The STAR Integrated Tracking Upgrade Project Frank Simon

The STAR Integrated Tracking Upgrade Project Frank Simon (MIT) for the STAR Collaboration CIPANP 2006, May 30 - June 3, 2006, Puerto Rico § Current Capabilities § Heavy Flavor Physics § W Program § Upgrades: Plans & Technologies § Summary & Outlook

The STAR Experiment: Current Capabilities Magnet § 0. 5 T Solenoid Tracking § Large-volume TPC § | | < 1. 5 § particle ID via d. E/dx § SVT/SSD § Silicon trackers: improved vertex reconstruction, displaced vertices for strange particle decays § Forward TPC § 2. 5 < | | < 4. 0 Calorimetry § Barrel EMC / Endcap EMC § -1. 0 < < 2. 0 § Forward Pion Detector § 3. 3 < | | < 4. 1 Particle ID § Time-of-Flight detector § | | < 1 Frank Simon: STAR Tracking Upgrade 06/02/2006 2

Heavy Flavor in Heavy Ion Collisions § Mesons and baryons containing light quarks (u, d, s) show strong elliptic flow § Heavy quark mass dominated by intrinsic mass: c and b quarks are also heavy in a QGP Heavy quark flow needs frequent interactions among all quarks If c, b quarks flow light quarks very likely to be thermalized Heavy flavor a good probe of the medium created at RHIC § Energy loss in the medium § Spectra §… Direct observation of mesons containing heavy quarks crucial Frank Simon: STAR Tracking Upgrade 06/02/2006 3

Heavy Flavor in Spin Physics Use polarized p+p collisions to access the helicity distribution of the gluons in the proton (so far largely unconstrained) Measure double spin asymmetries for a variety of channels (Currently jets, neutral and charged pions) Heavy flavor production in p+p collisions: gluon-gluon fusion § one partonic subprocess dominates contributions from quark helicities negligible ALL g g Inclusive electrons from charm; ~100 pb-1, 70% pol. clean theoretical connection from the experimentally accessible spin asymmetry to g GRSV-std the challenge: directly identify charm & bottom mesons GRSV-min § D 0 c ~ 123 m § B 0 c ~ 460 m GRSV-max Precision vertexing needed! Frank Simon: STAR Tracking Upgrade p. T (Ge. V/c) 06/02/2006 4

Flavor Structure of the Proton Spin § Flavor structure of the proton sea can be probed via W± production: flavor separation possible experimental signature: high p. T lepton from W decay Study flavor-separated quark polarization via parity violating single spin asymmetries in polarized p+p collisions at 500 Ge. V Simple ratio of PDFs in extreme kinematics: Frank Simon: STAR Tracking Upgrade 06/02/2006 5

W Production at RHIC d/d u/u Single spin asymmetry as a function of lepton rapidity d/d u/u Frank Simon: STAR Tracking Upgrade charge sign identification of high p. T electrons at forward rapidity 06/02/2006 6

Planned Upgrades: Overview Forward Tracking § charge sign identification for high momentum electrons from W± decay (energy determined with endcap EMC) Inner Tracking § precision vertexing for charm & bottom reconstruction Frank Simon: STAR Tracking Upgrade 06/02/2006 7

Heavy Flavor & Inner Tracking IST Intermediate Silicon Tracker: 3 layers of 2 x single sided Si (1 strip, 1 pad), 7, 12 & 17 cm radius fast tracker to resolve individual bunch crossings HFT pointing accuracy to HFT < 150 m replaces current SVT, and should not exceed its material budget of ~ 4. 5% X 0 Existing SSD will be used Heavy Flavor Tracker: § 2 layers of Si-Pixel, 1. 5 & 5. 0 cm radius § very low material budget: X 0 ~ 0. 3% per ladder § spatial resolution < 10 m Frank Simon: STAR Tracking Upgrade 06/02/2006 8

Inner Tracker Technology Choices Heavy Flavor Tracker § Active Pixel Sensor Technology silicon thinned to 50 m ladder prototype with 4 wafers Intermediate Silicon Tracker Back-to-back single sided Si-Strip/Pad detectors Fast Readout based on APV 25 S 1 front-end chip (developed by CMS) Inner tracker a combination of new (APS) and proven (Si-strip, APV 25) technology to achieve desired performance and reliability Frank Simon: STAR Tracking Upgrade 06/02/2006 9

Forward Tracking 2 separate detectors: Forward Silicon Tracker (FST): § forward tracking close to the primary vertex, 1 < < 2 § 4 silicon disks, consisting of back-to-back strip sensors (same technology as IST) A B Forward GEM Tracker (FGT) § large lever arm, tracking 1 < < 2 2 Options (resolution < 100 m) § A) large area tracker in front of EEMC, problem: TPC electronics § B) GEM barrel (or disks) Frank Simon: STAR Tracking Upgrade 06/02/2006 10

Forward Tracking Technology GEM technology a natural choice for large area forward trackers § Triple GEM trackers ~ 70 m spatial resolution in high occupancy environment § significantly cheaper than silicon per area § fast detectors, low material budget ~ 0. 7% X 0 per detector (2 D readout) § APV 25 chip can be used (as for the IST and FST) GEM: copper-clad insulator foil with a large number of small (~70 m diameter) holes, voltage across the foil leads to charge amplification in the holes 55 Fe spectrum Cooperation with company Tech. Etch to establish a commercial source of GEM foils First promising results with test detector Frank Simon: STAR Tracking Upgrade 06/02/2006 11

Summary & Outlook § STAR has a rich physics program both in heavy ion collisions and in polarized p+p collisions § Several key measurements require upgrades of the STAR tracking system § Investigation of heavy flavor properties in the medium created in Au+Au collisions § Accessing g via heavy quark production § Flavor separation of proton spin structure via forward W± production § Plans for an integrated STAR tracker: § High resolution inner tracker: HFT and IST (silicon pixel & strips) 2009 § Charge-sign resolution for high-p. T electrons in the forward direction: FST and FGT (silicon strips & GEM) 2011 Frank Simon: STAR Tracking Upgrade 06/02/2006 12