Transcript Recent Results from STAR at RHIC (with focus on bulk properties) Nu Xu

Recent Results from STAR
at RHIC
(with focus on bulk properties)
Nu Xu
Nuclear Science Division
Nu Xu
RPM, March 23, 2006
1
Phase diagram of strongly
interacting matter
CERN-SPS, RHIC, LHC: high temperature, low baryon density
AGS, GSI (SIS200):
Nu Xu
moderate temperature, high baryon density
RPM, March 23, 2006
2
RHIC
Au+Au, Cu+Cu, d+Au
p+p (polarized)
Nu Xu
200 GeV
200, 500 GeV
RPM, March 23, 2006
QGP
g
3
RHIC performance
Au+Au
p+p
(~70% polarization)
Nu Xu
L= 8x1026cm-2s-1 at 100GeV/u
L= 6x1031cm-2s-1 at 100GeV/u
L= 8x1032cm-2s-1 at 250GeV/u
RPM, March 23, 2006
4
STAR experiment at RHIC
Run
Year
Species
sNN [GeV ]
Ldt
01
2000
Au+Au
130
1 b-1
02
2001/2
Au+Au
p+p
200
200
24 b-1
0.15 pb-1
03
2002/3
d+Au
p+p
200
200
2.74 nb-1
0.35 pb-1
04
2003/4
Au+Au
Au+Au
200
62
241 b-1
9 b-1
05
2004/5
Cu+Cu
Cu+Cu
Cu+Cu
p+p
200
62
22.5
200
3 nb-1
0.19 nb-1
2.7 b-1
3.8 pb-1
The STAR Collaboration: 50 Institutions, ~ 500 People
Brazil, China, Croatia, Czech Republic, England, France,
Germany, India, Netherlands, Poland, Russia, Switzerland and USA
Nu Xu
RPM, March 23, 2006
5
STAR TPC
Nu Xu
RPM, March 23, 2006
6
Detector Configuration
EMC
Full
Barrel
2005
STAR
TPC
BBC
East
EMC
(Half)
Barrel
Full
EndCap
2004
BBC
West
EndCap
EMC (1/3)
Magnet
Full TOF 2008
Nu Xu
RPM, March 23, 2006
7
STAR
Au + Au Collisions at 130 GeV
Central Event
Nu Xu
RPM, March 23, 2006
8
STAR Barrel EMCal
Nu Xu
RPM, March 23, 2006
9
S. Bass
High-energy nuclear collisions
CYM & LGT
Initial conditions
Initial high Q2
Partonic matter - QGP
PCM & clust. hadronization
interactions
- The hot-QCD
Hadronization
and Freeze-out
NFD
(1) Hard scattering productionNFD
- QCD
prediction
& hadronic
TM
(2) Interactions with medium - deconfinement/thermalization
string & hadronic TM
(3) Initial parton density
PCM & hadronic TM
(1) Initial condition in high-energy nuclear collisions - Color Glass Condensate
(2) Cold-QCD-matter, small-x, high-parton density
- parton structures in nucleon / nucleus
Nu Xu
RPM, March 23, 2006
10
High-energy nuclear collisions
Tfo
- Thermal freeze-out
Tch
- Chemical freeze-out
Tcritical
- Hadronization
=============
 Extract EoS
prior to
hadronization
Nu Xu
RPM, March 23, 2006
11
Physics goals at RHIC
Identify and study the properties of
matter with partonic degrees of
freedom.
Penetrating probes
Bulk probes
- direct photons, leptons
- “jets” and heavy flavor
- spectra, v1, v2 …
- partonic collectivity
- fluctuations
=

Hydrodynamic
Local
jets
- observed high pT hadrons (at RHIC, pT(min) > 3 GeV/c)
Collectivity
collectivity
- collective motion of observed hadrons, not necessarily
reached
Flow
Thermalization
thermalization among them.
Nu Xu
RPM, March 23, 2006
12
Collision Geometry, Flow
Au + Au sNN = 200 GeV (|| < 0.75)
Non-central Collisions
Number of participants: number of incoming nucleons in the overlap region
Number of binary collisions: number of inelastic nucleon-nucleon collisions
Charged particle multiplicity
Reaction plane: x-z plane
Nu Xu
 collision centrality
RPM, March 23, 2006
13
Hadron spectra from RHIC
p+p and Au+Au collisions at 200 GeV
Nu Xu
ud
ss
uud
sss
RPM, March 23, 2006
14
Yields ratio results
- In central collisions, thermal model fits well with S = 1. The system is
thermalized at RHIC.
- Short-lived resonances show deviations. There is life after chemical
freeze-out.
RHIC white papers - 2005, Nucl. Phys. A757, STAR: p102; PHENIX: p184.
Nu Xu
RPM, March 23, 2006
15
Energy loss in A+A collisions
leading particle suppressed
p+p
Au + Au
back-to-back jets disappear
Nuclear Modification Factor:
1 d 2 N AA / dpT d
RAA ( pT ) 
TAA d 2 NN / dpT d
Nu Xu
RPM, March 23, 2006
16
Suppression and Correlation
In central Au+Au collisions: hadrons are suppressed and back-to-back ‘jets’
disappear. Different from p+p and d+Au collisions.
Energy density at RHIC:  > 5 GeV/fm3 ~ 300
Parton energy loss:
Bjorken
(“Jet quenching”)
Gyulassy & Wang
…
Nu Xu
RPM, March 23, 2006
1982
1992
17
Jet-like di-hadron correlations
New results, year-4
Larger data sample (year-4)
allows analysis at higher pT:
8 < pT,trig < 15 GeV
- Emergence of the away side
peak
- Background negligible at
higher pT,assoc
take from Marco van Leeuwen
Nu Xu
RPM, March 23, 2006
18
Electrons: a mixture c- & b- hadrons
M. Djordjevic, et. al. nucl-th/0507019
Partonic energy loss - strongly interacting matter produced at RHIC!
Energy loss mechanism: under study
M. Gyulassy et al.
Problem: isolation of Charm hadron contributions from Beauty-hadrons
Nu Xu
RPM, March 23, 2006
19
Anisotropy Parameter v2
coordinate-space-anisotropy

momentum-space-anisotropy
y
x
 y2  x2
 2
 y  x2

py
v 2  cos2 ,   tan ( )
px
1
Initial/final conditions, EoS, degrees of freedom
Nu Xu
RPM, March 23, 2006
20
v2 at low pT region
- Minimum bias data! At low pT, model result fits mass hierarchy well!
- Details do not work, need more flow in the model!
Nu Xu
RPM, March 23, 2006
21
Collectivity, Deconfinement at RHIC
- v2, spectra of light hadrons
and multi-strange hadrons
- scaling of the number of
constituent quarks
At RHIC, I believe we have
achieved:
 Partonic Collectivity
 Deconfinement
PHENIX: PRL91, 182301(03)
STAR: PRL92, 052302(04)
S. Voloshin, NPA715, 379(03)
Models: Greco et al, PRC68, 034904(03)
X. Dong, et al., Phys. Lett. B597, 328(04).
….
Nu Xu
RPM, March 23, 2006
22
LGT predictions
1) Large increase in 
a fast cross cover !
2) Does not reach ideal,
non-interaction S. Boltzmann
limit !
 many body interactions
 Collective modes
 Quasi-particles are necessary
3) TC ~ 170 MeV robust!
Lattice calculations predict
TC ~ 170 MeV
Nu Xu
Z. Fodor et al, JHEP 0203:014(02)
Z. Fodor et al, hep-lat/0204001
C.R. Allton et al, hep-lat/0204010
F. Karsch, Nucl. Phys. A698, 199c(02).
RPM, March 23, 2006
23
“Perfect liquid” at RHIC
Kovtun, Son and Strainets, PRL94, 111601(05)
Teaney, PRC68 034913(03)
1) Experimental data favor hydrodynamic model calculations
with small viscosity
2) These results led someone to call the system a “perfect
liquid”
Nu Xu
RPM, March 23, 2006
24
Late Breaking News
November, 2005, Scientific American
“The Illusion of Gravity”
-- J. Maldacena
A test of this prediction comes from the
Relativistic Heavy Ion Collider (RHIC) at
Brookhaven National Laboratory, which
has been colliding gold nuclei at very
high energies. A preliminary analysis of
these experiments indicates the
collisions are creating a fluid with very
low viscosity. Even though Son and his
co-workers studied a simplified version
of chromodynamics, they seem to have
come up with a property that is shared
by the real world. Does this mean that
RHIC is creating small five-dimensional
black holes? It is really too early to tell,
both experimentally and theoretically.
Nu Xu
RPM, March 23, 2006
25
The fate of the Spinosaurid …
P.C. Sereno et al. Science, Nov. 13, 1298(1998).
(Spinosaurid)
For about 50 years Spinosaurid has been vegetarian, now it is a carnivore.
For about 20 years, QGP (1980)  sQGP (02)  ‘perfect liquid’ (04) …?
Nu Xu
RPM, March 23, 2006
26
-meson flows
STAR Preliminary, QM05 conference
S. Blyth et al.
Nu Xu
RPM, March 23, 2006
27
hard-soft interactions
Away side <pT> (GeV/c)
STAR, nucl-ex/0501016 / PRL 95, 120301(05).
Two sources of particles:
hard: hard scattering products.
soft: bulk medium constituents.
Very different as seen in peripheral.
Become similar in central.
near
Leading
hadrons
away
Medium
- PID correlation analysis
- Search for signal of shock-wave.
Nu Xu
RPM, March 23, 2006
28
What we have learned at RHIC
In Au + Au collisions:
(1) Partonic energy loss - tense interactions amongst
partons, strongly interacting matter
(2) Partonic collectivity and de-confinement
(3) Hadron yields in the state of equilibrium
In order to demonstrate the possible early
partonic thermalization - QGP, we need to
measure heavy flavor collectivity.
This is an experimental issue.
Nu Xu
RPM, March 23, 2006
29
Physics goals at RHIC
Identify and study the properties of
matter with partonic degrees of
freedom.
Penetrating probes
Bulk probes
- direct photons, leptons
- “jets” and heavy flavor
- spectra, v1, v2 …
- partonic collectivity
- fluctuations
=

Hydrodynamic
Local
jets
- observed high pT hadrons (at RHIC, pT(min) > 3 GeV/c)
Collectivity
collectivity
- collective motion of observed hadrons, not necessarily
reached
Flow
Thermalization
thermalization among them.
Nu Xu
RPM, March 23, 2006
30
QCD Energy Scale
mC
mc ~ 1.2 - 1.5 GeV >> QCD
ms ~ 0.2 GeV, similar to values
TC
QCD
TCH
critical temperature
QCD scale parameter
chemical freeze-out temperature
 = 4f scale for  symmetry breaking
u-, d-, s-quarks: light-flavors
Nu Xu
- pQCD production - parton density at small-x
- QCD interaction - medium properties
Rcc ~ 1/mC => color screening
J/ => deconfinement and thermalization
c-, b-quarks: heavy-flavors
RPM, March 23, 2006
31
quark mass
1)
2)
Higgs mass: electroweak symmetry
breaking. (current quark
mass)
QCD mass: Chiral
symmetry breaking.
(constituent quark mass)
 Strong interactions do
not affect heavy-quark
masses.
Nu Xu
RPM, March 23, 2006
32
Reconstructed Open Charm Hadrons
• Measure Do  Kin d + Au and Au + Au for pT < 3 GeV/c
• Investigating D±  K
D0
STAR, Phys. Rev. Lett. 94 (2005) 062301
Nu Xu
H. Zhang (STAR preliminary) QM2005
RPM, March 23, 2006
33
Charm cross sections
First set of measurements, systematic errors are large. Precision
data are needed:
- energy loss analysis  test pQCD in hot and dense medium
- J/ analysis  test Charm thermalization and de- confinement
Nu Xu
RPM, March 23, 2006
34
Non-photonic electron v2
Charm flows - a hint for partonic thermalization at RHIC!
Problem: Decay effect?
Nu Xu
RPM, March 23, 2006
35
Decayed electron pT versus D- and B-hadron pT
The correlation between the decayed electrons and heavy-flavor
hadrons is weak.
Pythia calculation Xin Dong, USTC October 2005
Nu Xu
RPM, March 23, 2006
36
Direct Topological Identification
of Charm-Hadrons in STAR
Nu Xu
RPM, March 23, 2006
37
The Heavy Flavor Tracker
The HFT: 2 layers
of Si at mid-y
1) A new detector: 30 m silicon pixels to get excellent resolution at the vertex
2) Direct topological reconstruction of Charm hadrons
3) Analyze charm hadron Flow and Energy loss
Nu Xu
RPM, March 23, 2006
38
The HFT Mechanical Design
•
•
Collaboration with LHC
Two Layers of Si
– 1.5 cm radius
– 5 cm radius
•
High Resolution
– 100M pixels
– 30 x 30 m2
•
Thin – with low MCS
–
–
–
–
•
50 m thinned Si
0.38% radiation length
0.5 mm beam pipe
CMOS APS technology
side-view
24 Ladders
– 10 chips, 2 x 20 cm2
– 100 mW/cm2 power budget
– air cooled
Nu Xu
end-view
RPM, March 23, 2006
39
Open-charm hadron reconstructions
1) D0, Ds, D+, c and their anti-particles can be reconstructed with
the combination of the HFT+SSD*+TOF+TPC.
2) Decent reconstruction efficiencies at low pT region - important for
flow analysis.
* Place holder for any adequate intermediate tracking device, such as IST.
Nu Xu
RPM, March 23, 2006
40
Outlook
(1) Test pQCD properties in hot and dense medium
- Charm- and bottom-hadron spectra, RAA, charm correlations
- Sensitive and detailed study for partonic energy loss 
`falsify pQCD,
a la Miklos’
- Precision Charm cross section for J/ analysis - direct test
de-confinement and Charm thermalization
(2) Test light-flavor thermalization
- Charm-hadron v2 - partonic thermalization
- Di-lepton invariant mass distributions - c symmetry
Nu Xu
RPM, March 23, 2006
41
STAR -vertex Detector
J. Thomas, H. Wieman et al., STAR Collaboration
Nu Xu
RPM, March 23, 2006
42