1. Plans & Prospects for W Physics with STAR Frank Simon, MIT for the STAR Collaboration Parity Violating Spin Asymmetries at RHIC, BNL, April 27, 2007

2. Frank Simon: Plans & Prospects for W Physics at STAR 2 04/27/2007 Outline  STAR: Present Capabilities  W Production and Detection  Electron ID in the Calorimeter  Forward Tracking Upgrade: The Forward GEM Tracker  Simulations:  tracking and charge sign reconstruction efficiency  influence of vertex distribution  Requirements for Forward Tracking Technology  GEM Trackers  Technology  COMPASS Experience  STAR R&D  Summary

3. Frank Simon: Plans & Prospects for W Physics at STAR 3 04/27/2007 The STAR Experiment Central Tracking  Large-volume TPC  |  | < 1.3 Calorimetry  Barrel EMC (Pb/Scintilator)  |  | < 1.0  Shower-Maximum Detector  Pre-Shower Detector  Endcap EMC (Pb/Scintilator)  1.0 <  < 2.0  Shower-Maximum Detector  Pre- and Post-Shower Detectors 2005 run … and many other detectors not discussed here

4. Frank Simon: Plans & Prospects for W Physics at STAR 4 04/27/2007 W Kinematics at RHIC  large x accessible at manageable rapidities!

5. Frank Simon: Plans & Prospects for W Physics at STAR 5 04/27/2007 W Production: What Asymmetries do we expect?  Largest sensitivity at forward rapidity, in particular for W -  Δd/d  Δu/u  Δd/d

6. Frank Simon: Plans & Prospects for W Physics at STAR 6 04/27/2007 Forward W production: Leptonic Signals  W production is detected through high p T electrons / positrons  Rapidity cut on electron reduces the p T : p T (lepton) = M W /2 x sin  *

7. Frank Simon: Plans & Prospects for W Physics at STAR 7 04/27/2007 W Decay Kinematics  Partonic kinematics related to W rapidity:  W rapidity related to lepton rapidity:  lepton rapidity determined from p t :

8. Frank Simon: Plans & Prospects for W Physics at STAR 8 04/27/2007 W Production in STAR  400 pb-1 will result in 47 (12)k W +(-) events  Every event counts, certainly for W - !

9. Frank Simon: Plans & Prospects for W Physics at STAR 9 04/27/2007 A W event in STAR  Charged tracks at mid- rapidity to reconstruct the primary event vertex  outgoing electron tends to be isolated e

10. Frank Simon: Plans & Prospects for W Physics at STAR 10 04/27/2007 Backgrounds  Simulations for PHENIX geometry at mid-rapidity, also applicable for STAR  Dominating QCD charged hadron background  clean electron / hadron separation mandatory

11. Frank Simon: Plans & Prospects for W Physics at STAR 11 04/27/2007 Electron/Hadron Separation in EEMC electron ++  Difference in Shower Shape can be exploited to reject hadrons

12. Frank Simon: Plans & Prospects for W Physics at STAR 12 04/27/2007 Electron/Hadron Separation  EEMC provides a wealth of shower shape information  Hadrons have different longitudinal profile than electrons  high rejection power! Additional separation cuts:  E/p (especially at mid- rapidity)  isolation  large missing p t Preshower 1Preshower 2 SMD 1 SMD 2 TowerPostshower

13. Frank Simon: Plans & Prospects for W Physics at STAR 13 04/27/2007 Effectiveness of cuts  Isolation cut R = 0.26  Large missing pt  Together ~ x100 reduction of charged hadrons, only small reduction of signal

14. Frank Simon: Plans & Prospects for W Physics at STAR 14 04/27/2007 Forward Tracking: The Challenge  To provide charge identification at forward rapidity the sign of the curvature of tracks with a sagitta of less than 0.5 mm has to be correctly identified  Presently not possible in STAR! simulated electrons: 1 <  < 2, 5 GeV/c < p T < 40 GeV/c, flat distributions

15. Frank Simon: Plans & Prospects for W Physics at STAR 15 04/27/2007 Forward Tracking: Baseline Design I Inner Tracking Forward Tracking

16. Frank Simon: Plans & Prospects for W Physics at STAR 16 04/27/2007 Forward Tracking: Baseline Design II  6 triple-GEM disks covering 1 <  < 2  outer radius ~ 43 cm  inner radius varies with z position  size and locations driven by the desire to provide tracking over the full extend of the interaction diamond (±30 cm)

17. Frank Simon: Plans & Prospects for W Physics at STAR 17 04/27/2007 Forward Tracking Simulations  Simulations used to investigate:  Capabilities:  tracking efficiency  charge sign reconstruction efficiency  acceptance of vertex distribution  Detector configurations:  currently existing STAR Detector  baseline design: 6 triple-GEM disks  Resolution requirements  beam line constraint sufficient as transverse position of the primary vertex assumed resolution 200 µm (200 GeV: 250 µm, transverse size scales with √E)  constraints on the spatial resolution of the chosen detector technology  Simulation Procedure:  single electrons, p T = 30 GeV/c, 1 <  < 2, vertex positions at -30 cm, 0 cm, +30 cm  Full GEANT simulations with STAR detector  smearing of the hits in each detector by the respective resolution  reconstruction with helix fit (2 stage: circle fit in x,y; straight line fit in r,z)

18. Frank Simon: Plans & Prospects for W Physics at STAR 18 04/27/2007 Hit distribution vs   Position of the primary vertex determines which detectors see tracks at a given  TPC ≥ 5 hits SSD+IST EEMC SMD vertex FGT vtx z = -30 cm vtx z = 0 cm vtx z = +30 cm

19. Frank Simon: Plans & Prospects for W Physics at STAR 19 04/27/2007 Simulations: Present Capabilities  Spatial resolution of the EEMC SMD: ~1.5 mm  Charge sign reconstruction impossible beyond  = ~1.3 TPC Only TPC + EEMC SMD

20. Frank Simon: Plans & Prospects for W Physics at STAR 20 04/27/2007 Simulations: Baseline Design  6 triple-GEM disks, assumed spatial resolution 60 µm in x and y  charge sign reconstruction probability above 80% for 30 GeV p T over the full acceptance of the EEMC for the full vertex spread, >90% out to  = 1.8  the addition of two high-resolution silicon disks does not provide significant improvement and is thus not considered further  4 GEM disks might be sufficient, but the added redundancy of 6 disks comes at low cost

21. Frank Simon: Plans & Prospects for W Physics at STAR 21 04/27/2007 Simulations: How Critical is Spatial Resolution?  Simulations with different spatial resolutions for the triple GEM disks:  80 µm, 100 µm, 120 µm 80 µm 100 µm120 µm  Charge Sign resolution deteriorates with decreasing resolution  80 µm spatial resolution is certainly sufficient, 100 µm might also do

22. Frank Simon: Plans & Prospects for W Physics at STAR 22 04/27/2007 Technology Requirements  Spatial resolution ~80 µm (or better)  High intrinsic speed: Discrimination of individual bunch crossings mandatory for the Spin program (107 ns)  Rate capability: Detector upgrade has to be able to handle RHIC II luminosities ( 4 x 10 32 cm -2 s -1 at 500 GeV p+p)  Low cost to cover larger areas (~ 3 m 2 )  GEM Technology a natural choice

23. Frank Simon: Plans & Prospects for W Physics at STAR 23 04/27/2007 GEM: Gas Electron Multiplier Metal-clad insulator foil with regular hole pattern  Hole Pitch 140 µm  Outer diameter ~70 µm, Inner diameter ~60 µm  Voltage difference between foil sides leads to strong electric field in the holes  Electron avalanche multiplication F.Sauli, 1997

24. Frank Simon: Plans & Prospects for W Physics at STAR 24 04/27/2007  Amplification stage separated from readout: Reduced risk of damage to readout strips or electronics  Readout on ground potential  Fast signal: Only electrons are collected  Intrinsic ion feedback suppression  Several foils can be cascaded to reach higher gains in stable operation  typical choice for MIP tracking: triple GEM  Many different readout designs possible (1D strips, 2D strips, pads, …) GEM Detector Principles

25. Frank Simon: Plans & Prospects for W Physics at STAR 25 04/27/2007 GEM Trackers: First Large-Scale Use: COMPASS  Mechanical stability provided by honeycomb plates  average material budget 0.71 % radiation length  reduced material in the center (where the beam passes through) ~ 0.42 X 0  2D orthogonal strip readout Small angle tracker uses GEMs  Triple GEM design, low mass construction, 30 cm x 30 cm active area

26. Frank Simon: Plans & Prospects for W Physics at STAR 26 04/27/2007 COMPASS: Readout: Cluster Size  400 µm strip pitch chosen to get good spatial resolution while keeping number of channels reasonable

27. Frank Simon: Plans & Prospects for W Physics at STAR 27 04/27/2007 COMPASS Trackers: Efficiency  Efficiency for space points ~ 97.5% (stays above 95% for intensities of 4 x 10 7  + /s, at rates of up to 25 kHz/mm 2 )  uniform efficiency over detector area (no effects from particle density)  local reductions in efficiency due to spacer grid 2D Efficiency

28. Frank Simon: Plans & Prospects for W Physics at STAR 28 04/27/2007 COMPASS Trackers: Resolutions  time resolution ~ 12 ns (convolution of intrinsic detector resolution and 25 ns sampling of APV25)  spatial resolution ~ 70 µ m in high intensity environment with COMPASS track reconstruction  50 µ m demonstrated in test beams

29. Frank Simon: Plans & Prospects for W Physics at STAR 29 04/27/2007 Establishing a Commercial Source  Currently CERN is the most reliable supplier of GEM foils  Essentially a R&D Lab, not well suited for mass production: quite high price, limited production capability  Small Business Innovative Research: Funded by DOE  Phase I: Explore feasibility of innovative concepts with an award of up to $100k  Phase II: Principal R&D Effort with award of up to $750k  Phase III: Commercial application  Collaborative effort of Tech-Etch with BNL, MIT, Yale  Development of an optimized production process  Investigation of a variety of materials  Study post-production handling (cleaning, surface treatment, storage…)  Critical Performance Parameters  Achievable gain, gain uniformity & stability  Energy resolution  SBIR Phase II approved, $750k awarded

30. Frank Simon: Plans & Prospects for W Physics at STAR 30 04/27/2007 Testing of Foils at MIT: Optical Scanning  2D moving table, CCD camera, fully automated, developed at MIT  Scan GEM foils to measure hole diameter (inner and outer)  Check for defects  missing holes  enlarged holes  dirt in holes  etching defects  Electrical tests  Foils are required to have a high resistance (>> 1 G  )  GEM foils are tested in nitrogen up to 600 V : no breakdowns  Optical tests U. Becker, B. Tamm, S.Hertel (MIT)

31. Frank Simon: Plans & Prospects for W Physics at STAR 31 04/27/2007 Optical Scanning: Hole Parameters  Geometrical parameters are similar for foils made at Tech-Etch and foils made at CERN CERN Tech-Etch

32. Frank Simon: Plans & Prospects for W Physics at STAR 32 04/27/2007 Optical Scanning: Homogeneity Outer holesInner holes Tech-Etch CERN  Homogeneity for CERN and TE foils similar

33. Frank Simon: Plans & Prospects for W Physics at STAR 33 04/27/2007 Triple-GEM Test Detector at MIT Components: 1. 2D readout board (laser etched micro-machined PCB) 3. Bottom Al support plate 4. Top spacer (G10): 2.38mm 5. Bottom spacer (G10) 6. plexiglass gas seal frame 7. Top Al support cover 8. GEM 1&2 frames (G10): 2.38mm 9. GEM 3 frame (G10): 3.18mm 10. Drift frame (G10) Detector constructed to allow rapid changes of foils, readout board and other components, not optimized for low mass Detector operated with Ar:CO 2 (70:30) gas mixture

34. Frank Simon: Plans & Prospects for W Physics at STAR 34 04/27/2007 55 Fe Tests  Triple GEM test detectors are tested with a low intensity 55 Fe source (main line at 5.9 keV)  Both Detectors (based on CERN and on Tech-Etch foils) show similar spectral quality and energy resolution (~20% FWHM of the Photo Peak divided by peak position) CERNTechEtch

35. Frank Simon: Plans & Prospects for W Physics at STAR 35 04/27/2007 Gain Uniformity  Good uniformity of the gain (measured after charging up of the detectors) for both the CERN foil based and the TE foil based detector RMS = 0.064 RMS = 0.077 CERN TechEtch

36. Frank Simon: Plans & Prospects for W Physics at STAR 36 04/27/2007 Electronics & Data Acquisition  Detector electronics based on APV25S1 front-end chip  Front-end chips and control unit designed and available, undergoing tests  Proof of principle with the full STAR trigger and DAQ chain APV chip & front-end board Control Unit (programmable FPGAs) Test Interface  Beam test with full electronics & 3 test detectors starting at FNAL next week!

37. Frank Simon: Plans & Prospects for W Physics at STAR 37 04/27/2007 Electronics Test with RPC  First tests at ANL with a RPC on top of the test detector readout board  Induced signals (GEM: electron collection) => Very wide signals  Very high amplitudes (RPCs in avalanche mode, signals typically 0.2 to 2 pC (GEM: ~10 fC) Typical Signal in RPC

38. Frank Simon: Plans & Prospects for W Physics at STAR 38 04/27/2007 Towards a “real” detector  Development of a low mass prototype  use of low mass materials, e.g. carbon foam or honeycomb for mechanical structure, thin readout board,…  Disk design: similar to the one used by the TOTEM experiment at LHC (forward region of CMS)  FGT significantly larger than the TOTEM detectors  Tech-Etch can provide GEM foils at least 40 cm x 40 cm  build the detector from 90° quarter sections  12 GEM foils per detector disk needed (get at least 24 to be safe)  total number of foils ~200 including some spare detector modules

39. Frank Simon: Plans & Prospects for W Physics at STAR 39 04/27/2007 Towards a “real” detector II  Readout Geometry: Currently under investigation, for example 2D strips (as in COMPASS)  strip pitch ~ 400 µm  shorter strips at inner radius to allow for high occupancy  challenge to produce, investigating with company  ~50 k to 70 k channels total  ~400 to 550 APV chips total

40. Frank Simon: Plans & Prospects for W Physics at STAR 40 04/27/2007 Mechanical Design: Support Structure

41. Frank Simon: Plans & Prospects for W Physics at STAR 41 04/27/2007 Construction Schedule  Design phase (Support structure / Triple-GEM chambers): 12 weeks  Procurement of material: 6 weeks  Construction of detector quarter sections: 18 weeks  Delivery of 10 GEM foils from Tech-Etch per week  Test of GEM foils (Electrical tests, optical scan on flatbed scanner): 0.5 week  Test of readout board (Parallel to GEM foil tests): 0.5 week  Construction of GEM detectors: Mechanical assembly, foil mounting, testing between each gluing step: 2 weeks  Test of assembled chamber: Gas tightness, X-ray test, Gain map: 2 weeks  Estimated total construction of one quarter section: 5 weeks  Assume: 2 detectors in parallel starting every week  Construction of full system: 10 weeks  Assemble 6 disks on support frame from 4 quarter sections each: 1 week  Assemble electrons and test: 2 weeks  Test disk electrons and detectors and full system test (Cosmic ray test): 7 weeks  Installation: 3 weeks  Integration: 5 weeks  total construction time: ~54 weeks  Aim for Installation for FY2010 run, total project costs below $2M

42. Frank Simon: Plans & Prospects for W Physics at STAR 42 04/27/2007 Institutes on the FGT Project  Argonne National Laboratory  Indiana University Cyclotron Facility  Kentucky University  Lawrence Berkeley National Laboratory  Massachusetts Institute of Technology  Valparaiso University  Yale University

43. Frank Simon: Plans & Prospects for W Physics at STAR 43 04/27/2007 Summary  STAR is in a good position to make competitive W measurements  Forward Tracking Upgrade is needed to ensure charge sign identification for high p T electrons from W decays in the forward region  Baseline design: 6 triple-GEM tracker disks  cover the region 1 <  < 2 for vertex distributions of ±30 cm  Extensive simulations with GEANT modeling of the detector  spatial resolution of ~80 µm necessary  GEM technology satisfies the requirements of forward tracking in STAR  R&D Effort currently under way to establish commercial GEM foil production  Phase II of a funded SBIR proposal, collaboration of Tech-Etch, BNL, MIT, Yale  Promising results with detector prototypes  First successful tests with APV25 electronics and DAQ integration, Beam test at FNAL coming up  Design effort for final disk configuration  low mass materials  large area GEM foils  specialized readout geometry