Transcript Slide 1

Systematics of Chemical Freeze-Out
Daniel Cebra
University of California, Davis
for the
STAR Collaboration
Daniel Cebra
11/17/2014
CPOD2014
CPOD 2014
Bielefeld, Germany
Slide
Slide11ofof37
37
Exploring the Phase Diagram of QCD Matter
What was known prior to the RHIC Beam Energy Scan Program?
1) High Energy Heavy-ion Collisions  partonic matter
2) Highest energies  transition is a cross over
3) At increased mB, there might be a first-order phase transition
4) And if so, there should be a critical point
BES program searches for:
• Turn-off of QGP signatures
• First order phase transition
• Critical point
Cross-Over
2010: 62.4, 39, 11.5, 7.7
2011: 19.6, 27 GeV
2014: 14.5 GeV
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
LHC
RHIC
RHIC
RHIC
RHIC
RHIC
RHIC
SPS
RHIC
SPS
RHIC
SPS
RHIC
SPS
SPS
AGS
AGS
AGS
AGS
AGS
SIS
Energy
(GeV)
2760.0
200.0
130.0
62.4
39.0
27.0
19.6
17.3
14.5
12.4
11.5
8.8
7.7
7.7
6.4
4.7
4.3
3.8
3.3
2.7
2.3
Chemical
Potential
mB
2
24
36
73
112
156
206
229
262
299
316
383
422
422
476
573
602
638
686
752
799
Pred.
Temp.
(MeV)
166.0
165.9
165.8
165.3
164.2
162.6
160.0
158.6
156.2
153.1
151.6
144.4
139.6
139.6
131.7
114.6
108.8
100.6
88.9
70.4
55.8
Slide 2 of 37
Setting the Scene
Using a statistical equilibrium model and the
measured particle yields (p, K, p, L, X, f, W), one
can estimate the location in the phase diagram.
BES-I: mB = 20 – 400 MeV
BES-II White Paper
STAR Preliminary
S.Mukhergee
Chemical Potential mB (MeV)
Some Lattice Gauge Theory
predictions suggest that the
low end of the BES-I scan one
may find the critical point
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 3 of 37
ks2 signals may relate to critical behavior
CPOD2014
Bielefeld, Germany
Phys. Rev. Lett. 112 (2014) 32302
BES-II White Paper
Daniel Cebra
11/17/2014
Several features are consistent with a
softening of the equation of state
Phys. Rev. Lett. 112 (2014) 162301
E. Sangaline QM2012
Low Mass
excess fit with
medium
calculation
including HG
and QGP
BES I – Highlights
dv1/dy
Several QGP signatures are seen to evolve
Slide 4 of 37
BES Phase I – What have We Learned So Far?
• The BES at RHIC spans a range of mB that could contain features of the QCD
phase diagram.
• Signatures consistent with a parton dominated regime either disappear, lose
significance, or lose sufficient reach at the low energy region of the scan.
• There are indicators pointing towards a softening of the equation of state
which can be interpreted as evidence for a first order phase transition.
• The higher moment fluctuation is sensitive to critical phenomena, but these
analyses place stringent demands on the statistics.
• Dilepton mass spectra show a broadening consistent with models including
hadron gas and quark-gluon plasma components.
What still needs to be done?  We still need to complete the analysis of the identified
charged particle spectra to determine location on the phase diagram
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 5 of 37
Charged Particle Spectra
Particle
Identification
though dE/dx
and TOF
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 6 of 37
Charged Particle Spectra – compare to SPS
The identified particle
spectra can be compared to
previously published results
from the SPS program
There is general agreement,
although the difference in
collision energy effects the
anti-proton yields which are
rising rapidly in this energy
regime.
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 7 of 37
Charged Particle Spectra – compare to SPS
The identified particle
spectra can be compared to
previously published results
from the SPS program
The NA49 spectra are feeddown corrected which
results in discrepancy for
protons and anti-protons.
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 8 of 37
High pT Charged Particle Spectra
STAR Preliminary
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Using time-of-flight
and dE/dx in the
relativistic rise has
allowed STAR to extend
the identified spectra
analysis to high pT
Slide 9 of 37
RCP at high pT
The high pT suppression provides insights into jet
quenching and parton energy loss.
At lower pT, there is a rise associated with radial flow.
QGP-like behavior goes away at the lowest BES
energies
Daniel Cebra
11/17/2014
BES-II White Paper
STAR Preliminary
CPOD2014
Bielefeld, Germany
HIJING with jet
quenching turned off
Slide 10 of 37
RCP of identified particles
We get further
insight into the
nature of the
suppression by
looking at RCP for
identified particles
Baryons and
mesons show very
different behavior
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 11 of 37
RCP of identified particles
BES-II White Paper
pQCD models show
suppression at high
pT for 20 and 40
GeV, but not for 10
Gev.
UrQMD-Hybrid
models describe
the behavior below
2 GeV/c for the
lower energies
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 12 of 37
Evidence of a phase transition
This was seen in the search for the nuclear liquid gas
phase transition
Phys. Rev. Lett. 75, 1040 (1995)
As new degrees of freedom open up at a phase
transition, one might expect to an inflection in the rise
in thermal energy with collision energy.
Various variables show suggestive behavior
STAR Preliminary
BES-II White Paper
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 13 of 37
Slopes of the Kaon Spectra
The step in the slope parameter is
seen as evidence that energy is
going into other channels.
M. Gazdzicki arXiv:1109.3653
BES kaon slopes are
not inconsistent with
the NA49 data,
however the exact
location of the step
remains ambiguous
The ALICE point
adds to the
“step” concept
STAR Preliminary
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 14 of 37
Evidence of a phase transition
A similar analysis with pions
shows a more gradual
transition
STAR Preliminary
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 15 of 37
Pion Yield Systematics
NA49 data shown an inflection
(kink) in the rate of increase of pion
production, suggesting a opening of
new degrees of freedom  Onset
of deconfinement.
M. Gazdzicki arXiv:1109.3653
Daniel Cebra
11/17/2014
RHIC BES results are
consistent, but leave
the exact location of
the kink ambigious
STAR Preliminary
CPOD2014
Bielefeld, Germany
Slide 16 of 37
Pion Yield Systematics
The yield increases roughly
linearly with √s
S.Das SQM2013
STAR Preliminary
The relative difference
between positive and
negative pions is largest at
lowest √s
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 17 of 37
p+/p- Ratio
Pions are effected by the positive
charge of the source  stopping
arXiv:1408.1369
p
( E - Vc ) 2 - m 2
2Vc / T E - Vc
mt   R e
p
E  Vc ( E  Vc ) 2 - m 2
arXiv:1408.1369
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 18 of 37
Kaon Yield Systematics
The is an excess of K+ due to
associated production
S.Das SQM2013
STAR Preliminary
The K-/K+ ratio rises with √s
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 19 of 37
K/p Ratio
The RHIC data are consistent with NA49,
however they do not suggest as sharp a
peak in the “horn”
The peak in the K/p ratio is seen as
evidence of the opening of the
strangeness channel which may
indicate the onset of deconfinement
M. Gazdzicki arXiv:1109.3653
STAR Preliminary
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 20 of 37
Particle Production and Chemical Equilibrium
J. Cleymans ISMD2010
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 21 of 37
What About the System Size Dependence?
It had been expected that the
temperature would increase with
smaller system size, which would
indicate an earlier freeze-out  maybe
closer to the phase transition line
predicted by lattice QCD.
This had motivated NA61/SHINE.
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 22 of 37
System Size Dependence
Cu+Cu produced
an unexpected
result, with mB
lowering
compared to
Au+Au
Daniel Cebra
11/17/2014
STAR Preliminary
O. Mall SQM2011
Using the
particle ratios
from the p, K,
and p and a
thermal model,
we can
determine our
location on the
phase diagram
STAR Preliminary
We can vary system size with centrality
CPOD2014
Bielefeld, Germany
Slide 23 of 37
Centrality Dependence
S.Das SQM2013
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 24 of 37
Grand Canonical Fits to Ratios
See Xianglei Zhu – Monday 15:30
S.Das SQM2013
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 25 of 37
Grand Canonical Fits to Ratios
For central data, the
GCE fits to the particle
ratios give freeze-out
conditions that are
consistent the world
trends (Cleymans,
Andronic).
STAR Preliminary
S.Das SQM2013
The GCE fits suggest
that for peripheral
collisions there is only
a small change in
freeze-out
temperature, but a
more significant
reduction in the
baryon chemical
potential.
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 26 of 37
Extracted Parameters -- GCE
Let’s look at all
four of the
extracted freezeout parameters.
Note also that gS
for BES energies
is consistent with
that found at the
SPS (0.862)
Daniel Cebra
11/17/2014
STAR
Preliminary
S.Das SQM2013
Note the strong
co-variance of mB
and mS. These
generally counter
act each other.
STAR Preliminary
STAR
Preliminary
CPOD2014
Bielefeld, Germany
STAR Preliminary
Slide 27 of 37
GCE Fits Compared to Strangeness CE
STAR Preliminary
STAR Preliminary
S.Das SQM2013
These comparison motivated fitting the BES data with a canonical ensemble that explicitly
conserved strangeness (SCE)  the apparent discrepancies are much reduced.
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 28 of 37
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 29 of 37
Beam Energy Scan
Phase II
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 30 of 37
STAR and PHENIX BES-II White Papers
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 31 of 37
Low Energy Electron Cooling at RHIC
Electron Cooling can
raise the luminosity by
a factor of 3-10 in the
range from 5 – 20 GeV
RHIC with cooling and long
bunches (Vz = +/- 1m)
Minimum
Projection
Long Bunches
increase luminosity by
factor of 2-5
Stage I
√sNN = 5-9 GeV
Stage II -- 3 MeV booster
cavity
√sNN = 9-20 GeV
BES I Performance
100 MHz SRF Gun
SRF Cavity
electron
u-turn,
delay
line
58 m from IP2
Daniel Cebra
11/17/2014
11.2 m
cooling
section
250 kW
Beam dump
11.2 m
cooling
section
3 MeV booster
CPOD2014
cavity needed for
Bielefeld, Germany
2nd stage.
energy
correction
cavity
gun
Slide 32 of 37
The STAR Upgrades and BES Phase II
Major improvements
for BES-II
EPD Upgrade:
iTPC Upgrade:
• Rebuilds the inner
sectors of the TPC
• Continuous Coverage
• Improves dE/dx
• Extends h coverage
from 1.0 to 1.7
• Lowers pT cut-in from
125 MeV/c to 60 MeV/c
Daniel Cebra
11/17/2014
EndCap TOF Upgrade:
• Rapidity coverage is critical
• PID at forward rapidity
CPOD2014
Bielefeld, Germany
• Improves trigger
• Reduces background
• Allows a better and
independent reaction
plane measurement
critical to BES physics
Slide 33 of 37
BES Phase II Proposal
BES Phase II is planned for two 22 cryo-week runs in 2018 and 2019
√SNN (GeV)
mB (MeV)
5.0
550
7.7
420
9.1
370
11.5
315
13.0
290
14.5 19.6
250 205
BES I (MEvts)
---
4.3
---
11.7
---
24
36
Rate(MEvts/day)
0.25
1.7
2.4
4.5
BES I L (1×1025/cm2sec)
0.13
1.5
2.1
4.0
BES II (MEvts)
100
160
230
250
300
400
3
4
6
8
11
15
14
9.5
5.0
3.0
2.5
3.0
eCooling (Factor)
Beam Time (weeks)
Daniel Cebra
11/17/2014
2
CPOD2014
Bielefeld, Germany
Slide 34 of 37
RHIC Fixed-Target Program
Should measurements below 7 GeV prove essential, a fixed
target program is being developed
Au+Au event at 3.9 GeV from a test in Run 14
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 35 of 37
Aulike+Al Fixed-Target Results
STAR Preliminary
STAR Preliminary
STAR Preliminary
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 36 of 37
Conclusions
•RHIC BES-I is complete (2010 to 2014)
•Results from BES-I show evidence is a change in the nature of
the system
•Analysis of charged particle spectra allows extraction of the
yields, which can be used to determine location in the phase
diagram
•mB is influenced by stopping and thermalization
•RHIC BES-II will run in 2018-2019 and will open up new avenues
to study the phase diagram
Daniel Cebra
11/17/2014
CPOD2014
Bielefeld, Germany
Slide 37 of 37