Recent developments in
femtoscopy at RHIC*
Mike Lisa
Ohio State University
* not an overview talk
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
1
Outline
• Motivation & Reminders: space-time, H.I.C., pion correlations
• Status of present program: exploiting huge systematics
• Selected results
• femtoscopy of identical and non-identical particles
• Harmonic decomposition - isolating geometrical effects
• comparison with p+p collisions (in same detector!)
• Harmonic decomposition - isolating non-femtoscopic correlations
• Summary
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
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R(√S
– simple
R(√SNN), b,
Npart, A,signal
B, mT,?y, , PID)
No glaring signal in simple
measures
Rout/Rside
The „real” (experimentalist’s)
„puzzle”
mass
|b|
“e”
Rischke, Gyulassy, NP A 608 (1996) 479
pT
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
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R(√SNN, b, Npart, A, B, mT, y, , PID)
• Vary colliding system
• does physics change?
• requires dedicated program
• Vary kinematic variables
• space-time dynamics
• requires large acceptance
• Vary particle type
• consistent picture?
• unique probe of dynamical structure
• requires good particle identification & acceptance
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
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Possibilities in a dedicated program: 5 years @RHIC
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Also: p+p @ 62.4 & 200 GeV
Gunther Roland, QM05
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
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MAL, Pratt, Soltz, Wiedemann nucl-ex/0505014
R(√SNN, b, Npart, A, B, mT, y, , PID)
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
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Lisa, Pratt, Soltz, Wiedemann, nucl-ex/0505014
R(√SNN, b, Npart, A, B, y, mT, , PID)
Z. Chajecki, QM05
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
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Lisa, Pratt, Soltz, Wiedemann, nucl-ex/0505014
R(√SNN, b, Npart, A, B, y, mT, , PID)
MAL, Pratt, Soltz, Wiedemann nucl-ex/0505014
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
STAR, PRL 2004
Z. Chajecki, QM05
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
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1D projections: a limited view
STAR PRC71 044906 (2005)
• Usual 1D out-side-long
“Cartesian projections”
• limited view of data
• ~set of zero measure of
3D CF
• Fit-violating trends may
be hidden
• Salient geometrical
effects non-trivially
convoluted
• acceptance-dependent
(unlike 3D CF)
Harmonic Decomposition Analysis
• exploits full out
symmetry of q-space
“Gaussian fit”
• explicit isolation of femtoscopic
(remember: not
(& non-femtoscopic) effects
Gaussian CF)
• full 3D CF seen clearly in few plots
• acceptance-robust (*)
side
long
• Cartesian HD
Danielewicz & Pratt nucl-th/0501003
• Spherical HD
Chajecki,Gutierrez,MAL,Lopez nucl-ex/0505009
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
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Spherical harmonic decomposition of CF
• Cartesian-space (out-side-long) naturally
encodes physics, but is “inefficient”
representation
2
2
2
Q  QOUT
 QSIDE
 QLONG
cos( ) 
QLONG
QTOT
  arctan
• Harmonic Moments -- 1::1 connection to
source geometry
[Danielewicz,Pratt: nucl-th/0501003]
QSIDE
QOUT
• ~immune to acceptance
• full information content at a glance
[thanks to symmetries]

Al ,m (| Q |) 
 cos  
4
all.bins
QLONG

 Yl ,m ( i ,i )C(| Q |, cos  i ,i )
i
QSIDE
Q

QOUT

mike lisa - Recent developments in femtoscopy at RHIC
Chajecki.,
- ISMD
Gutierrez,
Aug 2005MAL,
- Kroměříž
Lopez-Noriega,
Czech Republic
nucl-ex/0505009
12
STAR Central Au+Au collisions -- Spherical HD
1D o-s-l projections
SH Moments
C(Qout)
A00
A20
C(Qside)

C(Qlong)
Al ,m (| Q |) 
 cos 
4
all.bins


Yl ,m ( i , i )C (| Q |, cos i , i )
i
A22
Chajecki., Gutierrez, MAL
Lopez-Noriega, nucl-ex/0505009
STAR preliminary
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
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“Mental calibration” - a Gaussian CF
~acceptance free
RL < RT
RL > RT
Simple, Gaussian
source calculations
RO < RS
RO > RS
• Full 3D structure
• (high-L (fine structure) coefficients drop off)
• Different geometrical aspects separate &
use “all” relevant information in the CF
• AL≠0 vanishes in non-femtoscopic region
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
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P. Chung, QM05
Alternative: Cartesian Harmonic Decomposition
l
R1 ....l
2l  1!!

(q) 
d q

l
(q ) R(q ) (4)
l!
4
2l  1!! d r l

l
S1 ....l (r ) 
 .... (r ) S (r )

1
l
l!
4
Correlation function
R(q )  
l
Source function
1
S (r )  
l
....l

 
Rl 1 ....l  q  l

 
Sl 1 ....l  r  l
(5)
1 .... l
1 .... l
1
1 .... l
.... l
( q )
( r )
(1)
(2)
3
R
(
q
)

C
(
q
)

1

4

dr
KooninPratt
 K (q, r )S (r )
R1 ....l (q)  4  drr Kl (q, r )S
l
2
l
1 ....l
(r )
(4)
Danielewicz
and Pratt
nucl-th/0501003
mike lisa - Recent developments in femtoscopy at RHIC - ISMD
Aug 2005 - Kroměříž
Czech
Republic
15
P. Chung, QM05
PHENIX Preliminary
CHD:  from central Au+Au collisions
L=0
L=1
• “Size”
• C0(qinv)  C1D(qinv)
out
side
• symmetry: odd L vanish here
• But, interesting for non-id
L=2
out
long
L=4
• Source deformation manifest
• “Rlong” > “Rout” > “Rside”
side
out
side
• higher-order structure
long
long
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
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RHIC femtoscopy with wide variety of particle species
R(√SNN, b, Npart, A, B, mT, y, , PID1, PID2)
+
-
K+
K-
p
p










+







-

-


K+



K-
-
-
K 0S




p



p
K 0S



!

 = prelim or final result available



mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
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P. Chaloupka, QM05
±-± correlations in 200 GeV Au+Au
like-sign vs unlike-sign
central vs peripheral
Wonderful...but there’s
++ & -• consistent
• Coulomb-dominated
+- & -+
• consistent
• Coulomb + strong
more!...
Expected centrality
dependence
• “*” sensitive
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
18
Geometric effects of collective flow
Emission points from Blast-wave
βt = 0.73 for all species
●
●
Pion
pt = 0.15 GeV/c
Ξpt = 1.4 GeV/c
Proton
pt = 1. GeV/c
-
Ω
pt = 1.8 GeV/c
●
Correlation between
momentum and emission point
reduces source size
shifts average emission point
Effect increases with mT
Non-identical particle correlations
uniquely probe dynamic structure
R. Lednicky, nucl-th/0112011
Retiere & MAL, PRC70 044907 2004
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
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SHD of non-identical particle correlations
• A00 - monopole  size
• A11 - dipole  shift
• A2m - quadrupole  shape
• .....
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
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Accessing asymmetry
• A11 ≠ 0 in correlation
regions
 Asymmetry in the
average emission point
between p-X
• In the “right” direction
(cf BW)
details: P. Chaloupka @ WPCF
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
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Zbigniew Chajecki QM05
R Z(fm)
1. Heisenberg
uncertainty?
Z0 decay @ LEP
•2.e.g.
G. fragmentation?
Alexander
String
(Lund)
••3.“plausible”
ineffects?
z-direction
pResonance
maybe (??)
T dependence
•• unlikely
in transvrseprobably no
dependence
• mass
e.g. Wiedemann
& DELPHI
Heinz ‘97
[Andersson,
Moriond 2000]
• maybe,
but presumably
 different effect
significantly
femtoscopy in p+p @ STAR
p+p and A+A measured in same
experiment
• great opportunity to compare physics
• what causes pT-dependence in p+p?
• same cause as in A+A?
than for Au+Au
R (fm)
• under investigation

K
p 
STAR preliminary
hep-ph/0108194
m, mT (GeV)
mT (GeV)
mT (GeV)
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
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Zbigniew Chajecki QM05
3. Resonance effects?
4. Bulk system („hydro”)
in pp?
DELPHI
flow not expected in such
a small system as p+p
R (fm)
e.g. Shuryak: hep-ph/0405066

 Csorgo et al.:
K Buda-Lund
treatment of p+p collision as
d+Au : Rlong doesn’t change
bulk
system
with centrality
p 
(w/ temperature gradients)
hep-ph/0406042
femtoscopy in p+p @ STAR
p+p and A+A measured in same
experiment
• great opportunity to compare physics
• what causes pT-dependence in p+p?
• same causeas in A+A?
1/(2mT)d2n/(dmTdy)
R Z(fm)
1. Heisenberg
uncertainty?
Z0 decay @ LEP
2. String fragmentation? (Lund)
K
p
mT-m (GeV)
RSIDE
ROUT
RLONG
STAR preliminary
hep-ph/0108194
m, mT (GeV)
mT (GeV)
mT (GeV)
mT (GeV)
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
24
Surprising („puzzling”) scaling
Ratio of (AuAu, CuCu, dAu) HBT
radii by pp
 All pT(mT) dependences of
HBT radii observed by STAR
scale with pp although it’s
expected that different origins
drive these dependences
HBT radii scale with pp
Scary coincidence
or something deeper?
pp, dAu, CuCu - STAR preliminary
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
25
Baseline problems with smallest systems
STAR preliminary
d+Au peripheral collisions
Gaussian fit
ad hoc, but try it...
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
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Try NA22 empirical form
STAR preliminary
d+Au peripheral collisions
Spherical harmonics
NA22 fit
data
L =1
M=0
L =2
M=0
NA22 fit
L =1
M=1
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
L =2
M=2
27
“account for” constant offset in L=2 components
STAR preliminary
d+Au peripheral collisions
A 00
A 02
Gaussian fit
b
|Q|
Gaussian
|Q|
z
+ constant A02, A22
A 22
|Q|
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
28
With L=2 shifts, message remains
STAR preliminary
Ratio of (AuAu, CuCu, dAu) HBT
radii by pp
Fit w/o baseline parameterization
NEW fit w/ baseline parameterization
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
29
Summary
• Very active, systematic femtoscopic program at RHIC
R(√SNN, b, Npart, A, B, mT, y, , PID1, PID2)
• A few new results
• detailed shape studies: (for many particle types)
• exotic correlations: substructure of space-time dynamics of 
• experimental comparison of femtoscopy in hadronic/nuclear collisions
• New methods
• Harmonic analysis : much to offer
• New questions
• dynamic substructure picture “confirmed”... eliminate theories/models?
• similarity of p+p & Au+Au (& d+Au) : “deep” or coincidental?
• A healthy, important (sub)field !
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
30
Conclusion/summary
• COMPLETE experimental program: huge multidimensional systematic effort at
dedicated facility with large acceptance
• new method [important to exploit the new data]
• fully exploits q-space symmetries: efficient representation of full 3D correlation
function [my opinion: this is the end of Cartesian projections]
• different physics aspects separated cleanly (l=0,1,2...)
• excellent diagnostic for identifying/characterizing nonfemtoscopic correlation
effects (& including them in fit)
• new data
• extend PID beyond pions for sizes: consistency of scenario
• non-id for shifts: new information also (qualitatively) consistent
• vary system [A,B,√s, Npart] (CuCu,AuAu,dAu,200,64GeV)
• multiplicity scaling
• “elementary” systems “3rd HBT puzzle”
• Insert closing comment / “big picture conclusion” here
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
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Petr Chaloupka QM05
Geometric effects of collective flow
Emission points from Blast-wave
βt = 0.73 for all species
●
Comment:
• Cramer/Miller: 12 parameters to
Proton
Pion
reproduce one particletype
pt = 0.15 GeV/c
●
pt = 1. GeV/c
●
• BW+stat: 5+2 parameters to reproduce
“all” particletypes
Ξpt = 1.4 GeV/c
-
Ω
pt = 1.8 GeV/c
Correlation between
momentum and emission point
reduces source size
shifts average emission point
Effect increases with mT
Non-identical particle correlations
uniquely probe dynamic structure
R. Lednicky, nucl-th/0112011
Retiere & MAL, PRC70 044907 2004
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
33
Spacetime - an annoying detail in H.I.C. ?
STAR, PRC66 (2002) 034904
STAR, PRL93 (2004) 252301
• 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
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
34
Hanbury Brown-Twiss interferometry
• Two-particle interferometry: p-space separation  space-time separation
x1
p1

q
qside
Rside
x2
p2
qout
  
q  p2  p1
 1  
k  p 2  p1 
2
qlong
Rout
• HBT: Quantum interference between identical particles
C (q)
P( p1 , p2 )
real event pairs
C ( p1 , p2 ) 

P( p1 )P( p2 ) mixed event pairs
2
2
2
2
2
2
Gaussian
 qout
 
Rout
 qside
Rside
 qlong
Rlong
model (3-d): C (q , k )  1  (k ) e
~
2
1
R
1
• Final-state effects (Coulomb, strong) also can
cause correlations, need to be accounted for
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
q (GeV/c)
35
Hanbury Brown-Twiss interferometry
• Two-particle interferometry: p-space separation  space-time separation
x1
p1

q
qside
Rside
x2
p2
qout
  
q  p2  p1
 1  
k  p 2  p1 
2
qlong
Rout
Rside
Rout
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
36
Spacetime - an annoying detail in H.I.C. ?
Ann.Rev.Nucl.Part.Sci. 46 (1996) 71
QuickTime™ and a
TIFF (L ZW) d eco mpres sor
are nee ded to s ee this picture.
• 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 (?)
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
37
STAR Central
Au+Au collisions -- Spherical HD
SH Moments
1D o-s-l projections
A04
A00
A20
C(Qout)
C(Qside)
A24
A22

 cos 
Al ,m (| Q |) 
C(Qlong) 4
all.bins


Yl ,m ( i , i )C (| Q |, cos i , i )
i
STAR preliminary
Chajecki., Gutierrez, MAL
Lopez-Noriega, nucl-ex/0505009
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
A44
38
Baseline in p+p, d+Au and Au+Au
 Some coefficients don’t vanish for large Q
 Bias from zero is larger for more peripheral
collisions
 This problem is getting more significant for small
systems (pp & dAu)
 It can be due to
 an experimental artifact
 long range correlations (e.g. Jets)
 problem with momentum conservation ?
 or ?
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
39
Long-range correlations : JETS ?
Jets as a origin of
the baseline problem ??
The idea was to try to eliminate pions coming
from jet fragmentation from data sample. It
can be done by applying an event cut which
accepts only events that have no high-pt
tracks (jets).
HBT analyses where done for three classes
of events
 all - all events accepted – as a reference
 soft – only events without high-pT tracks
( highest-pT < 1.2 GeV/c was chosen)
 hard - only events with least one
track with pT > 2 GeV/c
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
40
Momentum conservation study with Nexus
Nexus, p+p @ 200 GeV
D
 Correlation function for pions
from events generated with
EPOS
 No correlation effect included
(as BE, FSI)
 Background created by mixing
particles comming from
different events
(same procedure like for
experiemental CF)
No evidence of a problem with
baseline of CF !
mike lisa - Recent developments in femtoscopy at RHIC - ISMD Aug 2005 - Kroměříž Czech Republic
41