An Update from STAR –
Using Strangeness to Probe
Collisions
You are never too old to set
another goal or to dream a new
dream
C.S.Lewis 1898-1963
Helen Caines
Yale University
March 2003
Outline
Soft - Bulk of the production
- v2 flow - Charged hadrons, L, K
- Chemical freeze-out – Strangeness enhancement?
- Rescattering – K*,L(1520)
- Thermal Freeze-out – X,W,f different behaviour?
- Radii – K0s HBT
Hard – Early times
- Quark vs Gluon production – p/p and L/L
- High pt suppression – charged hadron vs K0s vs L
p-p
- <pt> - Mini jets?
Outlook – Look out for at QM2004
- Comparison p-p data – Relative rates
- d-Au – Cold vs hot nuclear matter
- FTPC - L at high y
Helen Caines
SQM – March 2003
2
STAR Strange Spectra @ 200 GeV
X
STAR
Preliminary
K0s
f
STAR
Prelimin
STAR
Preliminary
ary
K*
preliminary
L
W
STAR
Prelimin
ary
Preliminary
K
preliminary
Helen Caines
SQM – March 2003
3
The STAR Detector (Year-by-Year)
Magnet
Coils
TPC Endcap &
MWPC
Time
Projection
Chamber
Silicon
Vertex
Tracker *
FTPCs
ZCal
Endcap
Calorimeter
Barrel EM
Calorimeter
ZCal
Vertex
Position
Detectors
Central Trigger
Barrel
+ TOF patch
RICH
Helen Caines
* yr.1 SVT ladder
Year 2000, year 2001, year-by-year until 2003,
SQM – March 2003
4
installation
in 2003
130 GeV Data
STAR Preliminary
W+W
Helen Caines
All strange particles seem to increase linearly with h– March 2003
No stepSQM
functions,
no big surprises
5
Improvements with 200 GeV Data
STAR Preliminary
18% extrapolation
Better stats. W and W measurements
L+L
X+X
STAR Preliminary
K+
Much higher reach in pt
STAR Preliminary
STAR Preliminary
Finer centrality binning
Helen Caines
SQM – March 2003
6
B/B Ratios
STAR p+p √s = 200 GeV
Au+Au
All data:
• mid-rapidity
• ratios from raw yields
Talk: Anja Billmeier,
STAR preliminary
Helen Caines
Fri
Similar net baryon
in all 3 collision data
SQMdensities
– March 2003
7
Statistical models
As we know beautiful agreement between models and data
Helen Caines
SQM – March 2003
8
Centrality Systematics of Chemistry
Appears to be a saturation of strangeness
Helen Caines
SQM – March 2003
9
Statistical models
What about the
resonances?!?
As we know beautiful agreement between models and data
Helen Caines
SQM – March 2003
10
Resonances and Survival Probability

K*
• Decays in fireball mean daughter tracks
K
measured
can rescatter destroying part of signal

K*
K lost

K*

K*
K
K
Chemical
freezeout
time
• Initial yield established at chemical
freeze-out
Kinetic
freezeout

• Rescattering also causes regeneration
which partially compensates
• Ratio to “stable” particle reveals
information on behaviour and timescale
K
measured
between chemical and kinetic freeze-out
Two effects compete –
Dominance depends on decay products and lifetime
Need more than one resonance
Helen Caines
SQM – March 2003
11
Resonance Ratios
STAR Preliminary
Au-Au and p-p
√s=200GeV
L(1520) ->pK (13 fm/c)
K*
-> K ( 4 fm/c)
r
->  (1.3 fm/c)
UrQMD: signal loss
Talks: Patricia Fachini,
Ludovic Gaudichet & Haibin
Zhang, Sun.
Helen Caines
SPS
SQM – March 2003
K*(892) L(1520)
(17 GeV) [1]
66%
50%
RHIC (200GeV) [2]
55%
30%
12
Hydro-dynamically motivated fit
Shape of the mT spectrum depends
on particle mass
STAR Preliminary
R
dn
m cosh r   pT sinh r 
  r dr mT K1  T
I0



lead
mT dmT 0
T
T
Multiple interactions
1/mT dN/dmT (a.u.)
-
solid : used in fit
K-
to thermalization
p flow
-> limiting behaviour ideal hydrodynamic
where
r  tanh 1 r
E.Schnedermann et al, PRC48 (1993) 2462
s
R
r =s (r/R)n
Two Parameters: T and 
Helen Caines
SQM – March 2003
L
mT - m0 (GeV)
13
Thermal freeze-out at 130 GeV
Assume r= s(r/R)
Tfo - r(), 1 and 2  contours
X
•X, (W?): Show different
thermal freeze-out behaviour:
W
,K,P,L
STAR Preliminary
• , K, P, L: Common thermal
freeze-out at T~100MeV and
<>~0.52c
Early freeze-out due to
smaller cross-section ?
Radial flow developing at
early times?
,K,P,L
Talk: Javier Castillo, Mon
Helen Caines
SQM – March 2003
14
<pt> vs Centrality
, K, p
- <pt> increase
with centrality
- Heavy mass
increase faster
All consistent with radial
flow
Talk: Jinguo Ma, Sun
Helen Caines
f seems to flowSQM
differently
– Early freeze-out too?
– March 2003
15
Elliptic Flow and the Hydro limit
coordinate space
•
Coordinate space configuration anisotropic
(almond shape) however, initial momentum
distribution isotropic (spherically symmetric)
•
Only interactions among constituents generate
a pressure gradient, which transforms the
initial coordinate space anisotropy into a
momentum Zhang,
space
anisotropy (no analogy in
Gyulassy, Ko, PL B455 (1999) 45
pp)
y
x
Momentum space
d 3N 1 d 2N  

E 3 
1 +  2vn cos  n    r   

d p 2 pt dpt dy  n1

py
1
v2  cos 2(   r ) ,   tan ( )
px
Helen Caines
High v2 evidence of early thermalization
SQM – March 2003
16
Strange particle v2 at low pt
V2
Mass dependence
well described by blastwave model
modified to allow for an azimuthal
modulation of the second harmonic
to the transverse rapidity:
r= r0 +racos(2f)
and a variation in the azimuthal
density:
s2.
Combined fit to K0s and L gives
Tfo ~ 100 MeV
r0 ~ 0.66
ra ~ 0.04
1
s2 ~ 0.04
Pt GeV/C
In good agreement with mt spectra
Also seen at 130 GeV 2002, Phys. Rev. Lett. (2002) 132301-1
Do X and W agree?
STAR Preliminary
Au-Au 200 GeV
Helen Caines
SQM – March 2003
17
K0sK0s Correlations
X 10
K0s
Enough K0s/event to perform
HBT measurement
C2
Fit to a gaussian
M (GeV/C2)
C ( P, q)  1 +  exp(  R q )
2 2

= 0.5 0.1
Rinv = 5.8  0.7
Talk: Selemon Bekele, Thurs
Helen Caines
SQM – March 2003
18
HBT vs mt
Wiedemann and Heinz expect:
RHBT  V 1/ 3
to drop with
1/mat
(a ~ 0.5)
due to collective flow.
Rinv for K0s does not
seem to obey same mt
scaling
Need more detailed studies before conclusive statement made
Helen Caines
SQM – March 2003
19
Observing Hadronization Timescale
The Premise:
STAR pairs
Preliminaryare created
• Charge/anti-charge
in Au-Au
space-time
Kaonsclose
200 GeV
• Early creation (hadron gas)
• Longitudinal expansion and rescattering pulls pairs apart
– Loose correlation in rapidity
• Late creation (after deconfined phase?)
• Pairs only form at hadronization, late in collision
• Less rescattering
– Less loss of correlation in rapidity
Balance function tries to measure this correlation
Width of balance function then related to time
between hadronization and freeze-out
Helen Caines
SQM – March 2003
20
Balance Function at 200 GeV
STAR Preliminary
Smooth transition from
p-p to Au-Au
K narrower than 
just mass effect?)
Talk: Gary Westfall, Fri
Narrower widths for more central data: Delayed hadronziation?
Helen Caines
SQM – March 2003
21
Summary of Low pt Observations
– Particle production is large
• Small change from 130 to 200 GeV
– Vanishing anti-baryon/baryon ratio (0.7-0.8)
• close to net baryon-free but not quite, ~same for 130, 200 and pp
– Particles ratios suggest chemical equilibrium
• Tch170 MeV, mb<50 MeV  near lattice phase boundary
– Resonances appear strongly affected by rescattering in medium
• Need
Rescattering
and regeneration
competepicture
more Au-Au
data to get clearer
– System exhibits collective behavior (radial + elliptic flow)
• strong internal pressure that builds up very early
• Some particles appear to freeze-out at earlier times
– The system appears to hadronize late
• Balance function results
– Large system at freeze-out
• K0s appear to break mt scaling
Overall picture: system appears to be in equilibrium, but it explodes
and hadronizes rapidly SQM – March 2003
Helen Caines
22
Strange Particles at High pt
preliminary
preliminary
Change in shape at higher pt.
Helen Caines
SQM – March 2003
23
“Soft” vs “Hard” Physics
“Soft” Physics “Hard” Physics -
Npart: Number of participants
number of incoming nucleons (participants) in the
overlap region
Nbin: Number of binary collisions
number of equivalent inelastic nucleon-nucleon collisions
Nuclear
2
AA
d
N
/ dpT d
Modification RAA ( pT ) 
2 NN
T
d
 / dpT d
Factor:
AA
N-N cross section
<Nbin>/inelp+p
If no “effects”:
R < 1 in regime of soft physics
R = 1 at high-pt where hard
scattering dominates
Helen Caines
SQM – March 2003
24
Identified Particle Measurements
A significant difference is seen
between the pt dependence of
K0S and Λ RAA.
preliminary
For pt from 1.8-3.2 GeV/c in
central collisions Λ production
approximately follows Nbin
scaling.
At higher pt however, a
suppression with respect to Nbin
scaling is seen for both –
“standard” fragmentation?
preliminary
Baryon/Meson difference or merely mass?
Helen Caines
SQM – March 2003
Talk: Hui Long, Thurs
25
Minimum bias v2
Au-Au 200 GeV
At high pt Hydro-like
behaviour stops
Deviation occurs earlier
For K0s than for L
preliminary
Talk: Paul Sorensen,
Thurs
preliminary
Helen Caines
Again mass or baryon/meson dependence?
SQM – March 2003
26
Interplay of soft and hard processes
GLV theory
Hydrodynamics plus jet
quenching describes general
form of v2 pt dependence
Moderate pt
- pion dominated by
quenched pQCD,
- baryon production
dominated by non pQCD
effects (e.g.baryon junctions
or hydro)
expect qualitative different v2
behaviour for different particle
species
Does it explain RAA?
Helen Caines
SQM – March 2003
27
Recombination vs Fragmentation
Lower pt
-Recombination dominates
High pt
- Fragmentation dominates
Bass et al.,
nucl-th/0301087
Intermediate pt
- Two processes compete
Also S. Voloshin QM2002
Recombination dominates out to
higher pt for baryons (3 q)
- hadron suppression due
to parton energy loss dominates
later
RAA different for mesons and baryons,
What about v2 ?
Helen Caines
SQM – March 2003
28
B/B ratio at High Pt
L/L
Both Ratios fall at High pt
Talk: Ben Norman, Thurs
Seeing difference in quark vs gluon production mechanisms?
Helen Caines
SQM – March 2003
29
Summary of High pt Observations
•Strong hadronic suppression
•Onset at different times for different species
• Azimuthal anisotropy at high pt
Plateau occurs at different times for different species
• Suppression of back-to-back hadron pairs
(Not shown here)
large parton energy loss and surface emission?
Need
d-Au
disentangle initial state effects in jet production
(shadowing, Cronin enhancement)
 resolution of jet quenching picture
J/ and open charm: direct signature of deconfinement?
Helen Caines
SQM – March 2003
30
<pt> and p-p collisions
K0s
L
K0s
STAR Preliminary
p-p 200 GeV
STAR Preliminary
p-p 200 GeV
X
Power Law fits
Talk: Richard Witt, Thurs
STAR Preliminary
p+p @s = 200 GeV
Not flow in p-p so evidence for mini-jets?
Helen Caines
SQM – March 2003
31
News from the front - Latest d-Au update
STAR running since January
√s = 200 GeV
K0s
already > 40M events taken!
L, L
X
Helen Caines
Varying Number of events in each plot, NO PHYSICS!!!!
But
will
be..
SQMthere
– March
2003
32
High Rapidity Ls?
Not only use the FTPC’s for multiplicity at high y
Results from ~ 2 M
dAu minbias events
FTPC west only
(d side)
First hint of L signal in d-Au at forward rapidity
Helen Caines
SQM – March 2003
33
B(arrel)EMC
• dAu run (January 2003)
– 60 modules instrumented
– (D, Df) ~ (1.0, 2p)
– 2400 towers
pp run
16/22 modules
13% full EMC

RICH
dAu run
60 modules
50% full EMC
Physics with the BEMC
• Et
• 0
•
High-pt trigger
x100 enhancement at 5 GeV
•Jet and Quarkonia Trigger
Under commisioning
0 d-Au
  +   
Not working
Helen Caines
Poster – Manual Calderon
Thorsten Kollegger
  +
SQM – March 2003
34
The STAR Collaboration
Brazil:
more
Universidade de Sao Paulo
China:
IHEP – Beijing
IMP - Lanzou
IPP – Wuhan
USTC
Javier
SINR – Shanghai
Tsinghua University
Russia:
than 450 collaborators, 46 institutions, 9 countries
MEPHI - Moscow
Many here today:
Talks:
LPP/LHE JINR - Dubna
IHEP - Protvino
Selemon Bekele – Kaon HBT
U.S. Laboratories:
Anja Billmeier – Strange particle ratios in p-p Argonne
Berkeley
Castillo – Multi-strange baryons and thermal freeze-out
Brookhaven
Patricia Fachini – r and f0 production
Ludovic Gaudichet – L(1520) production U.S. Universities:
Great Britain:
Arkansas University
University of BirminghamHui Long – Suppression of high pt strange hadrons
UC Berkeley
UC Davis
Jinguo Ma – f production
France:
UC Los Angeles
Ben Norman – Ratios as function pt and centrality
IReS Strasbourg
Carnegie Mellon
0
SUBATECH - Nantes
University
Paul Sorensen – K s and L Azimuthal Anisotropy
Creighton University
Gary Westfall – Balance functions
Germany:
Indiana University
MPI – Munich
Richard Witt – Strange particle spectra in p-p Kent State University
University of Frankfurt
Michigan State University
Haibin Zhang – K* production
City College of New York
India:
Posters:
Ohio State University
IOP - Bhubaneswar
Penn. State University
John Adams – L reconstruction
VECC - Calcutta
Purdue University
Panjab University
Manuel Calderon de la Barca Sanchez – J/ triggering
Rice University
University of Rajasthan
Texas A&M
Magali Estienne – X reconstruction
Jammu University
UT Austin
IIT - Bombay
Julien Faivre – Improving reconstruction with LDA methods?
Washington University
VECC – Kolcata
Wayne State University
Mark Heinz – K0s reconstruction
Yale University
Poland:
Thorsten Kollegger – Heavy flavour reconstruction
Warsaw
University of Tech.
SQM – March 2003
35
Helen Caines
Sevil Salur – S* reconstruction