RHIC Beam Energy Scan

Hiroshi Masui / University of Tsukuba
Hadrons and Hadron Interactions in QCD 2015,
Symposium: QCD phase diagram and heavy ion collisions,
Kyoto, Mar/4/2015

H. Masui / Univ. of Tsukuba

1 /31

Outline• Introduction‣ RHIC Beam Energy Scan (BES) phase-I‣ PHENIX & STAR experiments• Review selected results from year 2010 & 2011
• Future upgrade for BES phase-II• Summary

H. Masui / Univ. of Tsukuba

2 /31

RHIC Beam Energy Scan (BES)
http://www.bnl.gov/bnlweb/pubaf/pr/photos/2012/07/RHIC_Graphics_Fig1-HR.jpg• Cross-over transition at µ =0
B

‣ from 1st principle Lattice QCD

calculations• If phase transition is 1st orderat high baryon density, theend point is QCD critical point

critical point ?
First orderphase transition ?

• Beam energy scan → reachhigh baryon density• Goals of BES at RHIC:‣ Search for turn-off QGP signals‣ Search for signals of 1st orderphase transition‣ Search for signals of QCD criticalpoint
H. Masui / Univ. of Tsukuba

3 /31

RHIC heavy ion collisions√sNN
2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014
(GeV)

200
130
62.4
39
27
22.5
19.6
14.5
11.5
7.7
Test
run

• Beam Energy Scan (BES) phase-I(year 2010, 2011)‣ 7.7, 11.5, (14.5), 19.6, 27, 39, 62.4

GeV

• 14.5 GeV has been taken last year
9.2 GeV

Au+Au

Cu+Cu

d+Au

He+Au

5 GeV

U+U (193 GeV) & Cu+Au
H. Masui / Univ. of Tsukuba

4 /31

Relativistic Heavy Ion Collider
photo from https://www.flickr.com/photos/brookhavenlab/sets/72157613690851651/• ~3.8 km circumference• Maximum 200 GeV (500 GeV)
in A+B (p+p) collisions incenter of mass energy• Wide variety of beams; p, d,
He, Cu, Au, U• Two running experiments:
PHENIX, STAR

H. Masui / Univ. of Tsukuba

5 /31

PHENIX & STAR experiments• PHENIX: the Pioneering High Energy Nuclear Interaction
eXperiment‣ Rare probes by electrons & photons with fast triggers• STAR: Solenoidal Tracker At RHIC
‣ Hadrons with large acceptance

H. Masui / Univ. of Tsukuba

6 /31

PHENIX & STAR experiments
STAR
TOF

MTD
TPC

EMCal

HFT

• Detector upgrades madetwo experiments similar‣ in terms of observables• sPHENIX upgrade isconsidered around 2017
H. Masui / Univ. of Tsukuba

7 /31

Where are we in QCD phase diagram ?

Beam Energy Scan at the Relativistic Heavy The
IonBeamCollider7
Energy Scan at the Relativistic Heavy Ion Collider

2760 GeV(b) LGT CP Predictions 200 GeV
200
62.4 GeV
39 GeV(a) Chemical Freeze-out Data
200

27 GeV19.6 GeV
11.5 GeV
7.7 GeV

Tkin (MeV)

Temperature Tch (MeV)

250

150

150

100

100

5% Au+Au collisions at RHIC

S. Datta, et al.,NPA904-905, 883c(13)50Z. Fodor and S. Katz, JHEP04, 50(04)A. Andronic, et al., NPA834, 237(10)J. Cleymans, et al., PRC73, 34905(06)(TC = 170 MeV)

50

STAR Preliminary

0
10

100

1000

10

100

0

0.1

Baryonic
ChemicalBaryon chemical
potentialµB (MeV)Potential µB (MeV)

•

1000
0.2
0.3

0.4

0.5

0.6

0.7

〈 β 〉 (c)Figure 4. Kinetic freeze-out temperature (T ) versus the average collective flow in the tra
RHIC
BES
phase-I
coversup tochemical
~ 400
MeV
µB
re 3. (a) Chemical freeze-out temperature (Tch ) versus
potential(µBin) obtained
directionbaryonic(hbi) in highenergy heavy-ion
collisions
for different collision centralities. At each ckina statistical[20, 19] fit to yields of hadrons
producedcentralAu+Au
atperipheral collisions and thoseenergy,the datain
pointswithlower hbi
values collisions
correspond to‣ modelChemicalfreeze-out temperature&0-5%baryonchemicalpotentialfromlargerhbi
valuescorrespondtocentralcollisions.
C. The yellow bands are the empirical results from fitting experimental data acquired prior to theparticle ratio-I program by a statistical model. (b) The positions of the QCD critical point from two different‣ Kinetic
freeze-out
temperaturefrompT spectra
e gauge theory
calculationsin the Tch versusµB planeare mshown.
fits to them distributionsof p, K, and p (as shown in the representative plot inT• Can we observe onset (turn-off) of QGP at high µ ?

at midrapidity at RHIC for various collision energies are shown in Fig. 4. Also shopB
the corresponding results from Pb+Pb collisions at sNN = 2.76 TeV from ALICELHC [33]. The Tkin values in central collisions are lower than the corresponding va
d lead to further development, understanding, and refinementof the statistical models.
Tch (shown in Fig. 3) although the difference
decreases
atof
lower
beam energies.
At all th
H. Masui/ Univ.
Tsukuba
8 /31

Search for turn-off
QGP signals

H. Masui / Univ. of Tsukuba

9 /31

Jet quenching
VOLUME 88, NUMBER 2

PHENIX: PRL88, 022301 (2002)

PHYSICAL REVIEW LETTERS

14 JANUARY 2002

dN AA /dpT d⌘
RAA =hNcoll i dN p+p /dpT d⌘
Ncoll : Number of binary collisions
RAA = 1
if A+A is superposition of p+p
Initial hard scattering - Binary collision scaling• Suppression of hadron yields at high p

FIG. 3. Ratio of yield per event in central vs peripheral Au 1
FIG. 2. The ratio RAA for charged hadrons and neutral pions
Au collisions,Twith each divided by $Nbinary % for that class. For(weighted average of PbSc and PbGl results) in central Au 1
p 0 the weighted average of PbSc and PbGl results is shown.
Au collisions. The error bars indicate the statistical errors on the
The error bars indicate the statistical errors on the spectra. The‣ Energy
loss ofpartonsthemediumbracketsmeasurement.
The surrounding
bands[shaded forin
p 0 ’s,surrounding bands [shaded for p 0 ’s, brackets for !h1 1 h2 "#2]
for !h1 1 h2 "#2] are the quadrature sums of (i) the systematic
are the quadrature sums of (i) the parts of the systematic errors
errors on
measurement,(ii) medium
the uncertaintyininterms
the N 1 of
N color‣ theVeryopaquechargeonthespectra that do not cancel in the ratio, and (ii) the uncerreference, and (iii) the uncertainty in $Nbinary %. Also shown
tainty in $Nbinary% (see Table I).
are the ratio of
inclusivecross
sectionsina1acomparedp
to p 1 p at sNN ! 31 GeV [18], and spectra frompcentral
Pb 1 Pb, Pb 1 Au compared to p 1 p collisions at sNN !
in contrast, are systematically below the scaled N 1 N ex17 GeV [17] shown as a band indicating the range of uncertainty.

• What happens in lower energies ?

H. Masui /both
Univ. toof Tsukuba
pectation, when compareddata from p 110p/31
colli-

with increasing centrality even for the lowest-energy system. Similarly, as already discussed in the context of Fig. 2,
at highAAenough pT the suppression is the same at 62.4 and
200 GeV, at all centralities. This is remarkable because thepower nPRL109,of the fit
to the(2012)
spectra changes approximately by
PHENIX:152301

R

at low energies
AuAu, π0, |η|<0.35|
sNN = 39 GeV
sNN = 62.4 GeV
sNN = 200 GeV

1T

RAA (p > 6 GeV/c)

1.5

Hijing Sim

0.5

0

0

100

200

300

400

Npart

STAR Preliminary

FIG. 3 (color online). Nuclear modification factor averaged forpT > 6 GeV=c. Uncertainties are shown as error bars (statistical), boxes (sum of pT -uncorrelated and Ncoll ), boxes around one(types B and C and uncertainties from the p þ p-collisionreference).

Hijing qualitatively
Exhibit suppression down to 39 GeV
between energie
301-5 •‣ π0 RAA is suppressed in most central 0-10% at √sNN = 39 GeV
quenching e- Results in Cu+Cu 22.5 GeV show enhancement in pT = 4 GeV/c• R > 1 below 39 GeV
AA

QM 2012

Evan Sangaline for the STAR
H. Masui / Univ. of Tsukuba

11 /31

Quark (parton) coalescence
Coalescence

D. Molnar and S. A. Voloshin, PRL91,
092301 (2003), R. C. Hwa and C. B. Yang,
PRC66, 025205 (2002), V. Greco et al,
PRL90, 202302 (2003), R. J. Fries et al,
PRL90, 202303 (2003), ....

Hadrons from coalescencehave larger momentum than
the quark momentum

Fragmentationhv2 (pT )q⇡ nq v2 (pT /nq )Carry only a fraction(z < 1) of the initial quark
momentum• Hadron productions by quark coalescence picture• Specific scaling pattern for meson and baryon v
2

H. Masui / Univ. of Tsukuba

12 /31Elliptic flow v2

PHYSICAL REVIEW C 88, 014902 (IC FLOW OF IDENTIFIED HADRONS IN Au + . . .

(a)

0.1 7.7 GeV

Au+Au, 0-80%
η-sub EP

STAR: PRC88, 014902 (2013)11.5 GeV

19.6 GeV

39 GeV62.4 GeV

v2/nq

0.05
0
0.1 27 GeV
0.05
0
0

0.5

1

1.5

20

0.5 1 1.5 2 0(m -m0)/nq (GeV/c2)

0.5

1

1.5

2

T

of
constituent
quark
(NCQ)
scaling
partonicd.o.f• (b)Number
0.1‣

7.7 GeV11.5 GeV
19.6 GeV
Au+Au, 0-80%
Hold separately
for particles and anti-particles
η-sub EP

0.05 more statistics in high mT-m0 at lower energies‣ NeedH. Masui / Univ. of Tsukuba

13 /31v2; particles vs anti-particles

The Beam Energy Scan at theRelativistic
Heavy044903
Ion Collider
Hybridmodel: PRC86,(2012)

STAR: PRL110, 142301 P(2013),HYSICAL
110, 142301 (2013)
PRC88, 014902 (2013)

wee
5 AP

R E V I ENJL
W model:
L EPRL112,
TTER
S (2014)0123010-80% Au + Au Collisions at RHIC

Most of the published theoretical calculations ca
(a)
(b)
duce
the
basic
pattern
but fail to quantitatively reExp. data Hybrid model
Exp. data NJL modelpthev2 difference[25–28]. So far, non
0.03
p measured
p
0.04
K
Λ
Λ
theorycalculations
describes
the observed ord
π
K
K
0.02
the
particles.
Therefore,ππmore accurate calculatio
theory are needed to distinguish between the
0.02
0.01
possibilities. Other possible reasons for the obs
%
þ
that
the
!
v
ðp
Þ
is
largerthan
the!
v2 ðpT2
T
00
Coulomb repulsion of !þ by the midrapidity net(only
at200low 300pT ) andthe100chiralmagnetic
effect
0
20
40
60
0
100
400 0
200
300
400
baryon-density
matterPotential[29]. Simulations
have to bsNN (GeV)
Baryonic ChemicalµB (MeV)out to quantify if those effects can expl
(color online). The difference in v2 between particles
observations.
8. Theasmeasured
difference in integrated v2 between particles and their corre! Figure
d their corresponding antiparticles (X)(see legend)aIn
Ref. [21], thestudyof the centrality depen
pﬃﬃﬃﬃﬃﬃﬃﬃ Relative differenceofv
betweenparticles
andanti-particles
2
pions(filled triangles), kaons (open squares), Ls (open triangles), and proto
Au collisions.
The
on of sNN for 0%–80% central Au þ antiparticles:"v2 for protons and antiprotons is extended to inv
circles),
all shown
as a function of baryonic chemical potential and collision energy for 0–80%
lines in theincreaseplot are fits witha power-law
function.
The
in lower
beam
energies
if different production rates for protons and antipr
collisions
[83,
84].
Only
statisticalerror bars are shown. Panels (a) and (b) show the compar
ars depict the combined statistical and systematic errors.
aparticles
functionof88],
centrality
could cause the observe‣ NCQ scaling breaks
down
betweenantiparticles
model
calculations
from Refs.
[86] and [87, andrespectively.
ences. It was observed that the differences, "Qualitative agreement with several
modelssignificant
at all centralities.
pﬃﬃﬃﬃﬃﬃﬃﬃ
Thev2 ðmTanisotropy% m0 Þ andpossible
NCQstudied
scalingw
ile in Au
þAu
collisions
at
s
¼
200
GeV
a
earlier,
there
are
two
types
of
azimuthalthatarecommonlyinhNN‣ No quantitative explanations on theinvestigateddifference forof vparticles
2
andsubsection,
antiparticles
se
NCQ scaling can be observed forparticles
andflow (v1 ) and elliptic flow (v2 ). In thiscollisions,directed
we concen
v2Masui
as mosta/ Univ.
functionof the reduced
tr
rticles, the observed difference in vv2 . atlower
beam hasFigureThe
v2 coefficient
proven 3to shows
be one H.
ofthediscussedthedynof Tsukubaprobes of
14 /31••

Au+Au, 0%-80%
η-sub EP

-

+

Ξ -Ξ
p-p
Λ-Λ
K+-K
π+-π-

200

39

27 19.6

11.5

7.7 (GeV)

200

39

27 19.6

11.5

7.7 (GeV)

0.04

v2(part.) - v2(anti-part.)2

v2(X)-v (X)0.06

RV=1.1

RV=0.5Di-electron mass spectra
STAR, QM2014• Chiral symmetry restoration,
thermal radiation‣ STAR measured di-electron

spectra in √sNN = 19.6 - 200
GeV‣ Excess in Mee < 1.1 GeV/c2(LMR) observed at all energies‣ In-medium modification of ρ

spectral function describe LMR
enhancement‣ No energy dependence of LMR

excess• Need more statistics below
20 GeVH. Masui / Univ. of Tsukuba

15 /31

Search for signals of 1storder phase transition

H. Masui / Univ. of Tsukuba

16 /31Equation of state → flow systematics
P. F. Kolb et al, PRC62, 054909 (2000)• 1st order phase transition affects
the build up of spatial &momentum anisotropy➡ Look at flow systematics

Elliptic Flow: A Brief Review

7with 1st order phase transition
2 0.35

εp

cs

0.3

EoS Lattice
EoS Q

0.1

EoS Lattice
EoS Q
EoS HRG

0.25

0.12

0.08

350
T [MeV]

0.06
0.04

0.2

0.02
0.15
150

300

450

600

750

T [MeV]R. Snellings, New J. Phys.13, 055008 (2011)

0

300
250
200
150

τ [fm]
0

0

2

4

6

2

8

4

6

10

8

10

12
τ [fm]

H. Masui / Univ. of Tsukuba

17 /31

informative. We define the slope Fnet-p based on expressing
130
the rapidity dependence of directed flow for all protons as½v1 ðyÞ%p ¼ rðyÞ½v1 ðyÞ%p̄ þ ½1 − rðyÞ%½v1 ðyÞ%1
net-p , where rðyÞis the observed rapidity dependence of the ratio of

Directed flow v

H. Stöcker / Nuclear Physics A 750 (2005) 121–147

H. Stocker: NPA750 (2005) 121-147

STAR: PRL112, 162301 (2014)
010-40% Centrality-0.02(a) antiproton-0.04

dv 1/dy|y=0

EXAMINATION OF DIRECTED FLOW AS A SIGNAL FOR . . .

0.01(b) proton

0√sNN (GeV)

4.3 6.1

13.7

PHYSICAL REVIEW C 89, 054913 (2014)

Fig. 7. Measured SIS and AGS proton (dpx /dy)-slope data compared to a three-fluid hydro calculation. A linear
extrapolation of the AGS data indicates a collapse of flow at ELab ≈ 30 A GeV, i.e., for the lowest SPS- and theupper FAIR-energies at GSI [59].

J. Steinheimer et al,
PRC89, 054923 (2014)2(c) net10 proton

10

0.01

0

Data
UrQMD

10

√ sNN (GeV)

102

Fig. 8. Directed flow v1 of protons versus rapidity at 40 A GeV Pb + Pb collisions [60] as measured by NA49 forthree centrality bins: central (dots), mid-central (squares) and peripheral (triangles). The solid lines are polynomial
fits to the data [60]. The proton antiflow is observed in the NA49 experiment even at near central collisions, which
FIG.
7. (Color
online)Comparison
is in contrast to the
UrQMD-model
involvingno phasetransition (Fig.of
9). results for pure hydro and• Early prediction shows the minimum around ~ 5 GeV

FIG. 4 (color online). Directed flow slope (dv1 =dy) nearhybrid model calculations with a first order EOS. Shown is the slope
andmidrapidity
toof vsubstantial
1 of protons
supportforantiprotons
this predictionaroundhas been
obtained by compared
the low energy
midrapidity versus beam energy for intermediate-centralityRecently,
40is
A GeV
SPS data of theNA49 Collaboration[60]prediction(cf. Fig. 8). These data clearly show
experimental
data.
Non-monotonic
behavior,
similarwith
early
Au+Au. ‣Panels(a), (b) and (c) reportmeasurementtrend
for antithe first proton “antiflow” around mid-rapidity, in contrast to the AGS data as well as
to the UrQMD calculations involving no phase transition (Fig. 9). Thus, at bombarding
protons, protons, and net protons, respectively, along with
Recentmore
hybridcalculation
theto datafrom below.can’t
Also the reproduce
overall magnitude seems
be strongly
UrQMD ‣calculations
subject
to therealistic
same cuts andfit conditions.
overestimated.
Systematic uncertainties are shown as shaded bars. Dashed
H. Masui / Univ. of Tsukuba
curves are a smooth fit to guide the eye.
18 /31Azimuthal
sensitive
HBT
Ellip,c#ﬂow#101#

with#
1st(order#PT#
24

STAR: arXiv:1403.4972 [nucl-ex]

E895 (-0.6<y<0.6, 7.4-29.7%)

0.35STAR (-0.5<y<0.5, 10-30%)

εF

0.4

UrQMD
(2+1)D hydro EOS-Q(2+1)D hydro EOS-H

CERES (-1<y<-0.5, 10-25%)

0$fm/c$(2+1)D hydro EOS-I(2+1)D hydro MC-KLN

STAR (-1<y<-0.5, 10-30%)

0.3

by M. Lisa
without#
1st(order#PT#

STAR (0.5<y<1, 10-30%)(2+1)D hydro MC-GLB

0.25

2$fm/c$π ±- π ±kT = 0.15-0.6 GeV/c

0.2

4$fm/c$

0.15
0.1
0.05

6$fm/c$

0
10

3

2

10

sNN [GeV]

10• STAR results show monotonic decrease(Color online) The dependence of the kinetic freeze-out eccentricity of pions on collision energy in mid-central Au+Au collisions
TAR) and Pb+Au collisions (CERES) for three rapidity regions and with ⟨kT ⟩ ≈ 0.31 GeV/c. For clarity, the points for forward andd rapidity from STAR are offset slightly. Error bars include only statistical uncertainties. Several (2+1)D hydrodynamical models andcalculations are shown. Model centralities correspond to the data. The trend is consistent with a monotonic decrease in eccentricity
m energy.

of freeze-out eccentricity

8$fm/c$‣ No sudden change on the STAR data

global fit method has been developed.
entricities at kinetic freeze-out in Fig. 27 were madeIdeal#hydro#calcula,ons#(#Kolb#&#Heinz#
QMD in cascade mode and so do not incorporate thisA wide variety of HBT measurements have been performed
al between string fragments.
and the comparison of results at different energies H.
is greatly
MA#Lisa#(#Rela,vis,c#Aspects#of#Nuclear#Physics#/#RANP#(#Rio#di#Janiero,#Brasil#(#Sept#2013#
Masui / Univ. of Tsukuba
19 /31

HBT radii

7

+*.
2

(Rout) - (Rside) (fm )

15

(a)

Au+Au
Au + Au
Pb + Pb

0-5%

2

mT = 0.26 GeV/c2

0.6
0.5
0.4

5

0.3
0.01 0.1

+:.

(b)

10

2

+=.

PHENIX/STAR
STAR
ALICE

' /R ()*+
R !"#$ − 2 ∙ R

PHENIX: arXiv:1410.2559 [nucl-ex]

10.01 0.1
sNN TeV1• FIG. 5. (Color online) The s

Non-monotonic behavior on√(Rout)2-(Rside)2, Rside/Rlong

2
dependence
of
(a)
(R
−
out
NN
‣ (Rout)2-(Rside)2 ~ emission
duration,
R
/R
~
proxy
of
sound
speed
side
long
√
2
Rside
), (b) [(Rside − 2R̄)/Rlong ]. The HBT radii are taken
H. Masui / Univ. of Tsukuba

20 /31

Search for signals of
QCD critical point

H. Masui / Univ. of Tsukuba

21 /31

Fluctuation of conserved charges• At critical point (with infinite volume)‣ susceptibilities and correlation length diverge‣ but both quantities cannot measure directly in the experiments• Observables‣ Moment (or cumulant) of conserved quantities: e.g. net-baryons, net-

charge, net-strangeness‣ Product of moments (ratio of cumulants) ↔ ratio of susceptibilities⌦2 = ( N )
3
S =
⇠
2

2

↵

2

⌦

3

↵

⇠ ⇠ , 3 = ( N ) ⇠ ⇠
4
3
4
2
, K =
⇠
2
2
2

4.5

⌦

, 4 = ( N )

4

↵

2

3 h( N )i ⇠ ⇠ 7* M. A. Stephanov,
PRL102, 032301 (2009)- directly related to the susceptibility ratios (Lattice QCD)
- higher moments (cumulants) have higher sensitivities to correlation length*• Signal = non-monotonic energy dependence of moment

products (cumulant ratios) for conserved charges vs √sNN
H. Masui / Univ. of Tsukuba

22 /31

Non-gaussian fluctuations
From Wikipedia• 3rd moment = skewness‣ asymmetry• 4th moment = kurtosis‣ peakedness• Both moments = 0 for gaussian distribution• Critical point search → non-gaussian fluctuations
H. Masui / Univ. of Tsukuba

23 /31

Net-proton & net-charge fluctuations
PRL 112, 032302 (2014)

STAR: PRL112, 032302 (2014)
1.2

P H Y S I C A L R E V I E W PRL
L E113,
T T E092301
R S (2014)

week ending
P24HJANUARYY S I C A 2014
L REVIEW

STAR: PRL113, 092301 (2014)the κσ 2 and Sσ2 from(a) UrQMD
Net-charge[23] (not shown in the figures)
10
1.0
Au+Au
closely follows the dataat the lower beam energies of 7.7|η| < 0.5
SkellamDistribution
0.8
and 11.5 GeV. Their values are, in general, larger compared
70%-80%
to data for the higher beam energies.
0.6
0%-5%
10
The current data provide the most relevant measurements
0.4
Net proton
over the widest range in μB (20–450 MeV) to date for the
0.2 0.4<p <0.8 (GeV/c),|y|<0.5
T
CP search, and for comparison with the baryon number
1.2
susceptibilities
from QCD to understand the(b)
0.6 computed
various features of the QCD phase structure [6,16,17]. The
1.0
0.4
deviations ofSσ and κσ 2 below the Skellam expectation
0.8
p+p data
are qualitatively
0.2 consistent with a QCD-based model which
Au+Au
70%-80%0.6
includes a CP [33]. However, the UrQMD model which
Au+Au 0%-5%0
Au+Au 0%-5% (UrQMD)
does not include
a CP also shows deviations from the
0.4
Ind. Prod. (0-5%)(c)Skellam expectation.
Hence, conclusions on the existence
1.05
of CP can 5be made only after comparison to QCD
1.00
0calculations with
CP behavior which include the dynamics
0-5%
associated withfinite corre0.95-5 heavy-ion collisions, such as70-80%
0-5% NBD
lation length and freeze-out effects.
70-80% NBD
0.90-100-5% Poisson
In summary, measurements of the higher moments
and70-80%
Poisson0.85-15 (Sσ and κσ 2 ) of the net-proton distributions
their products
5 6
20 30
200
10
100
5 6 7 8 10
20
30 40
200
100
at
midrapidity
(jyj
<
0.5)
within
0.4
<
p
<
0.8
GeV=c
in
T ﬃﬃﬃﬃﬃﬃﬃﬃ
Colliding Energy sNN (GeV)√sNN(GeV)pAu þ Au collisions over a wide range of sNN and μB havebeen presented
to searcha possible CP
and signals
FIG. 4 (color
online). forBeam-energy
dependenceof (a)of
σ 2a=M,
FIG. 4 (color online). Collision energy and centrality depende2
phase(b)transitiontheκσcollisions.
observables
showaSσ, andin(c), after allThese
corrections,for most
centralnce of the net proton Sσ and κσ 2 from Au þ Au and p þ p(0%–5%)
peripheral(70–80%)whichbins. are
The not
errorreprobars arecentrality
and andenergydependence,collisions at RHIC. Crosses, open squares, and filled circles
the capstransport
represent model
systematic
errors. Results
from
ducedstatisticalby eitherandnon-CP
calculations
or by
are for ‣the efficiency
corrected
results ofdeviationp þ p, 70%–80%,fromand
But only~20%
poissonbaseline
ﬃﬃﬃﬃﬃﬃﬃ
ﬃp
the Poisson
and NBDare superimposed.
valuesa hadronresonancegas baselines
model. For
sNN > 39 The
GeV,
Sσ of
0%–5% Au þ Au collisions, respectively. Skellam distributions
2
for the Poisson baseline are always unity.
for corresponding collision centralities are shown in the top
and κσκσ2 values
are similar for central, peripheral Au þ Au
panel. Shaded hatched bands are the results from UrQMD [22].
collisions, and p þ p collisions. Deviations for both κσ 2
In the middle and lower panels, the shaded solid bands are theand Sσfrom HRG and Skellam expectations
are observed
are always
unity. For
ﬃﬃﬃﬃﬃﬃﬃﬃ for the Poisson baselines
pvalues
expectations assuming independent proton and antiproton profor peripheralsNN ≤ 27 GeV.
The themeasurements
reasonably
collisions
κσ 2 values areshowalmost no
duction. The width of the bands represents statistical uncertainMasui/ Univ.andof Tsukuba
described
by assuming
independent
productionofandthevariation
as a functionofH.beam
energylie Nabove
Sσ

σ2
M

κ σ2

Sσ

(S σ)/Skellamκσ2

Au+Au Collisions at RHIC

• Largest deviation around 19.6 GeV for net-proton• Need more precise measurements below 20 GeV

LE

hadron yie
chemical fresonanceorder corre
thermal equfreeze-out
data on m
obtained [4analyses [4results for c
extracted
151 MeV aerrors in thfunction of
the statistiments. Mor
this is the fi
moments hout condit
freeze-out t
analysis ar[25,46]. Th
to freeze-ou
investigatio
In summcharge mulof centralienergies fr
These data
QCD phase
We observ
with increa
is observed

24 /31

Upgrade plans for BES
phase-II

H. Masui / Univ. of Tsukuba

25 /31

RHIC luminosity improvementswith electron coolingand long buncheswith electron cooling

BES-I• Electron cooling will be available for BES-II‣ Electron cooling: by a factor of 3-10 increase in 5-20 GeV‣ Electron cooling + long bunches: by a factor of 2-5
H. Masui / Univ. of Tsukuba

26 /31effectively a first stage implementation of the tracking detector considered for ePHENIX aan Electron Ion Collider [3].

sPHENIX upgrade for BES-II•• Possible configurations inFocus on hard probes

OUTER HCAL

INNER HCAL

year 2019

BABAR MAGNET

Acceptance:- |η| < 1
- Full azimuth‣ Option 1: EMCAL+VTX‣ Option 2

EMCAL- Option 1+ Additional silicon
trackers

BEAMPIPE
VTX‣ Option 3: Option 1+ TPC
OUTER HCALOUTER HCAL

INNER HCAL

INNER HCALBABAR MAGNETBABAR MAGNET

EMCAL

EMCAL

TPC

OUTER SILICON
TRACKER
BEAMPIPE

BEAMPIPE
VTX

VTX

H. Masui / Univ. of Tsukuba

27 /31STAR upgrade for BES-II
inner TPC upgrade
Event Plane Detector• Event Plane Detector, 1.8 < |η| < 5‣ Trigger, event plane, centrality- suppress backgrounds on flow measurements, independent centrality determination• inner TPC upgrade‣ increase TPC acceptance from 1 to 1.5 in η
‣ improve dE/dx resolution → better PID
H. Masui / Univ. of Tsukuba

28 /31

BES-II white papers

NOTES:
1. MATERIAL: BLACK DELRIN OR EQUIV.

http://www.phenix.bnl.gov/phenix/WWW/publish/
dave/sPHENIX/BES_II_whitepaper.pdf

https://drupal.star.bnl.gov/STAR/system/files/BES_WPII_ver6.9_Cover.pdf

Studying the Phase
Diagram of QCD
Matter at RHIC

Beam Energy Scan II (2018–2019)PHENIX Collaboration White Paper
NOTES:
1. MATERIAL: BLACK DELRIN OR EQUIV.

NOTES:
1. MATERIAL: BLACK DELRIN OR EQUIV.

A STAR white paper summarizing
the current understanding anddescribing future plans

OUTER HCAL

INNER HCALBABAR MAGNET

01 June 2014

EMCAL

BEAMPIPEVTXOUTER HCALOUTER HCAL

INNER HCAL

INNER HCALBABAR MAGNETBABAR MAGNET

EMCAL

EMCAL

TPC

OUTER SILICON
TRACKER
BEAMPIPE

BEAMPIPE
VTX

VTX

Version 1: March 1, 2014

H. Masui / Univ. of Tsukuba

29 /31

Projections for BES-II; fluctuations
Higher order cumu
Physics Goals for the BES II

Fluctuations
andAnalysisof Higher
Moments
The Beam Energy
Scan at theRelativistic
Heavy
Ion CollidersPHENIX
Net-proton
Au+Au 0-5% Central

STAR

curr
achi

κσ2

1

0.5
sPHENIX 2019 BES-2
UrQMD
STAR 2010-11 BES

0

10

2

10
Beam Energy (s1/2)
NN

Figure 26. Collision energy dependence of net-proton ks2 from central 0-5% (filledth4oFigure 3.3: Estimates for sPHENIX sensitivity
to measurementof net proton
for Auerror+Au
70-80% (open-squares)
Au+Au collisions
at RHIC. ks
The2 verticalbars are statisticalpcorrespondto systematic
errors.andThe yellow
solidband represents
central Au+Au
collcollisions as a function of s NN are shownon theleft panel,similarestimatesfor 0-5%STAR
futu
from UrQMD
simulations. The
shaped bandshows
the estimatedare‣shown on the right panel. Both estimates
are compared
thegreen
publishedSTAR
results
fromstatistical errors
8th oassuming the requested events listed in Table 2.
the first beam energy scan. See text forPhase-II,details.

• Net-proton moments

By a factor of 2-4 improvements on statistical precision below 20 GeV‣ Similar statistical errors for sPHENIX (with TPC) and STAR

3.5.1

Net Proton Fluctuations increased sensitivity to the criticality. In addition, we will also study the higher m
the net-kaons.

With the benefit of a TPC, described in Section 2.4, sPHENIX will
have/ Univ.
the ofcapability
to 30 /31
H. Masui
TsukubaSummary• Success of RHIC Beam Energy Scan phase-I‣ Several observables show a hint of possible turn-off signature of QGP- Turn-off/onset of QGP ? → BES phase II, future FAIR, J-PARC heavy ion programs‣ Non-monotonic behavior of directed flow and HBT radii- 1st order phase transition ? → Quantitative and systematic model comparisons‣ Possible non-monotonic behavior of conserved charge fluctuations- QCD critical point ? → Precision measurements & Lattice QCD calculations• We need precision measurements below 20 GeV‣ BES phase-II‣ Significant improvements on statistical precisions by RHIC luminosity& sPHENIX/STAR detector upgrades‣ BES-II white papers- sPHENIX: http://www.phenix.bnl.gov/phenix/WWW/publish/dave/sPHENIX/
BES_II_whitepaper.pdf- STAR: https://drupal.star.bnl.gov/STAR/system/files/BES_WPII_ver6.9_Cover.pdf
H. Masui / Univ. of Tsukuba

31 /31

The 25th International Conference on
Ultra-relativistic Nucleus-Nucleus Collisions
Kobe Fashion Mart, Rokko Island, Kobe, Japan
Sep. 27 (Sun) – Oct. 3 (Sat), 2015
[Registration will start from April 27, 2015]

http://qm2015.riken.jp

H. Masui / Univ. of Tsukuba

32 /31

Back up

H. Masui / Univ. of Tsukuba

33 /31

0 0.5 1 of
1.5 v220 for
0.5 anti-particles
1 1.5 2 0 0.5 1 1.5
NCQ scaling(m -m )/n (GeV/c )T(b)0.1 7.7 GeV

Au+Au, 0-80%
η-sub EP

0

2

q

2

STAR: PRC88, 014902 (2013)11.5 GeV

19.6 GeV

39 GeV62.4 GeV

v2/nq

0.05
0
0.1 27 GeV
0.05
0
0

0.5

1

1.5

20

0.5 1 1.5 2 0(m -m0)/nq (GeV/c2)

0.5

1

1.5

2

T

. (Color online) The NCQ-scaled elliptic flow, v2 /nq versus (mT − m0 )/nq , for 0%–80% central Au + Au collisions for) and corresponding antiparticles (b). Only statistical error bars are shown. The dashed lines show the results of simultan7) to all particles except the pions.
H. Masui / Univ. of Tsukuba

34 /31

The Beam Energy Scan at the Relativistic Heavy Ion Collider

22

Charge separation w.r.t.
event
plane
PHYSICAL REVIEWPRL 113, 052302 (2014)
STAR: PRL103, 251601 (2009), PRL113, 052302 (2014),
ALICE: PRL110, 012301 (2013)
5

5

0

0

-5

-5

-10

(a)-101062.4 GeV Au+Au 10

5

5

0

0

-5

(c) -5

5200 GeV Au+Au

0

30

30

27 GeV Au+Au

20

opposite charge
same charge

10

κ=1
κ = 1.5
κ=2

-5

(b)

UrQMD (κ =1)-10
2

39 GeV Au+Au

(d)

β

RP

[γ ≡ 〈cos(φα+φ -2ψ )〉] × 104

10

104 × (HSS - HOS)

2.76 TeV Pb+Pb

10

incre
and
deter

60 - 80%

19.6 GeV Au+Au

20

30 - 60%

1

0

Au+Au

-1

Pb+Pb

10

(e)

(f)

0

10 - 30%

0
0

20

40

60

80 0

40

11.5 GeV Au+Au 40

30

30

20

20

10

0.5
20

40

60

7.7 GeV Au+Au
0

10

(g)

0
80

60

40

20

0
0 80

80

W
the N
and
resou
by th
of Sc
Braz
Russ
Chin
the C
CSIR
the N
Mini
of C

(h)
60

40

20

10

0

Collision centrality (% Most Central)

102

10

3

sNN (GeV)• Chiral magnetic effect + Local parity violationp
FIG.
4. HSS − HOS , as a function of beam energy for three
Figure 14. The three-point correlator (g) as a function of centrality for Au+Au collisions at sNN=p
7.7-200 GeV. Also shown are the corresponding results for Pb+Pb collisions at sNN = 2.76 TeV from
centrality bins in Au þ Au collisions. The default values (dotted
ALICE at the LHC [125]. Note that the vertical scales are different for the different rows. The plottedcurves) are for Hκ¼1, and the solid (dash-dotted) curves areNN
systematic errors (shaded rectangles) reflect the extra conditions of DpT > 0.15 GeV/c and Dh > 0.15
obtained with κ ¼ 1.5 (κ ¼ 2). For comparison, the results forto suppress HBT + Coulomb effects.
Au þ Au collisions at 200 GeV [11] and Pb þ Pb collisions at‣ Signal ~ 0 in √s= 7.7 - 19.6 GeV

measurements below 20 GeV‣ Need better estimate of κ & precision
2.76 TeV [16] are also shown. The systematic errors of the STAR

[1]
[2]
[3]
[4]
[5]
[6]
[7]

data (filled boxes) bear the same meaning as those in Fig. 2.
Univ.shownof Tsukuba
UrQMD calculations with H.
κ ¼Masui1 are/ also
as solid shaded
35 /31 [8]CME signal

251601 (2009), PRL113,
P H Y052302
S I C A(2014),
L REVIEWPRLSTAR:113, PRL103,
052302 (2014)
ALICE: PRL110, 012301 (2013)60 - 80%50

κ=1
κ = 1.5
κ=2-5

UrQMD (κ =1)

104 × (HSS - HOS)

-10230 - 60%

1

0

Au+Au

-1

Pb+Pb

10 - 30%
0.5

LETTERS

week ending
1 AUGUST 2014

increase the statistics by a factor of 10 for the low energies
and if we can reduce the uncertainty associated withdetermination
κ. )i = v2 F⌘
hcos ( 1 of+the2value2of RP
H,
thank
RHIC)iOperations
⌘ We
hcos
( the
= F +GroupH, and RCF at BNL,
1
2
the NERSC Center at LBNL, the KISTI Center in Korea,
andCMEthe Open
Science Grid consortium for providingH:
contribution,
resources and support. This work was supported in part
Fby: backgroundcontribution,
: parameter
the Offices of NP and
HEP within the U.S.
DOE, Officeof Science; the U.S. NSF; CNRS/IN2P3; FAPESP CNPq of
Brazil; the Ministry of Education and Science of theRussian Federation; NNSFC, CAS, MoST, and MoE of
Decomposemeasured
China;
the Korean Research
Foundation; GA and MSMT ofthe
Czech Republic;toFIAS
of Germany;
DAE, DST, andcorrelation
CME
(H)
and
CSIR of India; the National Science Centre of Poland;backgroundcontributionsthe
National Research (F)Foundation(NRF-2012004024); theMinistry of Science, Education and Sports of the Republic
based onBzdak of
etRussia.
al, Lect. Notes Phys.
- Croatia;
of
andA.
RosAtom•

871, 503 (2013)

0

10

102

10

3

sNN (GeV)

FIG. 4. HSS − HOS , as a function of beam energy for three
centrality bins in Au þ Au collisions. The default values (dottedcurves) are for Hκ¼1, and the solid (dash-dotted) curves are
obtained with κ ¼ 1.5 (κ ¼ 2). For comparison, the results for
Au þ Au collisions at 200 GeV [11] and Pb þ Pb collisions atassumeγ is linearly proportional to v2‣ [1]
C. Vafa and E. Witten, Phys. Rev. Lett. 53, 535 (1984).
[2] T. D. Lee, Phys. Rev. D 8, 1226 (1973).
[3] T. D. Lee and G. C. Wick, Phys. Rev. D 9, 2291 (1974).
[4] D. E. Kharzeev, L. D. McLerran, and H. J. Warringa, Nucl.
Phys. A803, 227 (2008).
[5] D. Kharzeev, Phys. Lett. B 633, 260 (2006).
[6] D. Kharzeev and A. Zhitnitsky, Nucl. Phys. A797, 67(2007).
H. Masui / Univ. of Tsukuba
36 /31

two highest energies. The initial states in the PHSD and
HSD are simulated on an event-by-event basis taking into
account fluctuations in the position of the initially colliding
nucleons and fluctuations in the reaction plane. This procedure
is identical to that in the study of the elliptic flow in Ref. [44].
The average impact parameter for the selected events is
b = 7 fm. In the simulations the experimental acceptance
NATIONDIRECTEDPUZZLE. . . [39].
0.2 !OFpT THE! 2 GeV/c
is takenFLOW
into accountfor allIN
hadrons

and 200 GeV). However, v1 (y) for antiprotons agrees with thedata only for the highest energies where baryon-antibaryon
pairs are dominantly produced by hadronization. This becomes
evident from a comparison to the HSD results with v1 (y) ≈ 0.
The shape of the v1 (y) distribution for antiprotons starts
progressively
to differ from the measured data if we proceed√from sNN = 11.5 to 7.7 GeV. In the lower energy range
PHYSICAL
014903(2014)DIRECTED
FLOW
AS C
A 90,
SIGNALFOR...
the EXAMINATION
HSD
and PHSD OF
results
get very REVIEW
close whichindicates
V. P. Konchakovski et al, PRC90, 014903(2014)
the dominance of hadronic reaction channels (absorption andrecreation).
The direct flow distributions for negative and
0.04
STAR
proton b = 2 fm
pion πantiproton
Au+Au,
positive pions are close
to each other andantiprotons
also begin to disagree pions
protons
PHSD
0.02
STAR
STAR
HSD
0.02
with experiment in the same range of low STAR
collision energies as STAR0
for antiprotons(see Fig. 2). Again the PHSD results are very0-0.02
close to the experimental measurements at higher energies
200 GeV-0.02the 27
while
HSD
GeVresults deviate more sizeably, thus stressing
the role of partonic degrees of freedom in the entire collision
0.02
dynamics. The clear
overestimation of the p̄ and π − slopes at
019.6 GeV√
s0.02
NN = 7.7 GeV demonstrates that the heavy-ion dynamics
-0.02
is
not
yet fully understood within the string/hadron picture at
62.4 GeV0p
the lower energies.
0.02
-0.02
The characteristic slope of hadronic
the v1 (y) distributions at
p
dv1
midrapidity,
|
=
F
,
is
presented
in Fig. 3 for all cases
crossover0
dy y=0π+3FD: crossoverconsidered in Fig. 2. In a first approximation the v1 flow in the-0.02
π39 GeV 3FD: hadrons
0.02 11.5 GeV
center-of-masssystem may be well fitted by a linear function
v1 (y) 0= F y within the rapidity interval −0.5 < y < 0.5. A
0.02
3 4 5 6 7 8 910
20
30 40 50 6070
cubic equation is also used,

Directed flow, model calculations
PHYSICAL REVIEW C 89, 054913 (2014)

0

-0.02

-0.02

27 GeV

7. (Color online) Particle abundance at midrapidity calcucentral
0.02 collisions (b = 2 fm) in the 3FD model with ana pure hadronic
phase (dashed lines) and for the case of a0transition(solid lines). The experimental data are the same
-0.02
19.6 GeV
1.
0.02

v1

sNN [GeV]v1 (y) = F y + Cy 3 ,

(2)

7.7an
GeV
to 0.02
obtainestimate of the uncertainty in extracting thecoefficient F . The error bars in Fig. 3 just stem from the0
different fitting procedures. Note that the energy axis
√ in Fig. 3
is -0.02
extended by adding experimental results for sNN = 62
and 200 GeV [39]. This representation is more delicate as-0.04
compared-1to v1 (y)0 in Fig.
1 2. For-1protons
0 there1is a qualitative-1
0
1
agreement of the yHSD and PHSD results
y with the experimenty
measurements: the slope F > 0 at low energies, however,exceedingthe experimental
values bydistributions
up to√a factorofofthe
about
FIG. 8. (Color
online) Rapidity
directed flow
2; the slope crosses the line F = 0 at sNN ∼ 20 GeV,
for protons, antiprotons, and positive and negative pions from 10
which is twice larger than the experimental crossing point,
toand
40%
centralAu+online)Auand
collisions
differentenergies
FIG.
6. (Color
Slope
v1 of
(a) negatively
charged
pions
then
stays
negative
almostof atconstant
withcollision
further
calculated
withinthe
3FDmodel.
The
experimental
data
are
from
the
and
(b)
protonsandantiprotons
aroundmidrapidity
extracted
fromenergy increase. However, the absolute values of the calculated
theCollaboration
hybridinmodel
calculations
with
a bag
model
crossoverSTAR
The
dashedlines
correspondtoofa hadronic
protonslopesthis[39].
highenergyrange
areon theleveland−(0.01–0.02),
while
the
measured
ones
are
about
−0.005.
The
EOS.
We
comparewithstandard
UrQMD
andexperimental
data
EoS while the solid lines stand for a crossover transition.
standard
UrQMD model results, as cited in the experimental[11,12,23].
paper [39] and in the more recent theoretical work [40], aredisplayed inaccurate
Fig. 3 bycalculations
the wide and requirenarrow shaded
areas, memory
Therefore,
very highThetimefull
beamenergydependencethehybridmodel
respectively.
These
results
for protons
are close forto those
and
CPU
and,
accordingly,
calculations
for froma first-orderthe results
HSD model
andmidrapidity
essentially overestimate
thenegatively
slope for chargedof thev1 slopes fortransition
EoS∼30have
notbutbeen
completedyet. In
particular, forenergies
GeV
energy are
becomenegativepionsbelow
and protons
andat higher
antiprotons
shown
in Figs. 6(a)

v1

1

v1

v1

J. Steinheimer et al, PRC89, 054923 (2014)

experimental
data and, in the case of charged pions, in0
ter agreement
than in the HSD and PHSD approaches
-0.02
GeV
1). The purely hadronic11.5EoS
definitely overestimates
0.02
roton yield at midrapidity in this energy range, while0with thecrossover transition quite reasonably agrees-0.02
experimental data. Notethat the antiprotons are
7.7 GeVproducedfrom0 thefluid0 [29].
-1 -0.5
0.5 fireball1 -1 -0.5 (baryonless)
0 0.5 1 -1 -0.5
0.5 1
y
y
y
tain extent, this may be interpreted as being due toson formationof ponline)p̄ in equilibriumin analogy
HSDanFIG. 2. (Color
The directed flowv1 (y) for to
protons,
SD tiprotons
approaches
these
are central
not inAufull
as wellwhereas negative
pionschannels
from 10 to 40%
+ Au
√
s
=
7.7
to
200
GeV
collisionsatdifferent
collisionenergies
fromNN
um. The difference
between the two EoS’s is clearly√ lines)from HSD (dashedand PHSD (solid lines). Experimental dataigher energies sNN ! 20 GeV, where the crossover
are from the STAR Collaboration [39].
avorable for all hadronic species rather than only forthe samereasonwe√have failed
so far andto perform
calculations
and 6(b),respectively.
Both proton
antiproton
slopes are+¯¯
ons (p̄,!," ) as pointed out in Ref. [70].
for energies
above
s
=
30
GeV.
Note
that
the
changeof014903-4NN
overestimated for the whole examined collision energy range,otherwhileobservables,
analyzedso far[69–72],is15%
as
dv1 /dy|y=0
for pionsagreeswiththebelow
data atlower√
compared
to results
previous
B. Directed flow in the 3FD model
collisionenergiesofbutchangescalculations.
sign at sNN ≈ 10–15 GeV,The
directed
flow
v
(y)
as
a
functionof rapidity
y atwhich is not supported1 by the STAR
data. Whilethe difference
ent works [69–72] an analysis of the major part of bulk
BES-RHIC
energies
is ofpresented
Fig. rather
8 for
between bombarding
the investigatedequationsstate was inalready
bles has been performed: the baryon stopping [69],FIG. 7. (Color online) Comparison of results for pure hydro andhybrid model calculations with a first order EOS. Shown is the slopeof v1 of protons and antiprotons around midrapidity compared toexperimental data.

from below. Also the overall magnitude seems to be strongly
overestimated.
V. DISCUSSION

As observed in previous studies [21,24–26], the hybrid
model (and to some extent also standard UrQMD) usuallyshows a reasonable agreement with experimental particle
spectra, as well as the second and third order flow coefficients,
at the energies investigated in this article. Furthermore, it has
been shown [6,27–29] that fluid dynamical simulations canquite successfully account for the rapidity-even v1 moment,
which is caused by initial state fluctuations.
The strong deviation of the directed flow of all models, ascompared to data, noted in the previous section is therefore
surprising and requires a further discussion about the possible
sources of differences in the v1 extracted from the model ascompared to the experiment.
One particular difference, for example, lies in the determinationof the reaction
angles !RP used in Eq. (2). In
H. Masui/ Univ.planeof Tsukuba• PHSD (or HSD) vs hydro with hadronic, crossover EOS• Hybrid (UrQMD IS + Hydro + UrQMD hadronic phase) vshydro only with different freeze-out

37 /31

includes four weeks of full energy running split into two weeks of Au+Au and two weeks
of p+ p running. Running at 5 GeV is given a very low priority since a useful data set
would require an impractically long running time. It would take 218 days of running time
to record only 10 million events. Therefore, running at 5 GeV is not included in Table 4.2.

Beam time request for BES-IIAs detailed in Section 3.7, we request a short, of order two weeks, of running for p+ p andpAu+Au at s NN = 200 GeV. This critical pilot data taking would come at a small cost in
running time and help ensure a fully successful program for the full sPHENIX starting in
2021.

PHENIX

Table 4.2: An outline of the PHENIX run request for the BES II program. The running timeis integrated to cover a single year of RHIC running that spans 22 cryo-weeks, or 19 weeksof physics running depending on ramp-up and switching times. Higher priority is given
to the data sets listed first. The number of events refers to good events within the baselinesPHENIX configuration requiring |zvertex | < 10 cm including the PHENIX and RHIC duty
factor. Also included are event estimates with a wider |zvertex | < 30 cm and |zvertex | < 1 m
cut that could be applied if a TPC is installed.

Species

p

s NN

µB

(GeV) (MeV)

Au+Au

p+p

Run Time

Events(M)Events(M)(Days)|zvtx | < 10cm |zvtx | < 30cm |zvtx | < 1 m

315

45

15

45

112.5

13.0

281

23

17

50

125

9.0

376

41

6

17

42.5

19.6

205

4

33

100

2500

200

20

10

1200

3600

9000

10

1.2 pb 1

3.6 pb 1

9 pb 1• Focused on √s

44

Table 3. Beam Energy Scan Phase-II proposal for 22 weeks of RHIC running in each of the years
2018 and 2019.

Events(M)

11.5

200

STAR

The Beam Energy Scan at the Relativistic Heavy Ion Collider

Collision Energy (GeV)µB (MeV) in 0-5% Central Collisions
BES-I (Million Events)
BES-I Event Rate (Million Events/Day)
BES-I Int. Luminosity (1⇥1025 /cm2 s)
e-Cooling Luminosity Improvement Factor
BES Phase-II (Million Events)
Required Beam Time (Weeks)

7.7
420
4
0.25
0.13
4
100
14

9.1
370
–
0.6
0.5
4
160
9.5

11.5
315
12
1.7
1.5
4
230
5.0

14.5
260
20
2.4
2.1
8
300
2.5

19.6
205
36
4.5
4.0
15(4)
400
4.0+

measurements down to the region of the expected highest baryon density, which would be acollision energy of about 8 GeV.
The above paragraph outlines our best understanding of the most important energy ranges
and the necessary energy step sizes. The previous Section (3.1) detailed the required statistics
for the key measurements at each proposed energy. It is assumed that there will be 22
cryo-weeks of RHIC running in each of the years 2018 and 2019. Based on these goals,
requirements, constraints, and assumptions, we have developed a proposal for the BES PhaseII which is summarized in Table 3. The proposed number of weeks of RHIC running at 7.7
GeV has been estimated by considering the corresponding average event rate in the final week
25 of BES-I operations, BES-I luminosity, an electron cooling luminosity improvement factor
mid-way between the optimistic and pessimistic estimates (see Section 3.5), and the numberof events required for the physics program as per Table 2. The proposed number of weeks forbeam energies of 11.5 and 19.6 GeV are obtained using the average numbers for event rate andluminosity over the entire collider running period, and the event statistics as desired in BES
Phase-II (Table 2). There is an additional uncertainty on the rate estimates for the 19.6 GeV
system, and that arises because without an improvement to the trigger, the raw data rate will
exceed the limits of the STAR DAQ system. The situation should be significantly improved
with the help of the cleaner beam after electron cooling, and with the help of the Event Plane
Detector (EPD) upgrade described in Section 3.6. The numbers of weeks proposed for RHIC
H. Masui/ Univ. theof Tsukuba
38 /31running at 9.1 and 14.5 GeV are estimatedby interpolating
required numbers betweentheNN < 20 GeV‣ One year (2019) request from PHENIX‣ Two year (2018, 2019) request from STAR

BES-II projections
The Beam Energy Scan at the Relativistic Heavy Ion Collider

33

Rcp

Energy Scan at the Relativistic Heavy Ion Collider

The Beam Energy Scan at the Relativistic Heavy Ion Collider

34

v2

35

Figure 21. Number of constituent quark (NCQ) scaled event anisotropy parameter (v2 ) for identified
The Beam
EnergyScanfromat theRelativistic
Ion Collider
hadrons, including the f-meson(filledcircles)minimum
biasHeavy(0-80%)
Au+Au collisions at 7.7
Figure 20. The BES-I RCP data are are shown for p, K, and p for 7.7, 11.5, and 19.6 GeV. The BES
GeV (left) and 11.5 GeV (right). The projections of the statistical errors for the f-meson v2 , from BES
Phase-II projected error bands are for the same energies, 7.7 (red, scaled by 10), 11.5 (blue, scaled by
Phase-II are shown by the shaded bands in both plots. The shapes of the kaon v2 (pT ), dashed line,
60 - 80%dN/dy|/ 105100), and 19.6 (green, scaled by 1000).
52.8 57.6 60.8 77.2
5
4.5
were
used
in
the
estimation.
The Beam Energy Scan at the Relativistic Heavy Ion Collider
37

Di-lepton LMR excess

charge separation

0

LMR Excess Yield / dN/dy|/ (× 10-5)

Directed flow

κ=1

4

BES-II extrapolation
model expectation at BES-II
data

SS

- HOS) × 104

3.5
errors are displayed in Fig.
κ =20
1.5as colored bands. For clarity of presentation, the projected-5
error bands are scaled by κ10= 2(for 7.7 GeV), 100 (for 11.5 GeV), and 1000 (for 19.6 GeV). used in the estimation. As shown in Table32, 100M and 200M useful minimum bias eventsBES II error projection
The-10 error bands are truncated when the error reaches 50%; this represents the expected high are requireded from the Au+Au collisions at 7.7 and 11.5 GeV, respectively. The shape of the
2.5
pT2 limit for each measurement. For intermediate energies the expected error bands can be kaon v is assumed for the estimation up to p ⇡ 3 GeV/c where the scaling has been observed
30 - 60%
2
2Tinterpolated. It is also of interest to consider the inclusive charged hadron RCP measurementin high-energy nuclear collisions at the RHIC energies [34] in both plots. These measurements
1
1.5
(Fig.
12). We have also projected the expected error in BES Phase-II for this measurement,
will
answerdecisively
thequestionhowmuch
f meson flow there is compared to that of lighttherefore, we can report the high pT limits for the inclusive charged hadron RCP are found to1
quark hadrons. Lack of the collectivity of the f meson will provideof 2the
LMR: clear
0.30 < Mevidence
be0 5.2, 5.7, and 6.5 GeV/c for the 7.7, 11.5, and 19.6 GeV systems, respectively.
ee < 0.70 GeV/c
0.5
200 GeV: [arXiv:1312.7397](H

hadronic interaction dominated medium in the low energy heavy ion
Moreover,
BES: collisions.
STAR Preliminary
Au+Au
Pb+Pb
0
-1
parametersfor40multi-strange
3.1.2. The v2 of f mesons and NCQ scaling for indentified particles This measurement will with such statistics, information of the event anisotropy
7
10
20
60
100hadrons,
200
allow us to quantitatively address10thesuspected
decrease,followedbyanabsence,ofpartonic- 30%
3sNN (GeV)
such as X and W, can also be extracted.
p

0.5
collectivity
below sNN = 19.6 GeV. High-statistics data with a new event plane detector (asFigure 23.toLeft
panel:
Statistical errors
discussed below in section 3.6) are required. It is necessary
makemeasurements
upwithto narrowpT centrality bins for proton dv1 /dy near midrapidity
Three-particle correlators related to CME/LPV These measurements will allow us toat two sample beam energies for BES-I data sets 3.1.3.
= 03 GeV/c with a statistical error of less than 10% on
v2 . From this resolution requirement (blue error bars; the points are arbitrarily placed at
dv /dy = 0) and with the proposed BES Phase-II data sets (black error bars). RightFigure
panel:ofThe
same,
27.
This
plot summarizes
our current measurements.
data In
pointsare thetheturn-off
of CME/LPV-like
effects at 7.7The
GeV.
order
to integral
we can estimate the statistics necessary (see Table 2) 1for BES Phase-II to reach transverse corroborate the observation
2
but for net-protons.
excess(data-cocktail)and 700
the measured
p multiplicity
foon themeasuredbetween
CME300signalHSSMeV/c
HOSnormalized
by a factor
3 as showninmomenta beyond 2.5 GeV/c even at the lowest energies. This will allow us to test in NCQ reduce the statistical error
minimum-bias events. The grey dotted line below 20 GeV indicates the average normalized escaling10detail for many 10particle species,10including multi-strange particles.
Fig. 22, we propose to increase
the event statistics by factors of ten and four at 7.7 and 11.5
sNN (GeV)
while the grey band indicates the projected uncertainty in the proposed BES Phase-II measurem
The projection of the statistical errors for the f meson
for BEStoPhase-II
areifshown
it is notv2possible
determine
there isbyany
minimum
at all, muchlessrequires
identify where
GeV,
respectively.
This⇠ 50M events for each beam energy (see Table 2).
The purple dotted line shows the expected increase by a factor of two in normalized excess yieldtheshaded
bands
in
both
plots
in
Fig.
21.
The
shapes
of
the
kaon
v
(p
),
dashed
line,
were
it
might
lie
along
the
beam-energy
axis,
for
eithercentralor
peripheral
collisions.
T
2 error
Masui
Univ. of Tsukuba
The (HH ) difference as a function of beam energy is now shown with
Besides the chiral magneticWith
effect,H.thechiral / separation
effect (CSE) has also been
2

SS

OS

3

39 /31