Femtoscopy at RHIC : Overview

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Femtoscopy at RHIC Overview
or The HBT Puzzle from 10,000 meters

• Outline
• Review general trends from AGS to RHIC
• Discuss productive lines of inquiry
• Potential pitfalls

See Lisa, Pratt, Soltz, Wiedemann http//arxiv.org
/abs/nucl-ex/0505014
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Why Femtoscopy?

• Not just HBT, Interactions are now part of the
  measurement
• Femtoscopy any measurement that provides
  spatio-temporal information on fm scale,
  following Lednicky

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kT Dependence
Three experiments agree systematic errors 5-10
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System Size Npart Multiplicity

• Npart1/3 simple scaling
• dNch/d? may be simpler
• 2 quantities related

Rlong prefers dNch/d?
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Boost Invariance Yano-Koonin

• Boost Invariance holds approximately for 1 unit
  rapidity
• No longer holds beyond 1 unit for AGS/SPS

?gt1 for RHIC?
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mT Scaling
Long rescattering phase precluded?
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mT scaling vs. sqrt(s)
R(mT)RmT-?
R(mT)RmT-1/2
mT scaling appears energy independent What else
does it not depend on?
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mT scaling in ee-
Intriguing, but you have reason to be skeptical
of R0.15 fm
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Transport Models
Little sensitivity to cross-section?
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Previous AMPT conclusions
Dependence appears at low-Q, not in Gaussian Radii
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Hydro Models
Apples to Apples comparison Gaussian fit in LCMS
fails
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Overview (up to today)

• If we have created a QGP, then we do not yet
  understand its spatial-temporal evolution
• Show where models disagree with data too
• Feynmann (somewhere)
• And when you believe in things that you dont
  understand then you suffer...
• S. Wonder (Original Musiquarium)

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Line of Inquiry 1 Models

• Additions to Hydro
• realistic freeze-out
• Soff
• sensitivity to EOS and phase transition
• Rischke (1996), Zschiesche (chiral)
• viscous effects
• Teany

No Comprehensive Study
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Line of Inquiry 2 New analyses

• Other particle species
• STAR, PHENIX (?? through ??)
• Other methods to extract source (Imaging)
• David, Pavel, Roy
• Other orientations
• reaction plane (particle species)
• w.r.t. jet-axis (needs imaging)

Plenty of Room for Discovery
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Final warning devil in the details
Full Coulomb fit fails!
B-S Gaussian fit fails!