The%20STAR%20Heavy%20Flavor%20Tracker

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• The STAR Heavy Flavor Tracker
• Jim Thomas
• Lawrence Berkeley Laboratory
• 11 / 07 / 2006

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Heavy Flavor is the Final Frontier

• The QGP is the universally accepted hypothesis at
  RHIC
• The next step in confirming this hypothesis is
  the proof of thermalization of the light quarks
  in RHIC collisions
• The key element in proving this assertion is to
  observe the flow of charm because charm and
  beauty are unique in their mass structure
• If heavy quarks flow
• frequent interactions among all quarks
• light quarks (u,d,s) likely to be thermalized

Current quark a bare quark whose mass is due to
electroweak symmetry breaking
Constituent quark a bare quark that has been
dressed by fluctuations in the QCD sea
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Flow Probing Thermalization of the Medium
py
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Flow Constituent Quark Number Scaling
In the recombination regime, meson and baryon v2
can be obtained from the quark v2
Does it work in the Charm Sector? A strong test
of the theory
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Where does Charm come from?

• Gluon Fusion and qq-bar annihilation dominate the
  production of charm at RHIC
• Initial state
• Thermal processes are important but not dominant
• Final state effects
• Instantaneously equilibrated QGP shown for
  reference
• In the real world, thermal distributions are less
  important due to the large mass of the c quark
  (not true in the strange quark sector)

Levai, Mueller, and Wang, PRC 51, 3326 (1995).

• pre-thermal scattering between free streaming
  partons
• thermal assumes parton equilibration
• Assume 3.5 GeV/fm3 at instant of equilibration

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How many c c-bar pairs per collision?
Theory ?NN (c ) 289 - 445 µb Exp ?NN (c ) 900 - 1400 µb 20 - 30 c pairs per central AuAu collision at vsNN 200 GeV
Theory ?NN (b) 1.64 - 2.16 µb Exp ?NN (b) ?? 0.04 - 0.06 b pairs per central AuAu collision at vsNN 200 GeV

• Many ingredients are required to understand the
  formation of charmed hadrons at RHIC including
  the parton distribution functions for the
  projectile and target and the cross section for
  gluon fusion and qq-bar annihilation.
• The cross-sections can be calculated in NLO
  perturbative QCD
• The pdfs come from e-p data
• Ramona Vogt updates these estimates every few
  years
• R. Vogt, hep-ph/0203115, hep-ph/0203151
• The nucleon-nucleon cross sections are
  extrapolated to Au-Au by assuming 1000 binary
  scatterings in a central collision

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Direct Topological Identification of Open Charm
Goal Put a high precision detector near the IP
to extend the TPC tracks to small radius
The STAR Inner Tracking Upgrades will identify
the daughters in the decay and do a direct
topological reconstruction of the open charm
hadrons. No Mixed events, no random background
subtraction.
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The Heavy Flavor Tracker

• A new detector
• 30 mm silicon pixels
• to yield 10 mm space point resolution
• Direct Topological reconstruction of Charm
• Detect charm decays with small ct, including D0
  ? K ?
• New physics
• Charm collectivity and flow to test
  thermalization at RHIC
• Charm Energy Loss to test pQCD in a hot and dense
  medium at RHIC
• RD with HFT SSD
• A proposal has been submitted and a TDR is in
  preparation

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RD is Driven by the Fabrication Schedule
Driven by the availability of CMOS Active Pixel
Sensors
Fab-1999 Fab-2001 Fab-2003 Fab-2004 Fab-2005 Fab-2006 Fab-2007 Fab-2009
Mimosa-1 Mimosa-4 Mimosa-8 MimoSTAR-1 MimoSTAR-2 MimoSTAR-3 MimoSTAR-4 UltraSTAR
Build a full detector with each
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Alexandre Shabetai Xianming Sun
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Selected Parameters and Specifications
Min I efficiency 98
Accidental rate lt 100 /cm2
Position resolution lt 10 ?m
Number of pixels 135,168,000
Pixel dimension 30 ?m ? 30 ?m
Detector chip active area 19.2 mm ? 19.2 mm
Detector chip pixel array 640 ? 640
Number of ladders 33
Ladder active area 192 mm ? 19.2 mm
Number of barrels 2
Inner barrel (9 ladders) r 2.5 cm
Outer barrel (24 ladders) r 7.0 cm
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Surround the Vertex with Si
The HFT is a thin detector using 50 ?m Si to
finesse the limitations imposed by MCS
Add the HPD, IST, and SSD to form the STAR Inner
Tracking Upgrade ( ITUp )
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The Heavy Flavor Tracker
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• Goal graded resolution from the outside in
• TPC IST HPD HFT
• TPC pointing resolution at the SSD is 1 mm
• SSD pointing at the IST is 300 mm
• IST pointing at the HPD is 150 mm
• HPD pointing at the HFT is 100 mm
• HFT pointing at the VTX is 50 mm

Andrew Rose, Sevil Salur, et al.
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Keep the SSD, it is a beautiful detector!

• The SSD is thin
• 1 - double sided Si
• The SSD lies at an ideal radius
• 23 cm - midway between IP and IFC
• The SSD has excellent resolution
• (rumor says better than design)
• The SSD is too large to be replaced
• The money is better spent, elsewhere

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Hand Calculations of HFT TPC Performance
Yan Lu JT
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Hand Calculations
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The STAR Inner Tracking Upgrade is Unique at RHIC

• The Inner Tracking Upgrade will cover 2p in f
  azimuth
• PHENIX Si covers 2p in f but the rest of the
  detector is 2 arms of p/2
• The Inner Tracking Upgrade will cover 1 unit of
  h
• PHENIX Si covers 1 unit but the rest of the
  detector covers 1/3 unit
• The HFT uses 30x30 mm pixels for high resolution
  tracking
• PHENIX uses 50x425 mm pixels ( strips )
• The HFT uses 50 mm thick Si in each of 2 layers
• PHENIX uses 350 mm thick Si (sensor plus readout)
  in 2 layers and 1250 mm thick Si in 2 more layers
• The HFT is 0.25 radiation lengths thick per
  ladder
• PHENIX needs cooling their first layer is 1.2
  thick
• The HFT will have 10 mm pointing resolution
• PHENIX will have 50 mm pointing resolution
• Our pT threshold for D0s will be 700 MeV
• PHENIX will have 2 GeV ... we get 5 times the
  spectrum yield
• The large RHIC collaborations have similar
  physics goals
• PHENIX does single electron spectra very well
• We will do this plus the direct topological
  reconstruction of open Charm!

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Summary

• The STAR Inner Tracking Upgrade will explore the
  Charm sector
• We will do direct-topological-reconstruction of
  open Charm
• Our measurements will be unique at RHIC
• The key measurements include
• V2
• Energy Loss
• Charm Spectra, RAA Rcp
• Vector mesons
• Angular Correlations
• The technology is available on an appropriate
  schedule