Silicon Vertex Tracking for Spin and HI

1. Silicon Vertex Tracking for Spin and HI Yuji Goto (RIKEN/RBRC) June 14, 2002 PHENIX Core Plenary

2. Outline • Physics motivations • Requirements for detectors • Strawman design • Simulation studies Yuji Goto (RIKEN/RBRC)

3. GS95 DG(x) prompt photon cceX bbeX J/ x Physics motivations • Spin physics • to clarify contribution of quark spin and gluon spin to the proton spin 1/2 • gluon polarization • wider xg coverage • 0.002 < xg < 0.4 • clean process/channel • lower systematic uncertainties • higher statistics • prompt photon  photon + jet • heavy flavor  bottom/charm tagging • pp physics • yield & pT spectrum • test of the NLO pQCD calculations Yuji Goto (RIKEN/RBRC)

4. L. Frankfurt, M. Strikman Eur. Phys. J A5, 293 (99) prompt photon Q = 2 GeV Q = 5 GeV Q = 10 GeV Physics motivations • Gluon structure functions in nuclei • how partonic degrees-of-freedom are affected by a many-body system, how the gluon structure function is modified in nuclei • wide xg coverage, 0.002 < xg < 0.4, by charm/bottom production • suppression/shadowing  anti-shadowing Yuji Goto (RIKEN/RBRC)

5. Physics motivations • Probes of early, highest energy-density stage of heavy-ion reactions • yield and spectrum of heavy-flavor mesons will provide unique information on the earliest stages • open-charm and beauty • pT spectrum, near-angle and back-to-back correlations with other hadrons • energy-loss of heavy-quarks • enhancement of open-charm and beauty • inclusive electron spectra + displaced vertex • hadronic decay channel • J/y suppression • Upsilon spectroscopy Yuji Goto (RIKEN/RBRC)

6. Requirements for detectors • Intra-detector requirements • position resolution • displacement resolution, position matching • the 1st layer should be as close to the collision point as practically achievable • the 1st layer + beam-pipe should be as thin as possible • momentum resolution • jet-axis resolution, momentum matching • barrel outer layer (strips) configuration • ability to match tracks from the central arms and the muon arms • Au-Au background issues • occupancy  cell size • requirements for position matching & momentum matching Yuji Goto (RIKEN/RBRC)

7. Strawman design * pixel barrels * strip barrels * pixel disks each silicon layer has 1% radiation length detector + cooling + support Yuji Goto (RIKEN/RBRC)

8. Requirements for detectors • Inter-detector requirements • acceptance match of the endcap detectors with the muon arms conflicts with the HBD/TPC inner radius (20cm) • material of the barrel detectors may produce too many charged tracks for the HBD/TPC Yuji Goto (RIKEN/RBRC)

9. Simulation studies e-track dca • Open charm in the central arms • without cuts on displaced vertex • S/B ~ 1 for high pT • S/B ~ 0.1 for pT = 0.5 GeV/c • distance of closest approach (DCA) cut collision vertex Yuji Goto (RIKEN/RBRC)

10. Simulation studies • Open charm in the central arms • signal/background with DCA cut • S/B from ~1 to ~5  sample largely e from D-decay • large momentum range  spectra and yields of D Yuji Goto (RIKEN/RBRC)

11. Simulation studies • Open charm in the central arms • construct invariant mass  extract counts  spectra • multiple scattering, slow hadrons, makes this very tough • provides 2nd measurement of D spectra, consistency with De+X D+ K-p+p+ (BR 9%) full multiple-scattering three displaced tracks, parent points to collision Yuji Goto (RIKEN/RBRC)

12. Simulation studies • Open charm in the muon arms • mean decay vertex of the detected muon from the interaction vertex • 785mm • vertex cut • 1mm – 1cm • before cut • S/B < 1 for pT < 5 GeV/c • after cut • S/B > 2 for pT > 0.8 GeV/c • S/B > 10 for pT > 3 GeV/c Yuji Goto (RIKEN/RBRC)

13. Simulation studies • Open bottom in the muon arms • muon-pair vertex resolution • 133mm • mean decay length • 1.1mm • vertex cut to remove prompt J/y • 1mm • 39% of B decays retained • prompt J/y are attenuated by a factor of 2×10-4 Yuji Goto (RIKEN/RBRC)

14. Simulation studies • Au-Au background issues • track matching from the muon arms to the silicon vertex detector • occupancy of the 1st silicon plane: 0.15 % • momentum resolution: Dp/p ~ 25 % • track matching: s = 2 cm • by requiring X and Y track matching ±3 cm and momentum matching 50% Yuji Goto (RIKEN/RBRC)

15. Summary of strawman simulation studies • electron displaced vertex: rms(DCA) < 40 mm • (charm electrons)/(other electrons) at pT = 1 GeV/c • improves from S/B ~1 to ~5 with a DCA cut of 125 mm • D  Kpp seems feasible • measure muon displaced vertex: rms(z) ~ 100 mm • (charm muons)/(other muons) • improves from S/B < 1 to ~ 10 at pT ~ 3 GeV/c • J/y displaced vertex in B  J/y • muon channel simulated: rms(z) ~ 133 mm • mean decay position z ~ 1 mm • vertex cut ~ 1 mm removes several sigma of prompt J/y Yuji Goto (RIKEN/RBRC)

16. Next steps • more detailed simulations will be performed to confirm that the physics goals can be met with a realistic layout • a BNL silicon strip prototype is made, will be bench-tested in summer/early fall, and beam-tested in fall 2002 • readout electronics for silicon strips will be evaluated • a team is in place at CERN working with the ALICE pixel team, implementing a pixel detector for NA60 • the first MOSIS submission in June 2002 for the monolithic pixel by the ISU group • the details of the pixel layers (size, heat load, mechanical support, etc.) will be defined to decide whether it is feasible to design the mechanical structure Yuji Goto (RIKEN/RBRC)