femtoscopy at rhic
DESCRIPTION
Femtoscopy at RHIC. Sergey Panitkin Brookhaven National Lab. 99.5%. Importance of soft physics at RHIC. We want to create/study a new type of matter (= bulk system) large-scale (soft??) deconfinement Collective properties (T,p, flow?) Jets/hard probes are probes of this system - PowerPoint PPT PresentationTRANSCRIPT
Sergey Panitkin
Femtoscopy at RHIC
Sergey PanitkinBrookhaven National Lab
Sergey Panitkin
Importance of soft physics at RHIC
99.5%
• We want to create/study a new type of matter (= bulk system)
• large-scale (soft??) deconfinement• Collective properties (T,p, flow?)
• Jets/hard probes are probes of this system
• Crucial to understand bulk properties and dynamics in their own right
• Soft sector gives information about EoS
Sergey Panitkin
Collective behavior at RHIC
P. Kolb, J. Sollfrank, U. Heinz
Heinz & Kolb, hep-th/0204061
• Hydrodynamics seems to reproduce p-space aspects (spectra and elliptical flow) of particle emission up to pT~2GeV/c
Bulk system?! Perfect Liquid?Note: Hydro provides complete space-time evolution. Can and should be tested!
Sergey Panitkin
General Comment
Single particle spectrum is sensitive to momentum distribution only
Relative momentum distribution of particle pairs is sensitive to space-time information
Basis for Identical and Non-identical particle femtoscopy
•EoS determines S(r,q)
),(4 pp
xSdxddNE
),(|),(|)/)(/(
/)( 2
2111
2122 qrqrr
pppp
q SdddNddN
dddNC
Source functionFSI
Sergey Panitkin
Two Particle Interferometry: Idealized Case
y
X
1
2
Source
24
2xiq4
21)K,x(Sxd
e)K,x(Sxd1)p,p(C
21 ppq 2121 ppK
emission function
For non-interacting identical bosons:
C (Q
inv)
Qinv (GeV/c)
1
2
0.05 0.10
Width ~ 1/R
Sergey Panitkin
Correlation functions for different colliding systems
C2(
Qin
v)
Qinv (GeV/c)
STAR preliminary p+pR ~ 1 fm
d+AuR ~ 2 fm
Au+AuR ~ 6 fm
Correlations have more informationOne can use more sophisticated analysis to extract it
Sergey Panitkin
beam direction
p1 p2
Q T
Q
Q L
beam direction
p2p1
Q T
Q S
Q O
“Standard” Pratt-Bertsch coordinate system
)T2
PT1
P(2
1T
K
2long
2long
2side
2side
2out
2out)(1),(
RqRqRqekkqC
Sergey Panitkin
Pratt-Bertsch parameterization
Kt~x~KR
Kx~KR
Kt~x~KR
2llong
2l
2side
2s
2out
2o
xxx~
)K,x(Sxd
)x(f)K,x(Sxdf
4
4
Decompose q into components:qLong : in beam directionqOut : in direction of transverse momentum KT
qSide : qLong & qOut
222222
1),,( llssoo RqRqRqlso eqqqC
Radii are related to source variances:
221
21
ppk
ppq
In Longitudinally Co-Moving System (LCMS) l =0
Sensitive to emission time
Sensitive to transverse extent
Sensitive to longitudinal extent
Sergey Panitkin
In Search of the QGP. Generic Expectations.
“Energy density”
Hydro calculation of Rischke & Gyulassy expects Rout/Rside ~ 2->4 @ Kt = 350 MeV.
•Looking for a softest point in EoS
Sergey Panitkin
RHIC Energy Scan
•Measurements at 200, 130, 62 GeV
•No significant change with energy from AGS to RHIC
•Ro/Rs ~1
PHOBOS nucl-ex/0409001
Where are signs of softest point?!Lower energies?Smaller systems?
See talk by D. d’Enterria
Is HBT sensitive to geometry at all?!
Puzzle #1
Sergey Panitkin
More Experimental Systematics
STAR PRL 93:12301 (2004)PHENIX nucl-ex/0401003
Clear sensitivity to source geometry !
b≠0
Centrality dependence asHBT
Sergey Panitkin
Source expansion at RHIC
initi
al =
final
22
22
xy
xy
RR
RR
Rx
Ry
STAR preliminary
STAR Collaboration, nucl-ex/0312009
Expansion at low Pt Change in eccentricity of the source
Sergey Panitkin
Model Comparisons. Puzzle #2
Good agreement between experiments
Subset of models shown
Broad range of physics scenarios explored
Good description of p-space (Pt, V2)
Poor description of HBT data the puzzle
Sergey Panitkin
General observations
Each theory paper has explored systematic changes in at least one important variable– Tf = Freeze-out Temp/profile
– Tc = Critical Temp.
– el = parton scattering cross-section– E = Latent Heat/transition order
– Tch = chem. Freeze-out temp
– n = viscoscity (-20% Rout, -60% Rlong)D. Teany, nucl-th/0301099
• Femtoscopic observables are sensitive to a variety of parameters, at least in the models!
•Sensitivity to physics at early stages of reaction.•Still no compelling solution from dynamical models•Open questions about late stages effects•Hydro inspired parameterization can fit the data, but not hydro•More theoretical work is needed
Sergey Panitkin
Non identical particle correlations
No symmetrization or antisymmetrization requirement
Pair wave function is of general form Existence of odd terms in w.f. provides sensitivity
to space-time asymmetries f(x) ≠ f(-x) Now it matters (for example) what was emitted
earlier and what was emitted later Asymmetries can exist due to a variety of physics
phenomena: flow, sequence of emission, early decoupling, strangeness distillation, etc
Sergey Panitkin
Effect of space-momentum correlation
Evidence of a space – time asymmetry
– Qualitatively consistent with “default” blast wave calculation
• T=110 MeV, • <> = 0.6,
t=9,R=13fm– No need for extra time
shift
Kaon <pt> = 0.42 GeV/c
Pion <pt> = 0.12 GeV/c
STAR PRL 91 (2003)
Never compared with hydro, AFAIKMore measurements to come!
Sergey Panitkin
STAR Femtoscopy Matrix
+ - + - 0 p p ++ +
0 -
+
-
Sergei's HBT matrix 0
Y1 p
Y1 ? p
Y2
“traditional”femtoscopy axis
Analysisin progress
published
3 CorrelationsasHBTPhase space densityCorrelations with CascadesdAu, ppGamma-Gamma HBT
submittedNot shown:
Sergey Panitkin
RHIC as a QCD Machine
Strong interaction for many particle combinations that we want to study is poorly known
Non-identical correlations can shed light on that Sometimes the only way to study certain systems Fixing space time parameters from well known
correlations and models Determine scattering lengths Not the main goal of two particle correlations, but
a nice additional topic Interesting for theory of hadron interactions, hypernuclear community, exotic hadrons
H0,ppK-,..
Sergey Panitkin
What about RHIC II ?
Is there any soft physics left to do at RHIC II ? “RHIC is a worst enemy of RHIC II” - Anonymous
– Many things are and will be done at RHIC What is RHIC II in general terms ? –
– High luminosity, high rates– New detector capabilities (extended/improved pid to
higher Pt…)– Rare probes
Femtoscopy with rare probes– Photons, (electrons?)– HBT in Jets– Non-identical correlations with hyperons– Non-identical correlations with charm ?! Charm
thermalization and flow
Sergey Panitkin
Photon HBT
• Prospects• Photons are penetrating probes • Photons are emitted at all stages of collision• Can carry information from the earliest stages of
reaction (QGP?,PC)• Photons from different Pt can come from different
stages of collision ( QGP, Hadronic gas, resonances,…)• Very few experimental results
• Challenges• Relatively small yields• Large background (pi0 decays, eta decays, etc)
• Statistics is dominated by background
Same applies for electrons !
Sergey Panitkin
First measurements at SPS
WA98 PRL
Sergey Panitkin
Photon HBT at RHIC
Lots of theoretical activity: Different approaches (just to mention a few): VNI/BMS+hydro+HG
– S. Bass, B. Muller, D. Srivastava PRL 94(2005) Hydro inspired fireball
– T.Renk, hep-ph/050382 ; 0408218 HG
– J. Alam, et al - Phys. Rev. C67 (2003) Still large uncertainties about contributions from
different sources Pt>2 GeV may be a window to early stages
Experimental studies under way (see talk by J. Sandweiss today)
Sergey Panitkin
Photon correlation function predictions
Bass et al -PRL 94(2005)
VNI/BMS
No background. Realistic calculations are needed
Sergey Panitkin
Conclusions
Rich set of femtoscopic results already exists at RHIC Evidence that matter at RHIC exhibits collective bulk
properties Most models still can not reproduce simultaneously
experimental observables at low Pt: v2, spectra, correlations We are gaining better understanding of model failures Some promising solutions are offered Ball is in theory corner More detailed correlation measurements will be available soon:
non-identical correlations, HBT Pt>1 GeV/c, Kaons, protons, etc Lower energy scan? RHIC II will offer new opportunities for femtoscopy with rear
probes Will shed light on detailed properties of bulk matter at RHIC
Sergey Panitkin
Femtoscopy at RHIC Workshop
At RHIC/AGS Users Meeting- June 21, 2005