Selected Results from STAR
Beam Energy Scan Program
Michal Šumbera
Nuclear Physics Institute AS CR, Řež/Prague
(for the STAR Collaboration)
M. Šumbera NPI ASCR
1
The RHIC Beam Energy Scan Motivation
1) Turn-off of
sQGP signatures
2) Search for the
signals of phase
boundary
3) Search for the
QCD critical point
http://arxiv.org/abs/1007.2613
M. Šumbera
2
TPC:
Detects Particles in the |h|<1 range
p, K, p through dE/dx and TOF
K0s, L, X, W, f through invariant mass
Coverage: 0 < f < 2p |h| < 1.0
Uniform acceptance: All energies and
particles
3
BES Au+Au Data Taking
dNevt / (Nevt dNch)
BES-I Data:
Uncorrected Nch
Central Au+Au at 7.7 GeV in STAR TPC
M. Šumbera NPI ASCR
Year
√sNN [GeV]
events(106)
2010
39
130
2011
27
70
2011
19.6
36
2010
11.5
12
2010
7.7
5
2012*
5
Test Run
Triggering required effort,
but was a solvable problem.
Geometric acceptance remains the
same, track density gets lower.
Detector performance generally
improves at lower energies.
4
STAR TPC - Uniform Acceptance over all RHIC Energies
Au+Au at 7.7 GeV
Au+Au at 39 GeV
Au+Au at 200 GeV
 Crucial for all analyses
5
Selected Results
STAR publications on BES results
Observation of an energy-dependent difference in elliptic flow between particles and
antiparticles in relativistic heavy ion collisions, Phys. Rev. Lett. 110 (2013) 142301
Elliptic flow of identified hadrons in Au+Au collisions at √sNN= 7.7--62.4 GeV ,
Phys. Rev. C 88 (2013) 14902
Inclusive charged hadron elliptic flow in Au + Au collisions at √sNN= 7.7--62.4 GeV ,
Phys. Rev. C 86 (2012) 54908
Energy Dependence of Moments of Net-proton Multiplicity Distributions at RHIC
STAR , e-Print: arXiv:1309.5681 [nucl-ex]
+ many conference proceedings…
M. Šumbera
6
(0-5%/60-80%)
Suppression of Charged Hadrons …
M. Šumbera
PRL 91, 172302 (2003)
7
(0-5%/60-80%)
… and its Disappearance
PRL 91, 172302 (2003)
STAR Preliminary
M. Šumbera
RCP ≥ 1 at lower energies - Cronin effect?
8
Enhancement vs. QGP suppression
HIJING 1.35: Gyulassy M. and Wang X. Com. Phys. Com. 83 307(1994)
S. Horvat (STAR): arXiv: 1303.7260
Motivation: Agreement between the simulation and the data at low beam energies and its
break down at higher energies could help to find the energy at which QGP becomes dominant.
In HIJING (jet quenching off) RCP at lower energies is enhanced, but there is no quantitative
agreement with charged hadron RCP from data.
No suppression at higher energies observed, as expected (quenching was turned off).
M. Šumbera
9
RCP : Identified Particles
STAR Preliminary Positive particles
 Proton RCP > pion RCP, similar to d+Au at √sNN=200 GeV
⇒Pions may serve as a better gauge for jet quenching within
the pT range available through particle identification.
10
RCP : Identified Particles
STAR Preliminary Negative particles
 Antiproton RCP < pion RCP for pT <1GeV/c
 Pion RCP suppressed for √sNN ≥39GeV
11
 meson pT spectra
STAR Preliminary
Fit by Levy
(straight line) works well
12
RCP :  and Ks0
STAR Preliminary
 Ks0 RCP: (0-5%)/(40-60%)
 f RCP: (0-10%)/(40-60%) and (0-5%)/(40-60%) for 200GeV
13
 RCP: energy dependence
 f RCP ≥ 1 at intermediate pT for √sNN ≤ 39GeV
14
Strange Quark Dynamics
STAR Preliminary
 At intermediate pT Ω/ ratios show different behavior for √sNN ≥ 19.6
and √sNN = 11.5 GeV.
 Derived strange quark pT distributions show a similar trend.
Change of particle production mechanism ?
M. Šumbera NPI ASCR
Hwa & Yang, Phys. Rev. C 75, 054904 (2007), Phys. Rev. C 78, 034907 (2008).
15
NCQ Scaling Test: particles
STAR: Phys.Rev. C88, 014902 (2013)
 Universal trend for most of particles – ncq scaling not broken at low energies
 ϕ meson v2 deviates from other particles in Au+Au@(11.5 & 7.7) GeV:
~ 2σ at the highest pT data point. Needs more data to make clear conclusion.
Reduction of v2 for ϕ meson and absence of ncq scaling  during the evolution
the system remains in the hadronic phase [B. Mohanty and N. Xu: J. Phys. G 36, 064022(2009)]
M. Šumbera
16
NCQ Scaling Test: antiparticles
STAR: Phys.Rev. C88, 014902 (2013)
M. Šumbera
17
Δv2: v2(Particles) - v2 (Antiparticles)
STAR: PRL 110 (2013) 142301
STAR: Phys.Rev. C88, 014902 (2013)
The difference between particles and anti-particles is observed.
A linear increase Δv2 = a × μB for all particle species for 7.7 GeV ≤ √sNN ≤ 62.4 GeV.
 The baryon chemical potential is directly connected to the difference in v2
between particles and antiparticles.
M. Šumbera
18
Beam Energy Scan Phase- II
M. Šumbera
19
STAR BES Program Summary
√sNN (GeV)
BES phase-II
BES phase-I
112
206 420
mB (MeV)
5
2.5
Fixed Target
7.7
Explore QCD
Diagram
QGP properties
0
19.6
Test Run
39
585 775
Large range of mB in the phase diagram !!!
M. Šumbera
20
STAR BES Program Summary
√sNN (GeV)
BES phase-II
BES phase-I
112
206 420
mB (MeV)
5
2.5
Fixed Target
7.7
Explore QCD
Diagram
QGP properties
0
19.6
Test Run
39
585 775
Large range of mB in the phase diagram !!!
M. Šumbera
21
The Alternatives
Is there another way?
Can another facility do this faster?
Or better?
M. Šumbera NPI ASCR
22
Super Proton Synchrotron (SPS)
+ Running now, that’s good
+ Energy range is good
Runn
- But fixed-target
Not Ideal
- And light ions
•Time Line: 2009-2015
•Energy Range: √sNN=4.9 - 17.3 GeV
•mB = 0.560 - 0.230 GeV
BES I
M. Šumbera NPI ASCR
23
Nuclotron based Ion Collider fAcility (NICA)
•Time Line: Not yet funded. Plan is to submit documents by end of 2012.
Operations could not begin before 2017 (probably much later)
•Energy Range: √sNN = 3.9 - 11 GeV for Au+Au; mB = 0.630 - 0.325 GeV.
+ Collider, that’s good
+ High Luminosity expected
• MPD similar to STAR
• Maybe as early as 2017
- (But probably later)
- Energy is too low!
- Will miss the critical point
M. Šumbera NPI ASCR
Multi-Purpose
Detector (MPD)
24
Facility for Antiproton and Ion Research (FAIR)
Time Line:
SIS-100 is funded and will be complete by 2018
SIS-300 will need additional funding (no time estimate)
Energy Range:
SIS-100: Au+Au @ √sNN =2.9 GeV
SIS-300: Au+Au √sNN = 2.7 - 8.2 GeV
mB =0.730 - 0.410 GeV
Compressed Baryonic Matter (CBM)
TOF
++ Very High Interaction Rate
- Fixed target geometry
- No time estimate for SIS-300
Probably after 2022
- Even with SIS-300, the
energy is too low!
- Will miss the critical point
M. Šumbera NPI ASCR
RICH
ECAL
TRD
MVD
STS
25
Comparison of Facilities
Facilty
RHIC BESII
SPS
NICA
SIS-300
Exp.:
STAR
PHENIX
NA61
MPD
CBM
Start:
2017
2009
>2017?
>2022?
Au+Au Energy:
7.7– 19.6+
4.9-17.3
2.7 - 11
2.7-8.2
100 Hz
100 Hz
<10 kHz
<10 MHZ
CP&OD
CP&OD
OD&DHM
OD&DHM
√sNN (GeV)
Event Rate:
At 8 GeV
Physics:
CP = Critical Point
OD = Onset of Deconfinement
DHM = Dense Hadronic Matter
M. Šumbera NPI ASCR
Fixed Target
Lighter ion
collisions
Fixed Target
Conclusion:
RHIC is the best option
Fixed Target Proposal
- Annular 1% gold target inside the STAR beam pipe
- 2m away from the center of STAR
- Data taking concurrently with collider mode at beginning of each fill
M. Šumbera NPI ASCR
27
Fixed Target Proposal Simulation
UrQMD simulated Au+Al (beampipe) event ©Chris Flores, UC Davis
M. Šumbera NPI ASCR
28
Fixed-Target (Beampipe)Events
B. H a a g DNP F13
Event Selection & Kinematics
√sNN = 3.0 GeV
•Each set of points is
a different rapidity
slice; bottom to top:
0.0< y < 0.1 to
1.5< y <1.6
•Curves are offset by
powers of ten
•The nucleonnucleon center-ofmass rapidity slice is
indicated in red
B . H a a g DN P F 13
√sNN = 3.5 GeV
•Each set of points is
a different rapidity
slice; bottom to top:
0.0< y < 0.1 to
1.5< y <1.6
•Curves are offset by
powers of ten
•The nucleonnucleon center-ofmass rapidity slice is
indicated in red
B . H a a g DN P F 13
√sNN = 4.5 GeV
•Each set of points is
a different rapidity
slice; bottom to top:
0.0< y < 0.1 to
1.5< y <1.6
•Curves are offset by
powers of ten
•The nucleonnucleon center-ofmass rapidity slice is
indicated in red
B . H a a g DN P F 13
Rapidity Density Distributions
•The rapidity
density
distributions have
been measured
from target rapidity
to the nucleonnucleon center-ofmass rapidity.
•The distributions
are fit with
Gaussians.
Error are statistical only
•dN/dy
distributions for
AuLike+Al may not
peak at zero.
10.26.03
B. H a a g DNP F13
34
Summary
STAR results from BES program covering large mB
range provide important constraint on QCD phase
diagram:
– RCP of unidentified charged hadrons turns-off near 39 GeV.
– Identified RCP is qualitatively similar and suggests that pions are less
affected by (still unquantified) sources of enhancement.
– Particles-antiparticles v2 difference increases with decreasing √sNN and is
directly connected to baryon chemical potential.
– Baryon–meson splitting is observed when collisions energy ≥ 19.6 GeV
for both particles and the corresponding anti-particles.
– ...and many other results not covered in this talk.
Search for the critical point continues:
- Proposed BES-II program
- Fixed target proposal to extend mB coverage up to 800 MeV
M. Šumbera
35
Argonne National Laboratory, Argonne, Illinois 60439
Brookhaven National Laboratory, Upton, New York 11973
University of California, Berkeley, California 94720
University of California, Davis, California 95616
University of California, Los Angeles, California 90095
Universidade Estadual de Campinas, Sao Paulo, Brazil
University of Illinois at Chicago, Chicago, Illinois 60607
Creighton University, Omaha, Nebraska 68178
Czech Technical University in Prague, FNSPE, Prague, 115 19, Czech
Republic
Nuclear Physics Institute AS CR, 250 68 Řež/Prague, Czech Republic
University of Frankfurt, Frankfurt, Germany
Institute of Physics, Bhubaneswar 751005, India
Indian Institute of Technology, Mumbai, India
Indiana University, Bloomington, Indiana 47408
Alikhanov Institute for Theoretical and Experimental Physics, Moscow,
Russia
University of Jammu, Jammu 180001, India
Joint Institute for Nuclear Research, Dubna, 141 980, Russia
Kent State University, Kent, Ohio 44242
University of Kentucky, Lexington, Kentucky, 40506-0055
Institute of Modern Physics, Lanzhou, China
Lawrence Berkeley National Laboratory, Berkeley, California 94720
Massachusetts Institute of Technology, Cambridge, MA
Max-Planck-Institut f"ur Physik, Munich, Germany
Michigan State University, East Lansing, Michigan 48824
Moscow Engineering Physics Institute, Moscow Russia
M. Šumbera
NIKHEF and Utrecht University, Amsterdam, The Netherlands
Ohio State University, Columbus, Ohio 43210
Old Dominion University, Norfolk, VA, 23529
Panjab University, Chandigarh 160014, India
Pennsylvania State University, University Park, Pennsylvania 16802
Institute of High Energy Physics, Protvino, Russia
Purdue University, West Lafayette, Indiana 47907
Pusan National University, Pusan, Republic of Korea
University of Rajasthan, Jaipur 302004, India
Rice University, Houston, Texas 77251
Universidade de Sao Paulo, Sao Paulo, Brazil
University of Science \& Technology of China, Hefei 230026, China
Shandong University, Jinan, Shandong 250100, China
Shanghai Institute of Applied Physics, Shanghai 201800, China
SUBATECH, Nantes, France
Texas A&M University, College Station, Texas 77843
University of Texas, Austin, Texas 78712
University of Houston, Houston, TX, 77204
Tsinghua University, Beijing 100084, China
United States Naval Academy, Annapolis, MD 21402
Valparaiso University, Valparaiso, Indiana 46383
Variable Energy Cyclotron Centre, Kolkata 700064, India
Warsaw University of Technology, Warsaw, Poland
University of Washington, Seattle, Washington 98195
Wayne State University, Detroit, Michigan 48201
Institute of Particle Physics, CCNU (HZNU), Wuhan 430079, China
Yale University, New Haven, Connecticut 06520
University of Zagreb, Zagreb, HR-10002, Croatia
36
M. Šumbera
37
The RHIC Beam Energy Scan Project
• Since the original design of
RHIC (1985), running at lower
energies has been envisioned
• RHIC has studied the
possibilities of running lower
energies with a series of test
runs: 19.6 GeV Au+Au in 2001,
22.4 GeV Cu+Cu in 2005, and
9.2 GeV Au+Au in 2008
• In 2009 the RHIC PAC approved
a proposal to run a series of six
energies to search for the critical
point and the onset of
deconfinement.
• These energies were run during
the 2010 and 2011 running
periods.
M. Šumbera NPI ASCR
A landmark of the QCD phase diagram
38
Model summary
 HIJING captures beam energy dependence of
spectra.
 Jet quenching as modeled in HIJING has a greater
effect on higher beam energies.
 For AMPT, lower beam energies are better
matched by SM off, while SM on better captures
the beam energy dependence.
⇒Physics of hadronization shifts
from coalescence to fragmentation?
M. Šumbera
39
NCQ Scaling Quality: particles
STAR: Phys.Rev. C88, 014902 (2013)
M. Šumbera
40
NCQ Scaling Quality: antiparticles
STAR: Phys.Rev. C88, 014902 (2013)
M. Šumbera
41
Azimuthal Anisotropy
+¥
ö
dN æ
µ ç1+ 2å v n cos n (f - Yr ) ÷
df
è
ø
n -1
[
]
v n = cos(nf - Yr )
f = tan ( )
-1
px
py
 Directed flow v1 is due to the sideward
motion of the particles within the reaction
plane. It is sensitive to baryon transport,
space-momentum correlations and QGP
formation.
 Elliptic flow v2 results from the interaction
among produced particles and is directly
related to transport coefficients of
produced matter.
M. Šumbera
42
Directed Flow of p and π
p
π-
10 – 40%
STAR Preliminary
v1
STAR Preliminary
√sNN
STAR Preliminary
43
Directed Flow of p and π: mid-central
E895: PRL 84, 5488 (2000)
NA49: PR C68, 034903 (2003)
STAR: NP A904, 357 (2013)
STAR: PRL 108, 202301(2012)
STAR Preliminary
Proton v1 slope: changes sign from
positive at 7.7 GeV to negative at
11.5 GeV and remains small
negative up to √sNN =200GeV.
Pion and antiproton v1 slope:
always negative.
 For √sNN ≥11.5 GeV contradicts
baryon stopping picture predicting
opposite slope for protons and
pions.
Net-proton v1 slope: shows double
sign change. Can not be explained
by URQMD model but is
qualitatively consistent with a
prediction of hydrodynamic model
with a first order phase transition*.
*)H. Stocker, Nucl. Phys. A 750, 121 (2005).
44
v2(pT): Transport model comparisons
0-80% central Au+Au
 Purely hadronic system
(UrQMD) does not explain
relatively large elliptic flow
at these energies.
 AMPT-SM provides the best
description of the data
(except of protons and antiprotons @ 7.7 GeV).
 In all other cases both
AMPT and UrQMD underpredict v2(pT).
M. Šumbera
STAR: Phys.Rev. C88, 014902 (2013)
UrQMD 2.23: M. Bleicher et al, J. Phys. G 25, 1859 (1999).
AMPT 1.11: Z.-W. Lin et al., Phys. Rev. C 72, 064901 (2005).
AMPT-SM: string melting version
45
v2 vs. mT-m0
Corresponding
Particles anti-particles
STAR: Phys.Rev. C88, 014902 (2013)
 Baryon–meson splitting is observed when collisions energy ≥ 19.6 GeV
for both particles and the corresponding anti-particles
 For anti-particles the splitting is almost gone within errors at 11.5 GeV
M. Šumbera NPI ASCR
46
NCQ Scaling Test: particles
STAR: Phys.Rev. C88, 014902 (2013)
 Universal trend for most of particles – ncq scaling not broken at low energies
 ϕ meson v2 deviates from other particles in Au+Au@(11.5 & 7.7) GeV:
~ 2σ at the highest pT data point. Needs more data to make clear conclusion.
Reduction of v2 for ϕ meson and absence of ncq scaling  during the evolution
the system remains in the hadronic phase [B. Mohanty and N. Xu: J. Phys. G 36, 064022(2009)]
M. Šumbera
47
NCQ Scaling Test: antiparticles
STAR: Phys.Rev. C88, 014902 (2013)
M. Šumbera
48
Beam conditions: CERN vs. GSI/FAIR
SIS100/300
SPS
Energy range:
[AGeV]
10 – 158
beam
intensity
[Hz]
NA60
(2003)
interaction
rate
[Hz]
20%
5×105
108
10%
107
108
1%
106
2.5×106
new
injection
scheme
target
thickness
[λi ]
< 11 – 35 (45)
interaction
rate
[Hz]
105 - 107
5×104
LHC AA
Luminosity at the SPS comparable to that of SIS100/300
No losses of beam quality at lower energies except for emittance growth
RP limits at CERN in EHN1, not in (former) NA60 cave
Pb beams scheduled for the SPS in 2016-2017, 2019-2021
M. Šumbera NPI ASCR
H.J.Specht, Erice 2012
49
How to optimize the physics outcome for the next 10-15 y
Proposal: split HADES and CBM at SIS-100
HADES
at SIS-100
CBM
at SPS
Upgrade HADES,
optimized for e+e-, to
also cope with Au-Au
(now Ni-Ni)
Modify CBM to be
optimal (magnet) for
either e+e- or μ+μ-;
role of hadrons?
Merge with part of
personell of CBM
Merge with ‘CERN’ effort
towards a NA60
successor experiment
Profit from suitable
R&D of CBM
Profit from suitable
R&D of CBM, in
particular for Si
If SIS-300 would be approved in >2020, one could continue CBM there in >2027
M. Šumbera NPI ASCR
H.J.Specht, Erice 2012
50
v2( ) vs. v2(p)
• Mass: proton ~ 
• At low pT, v2( )/v2(p) decreases with decreasing beam energies
→ Indicating less partonic collectivity with decreasing beam
energy.
STAR Collaborat i on: arXiv: Phys. Rev. C 88, 014902 (2013) and Phys. Rev. Lett. 110, 142301
(2013). Phys. Rev C 87, 014903 (2013)