ma lisa - femtoscopy in small systems & emcics - kent state university - january 20071...
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ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 1
Conservation laws & femtoscopy of small systems
Zbigniew Chajeçki & Mike Lisa
Ohio State University
nucl-th/0612080
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 2
Outline
• Introduction– RHI, femtoscopy, & collectivity in bulk matter– including: new representation of correlation functions
• the p+p “reference”– intriguing features pp versus AA– non-femtoscopic effects
• Global conservation effects (EMCICs)– Restricted phasespace calculations: GenBod (FOWL)– Analytic EMCIC calculations– Experimentalists’ recipe:– Fitting correlation functions [in progress]
• Summary
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 4
RHIC BRAHMSPHOBOS
PHENIXSTAR
AGS
TANDEMS
Nuclear Particle
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 5
Why heavy ion collisions?
Nuclear Particle
STAR ~500 Collaborators
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 6
2 types (?) of collisions...
looks like fun...
looks like a mess...
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 7
A dynamical but crude view of the collision
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
In this model, insufficient re-interactionsc/o UrQMD Collaboration, Frankfurt
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 8
A dynamical but crude view of the collision
In this model, insufficient re-interactions
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 9
R.H.I.C. defined...
• collision of nuclei sufficiently large that nuclear details unimportant– distinct from nuclear or particle physics– “Geranium on Linoleum”
• sufficiently large for meaningful bulk & thermodynamic quantities
• non-trivial spatial scales & geometry drive bulk dynamics (e.g. flow)
• how big is “sufficient” ?– important reference issue
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 10
phase structure of bulk system:
• driving symmetries
• long-range collective behaviour
• “new” physics [superfluidity in l-He]
• relevance of meaningful EoS
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 11
Generating a deconfined state
Nuclear Matter(confined)
Hadronic Matter(confined)
Quark Gluon Plasmadeconfined !
Present understanding of Quantum Chromodynamics (QCD)• heating• compression deconfined color matter !
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 12
Expectations from Lattice QCD
/T4 ~ # degrees of freedom
confined:few d.o.f.
deconfined:many d.o.f.
TC ≈ 173 MeV ≈ 21012 K ≈ 130,000T[Sun’s core]
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 13
The four elements from 400 BC to 2000AD
400 BC : all creation
Earth Fire
Air Water
?
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 14
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
RHIC energies: the first quantitative success of hydro• direct access to EoS (phase transitions, lattice, etc.)
EoS: P versus versus n(Heinz et al)
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 15
Microexplosions Femtoexplosions
1017 J/m3 5 GeV/fm3 = 1036 J/m3
s 0.1 J 1 J
T 106 K 200 MeV = 1012 K
rate 1018 K/sec 1035 K/s
• energy quickly deposited• enter plasma phase• expand hydrodynamically• cool back to original phase• do geometric “postmortem” & infer momentum
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 16
Microexplosions Femtoexplosions
s 0.1 J 1 J
1017 J/m3 5 GeV/fm3 = 1036 J/m3
T 106 K 200 MeV = 1012 K
rate 1018 K/sec 1035 K/s
• energy quickly deposited• enter plasma phase• expand hydrodynamically• cool back to original phase• do geometric “postmortem” & infer momentum
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 17
Impact parameter & Reaction plane
b = 0 “central collision”many particles produced
“peripheral collision”fewer particles produced
br
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 18
Impact parameter & Reaction plane
b = 0 “central collision”many particles produced
“peripheral collision”fewer particles produced
br br
Reaction plane:
spanned by beam direction and br
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 19
How do semi-central collisions evolve?
br
1) Superposition of independent p+p:momenta pointed at randomrelative to reaction plane
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 20
How do semi-central collisions evolve?
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
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 21
How do semi-central collisions evolve?
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
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 22
Azimuthal distributions at RHIC
STAR, PRL90 032301 (2003)
b ≈ 4 fm
“central” collisions
b ≈ 6.5 fm
midcentral collisions
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 23
Azimuthal distributions at RHIC
STAR, PRL90 032301 (2003)
b ≈ 4 fmb ≈ 6.5 fmb ≈ 10 fm
peripheral collisions
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 24
Beyond press releases
Nature of EoS under investigation ; agreement with
data may be accidental ; viscous hydro under
development ; assumptionof thermalization in question
sensitive to modeling ofinitial state,
presently under study
The detailed work now underway is what can probe & constrain sQGP properties
It is probably not press-release material......but, hey, you’ve already got your coffee mug
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 26
Beyond press releases:Access to the dynamically-generated geometric substructure?
The feature of collectivity:
space
is globally correlated with
momentum
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 27
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 ρ+== 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 ρ(x,p) = U*U5 fm
1 m sourceρ(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
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 28
Correlation functions for different colliding systemsC
2(Q
inv)
Qinv (GeV/c)
STAR preliminary p+pR ~ 1 fm
d+AuR ~ 2 fm
Au+AuR ~ 6 fm
Different colliding systems studied at RHIC
Interferometry probes the smallest scales ever measured !
Au+Au: central collisions
C(Qout)
C(Qside)
C(Qlong)
3 “radii” by using3-D vector q
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 29
Femtoscopic information
€
C r P
ab(r q ) = d3 ′
r r ⋅Sr
P
ab( ′ r r )∫ ⋅ φ(
r ′ q ,r ′ r )
2
xaxb
pa
pbxa
xb
pa
pb
€
Sr P
ab( ′ r r ) =
r x a -
r x b( ) distribution
φ(r ′ q ,r ′ r ) = (a,b) relative wavefctn
• femtoscopic correlation at low |q|• must vanish at high |q|. [indep “direction”]
Au+Au: central collisions
C(Qout)
C(Qside)
C(Qlong)
3 “radii” by using3-D vector q
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 30
Femtoscopic information - Spherical harmonic representation
• femtoscopic correlation at low |q|• must vanish at high |q|. [indep “direction”]
Au+Au: central collisions
C(Qout)
C(Qside)
C(Qlong)
3 “radii” by using3-D vector q
QOUT
QSIDE
QLONG Q
∑→→ ΔΔ
=binsall
iiiiimlml QCYQA
.
,
cos
, ),cos|,(|),(|)(| φθφθπ
φθ
4
This new method of analysis represents a real breakthrough. ...(should) become a standard tool in all experiments.
- A. Bialas, ISMD 2005
nucl-ex/0505009
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 31
Femtoscopic information - Spherical harmonic representation
• femtoscopic correlation at low |q|• must vanish at high |q|. [indep “direction”]
•ALM(Q) = L,0
Au+Au: central collisions
C(Qout)
C(Qside)
C(Qlong)
3 “radii” by using3-D vector q
∑→→ ΔΔ
=binsall
iiiiimlml QCYQA
.
,
cos
, ),cos|,(|),(|)(| φθφθπ
φθ
4
L=0
L=2M=0
L=2M=2
nucl-ex/0505009
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 32
Why do the radii fallwith increasing momentum ??
€
(3 "radii" corresponding to the three components of r q )
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 33
It’s collective flow !!
Direct geometrical/dynamical evidencefor bulk behaviour!!!
Amount of flow consistent with p-space nucl-th/0312024
Huge, diverse systematics consistent with this substructurenucl-ex/0505014
Why do the radii fallwith increasing momentum ??
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 35
p+p: A clear reference system?
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 36
STAR preliminary
mT (GeV) mT (GeV)
Z. Chajecki QM05nucl-ex/0510014femtoscopy in p+p @ STAR
• Decades of femtoscopy in p+p and in A+A, but...
• for the first time: femtoscopy in p+p and A+A in same experiment, same analysis definitions...
• unique opportunity to compare physics
• ~ 1 fm makes sense, but...
• pT-dependence in p+p?
• (same cause as in A+A?)
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 37
Surprising („puzzling”) scaling
HBT radii scale with pp
Scary coincidence or something deeper?
On the face: same geometric substructure
pp, dAu, CuCu - STAR preliminary
Ratio of (AuAu, CuCu, dAu) HBT radii by pp
A. Bialasz (ISMD05):I personally feel that its solution may provide new insight into the hadronization process of QCD
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 38
BUT... Clear BUT... Clear interpretationinterpretation clouded by clouded by datadata features features
STAR preliminary d+Au peripheral collisions
Gaussian fitNon-femtoscopic q-anisotropicbehaviour at large |q|
does this structure affect femtoscopic region as well?
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 39
STAR preliminary d+Au peripheral collisions
Gaussian fit
∑→→ ΔΔ
=binsall
iiiiimlml QCYQA
.
,cos
, ),cos|,(|),(4
|)(| φθφθπ
φθ
Decomposition of CF onto Spherical Harmonics
Z.Ch., Gutierrez, MAL, Lopez-Noriega, nucl-ex/0505009
non-femtoscopic structure(not just “non-Gaussian”)
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 40
Just push on....?
• ... no!– Irresponsible to ad-hoc fit (often the practice) or ignore (!!) & interpret
without understanding data– no particular reason to expect non-femtoscopic effect to be limited to
non-femtoscopic (large-q) region• not-understood or -controlled contaminating correlated effects
at low q ?
• A possibility: energy-momentum conservation?– must be there somewhere!– but how to calculate / model ?
(Upon consideration, non-trivial...)
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 42
energy-momentum conservation in n-body states
€
f α( ) =d
dαM
2⋅Rn( )
where
M = matrix element describing interaction
(M =1 → all spectra given by phasespace)
spectrum of kinematic quantity (angle, momentum) given by
€
Rn = δ 4 P − p j
j=1
n
∑ ⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟ δ pi
2 − mi2
( )d4pi
i=1
n
∏4n
∫
where
P = total 4 - momentum of n - particle system
pi = 4 - momentum of particle i
mi = mass of particle i
n-body Phasespace factor Rn
€
pi2 − mi
2( )d
4pi =r p i
2
E i
dr p i ⋅d cosθ i( ) ⋅dφi
statistics: “density of states”
larger particle momentum more available states
P conservation
€
4 P − p j
j=1
n
∑ ⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟
Induces “trivial” correlations(i.e. even for M=1)
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 43
Example of use of total phase space integral
• In absence of “physics” in M : (i.e. phase-space dominated)
€
Γ pp → πππ( )Γ pp → ππππ( )
=R3 1.876;π ,π ,π( )
R4 1.876;π ,π ,π ,π( )
€
In limit where "α "="event" = collection of momenta r p i
"spectrum of events" = f α( ) =d
dαRn
→ Probevent α ∝d3n
dpi3
i=1
n
∏Rn
• single-particle spectrum of :
€
f α( ) =d
dαRn
• “spectrum of events”:
F. James, CERN REPORT 68-15 (1968)
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 44
Genbod:phasespace sampling w/ P-conservation
• F. James, Monte Carlo Phase Space CERN REPORT 68-15 (1 May 1968)
• Sampling a parent phasespace, conserves energy & momentum explicitly
– no other correlations between particles
Events generated randomly, buteach has an Event Weight
€
WT =1
Mm
M i+1R2 M i+1;M i,mi+1( ){ }i=1
n−1
∏
WT ~ probability of event to occur
ALL EVENTS ARE
EQUAL, BUT SOME EVENTS ARE
MORE EQUAL THAN OTHERS
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 45
“Rounder” events: higher WT
ALL EVENTS ARE
EQUAL, BUT SOME EVENTS ARE
MORE EQUAL THAN OTHERS
larger particle momentum more available states
€
Rn = δ 4 P − p j
j=1
n
∑ ⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟ δ pi
2 − mi2
( )d4pi
i=1
n
∏4n
∫
δ pi2 − mi
2( )d
4pi =r p i
2
E i
dr p i ⋅d cosθ i( ) ⋅dφi
6 particles
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 46
“Rounder” events: higher WT
ALL EVENTS ARE
EQUAL, BUT SOME EVENTS ARE
MORE EQUAL THAN OTHERS
larger particle momentum more available states
€
Rn = δ 4 P − p j
j=1
n
∑ ⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟ δ pi
2 − mi2
( )d4pi
i=1
n
∏4n
∫
δ pi2 − mi
2( )d
4pi =r p i
2
E i
dr p i ⋅d cosθ i( ) ⋅dφi
30 particles
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 47
Genbod:phasespace sampling w/ P-conservation
€
WT =1
Mm
M i+1R2 M i+1;M i,mi+1( ){ }i=1
n−1
∏
• Treat identical to measured events
• use WT directly• MC sample WT
• Form CF and SHD
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 48
Effect of varying frame & kinematic cuts
Watch the green squares --
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 49
N=18 <K>=0.9 GeV; LabCMS Frame - no cuts
Watch the green squares
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 50
N=18 <K>=0.9 GeV; LabCMS Frame - ||<0.5
kinematic cuts have strong effect!
Watch the green squares
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 51
N=18 <K>=0.9 GeV, LCMS - no cuts
kinematic cuts have strong effect!
as does choice of frame!
Watch the green squares
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 52
N=18 <K>=0.9 GeV; LCMS - ||<0.5
kinematic cuts have strong effect!
as does choice of frame!
Watch the green squares
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 53
N=18 <K>=0.9 GeV; PRF - no cuts
kinematic cuts have strong effect!
as does choice of frame!
Watch the green squares
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 54
N=18 <K>=0.9 GeV; PRF - ||<0.5
kinematic cuts have strong effect!
as does choice of frame!
Watch the green squares
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 55
Effect of varying multiplicity & total energy
Watch the green squares --
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 56
GenBod : 6 pions, <K>=0.5 GeV/c
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 57
GenBod : 9 pions, <K>=0.5 GeV/cincreasing mult reduces P.S. constraint
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 58
GenBod : 15 pions, <K>=0.5 GeV/cincreasing mult reduces P.S. constraint
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 59
GenBod : 18 pions, <K>=0.5 GeV/cincreasing mult reduces P.S. constraint
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 60
GenBod : 18 pions, <K>=0.7 GeV/cincreasing mult reduces P.S. constraint
increasing s reduces P.S. constraint
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 61
GenBod : 18 pions, <K>=0.9 GeV/cincreasing mult reduces P.S. constraint
increasing s reduces P.S. constraint
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 62
So...
• Energy & Momentum Conservation Induced Correlations (EMCICs) “resemble” our data
• So... on the right track...
• But what to do with that?– Sensitivity to s, Mult of particles of interest and other particles
– will depend on p1 and p2 of particles forming pairs in |Q| bins
risky to “correct” data with Genbod...
• Solution: calculate EMCICs using data!!– Danielewicz et al, PRC38 120 (1988)– Borghini, Dinh, & Ollitraut PRC62 034902 (2000)
– Chajecki & MAL, nucl-th/0612080 - generalization of the above
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 63
Distributions w/ phasespace constraints
€
˜ f ( pi) = 2E i f ( pi) = 2E i
dN
d3 pi
single-particle distributionw/o P.S. restriction
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 64
Distributions w/ phasespace constraints
€
˜ f ( pi) = 2E i f ( pi) = 2E i
dN
d3 pi
single-particle distributionw/o P.S. restriction
€
˜ f c(p1,...,pk ) ≡ ˜ f (pi)i=1
k
∏ ⎛ ⎝ ⎜ ⎞
⎠ ⎟⋅
d3pi
2E i
˜ f (pi)i= k +1
N
∏ ⎛
⎝ ⎜
⎞
⎠ ⎟∫ δ 4 pi
i=1
N
∑ − P ⎛
⎝ ⎜
⎞
⎠ ⎟
d3pi
2E i
˜ f (pi)i=1
N
∏ ⎛
⎝ ⎜
⎞
⎠ ⎟∫ δ 4 pi
i=1
N
∑ − P ⎛
⎝ ⎜
⎞
⎠ ⎟
= ˜ f (pi)i=1
k
∏ ⎛ ⎝ ⎜ ⎞
⎠ ⎟⋅
d4piδ(pi2 − mi
2)˜ f (pi)i= k +1
N
∏ ⎛ ⎝ ⎜ ⎞
⎠ ⎟∫ δ 4 pi
i=1
N
∑ − P ⎛
⎝ ⎜
⎞
⎠ ⎟
d4piδ(pi2 − mi
2)˜ f (pi)i=1
N
∏ ⎛ ⎝ ⎜ ⎞
⎠ ⎟∫ δ 4 pi
i=1
N
∑ − P ⎛
⎝ ⎜
⎞
⎠ ⎟
k-particle distribution (k<N) with P.S. restriction
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 65
Using central limit theorem (“large N-k”)
€
˜ f c(p1,...,pk ) = ˜ f (pi)i=1
k
∏ ⎛ ⎝ ⎜ ⎞
⎠ ⎟ N
N − k
⎛
⎝ ⎜
⎞
⎠ ⎟2
exp −
pi,μ − pμ( )i=1
k
∑ ⎛
⎝ ⎜
⎞
⎠ ⎟
2
2(N − k)σ μ2
μ = 0
3
∑
⎛
⎝
⎜ ⎜ ⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟ ⎟ ⎟
where
σ μ2 = pμ
2 − pμ
2
pμ = 0 for μ =1,2,3
(*) For simplicity, I from now on assume identical particles (e.g. pions). I.e. all particles have the same average energy and RMS’s of energy and momentum. Similar results (esp “experimentalist recipe) but more cumbersome notation otherwise
k-particle distribution in N-particle system
€
pμ2 ≡ d3p ⋅pμ
2 ⋅ ˜ f p( )unmeasuredparent distrib
{∫ ≠ d3p ⋅pμ2 ⋅ ˜ f c p( )
measured{∫N.B.
relevant later
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 66
Effects on single-particle distribution
€
˜ f c(pi) = ˜ f (pi)N
N −1
⎛
⎝ ⎜
⎞
⎠ ⎟2
exp −pi,μ − pμ( )
2
2(N −1)σ μ2
μ = 0
3
∑ ⎛
⎝
⎜ ⎜
⎞
⎠
⎟ ⎟
= ˜ f (pi)N
N −1
⎛
⎝ ⎜
⎞
⎠ ⎟2
exp −1
2(N −1)
px,i2
px2
+py,i
2
py2
+pz,i
2
pz2
+E i − E( )
2
E 2 − E2
⎛
⎝
⎜ ⎜
⎞
⎠
⎟ ⎟
⎛
⎝
⎜ ⎜
⎞
⎠
⎟ ⎟
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 67
k-particle correlation function
€
C(p1,...,pk ) ≡˜ f c(p1,...,pk )
˜ f c(p1)....̃ f c(pk )
=
N
N − k
⎛
⎝ ⎜
⎞
⎠ ⎟2
N
N −1
⎛
⎝ ⎜
⎞
⎠ ⎟2k
exp −1
2(N − k)
px,ii=1
k
∑ ⎛ ⎝ ⎜ ⎞
⎠ ⎟2
px2
+py,ii=1
k
∑ ⎛ ⎝ ⎜ ⎞
⎠ ⎟2
py2
+pz,ii=1
k
∑ ⎛ ⎝ ⎜ ⎞
⎠ ⎟2
pz2
+E i − E( )
i=1
k
∑ ⎛ ⎝ ⎜ ⎞
⎠ ⎟2
E 2 − E2
⎛
⎝
⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟
⎛
⎝
⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟
exp −1
2(N −1)
px,i2
px2
+py,i
2
py2
+pz,i
2
pz2
+E i − E( )
2
E 2 − E2
⎛
⎝
⎜ ⎜
⎞
⎠
⎟ ⎟
i=1
k
∑ ⎛
⎝
⎜ ⎜
⎞
⎠
⎟ ⎟
Dependence on “parent” distrib f vanishes,except for energy/momentum means and RMS
2-particle correlation function (1st term in 1/N expansion)
€
C(p1,p2) ≅1−1
N2
r p T,1 ⋅
r p T,2
pT2
+pz,1 ⋅pz,2
pz2
+E1 − E( ) ⋅ E 2 − E( )
E 2 − E2
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 68
€
C(p1,p2) ≅1−1
N2
r p T,1 ⋅
r p T,2
pT2
+pz,1 ⋅pz,2
pz2
+E1 − E( ) ⋅ E 2 − E( )
E 2 − E2
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟
2-particle correlation function (1st term in 1/N expansion)
“The pT term” “The pZ term” “The E term”
Names used in the following plots
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 69
Effect of varying multiplicity & total energy
Same plots as before, but now we look at:
• pT (), pz () and E () first-order terms
• full () versus first-order () calculation
• simulation () versus first-order () calculation
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 70
GenBod : 6 pions, <K>=0.5 GeV/c
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 71
GenBod : 9 pions, <K>=0.5 GeV/c
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 72
GenBod : 15 pions, <K>=0.5 GeV/c
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 73
GenBod : 18 pions, <K>=0.5 GeV/c
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 74
GenBod : 18 pions, <K>=0.7 GeV/c
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 75
Findings
• first-order and full calculations agree well for N>9– will be important for “experimentalist’s recipe”
• Non-trivial competition/cooperation between pT, pz, E terms
– all three important
• pT1•pT2 term does affect “out-versus-side” (A22)
• pz term has finite contribution to A22 (“out-versus-side”)
• calculations come close to reproducing simulation for reasonable (N-2) and energy, but don’t nail it. Why?– neither (N-k) nor s is infinite– however, probably more important... [next slide]...
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 76
Remember...
€
C(p1,p2) ≅1−1
N2
r p T,1 ⋅
r p T,2
pT2
+pz,1 ⋅pz,2
pz2
+E1 − E( ) ⋅ E 2 − E( )
E 2 − E2
⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟
€
pμ2 ≡ d3p ⋅pμ
2 ⋅ ˜ f p( )unmeasuredparent distrib
{∫ ≠ pμ2
c≡ d3p ⋅pμ
2 ⋅ ˜ f c p( )measured{∫
relevant quantities are average over the (unmeasured) “parent” distribution,not the physical distribution
€
expect pμ2
c< pμ
2
of course, the experimentalist never measures all particles(including neutrinos) or <pT
2> anyway, so maybe not a big loss
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 77
€
C(p1,p2) ≅ 1−2
N pT2
NEW PARAM 11 2 3
⋅r p 1,T ⋅
r p 2,T{ } −
1
N pZ2
NEW PARAM 21 2 3
⋅ p1,z ⋅p2,z{ }
−1
N E 2 − E2
( )
NEW PARAM 31 2 4 4 3 4 4
⋅ E1 ⋅E 2{ } +E
N E 2 − E2
( )
NEW PARAM 41 2 4 4 3 4 4
⋅ E1 + E 2{ } +E
2
N E 2 − E2
( )
UNIMPORTANT"NORMALIZED AWAY"
1 2 4 4 3 4 4
where
X{ } denotes the average of X over the (p1,p2) bin. (or r q - bin or whatever we are binning in)
I.e. it is just another histogram which the experimentalist makes, from the data
momenta and energy are measured in the lab frame.
The experimentalist’s recipeTreat the not-precisely-known factors as fit parameters (4 of them)• values determined mostly by large-|Q|; should not cause “fitting hell”• look, you will either ignore it or fit it ad-hoc anyway (both wrong)• this recipe provides physically meaningful, justified form
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 78
18 pions, <K>=0.9 GeV
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 79
Highly correlatedEMCIC parameters
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 80
€
C(p1,p2) = Norm 1− M1 ⋅r p 1,T ⋅
r p 2,T{ } − M2 ⋅ p1,z ⋅p2,z{ } − M3 ⋅ E1 ⋅E 2{ } + M4 ⋅ E1 + E 2{ }+"λ ⋅e
− Rα2 qα
2
α =o,s,l
∑"
⎡
⎣ ⎢ ⎢
⎤
⎦ ⎥ ⎥
The COMPLETE experimentalist’s recipe
€
C(q) + M1 ⋅r p 1,T ⋅
r p 2,T{ } + M2 ⋅ p1,z ⋅p2,z{ } + M3 ⋅ E1 ⋅E 2{ } − M4 ⋅ E1 + E 2{ }
femtoscopicfunction ofchoicefit this...
...or image this...
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 81
Summary• H.I.C raison d’etre & distinction from p+p
– bulk, thermalized, collective matter
• Momentum-space and femtoscopic probes support bulk collectivity
• The p+p “reference” - [femtoscopic apples-to-apples for the first time]– is it understood?– is it really different than a “small A+A” ?– full understanding must be high priority
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 82
Famous picture from famous article by famous guy
Energy loss of energetic partons in quark-gluon plasma:Possible extinction of high pT jets in hadron-hadron collisions
J.D. Bjorken, 1982b
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 83
Summary• H.I.C raison d’etre & distinction from p+p
– bulk, thermalized, collective matter
• Momentum-space and femtoscopic probes support bulk collectivity
• The p+p “reference” - [femtoscopic apples-to-apples for the first time]– is it understood?– is it really different than a “small A+A” ?– full understanding must be high priority
• Interpretation complicated by non-femtoscopic correlations
• May be largely due to P.S. restrictions (EMCICs)– numerical studies track data– analytic formulation of EMCIC projection onto femtoscopic analysis
presented– highly non-trivial interplay between cuts, frames, and conserved
components (pz, pT, E)– first-order expansion --> experimentalists’ formula– application to STAR underway
• Hotter spotlight due to impending LHC (December 2007!!)
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 84
ma lisa - Femtoscopy in small systems & EMCICs - Kent State University - January 2007 85
Thanks to...
• Alexy Stavinsky & Konstantin Mikhaylov (Moscow) [suggestion to use Genbod]
• Jean-Yves Ollitrault (Saclay) & Nicolas Borghini (Bielefeld)[original correlation formula]
• Adam Kisiel (Warsaw) [don’t forget energy conservation]
• Ulrich Heinz (Columbus)[validating energy constraint in CLT]