Aiwu Zhang , Vallary Bhopatkar, Marcus Hohlmann Florida Institute of Technology (FIT)

1. Study of Large-area GEM Detectorsfor a Forward Tracker at a Future Electron-Ion Collider Experiment Aiwu Zhang, Vallary Bhopatkar, Marcus Hohlmann Florida Institute of Technology (FIT) Kondo Gnanvo, Nilanga Liyanage University of Virginia (U.Va) for the EIC RD6-FLYSUB Consortium Electron Ion Collider Users Meeting June 24-27, 2014 at Stony Brook University, NY

2. Contents • Motivations (will skip) • FIT 1-m size zigzag GEM detector • U.Va 1-m size u-v strip GEM detector • Beam test configuration at Fermilab • Beam test results of the zigzag GEM detector • Beam test results of U.Va’s GEM detector • Summary A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

3. Zigzag-strip GEM @ FIT Zigzag strips, 1.37mrad pitch 1.37 mrad 0.5mm 7 2 1 8 6 5 4 3 -sectors 0.1mm • The zigzag strips run in radial direction and can measure the azimuthal direction. Opening angle is 10 degrees, angle pitch 1.37mrad. • The readout board is designed to fit a 1-m long trapezoidal GEM prototype (originally for CMS muon upgrade). It is divided to 8 η-sectors with radial length of each sector ~12cm, and 128 strips/sector. • For the same GEM prototype with straight strips, 24 APV chips are needed to fully read out the chamber. In the zigzag case, only 8 APV chips can fully read out the entire chamber. This means 2/3 electronic channels can be saved. • We use self-stretch technique so that GEM foils can be changed easily. A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

4. 2D u/v strip GEM @ U.Va • Key characteristics: • Largest GEM detector with 2D readout ever build • Low mass (narrow edge and honey comb support) and small dead area • Fine strips 2-dimensional flexible small stereo angle u/v readout so that good spatial resolution can be achieved, and with low capacitance noise • Gluing technique is used so that GEM foils can not be changed Pitch = 550 mm, Top strips = 140 mm, Bottom strips = 490 mm 44 cm 100 cm 12° 2D u/v readout strips Cross section of low mass triple GEM 22 cm Entrance window Gas inlet spacers Drift region Transfer region Transfer region Gasoutlet Induction region 2D readout board on Honeycomb support A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

5. Beam test setup @FNAL Trackers Trackers zigzag GEM and U.Va GEM • The RD6-FLYSUB consortium conducted a three-week beam test at Fermilab (Meson Test area 6, MT6) in Oct 2013, operated 20 GEM detectors. • The FIT group and U.Va group tested 10 GEMs as a tracking system. • 4 reference detectors (3/2/2/2mm gaps); the zigzag GEM gaps: 3/1/2/1 mm; Ar/CO2 (70:30) was used to operate all the detectors. • DAQ: RD51 SRS with SRU to read out 4FECs/64APVs simultaneously. A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

6. Beam test results of the zigzag GEM– basic performances MPV value of charge distribution vs. HV Cluster charge distribution peak pos. in sector 5 at 3200V Stat. errors smaller than marker size Mean cluster size vs. HV on sector 5 (number of hits in a cluster) • Cluster charge distribution fits well to a Landau function. • Mean cluster size (number of fired strips in one event) from each cluster size distribution shows approximately exponential dependence on HV. Stat. errors smaller than marker size A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

7. Beam test results of the zigzag GEM– basic performances (cont.) • On each sector, two points were measured. The response from sector to sector varies by ~20%. • The non-uniformity could be caused by bending of the drift board. The CMS-GEM group is investigating this aspect to avoid bending after chambers are assembled. • Detection efficiency in middle-sector 5. Fitted with a sigmoid function, plateau efficiency ~98.4%. • Different thresholds (N=3,4,5,6 times of pedestal width σ) were tested, the efficiency plateau is not affected by thresholds. A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

8. Beam test results of the zigzag GEM – spatial resolution studies Resolution in φ for trackers Inclusive residual for 1st tracker Aligning trackers to zigzag GEM det. vertex σ=21μrad 10° Y offset tracker Errors smaller than marker size Eta5 • The zigzag strips measure the azimuthal coordinate φ. Angle pitch between two strips is 1.73mrad. So we study its spatial resolution in polar coordinates. • Spatial resolution is calculated from the geometric mean of exclusive and inclusive residual widths: . Exclusive (Inclusive) means the probed detector is excluded (included) when fitting the tracks. • The trackers are aligned first and their spatial resolutions in (x, y) are found to be around 70μm, which is the typical resolution of a standard triple-GEM. Their resolutions in φ coordinate are then calculated to be 30-40μrad. X offset A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

9. Beam test results of the zigzag GEM– spatial resolution studies (cont.) Exclusive residual σ=281μrad Inclusive residual σ=223μrad • Residual distributions of the zigzag GEM in middle-sector 5 at 3350V • Hit positions are calculated with Center of Gravity (COG) method, and all cluster size >0 events are used. • Resolution is for this case. • Note that the resolution in number of strips is about ~18% A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

10. Beam test results of the zigzag GEM– spatial resolution studies (cont.) • Resolution of the zigzag-GEM vs. HV in middle-sector 5. • At highest tested voltage, resolution is ~240μrad. • If only use 2-strip events, resolution is smaller (especially at lower voltages). • Resolution of the zigzag-GEM on different sectors at 3200V (without cluster size cut). A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

11. Beam test results of the zigzag GEM– cluster position correction • Centroid position distribution from COG method (in middle-sector 5). 2-strip events 3-strip events • By further checking the centroid position distributions of fixed cluster size events, we observe that these distributions have apparent bumps around each strip. • This brings us to study the non-linear strip response of charge distribution on position reconstruction, and hence make these distributions flat. A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

12. Beam test results of the zigzag GEM– cluster position correction (cont) • The idea is to build strip response functions for different cluster sizes (η-algorithm). • , is defined as the centroid position (in strip units) minus the center of strip with maximum charge. • The position correction functions can be calculated: . h(η2) distribution h(η3) distribution Correction function for 3-strip events Correction function for 2-strip events A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

13. Beam test results of the zigzag GEM– cluster position correction (cont.) • After correction functions are figured out, the centroid position of an event can be corrected. Only clusters with 2,3 and 4 strips are because of better statistics (they make up ~90% of all clusters on the efficiency plateau). 2-strip after correction 2-strip before correction 3-strip after correction 3-strip before correction A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

14. Beam test results of the zigzag GEM– spatial resolution after correction Resolution vs. HV in middle-sector 5 after positions are corrected (with 2, 3, 4-strip events) • After position correction, we observe that resolution gets improved at higher voltages (to ~170μrad). • The results give us a clue that strip response correction is affected by gas gain and incident angle of particles. A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

15. Performances of the U.Va GEM Spatial resolution in (r, ) at different location in the chamber Position scan with 32 GeV hadron beam P4 P2 P1 P3 P5 ADC Charges distribution Efficiency vs. HV Nb of strips /cluster vs. HV A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

16. 4 new ideas from U.Va towards a lighter, better resolution GEM detector • Ultra low mass chamber to minimize multiple scattering and background • “Re-openable” chamber – without gluing GEM foils • “mini-drift” GEM tracker to improve spatial resolution at large angle tracks • All readout electronics arranged at the outer edge of the chamber, to further reduce dead area and get better radiation hardness. Gas out Top Entrance window Gas input Bottom gas window A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

17. Summary on the zigzag GEM • The zigzag-GEM detector worked well in the beam test at FNAL. • The 98% detection efficiency is good. The gain uniformity needs to be further investigated. • Corrections for non-linear strip responses bring the resolution from ~240μrad down to ~ 170μrad on the eff. Plateau, which could be transferred to 170μm at R=1m. The zigzag structures can probably still be optimized by interleaving zigs and zags more to improve resolution performance even further. • We conclude that a readout with zigzag strips is a viable option for cost efficient construction for a forward tracker with GEMs. • The U.Va u/v strip GEM detector also performance well in the beam test. A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

18. Summary on the dedicated EIC forward tracker with GEMs • Both FIT and U.Va groups have experience on building and operating large-area GEM detectors. • U.Va group has experience on low-materials for drift and readout; FIT group constructs GEMs without gluing foils, and are pursuing a optimized cost effective zigzag readout structure. • We are joining forces with Temple U. in designing and constructing a dedicated GEM prototype for the EIC forward tracker, which goes to even higher eta regions in the forward region. • We plane to work out entirely domestically sourced GEM foils (see the next talk from Temple U. group). A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

19. The FLYSUB consortium Thanks! 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. A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

20. Back up – align the zigzag detector Aligning trackers to zigzag GEM det. vertex 10° Chi2 vs. Y offset Y offset Residual mean vs. Y offset tracker At a fixed X offset, check residual mean and chi-2 Eta5 Residual sigma vs. X offset X offset Chi2 vs. X offset At a fixed Y offset, check residual sigma and chi-2 After checked (X,Y) groups in reasonable ranges, an intersecting point can be found from the scattering plot. A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

21. Back up - references • References on the strip response correction: • CERN-Thesis-2013-284 by Marco Villa. • G. Landi, NIMA 485 (2002) 698; NIMA 497 (2003) 511 • Reference about inclusive and exclusive residual study • R. K. Carnegie, NIMA 538 (2005) 327 A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC

22. Motivation Conceptual design of EIC detector Example of zigzag strips Forward/backward GEM trackers 2.5mm • The RD6-FLYSUB consortium is jointly working on tracking and particle ID,based on the Gaseous Electron Multiplier (GEM) technique,for a future EIC. • The zigzag-strip readout structure is proposed and under study by Florida Tech to make the forward tracker much less costly. • Each zigzag strip occupies more space than a straight strip so that the total readout channels can be reduced and hence reduce the cost significantly, while good spatial resolution can be conserved because of charge sharing on these zigs and zags. A. Zhang et al., Study of Large-area GEM Detectors as a Forward Tracker at an EIC