The most famous
femtoscopic systematic
Mike Lisa
Ohio State University
1
Wayne State University 22 Nov 05
Plan: wherefore, whence, whither
• Motivation (wherefore)
• Femtoscopy: two decades of progress (whence)
– 2xsNN in 20 years
• pT (mT) dependence (whence)
– spatial substructure: evidence of strong collective flow in R.H.I.C.
– similar behaviour in (very) low-energy H.I.C.
– unexpected (??) scaling w.r.t. pp
• pp in some more detail: SHD and long-range correlations (whither)
– (in progress)
• Summary
2
Wayne State University 22 Nov 05
Spacetime - an annoying bump on
the road to Stockholm?
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 & r.h.i.c
3
Wayne State University 22 Nov 05
Spacetime - an annoying bump on
the road to Stockholm?
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 & r.h.i.c
• Temporal scale sensitive to deconfinement transition (?)
4
Wayne State University 22 Nov 05
probing source geometry through
interferometry
pThe Bottom line…
1
r1
x1
  
  to
  i( r  x )p
if a pion is emitted, itis more
likely
i ( r emit
x )p another
1 {
U(x1, p1)e
U(x 2 , p2 )e
p source
T
2
 source
  
 
1 m momentum
(x) pion with very similar
 the
 if
issmall
i ( r  x )p
i ( r  x )p
1
 U(x 2 , p1)e
5 fm
p2
r2
2
1
1
2
U(x1, p2 )e

2
2
1
*TT  U1*U1  U*2 U 2  1  eiq( x1  x 2 )
experimentally measuring
this enhanced
Creation probability
(x,p) =probability:
U*U
quite challenging
P(p1, p 2 )
2
C(p1, p 2 ) 
 1 ~
 (q )
P(p1 )P(p 2 )
C (Qinv)
x2
1
1
2
}

Width ~ 1/R
2
1
Measurable!
F.T. of pion source
  
q  p 2  p1
5
Wayne State University 22 Nov 05
0.05
0.10
Qinv (GeV/c)
2
C2(Qinv)
Correlation functions for different colliding
systems
STAR preliminary
p+p
R ~ 1 fm
d+Au
Au+Au
R ~ 6 fm
Qinv (GeV/c)
Different colliding systems studied at RHIC
First opportunity to directly compare AA, pp, (&pA)
6
Wayne State University 22 Nov 05
Disintegration timescale
Relative momentum between pions is a vector q  p1  p 2
 can extract 3D shape information
Rlong – along beam direction
Rout – along “line of sight”  increases with emission timescale
Rside –  “line of sight”
K  p1  p 2
p1
q
Rside
Rout
K  p1  p2
p2

7
Wayne State University 22 Nov 05
R OUT

R SIDE
Disintegration timescale expectation
3D 1-fluid Hydrodynamics
Rischke & Gyulassy, NPA 608, 479 (1996)
with
transition
with
transition
“”
Long-standing favorite signature of QGP:
• increase in , ROUT/RSIDE due to deconfinement  confinement transition
• expected to “turn on” as QGP energy threshold is reached
8
Wayne State University 22 Nov 05
“”
Two decades of systematics
A.D. Chacon et al, Phys. Rev. C43 2670 (1991)
HBT
s ) Rep. Prog. Phys. 66 481 (2003)
G.(Alexander,
Boal/Jennings/Gelbke
20
15
10
Heinz/Jacak
Wiedemann/Heinz
Csorgo
Tomasik/Wiedemann
AGS/SPS/RHIC HBT papers (expt)
R = 1.2 (fm)•A1/3
“R = 5 fm”
5
‘85
‘90
‘95
‘00
‘05
• Pion HBT @ Bevalac: “largely confirming nuclear dimensions”
• Since 90’s: increasingly detailed understanding and study w/ high stats
9
Wayne State University 22 Nov 05
(√SNN, b, Npart, A, B, mT, y, , PID)
• Vary signal ()
• constrain multi-dimensional models
• requires flexible detectors, broad approach
mass
• Vary colliding system
• does physics change?
• requires dedicated program
|b|
• Vary kinematic variables
• dynamics and different regimes
• requires large acceptance
• Vary particle type
• consistent picture?
• unique probe of dynamical structure
• requires good particle identification & acceptance
10
Wayne State University 22 Nov 05
pT
Possibilities in a dedicated program:
5 years @RHIC
PHOBOS
PHENIX
1 km
RHIC
BRAHMS
STAR
v = 0.99995c = 186,000 miles/sec
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
AGS
Also: p+p @ 62.4TANDEMS
& 200 GeV
Gunther Roland, QM05
11
Wayne State University 22 Nov 05
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
12
Wayne State University 22 Nov 05
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)]
13
E877 PRC60 054905 (1999)
Wayne State University 22 Nov 05
R(√SNN, b, Npart, A, B, mT, y, , PID)
Varying initial “source size”
Au+Au sNN =200 GeV
Fixed b : vary A (& B!)
• Generalize A1/3 Npart1/3
•not bad @ RHIC!
•connection w/ init. size?
Fixed A+B : vary b
Likely scaling variable: Npart
PHENIX, PRL 2004
b
14
Wayne State University 22 Nov 05
R(√SNN, b, Npart, A, B, mT, y, , PID)
• Generalize A1/3 Npart1/3
•not bad @ RHIC!
•connection w/ init. size?
NB: not constant density
PHOBOS
• 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 < 5 GeV)
LPSW nucl-ex/0505014
15
Wayne State University 22 Nov 05
Entropy determines “everything” at bulk level (soft sector) ?
H. Caines (STAR) QM05
H.
Caines
(STAR)
QM05
Compiled
by A.
Wetzler (2005)
We are not alone...
NA57 (open)
STAR
(filled)
Tounsi,
Mischke,
Redlich
NA57 (open)
STAR (filled)
NPA715 565 (2003)
S. Manly (PHOBOS) QM05
NB: scaling violated s < 4 GeV
(as with femtoscopy)
16
Wayne State University 22 Nov 05
Refinement:
chemical effects
• different behaviour below/above AGS
– violates “universal” scaling
– baryon  meson dominance
Vf
• neglect time/dynamics: gross F.O.
geometry appears determined by
N
– chemistry
– “universal” mean free path ~ 1 fm (!?)
3/ 2
2
~ FO volumeV f  (2p ) Rlong Rside
CERES, PRL 90 (2003) 022301
x-section: N   Ni p i  N N  p N  Np  p p
i
m.f.p
17
 f Vf
f 

 ~ 1 fm
 N
Wayne State University 22 Nov 05
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!
c.f. Chajecki - lighter systems
18
Wayne State University 22 Nov 05
R(√SNN, b, Npart, A, B, mT, y, , PID)
Strongly-interacting 6Li released from an asymmetric trap
O’Hara, et al, Science 298 2179 (2002)
What can we learn?
?
in-planeextended
transverse FO shape
+ collective velocity
 evolution time estimate
check independent of RL(pT)
out-of-plane-extended
19
Teaney, Lauret,
Wayne&State
Shuryak
University
nucl-th/0110037
22 Nov 05
R(√SNN, b, Npart, A, B, mT, y, , PID)
small RS
• observe the source from all angles
with respect to RP
• expect oscillations in HBT radii
big RS
20
Wayne State University 22 Nov 05
R(√SNN, b, Npart, A, B, mT, y, , PID)
• observe the source from all angles
with respect to RP
• expect oscillations in HBT radii
(including “new” cross-terms)
R2out-side<0
when pair=135º
21
Wayne State University 22 Nov 05
R(√SNN, b, Npart, A, B, mT, y, , PID)
Measured final source* shape
STAR, PRL93 012301 (2004)
R2out-side<0
when pair=135º
ever see that symmetry at ycm ?
*22model-dependent, but see RetiereWayne
& MAL
PRC70
044907
2004
State
University
22 Nov
05
R(√SNN, b, Npart, A, B, mT, y, , PID)
Measured final source* shape
central
collisions
mid-central
collisions
peripheral
collisions
Expected evolution:
*23model-dependent, but see RetiereWayne
& MAL
PRC70
044907
2004
State
University
22 Nov
05
STAR, PRL93 012301 (2004)
Evolution of size and shape - “the rule of two”
R(√SNN, b, Npart, A, B, mT, y, , PID)
STAR PRL93 012301 (2004)

R 2y  R 2x
R 2y  R 2x
c.f. Chajecki - lighter systems
~ x2 size increase
24
~ 1/2 shape reduction
Initial size/shape estimated by Glauber calculation
Final
config
Wayne
Stateaccording
University to
22 Retiere
Nov 05 & MAL PRC70 044907 2004

“Anisotropic sanity check”
AGS: FO  init
• non-trivial excitation function
• does it make sense? Is it
related to bulk dynamics?
 YES
RHIC: FO < init
(approximately same centrality)
sNN (GeV)
    v2   ???
is relation b/t final and 
near quantitatively sensible?
25
Wayne State University 22 Nov 05
A simple estimate – 0 from init and final
• BW → X, Y @ F.O. (X > Y)
• hydro: flow velocity grows ~ t
  X ,Y ( t )   X ,Y (F.O.) 
t
0
• From RL(mT): 0 ~ 9 fm/c
consistent picture
• Longer or shorter evolution times
X inconsistent
P. Kolb, nucl-th/0306081
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
26
Wayne State University 22 Nov 05
MAL ISMD03
R(√SNN, b, Npart, A, B, mT, y, , PID)
rapidity of emitting source
briefly:
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
rapidity of emitted particle
? meaning ?
another “universal” behaviour
28
PHOBOS nucl-ex/0410022
Wayne State University 22 Nov 05
common plots
Heinz & Kolb, hep-ph/0204061
Hirano ‘02
N()
29
Wayne State University 22 Nov 05
R(√SNN, b, Npart, A, B, mT, y, , PID)
hydro
cascades
LPSW Ann. Rev. Nucl. Part. Sci 2005
Cascades more successful than hydro
• different EoS
• different assumptions
• different freezeout
• different methods of getting radii!!
30
qualitative pT
dependence generic
Wayne State University 22 Nov 05
R(√SNN, b, Npart, A, B, mT, y, , PID)
Why do the radii fall with increasing mT ??
31
Wayne State University 22 Nov 05
R(√SNN, b, Npart, A, B, mT, y, , PID)
Why do the radii fall with increasing mT ??
It’s collective flow !!
(we assume...)
Direct geometrical/dynamical evidence
for bulk behaviour
Amount of flow consistent with p-space
32
Wayne State University 22 Nov 05
Flow-dominated model w/ “hand-tuned” short timescales
• Blast-wave model (latest in
long series) reproduces
p- and x-space
• Also non-id, asHBT...
• quantitatively consistent
soft-sector description
F. Retiere, QM04
F. Retiere & MAL, PRC 70 (2004)
33
Wayne State University 22 Nov 05
Strong flow confirmed by all expts...
R(√SNN, b, Npart, A, B, mT, y, , PID)
LPSW(05) - DATA in color-- experimentalist’s plot
what agreement!! (what agreement?)
34
Wayne State University 22 Nov 05
Strong flow confirmed by all expts...
R(√SNN, b, Npart, A, B, mT, y, , PID)
Ri
R i mT    i
mT

Central (~10%) AuAu (PbPb) collisions at y~0
35
Wayne State University 22 Nov 05
Also: strong flow --> “universal” ~mT scaling
R(√SNN, b, Npart, A, B, mT, y, , PID)
Is ubiquitous beauty still beautiful?
36
Wayne State University 22 Nov 05
Is “famous” systematic everywhere?
p-p correlations
Gong et al, PRC43 1804 (1991)
45Sc(36Ar,pp)X
E=80 AMeV
sNN=1.92 GeV ; sNN-2mN=0.041 GeV
flow might be relevant...
37
Wayne State University 22 Nov 05
PRL70, 3709 (1993)
R (fm)
Is “famous” systematic everywhere?
p-p correlations
“out”
1000
vs 0
“side”
PRC49, 2788 (1994)
PRC49, 2788 (1994)
2000
4000
 (fm/c)
Who says femtoscopy can’t
measure long
Gonglifetimes?
et al, PRC43 1804 (1991)
129Xe(27Al,pp)X
E=31 AMeV
sNN=1.891 GeV ; sNN-2mN=0.0157 GeV
E*/AC.N.= 2.6 MeV
38
3000
Wayne State University 22 Nov 05
Ignore low-s (S.O.P.) use reference
of R(√SNN, b, Npart, A, B, mT, y, , PID)
• Au+Au reaction zone: x2 expansion
• Preliminary Cu+Cu, d+Au, p+p:
smooth interpolation
– central Cu+Cu = periph Au+Au
• Little expansion for small system
– shorter timescales?
– less bulk collectivity...?
N.B : dN/dy scaling preserved
39
Wayne State University 22 Nov 05
STAR prelim.
Ignore low-s (S.O.P.) use reference
of R(√SNN, b, Npart, A, B, mT, y, , PID)
• famous systematic
independent of |b|
200 GeV Au+Au
200 GeV p+p
• observed also for lightest
system (p+p)
STAR PRC71 044906 (2005)
STAR preliminary
mT (GeV)
40
Wayne State University 22 Nov 05
mT (GeV)
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
p different effect
significantly
p+p and A+A measured in same
experiment
• great opportunity to compare physics
• what causes pT-dep in p+p?
• same cause as in A+A?
200 GeV p+p
than for Au+Au
R (fm)
• under investigation
p
K
p 
STAR preliminary
mT (GeV)
hep-ph/0108194
41
m, mT (GeV)
Wayne State University 22 Nov 05
mT (GeV)
3. Resonance effects?
4. Bulk system („hydro”)
in pp?
DELPHI
flowp not expected in such
a small system as p+p
R (fm)
e.g. Shuryak: hep-ph/0405066
p
 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
hep-ph/0108194
42
1/(2pmT)d2n/(dmTdy)
R Z(fm)
1. Heisenberg
uncertainty?
Z0 decay @ LEP
2. String fragmentation? (Lund)
p+p and A+A measured in same
experiment
• great opportunity to compare physics
• what causes pT-dep in p+p?
• same cause as in A+A?
K
200
p GeV p+p
p
mT-m (GeV)
RSIDE
ROUT
RLONG
STAR preliminary
mT (GeV)
m, mT (GeV)
Wayne State University 22 Nov 05
mT (GeV)
mT (GeV)
Surprising („puzzling”) scaling
Ratio of (AuAu, CuCu, dAu) HBT
radii by pp
 first-ever pp/AA comparison
yields a surprise!
 similar underlying physics?
HBT radii scale with pp
Scary coincidence
or something deeper?
pp, dAu, CuCu - STAR preliminary
43
Wayne State University 22 Nov 05
What the “coincidence” does NOT mean
• pp appears to be blasting system (?!)
• AA ≠(pp)
• would mean local x-p correlations
(giving identical p-space...)
• More like pp = “little AA” !!
44
Wayne State University 22 Nov 05
Don’t forget where the “radii” come
from...
long-range correlations for small systems
45
Wayne State University 22 Nov 05
1D projections: a limited view
STAR PRC71 044906 (2005)
• Usual 1D out-side-long
“Cartesian projections”
• exploits full out
symmetry of q-space
• 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
“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
46
Wayne State University 22 Nov 05
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  
4p
all.bins
QLONG


 Yl ,m ( i ,i )C(| Q |, cos  i ,i )
i
QSIDE
47
Q
QOUT

Wayne State
Chajecki.,
University
Gutierrez,
22 Nov 05
MAL, Lopez-Noriega, nucl-ex/0505009
“Mental calibration” - a Gaussian CF
Chajecki., Gutierrez, MAL, Lopez-Noriega, nucl-ex/0505009
~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
48
Wayne State University 22 Nov 05
STAR Central Au+Au -- Spherical HD
1D o-s-l projections
SH Moments
C(Qout)
A00
A20
C(Qside)

C(Qlong)
Al ,m (| Q |) 
 cos 
4p
all.bins


Yl ,m ( i , i )C (| Q |, cos i , i )
i
A22
Chajecki., Gutierrez, MAL
Lopez-Noriega, nucl-ex/0505009
STAR preliminary
49
Wayne State University 22 Nov 05
Baseline problems with smallest systems
STAR preliminary
d+Au peripheral collisions
Gaussian fit
ad hoc, but try it...
50
Wayne State University 22 Nov 05
Try NA22 empirical form
STAR preliminary
d+Au peripheral collisions
Spherical harmonics
NA22 fit
data
L =1
M=0
NA22 fit
L =1
M=1
51
L =2
M=0
Wayne State University 22 Nov 05
L =2
M=2
“account for” constant offset in L=2 components
STAR preliminary
d+Au peripheral collisions
A 00
A 02
Gaussian fit

|Q|
Gaussian
|Q|
z
+ constant A02, A22
A 22
also ad-hoc, but with
correct symmetries, “simple” Q-dep
52
Wayne State University 22 Nov 05
|Q|
With L=2 shifts, message remains
STAR preliminary
Ratio of (AuAu, CuCu, dAu) HBT
radii by pp
• Ad hoc formulation not satisfying...
• Detector-induced? No.
• Potential physical non-femtoscopic effects at low multiplicity
• jet-induced? Studies so far: no
• global conservation laws...?
Fit w/o baseline parameterization
53
NEW fit w/ baseline parameterization
Wayne State University 22 Nov 05
EPOS v1.4
(Nexus++)
K. Werner
Conserves momentum...
... somehow
A00
A20
A22
Long-range correlation
not reproduced
(Gaussian HBT only)
54
Wayne State University 22 Nov 05
HEP’s secret weapon: GENBOD
(CERNLIB F. James 1968)
A. Stavinskiy, WPCF Aug ‘05
Phasespace weighting
factor - modified by global
conservation laws
3He(e,
Unknown (?) in RHI circles !
55
Wayne State University 22 Nov 05
p+p-)X
Phasespace
distortion
calculation
Very promising !!
GenBod...
Only p-conservation
A00
A20
?
A22
(Gaussian HBT only)
56
Wayne State University 22 Nov 05
• Bulk, collective physics
–
–
–
–
–
–
Summary
tied to spacetime - cannot ignore
femtoscopy measures spacetime
crucial for QGP study
well-established at RHIC: p- and x-space
really understood at RHIC? (coffee cup time?)
AA is “bulk” : AA ≠ (pp) .... but... AA = K(pp) ?
• Any femtoscopy signal at RHIC is subtle
– dedicated, systematic, broad program
– do we understand our reference?
– “universal” systematics a bit too universal !! (More than “R=5 fm”)
• universal laws hint at-- or obscure-- physics?
• pp collisions at RHIC
57
– first direct comparison HEP with RHI
– x-p correlations indistinguishable from AA - coincidence or deep?
– long-range correlations important
• useful harmonic analysis of CF developed
• accounting for non-femtoscopic
- on05the way...
Wayne Statecorrelations
University 22 Nov