. 63 (example) pedestal width: r.m.s 3 → 4 cts. GEM Workshop III - M. Hohlmann 8 straight strips zigzag strips APV25 Hybrid (using only 38% of channels) + SRS

9 Pedestals for all channels 4/20/2012 Pedestal width (rms) [ADC counts] APV channel number 48 channels connected to zigzag strips (24+24) channels not connected (open APV inputs) Channels connected to LEMO footpads (5) Readout Board with 10cm long zigzag strips covered with one GEM foil placed 2 mm above induction plane: GEM Workshop III - M. Hohlmann 9

10 First pulses with zigzag r/o 4/20/2012 GEM Workshop III - M. Hohlmann 10 GEM stack being assembled on zigzag r/o board Completed Triple-GEM with zigzag r/o board under gas, HV, and x-rays (Cd 109 ) Strips ganged together using adapter board plugged into a Panasonic connector Pulses recorded with ORTEC preamp and (slow) lin. amp. Currently setting up for cosmics test with APV + SRS…

11 30cm × 30cm zigzag PCB 4/20/2012 GEM Workshop III - M. Hohlmann 11 Plans for next design: Design and build a zigzag readout pcb for the 30cm × 30cm self-stretch CMS GEM (on order w/ Rui) 128 zigzag strips of 10cm length covering the full 30cm width & read out by a single APV25 hybrid + SRS Test also 30cm long strips on same board (given the good noise performance of the 10cm long strips) ~ 300 mm Photo-montage

12 Impact on electronics design 4/20/2012 GEM Workshop III - M. Hohlmann 12  Potential for removing the need for 2/3 of the electronics of current baseline design: from Paul Aspell’s talk on Thu. 1

13 Implications Potential for saving 70% of readout channels and ~50% (?) of electronics cost, could mean potentially saving MCHF on the project Simplifies also cooling, cabling, power, etc., which would lead to additional cost savings Total project cost < 5 MCHF possible ?! Analog pulse height measurement is mandatory for charge interpolation, so VFAT3 would not work → need a GdSP design 4/20/2012 GEM Workshop III - M. Hohlmann 13

14 Conclusion & Outlook Noise increases by only 1.5 ADC counts (~ 0.1% of range) for zigzag strips compared w/ straight strips. Encouraging! Can potentially read out one GE1/1 strip row with single 128-ch. front-end hybrid while improving spatial resolution; could lead to substantial channel number & cost savings. Next: –Measure spatial resolution using tracked cosmics –Test zigzag prototype in 2012 test beam –Design, produce & test larger prototype boards 4/20/2012 GEM Workshop III - M. Hohlmann 14


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