Femtoscopy in heavy ion collisions: Two decades of progress

1
Femtoscopy in heavy ion collisionsTwo decades
of progress

• Mike Lisa
• Ohio State University

An experimentalists view of the situation
B.Q.M.() cf. Bysterský, Chajecki, Chaloupka,
Chung, Kisiel, Kniege, Panitkin...
BQM Before Quark Matter
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Outline

• Relevance of femtoscopy to R.H.I.C.
• Growing activitiies of a (sub)field 2 decades
  of systematics
• R(vSNN, b, Npart, A, B, mT, y, ?, PID)
• what information is encoded?
• what have we mined so far?
• special attention to size and shape
• comments

blastwave
comparison to models
experimental details
3
Spacetime - an annoying bump on the road to
Stockholm?

• Non-trivial space-time - the hallmark of rhic
• Initial state dominates further dynamics
• Intermediate state impt element in exciting
  signals
• Final state
• Geometric structural scale is THE defining
  feature of QGP

4
Spacetime - an annoying bump on the road to
Stockholm?

• Non-trivial space-time - the hallmark of rhic
• Initial state dominates further dynamics
• Intermediate state impt element in exciting
  signals
• Final state
• Geometric structural scale is THE defining
  feature of QGP
• Temporal scale sensitive to deconfinement
  transition (?)

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Two decades of systematics
R 5 fm

• Pion HBT _at_ Bevalac largely confirming nuclear
  dimensions
• Since 90s increasingly detailed understanding
  and study w/ high stats

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Two decades of systematics

• Pion HBT _at_ Bevalac largely confirming nuclear
  dimensions
• Since 90s increasingly detailed understanding
  and study w/ high stats

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Repeating most basic sanity check at relativistic
energies...
Forget homogeneity regions or fancy stuff. Do
femtoscopic length scales increase when they
should?
p-p correlations big bump ? small source

• Also
• SPS NA44(99),NA49(00)
• RHIC STAR(05)

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• Generalize A1/3 ?Npart1/3
• not bad _at_ RHIC!
• connection w/ init. size?

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• Generalize A1/3 ?Npart1/3
• not bad _at_ RHIC!
• connection w/ init. size?
• Heavy and light data from AGS, SPS, RHIC
• ?s-ordering in geometrical Rlong, Rside
• Mult K(?s)Npart
• source of residual ?s dep?
• ...Yes! common scaling
• final state drives radii, not init. geometry
• (breaks down ?s lt 5 GeV)

NB not constant density
LPSW nucl-ex/0505014
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We are not alone...
Entropy determines everything at bulk level
(soft sector) ?
NB scaling violated ?s lt 4 GeV (as with
femtoscopy)
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Refinement chemical effects

• different behaviour below/above AGS
• violates universal scaling
• baryon ? meson dominance
• neglect time/dynamics gross F.O. geometry
  appears determined by
• chemistry
• universal mean free path 1 fm (!?)

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Messages from systematics

• AB, b, Npart systematics
• sanity check on overall size dependence ?
• final state multiplicity/chemistry determines
  rough geometry...

...and that geometry is 2x initial size
collective/flow-like expansion? ? probe
anisotropically!
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Strongly-interacting 6Li released from an
asymmetric trap OHara, et al, Science 298 2179
(2002)
What can we learn?
transverse FO shape collective velocity ?
evolution time estimate check independent of
RL(pT)
Teaney, Lauret, Shuryak nucl-th/0110037
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• observe the source from all angles with respect
  to RP
• expect oscillations in HBT radii

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• observe the source from all angles with respect
  to RP
• expect oscillations in HBT radii (including new
  cross-terms)

R2out-sidelt0 when ?pair135º
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Measured final source shape
R2out-sidelt0 when ?pair135º
ever see that symmetry at ycm ?
model-dependent, but see Retiere MAL PRC70
044907 2004
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Measured final source shape
Expected evolution
?
model-dependent, but see Retiere MAL PRC70
044907 2004
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Evolution of size and shape - the rule of two
1/2 shape reduction
x2 size increase
Initial size/shape estimated by Glauber
calculation Final config according to Retiere
MAL PRC70 044907 2004
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Anisotropic sanity check

• non-trivial excitation function
• does it make sense? Is it related to bulk
  dynamics?
• YES

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A simple estimate ?0 from ?init and ?final

• BW ? ?X, ?Y _at_ F.O. (?X gt ?Y)
• hydro flow velocity grows t
• From RL(mT) ?0 9 fm/c
• consistent picture
• Longer or shorter evolution times
• inconsistent
• toy estimate ?0 ?0(BW) 9 fm/c
• too short to account for expansion??
• Need a real model comparison? asHBT workable
  evolutionary clock constraint for models

MAL ISMD03
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Messages from systematics

• AB, b, Npart systematics
• sanity check on overall size dependence ?
• final state multiplicity/chemistry determines
  rough geometry...
• ?, b, ?s systematics
• sanity check on shape evolution ?
• geometric evolution consistent with collective
  bulk dynamics (flow)

look for dynamic signatures substructure

• more than T versus mass
• more than spectral shapes
• more than v2
• ...
• flow is defined by space-momentum correlations
• only femtoscopy can probe substructure
• of dynamic bulk behaviour

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Flow-dominated Blast-wave model PRC70 044907
(2004)
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• Decreasing R(pT)
• usually attributed to collective flow
• flow integral to our understanding of R.H.I.C.
  taken for granted
• femtoscopy the only way to confirm x-p
  correlations impt check

Kolb Heinz, QGP3 nucl-th/0305084
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• Decreasing R(pT)
• usually attributed to collective flow
• flow integral to our understanding of R.H.I.C.
  taken for granted
• femtoscopy the only way to confirm x-p
  correlations impt check

• Non-flow possibilities
• cooling, thermally (not collectively) expanding
  source
• combo of x-t and t-p correlations

early times small, hot source
late times large, cool source
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• Decreasing R(pT)
• usually attributed to collective flow
• flow integral to our understanding of R.H.I.C.
  taken for granted
• femtoscopy the only way to confirm x-p
  correlations impt check

• Non-flow possibilities
• cooling, thermally (not collectively) expanding
  source
• combo of x-t and t-p correlations

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• Decreasing R(pT)
• usually attributed to collective flow
• flow integral to our understanding of R.H.I.C.
  taken for granted
• femtoscopy the only way to confirm x-p
  correlations impt check

• Non-flow possibilities
• cooling, thermally (not collectively) expanding
  source
• combo of x-t and t-p correlations
• hot core surrounded by cool shell
• important ingredient of Buda-Lund hydro
  picturee.g. Csörgo LörstadPRC54 1390 (1996)

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Each scenario generates x-p correlations

• Decreasing R(pT)
• usually attributed to collective flow
• flow integral to our understanding of R.H.I.C.
  taken for granted
• femtoscopy the only way to confirm x-p
  correlations impt check

but
?x2?-p correlation yes ?x?-p correlation yes

• Non-flow possibilities
• cooling, thermally (not collectively) expanding
  source
• combo of x-t and t-p correlations
• hot core surrounded by cool shell
• important ingredient of Buda-Lund hydro
  picturee.g. Csörgo LörstadPRC54 1390 (1996)

?x2?-p correlation yes ?x?-p correlation no
t
?x2?-p correlation yes ?x?-p correlation no
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• flow-dominated models can reproduce soft-sector
  x-space observables
• imply short timescales
• however, are we on the right track? flow
• puzzles? ? check your assumptions!
• look for flows special signature ?x?-p
  correlation
• In flow pictures, low-pT particles emitted closer
  to sources center (along out)
• non-identical particle correlations(FSI at low
  ?v) probe
• ?(x1-x2)2? (as does HBT)
• ?x1-x2?

?
K
p
click for more details on non-id correlations
Csanád, Csörgo, Lörstad nucl-th/0311102 and
nucl-th/0310040
F. Retiere MAL, nucl-th/0312024
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• extracted shift in emission point ?x1-x2?
  consistent w/ flow-dominated blastwave

• In flow pictures, low-pT particles emitted closer
  to sources center (along out)
• non-identical particle correlations(FSI at low
  ?v) probe
• ?(x1-x2)2? (as does HBT)
• ?x1-x2?

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RHIC femtoscopy with wide variety of particle
species
R(vSNN, b, Npart, A, B, mT, y, ?, PID1, PID2)
? ?- K K- K0S p ?p ? ?? ? ??
? ? ? ? ? ? ? ? ?
? ? ? ? ? ? ? ?-
? - ? ? K
? ? ? K-
? - - K0S
? ? ? ? p
? ? ? ?p
?
??
?
??
? prelim or final result available
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Strong flow confirmed by all expts...
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Strong flow confirmed by all expts...
Central (10) AuAu (PbPb) collisions at y0
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Another implication of strong flow mT scaling
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Some longitudinal systematics
consistent with boost-invariance
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Dynamic BI without Chemical BI ? Only
femtoscopy can tell!
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Dynamic BI without Chemical BI ? Only
femtoscopy can tell!
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Greater detail - ?-p correlations _at_ AGS
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Comments

• massive systematic program provides tremendous
  geometric detail
• each element reasonable by itself not really
  puzzling.
• critical mass in the femtoscopy community
• Related, but not in my talk important new
  directions talks _at_ WPCF
• moments analysis
• imaging
• continued emphasis on non-identical particle
  correlations
• connection to elementary systems -
  communication across lines
• Important puzzles beyond central AuAu at top
  energy
• Ignoring femtoscopy to pursue perfection is
  unjustified
• Space-time is the defining feature of R.H.I.C.
• Femtoscopy does measure space-time
• The measurements are sensitive to underlying
  physics