Beam Test Results for a Largearea GEM Detector

Beam Test Results for a Large-area GEM Detector Read Out with Radial Zigzag Strips Aiwu Zhang, V. Bhopatkar, M. Hohlmann, M. Phipps, J. Twigger Dept. of Physics and Space Sciences, Florida Institute of Technology APS April meeting, Savannah, Georgia 08/04/2014

Outline Ø Motivation for the beam test Ø Large-area GEM detector & zigzag readout Ø Beam test setup at Fermilab Ø Basic characteristics of the GEM detector Ø Tracking & Resolution results Ø Summary 4/8/2014 Beam Test of a GEM Detector with Zigzag Readout / Aiwu Zhang 2

Motivation • The next QCD frontier can be explored at a new Electron-Ion Collider (EIC). The proposed EIC candidates are e. RHIC at BNL and MEIC at J-Lab. • The FLYSUB consortium is performing R&D on tracking and particle ID with GEM detectors at a future EIC detector. • FLYSUB: FLorida Tech (FIT), Yale U. , Stony Brook U. , U. of Virginia and Brookhaven National Lab. New members are joining into this consortium. • The consortium conducted a joint beam test at Fermilab in October 2013. • A 1 -m long trapezoidal GEM detector with zigzag readout strips designed by FIT was studied as an option for EIC forward tracking during this beam test. Conceptual design of EIC detector e. RHIC EIC at Brookhaven National Lab. 4/8/2014 Forward/backward GEM trackers EIC at Jefferson Lab. (MEIC/ELIC) Beam Test of a GEM Detector with Zigzag Readout / Aiwu Zhang 3

Large GEM detector with zigzag readout • CMS GE 1/1 -III GEM foils with trapezoidal shape (1 m long, 22 -45 cm wide) are used 8 7 6 5 4 3 -sectors • Readout boards Left: Zigzag strips designed by FIT Right: Straight strips (for CMS upgrade). 2 1 Zigzag strips (1. 37 mrad pitch) • 1. 37 mrad • 0. 1 mm 4/8/2014 Straight strips Both zigzag and straight strips are radial: strips develop in a fan-shape, full opening angle for zigzag strips is 10°. Eight sectors with 8 APVs (128 channels each) fully read out; need only 1/3 electronic channels of std. CMS GE 1/1 -III GEM detector (see Vallary Bhopatkar’s talk at beginning of this session). Beam Test of a GEM Detector with Zigzag Readout / Aiwu Zhang 4

Beam test setup at Fermilab • 4 reference GEM detectors (trackers) • Gas: Ar/CO 2 (70: 30) • Beam: 25 Ge. V, 32 Ge. V mixed hadrons (π, K etc. ) and 120 Ge. V protons • Zigzag 3 -GEM det. gaps: 3/1/2/1 mm Trackers 1 -m GEM w/ zigzag readout 4/8/2014 Beam Test of a GEM Detector with Zigzag Readout / Aiwu Zhang 5

Basic performances of the zigzag GEM Mean cluster size vs. HV on sector 5 (number of hits in a cluster) Stat. errors smaller than marker size Total cluster charge distribution • Cluster size: number of strips in a cluster. Mean cluster size value increases exponentially with HV (approximately). • Cluster charge distribution fits well to a Landau function. • We find the typical increase of “gain” with HV for the middlesector 5. MPV value of charge distribution vs. HV peak pos. in sector 5 at 3200 V Stat. errors smaller than marker size 4/8/2014 Beam Test of a GEM Detector with Zigzag Readout / Aiwu Zhang 6

Basic performances (cont. ) Charge in different sectors (uniformity) Detection efficiency • We scanned two positions on each sector from sector 1 to 7. From sector to sector the response varies by 20%, which is probably caused by uneven foil gaps. • Detector efficiency on sector 5 vs. HV can be fitted with a Sigmoid function. • Different thresholds were compared: N sigma, N=3, 4, 5, 6, where sigma is width of pedestal distribution. • Plateau efficiency with 5 sigma cut is (98. 4 ± 0. 2)% 4/8/2014 Beam Test of a GEM Detector with Zigzag Readout / Aiwu Zhang 7

Tracking method for the zigzag GEM Resolution in ϕ for trackers σ=21μrad Aligning trackers to zigzag GEM det. Y offset vertex 10° X offset Eta 5 REF Det. X Inclusive residual for 1 st tracker Errors smaller than marker size • After aligning the trackers to each other with shifts and rotations, they are giving resolutions of 70μm or better (≈ typical spatial resolution for std. GEM detectors) in both X and Y. • The radial zigzag strips measure the azimuthal coordinate ϕ and have a pitch of 1. 37 mrad, so we study the resolution in natural polar coordinates (r, ϕ). • Tracking in polar system was demonstrated to be working as well as in the Cartesian system. The trackers have azimuthal resolutions around 30μrad. • The ϕ resolution of the zigzag GEM detector can be studied if its vertex is taken as the origin of the tracking system. (X, Y) offsets need to be found to align the tracker origin to the vertex of the zigzag GEM detector. 4/8/2014 Beam Test of a GEM Detector with Zigzag Readout / Aiwu Zhang 8

Three alignment checks for (X, Y) offsets Residual mean should be centered at 0 Track χ2 in ϕ vs. tracker X offset for Y = -36. 5 mm Minimal point gives X = -1866. 4 mm Inclusive residual width 4/8/2014 Beam Test of a GEM Detector with Zigzag Readout / Aiwu Zhang 9

Residuals after the alignment Inclusive residual (zigzag GEM is included in track fit) Exclusive residual (zigzag GEM is excluded from track fit) σ = 215μrad σ = 270μrad • After (X, Y) offsets are optimized, both inclusive and exclusive residuals are calculated for the zigzag GEM detector. • The residuals shown above are for sector 5 @3300 V. 4/8/2014 Beam Test of a GEM Detector with Zigzag Readout / Aiwu Zhang 10

Spatial resolution for the zigzag GEM Resolution vs. HV in middle-sector 5 Resolution as a function of -sectors • Left: Higher voltage, i. e. higher gas gain, gives better resolution as expected. • Right: Resolutions in different sectors at 3200 V. We observe similar azimuthal resolutions (variation about 10%) in the first six sectors. Resolution in sector 7 is a little worse; the reason is likely to be lower gas gain in that sector. 4/8/2014 Beam Test of a GEM Detector with Zigzag Readout / Aiwu Zhang 11

Summary and Conclusion • The zigzag strip readout method reduces the number of strips and readout channels by a factor of 3 which reduces system cost. • The FNAL beam test was successful. We operated 10 GEM detectors including a large trapezoidal Triple-GEM with zigzag readout strips. • The large-area zigzag GEM detector was working quite well. It had high and stable gain, plateau detection efficiency of 98% and spatial resolution of 241μrad (449μm) at 3300 V. • The resolution is expected to be improved further by also correcting for the non-linearity of charge sharing between strips (response fct. ) • The structure of zigzag strips can be optimized to get even better resolution. For example, the interleaving between zigs and zags can be improved by industrial PCB factories to yield better charge sharing. • We conclude that a zigzag GEM detector can be an option for the cost -conscious construction of a forward tracker in an EIC detector. 4/8/2014 Beam Test of a GEM Detector with Zigzag Readout / Aiwu Zhang 12

The FLYSUB consortium We would like to acknowledge BNL for the support of this work through the EIC RD-6 collaboration and the staff of the FNAL test beam facility for all their help. 4/8/2014 Beam Test of a GEM Detector with Zigzag Readout / Aiwu Zhang 13

Backup - EIC physics • (inclusive or semi-inclusive) DIS is a powerful way to probe the internal structure of nucleons • Transverse Momentum Dependent parton distributions (TMDs) open a new window to understand some of the most fundamental aspects of QCD • Address the spin problem of the nucleon; illuminate the role played by angular momentum of partons • Two golden measurements on an EIC: ü 3 -d imaging of gluons and quarks, and their spins ü Di-jet measurements 4/8/2014 Beam Test of a GEM Detector with Zigzag Readout / Aiwu Zhang 14

Backup- how to transfer resolution from μrad to μm <r>[μm] σr [μm] <ϕ>[μrad] σϕ[μrad] <x>[μm] σx[μm] <y>[μm] σy[μm] REF 2 3. 6 46 4. 2 21 3. 7 46 9 45 45 REF 3 -3. 6 69 -5. 7 31 -3. 6 69 -12 69 66 UVA 3 -11. 6 55 -3. 6 23 -11. 6 55 -8 50 49 REF 1 10 59 5 25 10 59 10 55 53 • Resolutions in (x, y) are also calculated at this origin. • Resolutions in r are almost the same as resolutions in X. • The last column shows the calculated resolutions in y from resolutions in ϕ, they match with the measured resolutions in y. • Also, <x>≈<r> and <y>≈<ϕ>*L • Tracking in polar coordinates works well and gives high resolutions. σϕ L σy 4/8/2014 Beam Test of a GEM Detector with Zigzag Readout / Aiwu Zhang 15

Backup – electronics, SRU • The test beam took data for 60 APVs (128 ch/ea. ) simultaneously through the Scalable Readout Unit (SRU). • Data were taken with DATE and amore. SRS under Linux system. 4/8/2014 Beam Test of a GEM Detector with Zigzag Readout / Aiwu Zhang 16

Backup -- Rotation • The detector might be rotated a small angle relative to the first tracker. The angle should be close to 0 if alignment is correct. Rotation of the Zigzag detector should be minimal at 0 if the alignment is correct rotation 4/8/2014 Beam Test of a GEM Detector with Zigzag Readout / Aiwu Zhang 17