CMS GEM Workshop III, April 20, 2012 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

GEM Workshop III - M. Hohlmann 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

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

Zigzag strips vs. straight strips Pitch [mm] Typical Resolution [µm] Zigzag strips & analog r/o 2.0 80 Straight strips & VFAT (current design, short end) 0.6 300 Improvement factor w/ zigzag strips 3.33 3.75 Can reduce # of readout channels (and electronics cost) by 70% of current design & Improve resolution by factor 3-4 A “figure of merit”: 3.33 × 3.75 = 12.5 ~ Potential for order of magnitude improvement over current design  Well worth a try! 4/20/2012 GEM Workshop III - M. Hohlmann

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

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

GEM Workshop III - M. Hohlmann What about noise?  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? 4/20/2012 GEM Workshop III - M. Hohlmann

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

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

First pulses with zigzag r/o GEM stack being assembled on zigzag r/o board Completed Triple-GEM with zigzag r/o board under gas, HV, and x-rays (Cd109) 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… 4/20/2012 GEM Workshop III - M. Hohlmann

GEM Workshop III - M. Hohlmann 30cm × 30cm zigzag PCB 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) Photo-montage ~ 300 mm   4/20/2012 GEM Workshop III - M. Hohlmann

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

GEM Workshop III - M. Hohlmann Implications Potential for saving 70% of readout channels and ~50% (?) of electronics cost, could mean potentially saving 1-1.5 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

GEM Workshop III - M. Hohlmann 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