multi-hadron correlations and the space-time structure of (heavy ion) collisions
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mike lisa - University of Rochester nuclear seminar - 4oct2005 1
Multi-hadron correlations and the space-time structure of (heavy ion) collisions
Mike Lisa
Ohio State University
Featuring Work of:Zbigniew Chajeçki, Mercedes López-Noriega, Dan Magestro, Randy Wells
mike lisa - University of Rochester nuclear seminar - 4oct2005 2
Outline
• R.H.I.C. / RHIC - what and wherefore?
• geometry and bulk physics in p-space - brief
• ... & in x-space: pion femtoscopy at RHIC
• Au+Au
• d+Au , p+p
• new puzzles, new techniques, global conservation laws
• Summary
mike lisa - University of Rochester nuclear seminar - 4oct2005 3
• Vary signal ()• constrain multi-dimensional models• requires flexible detectors, broad approach
• Vary colliding system• does physics change?• requires dedicated program
• 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
(√SNN, b, Npart, A, B, mT, y, , PID)
mass
|b|
pT
mike lisa - University of Rochester nuclear seminar - 4oct2005 4
RHIC BRAHMSPHOBOS
PHENIXSTAR
AGS
TANDEMS
1 km
v = 0.99995c = 186,000 miles/sec
Possibilities in a dedicated program: 5 years @RHIC
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Also: p+p @ 62.4 & 200 GeV
Gunther Roland, QM05
mike lisa - University of Rochester nuclear seminar - 4oct2005 5
Possibilities in a dedicated program: 5 years @RHIC
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Also: p+p @ 62.4 & 200 GeV
Gunther Roland, QM05
mike lisa - University of Rochester nuclear seminar - 4oct2005 6
RHIC BRAHMSPHOBOS
PHENIXSTAR
AGS
TANDEMS
STAR ~600 Collaborators
Possibilities in a dedicated program: 5 years @RHIC
mike lisa - University of Rochester nuclear seminar - 4oct2005 7
The STAR Experiment
STAR: Solenoidal Tracker at RHIC
multipurpose detector system for hadronic measurements
• large coverage (geometrical acceptance)• tracking of charged particles in high multiplicity environment• measure correlations of observables• study of hard processes (jet physics)
Solenoidal Tracker At RHIC
goal: track “all” charged hadrons (bags of quarks) emitted in each collision
mike lisa - University of Rochester nuclear seminar - 4oct2005 8
Operation of a Time Projection Chamber
SCA/ADCDAQ
Copper pads ~ 1cm2
Amplifying and digitizing electronics connected to each pad
Anode wires with +HVsitting ~5 mm above pads
Charged particle fliesthru TPC gas…
..generating a clusterof liberated electrons
Electricfield
“Avalanche” as electronsapproach anode wire...
..capacitively inducinga signal on nearby pads... ..which is amplified, digitized, and recorded for later analysis
V
t AD
Cbucket #
mike lisa - University of Rochester nuclear seminar - 4oct2005 9
One collision seen by STAR TPC
Momentum determined by trackcurvature in magnetic field…
…and by direction relative to beam
mike lisa - University of Rochester nuclear seminar - 4oct2005 10
Generating a “deconfined” (?) state
Nuclear Matter(confined)
Hadronic Matter(confined)
Quark Gluon Plasmadeconfined !
“Present” understanding of Quantum Chromodynamics (QCD)• heating• compression deconfined color matter !
mike lisa - University of Rochester nuclear seminar - 4oct2005 11
Expectations from Lattice QCD
/T4 ~ # degrees of freedom
confined:few d.o.f.
deconfined:many d.o.f.
mike lisa - University of Rochester nuclear seminar - 4oct2005 12
baryon densityvacuum
Te
mp
era
ture
Neutron stars
Early universe
nucleinucleon gas
hadron gascolour
superconductor
quark-gluon plasmaTc
0
critical point ?
CFL
The phase diagram of QCD
mike lisa - University of Rochester nuclear seminar - 4oct2005 13
baryon densityvacuum
Te
mp
era
ture
Neutron stars
Early universe
nucleinucleon gas
hadron gascolour
superconductor
quark-gluon plasmaTc
0
critical point ?
CFL
The phase diagram of QCD
?
Au+Au
99.5%
• understanding a theory or
phenomenon (superconductivity...)
focus on phase transitions
• RHIC studies:
partonic condensed matter physics
• the crucial feature of QCD (theory):
long-range behaviour
• confinement, etc:
soft-sector crucial
mike lisa - University of Rochester nuclear seminar - 4oct2005 14
Spacetime - the defining aspect of RHI physics
• 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
STAR, PRC66 (2002) 034904 STAR, PRL93 (2004) 252301
mike lisa - University of Rochester nuclear seminar - 4oct2005 15
Spacetime - the defining aspect of RHI physics
• 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 (?)
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Ann.Rev.Nucl.Part.Sci. 46 (1996) 71
mike lisa - University of Rochester nuclear seminar - 4oct2005 16
Is it bulk? Is it a “system?”
br
1) Superposition of independent p+p:momenta pointed at randomrelative to reaction plane
mike lisa - University of Rochester nuclear seminar - 4oct2005 17
Is it bulk? Is it a “system?”
br
1) Superposition of independent p+p:
2) Evolution as a bulk system
momenta pointed at randomrelative to reaction plane
highdensity / pressure
at center
“zero” pressurein surrounding vacuum
Pressure gradients (larger in-plane) push bulk “out” “flow”
more, faster particles seen in-plane
mike lisa - University of Rochester nuclear seminar - 4oct2005 18
Is it bulk? Is it a “system?”
1) Superposition of independent p+p:
2) Evolution as a bulk system
momenta pointed at randomrelative to reaction plane
Pressure gradients (larger in-plane) push bulk “out” “flow”
more, faster particles seen in-plane
N
-RP (rad)0 /2 /4 3/4
N
-RP (rad)0 /2 /4 3/4
mike lisa - University of Rochester nuclear seminar - 4oct2005 19
Azimuthal distributions at RHIC
STAR, PRL90 032301 (2003)
b ≈ 4 fm
“central” collisions
b ≈ 6.5 fm
midcentral collisions
mike lisa - University of Rochester nuclear seminar - 4oct2005 20
Azimuthal distributions at RHIC
STAR, PRL90 032301 (2003)
b ≈ 4 fmb ≈ 6.5 fmb ≈ 10 fm
peripheral collisions
mike lisa - University of Rochester nuclear seminar - 4oct2005 21
Elliptic flow – collectivity& sensitivity to early system
STAR, PRL90 032301 (2003)
“v2”
“Elliptic flow”
• evidence ofcollective motion
• quantified by v2
• geometrical anisotropy momentum anisotropy
• sensitive to early pressure
• evidence for• early thermalization
• QGP in early stage
Hydrodynamiccalculation ofsystem evolution
mike lisa - University of Rochester nuclear seminar - 4oct2005 22
Perfect...?
mike lisa - University of Rochester nuclear seminar - 4oct2005 23
v2 - huge systematics...
Art’s talk. Compiled byA. Wetzler (2005)
6 decades of E/A(2 decades of sNN)Gyulassy 1995
Just oneevent!
Finally, weunderstand it!
mike lisa - University of Rochester nuclear seminar - 4oct2005 24
It starts... ideal hydro: sharp 1st-order rather than lattice EOS ?
P. Houvinen, nucl-th/0505036
Also: Hirano, Gyulassy...
mike lisa - University of Rochester nuclear seminar - 4oct2005 25
More direct connection to geometric substructure
• Two-particle correlation functions probe femtoscopic scales
• “HBT” etc.
mike lisa - University of Rochester nuclear seminar - 4oct2005 26
222111 p)xr(i22
p)xr(i11T e)p,x(Ue)p,x(U
rrrrrr rrrr ⋅−⋅−=ψ
probing source geometry through interferometry
12 ppqrrr −=
2
21
2121 )q(~1
)p(P)p(P)p,p(P
)p,p(C +== C (Qinv)
Qinv (GeV/c)
1
2
0.05 0.10
Width ~ 1/R
Measurable! F.T. of pion source
( ))xx(iq2
*21
*1T
*T
21e1UUUU −⋅+⋅⋅=ψψ
Creation probability (x,p) = U*U5 fm
1 m source(x)
r1
r2
x1
x2
{2
1
}e)p,x(Ue)p,x(U 212121 p)xr(i21
p)xr(i12
rrrrrr rrrr ⋅−⋅−+
p1
p2
The Bottom line…if a pion is emitted, it is more likely to emit another
pion with very similar momentum if the source is small
experimentally measuring this enhanced probability: quite challenging
mike lisa - University of Rochester nuclear seminar - 4oct2005 27
Correlation functions for different colliding systems
C2(
Qin
v)
Qinv (GeV/c)
STAR preliminary p+pR ~ 1 fm
d+Au
Au+AuR ~ 6 fm
Different colliding systems studied at RHIC
First opportunity to directly compare AA, pp, (&pA)
mike lisa - University of Rochester nuclear seminar - 4oct2005 28
beam directi
on
More detailed geometry
Relative momentum between pions is a vector can extract 3D shape information
1 2q p p= −r r r
p2
p1
q
12Kpp=+rrrR long
RsideRout
Rlong – along beam direction
Rout – along “line of sight”
Rside – “line of sight”
mike lisa - University of Rochester nuclear seminar - 4oct2005 29
• “observe” the source from all angles relative to the reaction plane
• expect oscillations in radii for non-round sources
big RSIDE
small RSIDE
Source shapeR
SID
E
-RP (rad)0 /2 /4 3/4
reaction plane
6Li released from an asymmetric trapO’Hara, et al, Science 298 2179 (2002)
mike lisa - University of Rochester nuclear seminar - 4oct2005 30
STAR, PRL93 012301 (2004)
Measured final source shape
centralcollisions
mid-centralcollisions
peripheralcollisions
Expected evolution:
initi
al= fin
al
Bulk shape evolution
mike lisa - University of Rochester nuclear seminar - 4oct2005 31
Disintegration timescale
Relative momentum between pions is a vector can extract 3D shape information
1 2q p p= −r r r
p2
p1
q
12Kpp=+rrr
Rout
Rlong – along beam direction
Rout – along “line of sight”
Rside – “line of sight”
Rside
increases with emission timescale
OUT
SIDE
R
R↔ τ
mike lisa - University of Rochester nuclear seminar - 4oct2005 32
Disintegration timescale - expectation
3D 1-fluid Hydrodynamics Rischke & Gyulassy, NPA 608, 479 (1996)
withtransition
withtransition
“” “”
Long-standing favorite signature of QGP:
• increase in τ, ROUT/RSIDE due to deconfinement confinement transition
• expected to “turn on” as QGP energy threshold is reached
mike lisa - University of Rochester nuclear seminar - 4oct2005 33
N(τ)
Heinz & Kolb, hep-ph/0204061
Hirano ‘02
HBT puzzle(s)
mike lisa - University of Rochester nuclear seminar - 4oct2005 34
Why do the radii fall with increasing momentum ??
mike lisa - University of Rochester nuclear seminar - 4oct2005 35
It’s collective flow !!
Direct geometrical/dynamical evidencefor bulk behaviour
Amount of flow consistent with p-space
Why do the radii fall with increasing momentum ??
mike lisa - University of Rochester nuclear seminar - 4oct2005 36
Flow-dominated model w/ “hand-tuned” short timescales
• Blast-wave model (latest in long series) reproducesp- and x-space
• Also non-id, asHBT...
F. Retiere & MAL, PRC 70 (2004)
F. Retiere, QM04
mike lisa - University of Rochester nuclear seminar - 4oct2005 37
Bulk size evolution - collisions at 200 GeV
• Au+Au reaction zone:two-fold expansion
• Preliminary Cu+Cu, d+Au, p+p:smooth interpolation
• central Cu+Cu = periph Au+Au
• Little expansion for small system• shorter timescales
or...• less bulk collectivity...?
mike lisa - University of Rochester nuclear seminar - 4oct2005 38
femtoscopy in p+p @ STAR
DELPHI
Z0 decay @ LEP
m, mT (GeV)
R (
fm)
R Z
(fm
)
hep-ph/0108194
K
p
STAR preliminary
mT (GeV) mT (GeV)
1. Heisenberg uncertainty?
• e.g. G. Alexander• “plausible” in z-direction• unlikely in transvrse
2. String fragmentation? (Lund)
• pT dependence maybe (??)
• mass dependence probably no
[Andersson, Moriond 2000]
3. Resonance effects?
• e.g. Wiedemann & Heinz ‘97
• maybe, but presumably significantly different effect than for Au+Au
• under investigation
Zbigniew Chajecki QM05
p+p and A+A measured in sameexperiment• great opportunity to compare physics• what causes pT-dep in p+p?• same cause as in A+A?
mike lisa - University of Rochester nuclear seminar - 4oct2005 39
femtoscopy in p+p @ STAR
DELPHI
Z0 decay @ LEP
m, mT (GeV)
R (
fm)
R Z
(fm
)
hep-ph/0108194
K
p
STAR preliminary
mT (GeV) mT (GeV)
1. Heisenberg uncertainty?
2. String fragmentation? (Lund)
3. Resonance effects?
Zbigniew Chajecki QM05
p+p and A+A measured in sameexperiment• great opportunity to compare physics• what causes pT-dependence in p+p?• same cause as in A+A?
d+Au : Rlong doesn’t change with centrality
flow not expected in such a small system as p+p
e.g. Shuryak: hep-ph/0405066
Csorgo et al.: Buda-Lund treatment of p+p collision as bulk system(w/ temperature gradients)hep-ph/0406042
ROUTRSIDE RLONG
mT-m (GeV)
1/(2m
T)d
2n
/(d
mTd
y)
K
p
mT (GeV)
4. Bulk system („hydro”) in pp?
mike lisa - University of Rochester nuclear seminar - 4oct2005 40
Surprising („puzzling”) scaling
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
Ratio of (AuAu, CuCu, dAu) HBT radii by pp
mike lisa - University of Rochester nuclear seminar - 4oct2005 41
• pp appears to be blasting system (?!)
• AA ≠(pp)• would mean local x-p correlations
(giving identical p-space...)
• More like pp = “little AA” !!
What the “coincidence” does NOT mean
mike lisa - University of Rochester nuclear seminar - 4oct2005 42
Don’t forget where the “radii” come from...
long-range correlations for small systems
mike lisa - University of Rochester nuclear seminar - 4oct2005 43
• 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)
1D projections: a limited view
“Gaussian fit”(remember: notGaussian CF)
out
side long
STAR PRC71 044906 (2005)
Harmonic Decomposition Analysis• exploits full symmetry of q-space
• explicit isolation of femtoscopic(& non-femtoscopic) effects
• full 3D CF seen clearly in few plots
• acceptance-robust (*)
• Cartesian HD Danielewicz & Pratt nucl-th/0501003nucl-th/0501003
• Spherical HD Chajecki,Gutierrez,MAL,Lopez nucl-ex/0505009nucl-ex/0505009
Michael Lisa:“Salient geometrical...” bullet just means: if I want to know “Rlong” or so, I *mostly* just look at width of long projection, but there are also acceptance effects
Michael Lisa:“Salient geometrical...” bullet just means: if I want to know “Rlong” or so, I *mostly* just look at width of long projection, but there are also acceptance effects
mike lisa - University of Rochester nuclear seminar - 4oct2005 44
Spherical harmonic decomposition of CFSpherical harmonic decomposition of CF
∑→→ ΔΔ
=binsall
iiiiimlml QCYQA
.
,
cos
, ),cos|,(|),(|)(| φθφθπ
φθ
4QOUT
QSIDE
QLONG Q
• Cartesian-space (out-side-long) naturally encodes physics, but is “inefficient” representation
• Harmonic Moments -- 1::1 connection to source geometry [Danielewicz,Pratt: nucl-th/0501003]
• ~immune to acceptance
• full information content at a glance[thanks to symmetries]
OUT
SIDE
TOT
LONG
LONGSIDEOUT
Q
Q
Q
Q
QQQQ
arctan
)cos(
222
=
=
++=
φ
Chajecki., Gutierrez, MAL, Lopez-Noriega, nucl-ex/0505009
mike lisa - University of Rochester nuclear seminar - 4oct2005 45
“Mental calibration” - a Gaussian CF
Simple, Gaussian source calculations
~acceptance freeRL < RT
RL > RT
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
Chajecki., Gutierrez, MAL, Lopez-Noriega, nucl-ex/0505009
mike lisa - University of Rochester nuclear seminar - 4oct2005 46
STAR preliminary
A00
A20
A22
SH Moments
STAR Central Au+Au collisions -- Spherical HDSTAR Central Au+Au collisions -- Spherical HD
C(Qout)
C(Qside)
C(Qlong)
1D o-s-l projections
∑→→ ΔΔ
=binsall
iiiiimlml QCYQA
.
,cos
, ),cos|,(|),(4
|)(| φθφθπφθ
Chajecki., Gutierrez, MALLopez-Noriega, nucl-ex/0505009
mike lisa - University of Rochester nuclear seminar - 4oct2005 47
Baseline problems with smallest systemsBaseline problems with smallest systems
STAR preliminary d+Au peripheral collisions
Gaussian fit
ad hoc, but try it...
mike lisa - University of Rochester nuclear seminar - 4oct2005 48
STAR preliminary d+Au peripheral collisions
NA22 fit
Try NA22 empirical formTry NA22 empirical form
NA22 fit
data
Spherical harmonics
L =1M=0
L =2M=0
L =1M=1
L =2M=2
mike lisa - University of Rochester nuclear seminar - 4oct2005 49
““account for” constant offset in L=2 account for” constant offset in L=2 componentscomponents
STAR preliminary d+Au peripheral collisions
Gaussian fit
|Q| |Q|
|Q|
A02
A22
A00
Gaussian
+ constant A02, A2
2
also ad-hoc, but withcorrect symmetries, “simple” Q-dep
mike lisa - University of Rochester nuclear seminar - 4oct2005 50
With L=2 shifts, message remains
Ratio of (AuAu, CuCu, dAu) HBT radii by pp
Fit w/o baseline parameterization NEW fit w/ baseline parameterization
STAR preliminary
• 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...?
mike lisa - University of Rochester nuclear seminar - 4oct2005 51
A00
A20
A22
EPOS v1.4 (Nexus++)K. Werner
(Gaussian HBT only)
Conserves momentum...... somehow
Long-range correlationnot reproduced
mike lisa - University of Rochester nuclear seminar - 4oct2005 52
HEP’s secret weapon: GENBOD (CERNLIB F. James 1968)
A. Stavinskiy, WPCF Aug ‘05
3He(e, +-)X
Phasespace weightingfactor - modified by global conservation laws
Unknown (?) in RHI circles !
mike lisa - University of Rochester nuclear seminar - 4oct2005 53
GenBod...Only p-conservation
A00 A20
A22
Phasespace distortion
calculation
(Gaussian HBT only)
Very promising !!
mike lisa - University of Rochester nuclear seminar - 4oct2005 54
Summary• Extracting subtle signals at RHIC
• dedicated, systematic, broad program• comparison to “elementary” p+p crucial
• understanding source of any differences also crucial (e.g. v2 in pp?)
• Bulk, collective physics• 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) ? [ pp = AA/K ?]
• pp collisions at RHIC• 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 correlations - on the way...
mike lisa - University of Rochester nuclear seminar - 4oct2005 55
THEEND
mike lisa - University of Rochester nuclear seminar - 4oct2005 56
pp (non?-)flow
non-flow (?)
flow
“v2”
mike lisa - University of Rochester nuclear seminar - 4oct2005 57
The phase diagram of water
Analogous graphs• superfluids• superconductors• metal/insulator• …
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