Plans Prospects for W Physics with STAR

Plans & Prospects for W Physics with STAR Frank Simon, MIT for the STAR Collaboration Parity Violating Spin Asymmetries at RHIC, BNL, April 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 Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 2

The STAR Experiment Central Tracking § Large-volume TPC 2005 run § | | < 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 … and many other detectors not discussed here Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 3

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

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

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) = MW/2 x sin * Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 6

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

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

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

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

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

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

Effectiveness of cuts § Isolation cut R = 0. 26 § Large missing pt Together ~ x 100 reduction of charged hadrons, only small reduction of signal Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 13

Forward Tracking: The Challenge simulated electrons: 1 < < 2, 5 Ge. V/c < p. T < 40 Ge. V/c, flat distributions § 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! Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 14

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

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) Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 16

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 Ge. V: 250 µm, transverse size scales with √E) § constraints on the spatial resolution of the chosen detector technology § Simulation Procedure: § § single electrons, p. T = 30 Ge. V/c, 1 < < 2, vertex positions at -30 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) Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 17

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

Simulations: Present Capabilities TPC Only TPC + EEMC SMD § Spatial resolution of the EEMC SMD: ~1. 5 mm § Charge sign reconstruction impossible beyond = ~1. 3 Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 19

Simulations: Baseline Design § 6 triple-GEM disks, assumed spatial resolution 60 µm in x and y § charge sign reconstruction probability above 80% for 30 Ge. V 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 Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 20

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

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 1032 cm-2 s-1 at 500 Ge. V p+p) § Low cost to cover larger areas (~ 3 m 2) GEM Technology a natural choice Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 22

GEM: Gas Electron Multiplier F. Sauli, 1997 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 Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 23

GEM Detector Principles § 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 (1 D strips, 2 D strips, pads, …) Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 24

GEM Trackers: First Large-Scale Use: COMPASS Small angle tracker uses GEMs § Triple GEM design, low mass construction, 30 cm x 30 cm active area § § 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 2 D orthogonal strip readout Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 25

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

COMPASS Trackers: Efficiency § Efficiency for space points ~ 97. 5% (stays above 95% for intensities of 4 x 107 +/s, at rates of up to 25 k. Hz/mm 2) 2 D Efficiency § uniform efficiency over detector area (no effects from particle density) § local reductions in efficiency due to spacer grid Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 27

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

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 $100 k § Phase II: Principal R&D Effort with award of up to $750 k § 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, $750 k awarded Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 29

Testing of Foils at MIT: Optical Scanning § 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 § § § 2 D 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 U. Becker, B. Tamm, S. Hertel (MIT) Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 30

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

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

Triple-GEM Test Detector at MIT Components: 1. 2 D readout board (laser etched micro-machined PCB) 3. Bottom Al support plate 4. Top spacer (G 10): 2. 38 mm 5. Bottom spacer (G 10) 6. plexiglass gas seal frame 7. Top Al support cover 8. GEM 1&2 frames (G 10): 2. 38 mm 9. GEM 3 frame (G 10): 3. 18 mm 10. Drift frame (G 10) 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 Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 33

55 Fe Tests CERN Tech. Etch § Triple GEM test detectors are tested with a low intensity 55 Fe source (main line at 5. 9 ke. V) § 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) Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 34

Gain Uniformity CERN RMS = 0. 064 Tech. Etch § 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. 077 Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 35

Electronics & Data Acquisition § Detector electronics based on APV 25 S 1 front-end chip APV chip & front-end board Test Interface § Front-end chips and control unit designed and available, undergoing tests § Proof of principle with the full STAR trigger and DAQ chain Control Unit (programmable FPGAs) Beam test with full electronics & 3 test detectors starting at FNAL next week! Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 36

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 p. C (GEM: ~10 f. C) Typical Signal in RPC Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 37

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 Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 38

Towards a “real” detector II § Readout Geometry: Currently under investigation, for example 2 D 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 Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 39

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

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 FY 2010 run, total project costs below $2 M Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 41

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 Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 42

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 APV 25 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 Frank Simon: Plans & Prospects for W Physics at STAR 04/27/2007 43