Disentangling ﬂow and signals of Chiral Magnetic Effect in ... · A 661 (2012) S110–S113 12/02/16 Time-Projection Chamber (used for this analysis) STAR Detector a,b v 2{2}2 =

February 6-11, 2017, Chicago, IL, USA

XXVI international conference on ultrarelativistic heavy-ion collisions: Quark Matter 2017

Prithwish Tribedy

Disentangling flow and signals of Chiral Magnetic Effect in U+U and Au+Au

collisions

(for the STAR Collaboration)

February 6-11, 2017, Chicago, IL, USA

XXVI international conference on ultrarelativistic heavy-ion collisions: Quark Matter 2017

Prithwish Tribedy

Disentangling flow and signals of Chiral Magnetic Effect in U+U and Au+Au

collisions

(for the STAR Collaboration)

2

Motivation : Separation of flow and CMESTAR Experiment at RHIC

Large Coverage: 0 < φ < 2π, |η| < 1.0 Uniform acceptance: transverse momentum (pT) and rapidity (y) Excellent particle identification capabilities (TPC and TOF)

5

Year √sNN (GeV)

Minimum Bias

Events(106)

2010 62.4 67

2010 39 130

2011 27 70

2011 19.6 36

2014 14.5 20

2010 11.5 12

2010 7.7 4

BES-I Dataset TPC MTD Magnet BEMC BBC EEMC TOF

HFT @ Maria & Alex Schmah

•  M. Anderson et al., Nucl. Instrum. Meth. A 499 (2003) 659 •  W. J. Llope., Nucl. Instrum. Meth. A 661 (2012) S110–S113

12/02/16

Time-Projection Chamber (used for this analysis)

STAR Detector

v2{2}2 = �cos(2(�1 � �2))��a,b � �cos((�a1 + �b

2 � 2�3))�v2{2}

Observables :

LPV correlator :

C112 = ⟨cos(φ1+φ2−2φ3)⟩

,

Three particle correlator :

CME : QCD anomaly driven chirality imbalance leads to current along B-field 3

Axial charge Vector charge j0

v

j0a

x

yz

FIG. 1. Illustration of real-time dynamics of the chiral magnetic wave for light quarks (mrsph ⌧ 1 ). Contour lines representthe distribution of axial and vector charges at times t/tsph = 0.6, 0.9, 1.1, 1.3, 1.6, 1.9 of the evolution. Simulations wereperformed on a 24⇥ 24⇥ 64 lattice.

the magnetic screening length (see e.g. [13, 43, 44]) a con-version to physical units can be achieved by assigning avalue of about 200�500 MeV to r�1

sph. If not stated other-wise we use a lattice spacing of rsph/a = 6, the durationof the sphaleron transition is chosen as tsph = 3/2rsph

(corresponding to ⇠ 0.6 � 1.5 fm/c) and the magneticfield strengths considered in this work is qB = 3.5r�2

sph

(corresponding to a few m2⇡

).Non-equilibrium dynamics of axial and vector

charges We will now analyze the dynamics of the axialand vector charges during and after a sphaleron transi-tion, and first focus on the anomalous transport of lightquarks with mrsph ⌧ 1, where dissipative e↵ects due to afinite quark mass can be neglected over the time scale ofa sphaleron transition. Our results for the time evolutionof the axial and vector densities j0

v/a

(t, x) in the presenceof an external magnetic field are compactly summarizedin Fig. 1 where we show contour lines of the distributionsat various stages of the time evolution.

We observe that during the sphaleron transition, a lo-cal imbalance of axial charge j0

a

is generated according tothe axial anomaly; at the same time the chiral magnetice↵ect induces a vector current jz

v

with a similar profilein coordinate space. Conservation of the vector current@

µ

jµ

v

= 0, implies that longitudinal gradients of the cur-rent @

z

jz

v

, lead to separation of electric charges alongthe direction of ~B; over time electric charge accumulatesat the edges of the sphaleron, resulting in a dipole likestructure of the vector charge density j0

v

observed e.g. att/tsph = 0.6, 0.9 in Fig. 1.

Since the local imbalance of vector charge j0v

in turninduces an axial current ~j

a

/ j0v

~B due to the chiral sep-aration e↵ect (CSE) [45], the combination of CME andCSE ultimately leads to the formation of a chiral mag-netic wave [18, 46]. We observe from Fig. 1, that the

chiral magnetic wave manifests itself as the propagationof a soliton-like wave-packet associated with the non-dissipative transport of axial and vector charges alongthe direction of magnetic field. We note that this is thefirst time that the emergence of such a collective exci-tation is confirmed in non-perturbative real-time latticegauge theory simulations.Chiral magnetic wave: The dynamics of the chiral

magnetic wave can be further investigated by integratingout the transverse coordinates to study the propagationof the wave-packet along the longitudinal direction. Thisallows us to compare the results of our microscopic simu-lations with a macroscopic description within the frame-work of anomalous hydrodynamics in a straightforwardway. In anomalous hydrodynamics [18–21], the coupleddynamics of axial and vector charges is described in termsof conservation laws and the constitutive relations of thecurrents, which to leading order in gradients and in pres-ence of an external magnetic field Bµ = (0, 0, 0, B) takethe form [19]

jµ

v,a

= nv,a

uµ + Dv,a

Oµnv,a

+ �B

v,a

Bµ . (7)

Specifically, for a system of non-interacting fermions, thedi↵usion constant D

v,a

, vanishes and the anomalous con-ductivities are simply given by �B

v,a

= na,v

/B when the

magnetic field strength is su�ciently large B � r�2sph, m2

[2]. In the local rest-frame uµ = (1, 0, 0, 0), the anoma-lous hydrodynamic equations of motion for the integratedquantities j0,z

v,a

(t, z) =R

d2x? j0,z

v,a

(t, x?, z) then take theform,

@t

✓j0v

(t, z)j0a

(t, z)

◆= �@

z

✓j0a

(t, z)j0v

(t, z)

◆+

✓0

S(t, z)

◆(8)

with the sphaleron induced source term given as S(t, z) =

� g

2

8⇡

2

Rd2x?Tr Fµ⌫ F̃

µ⌫

. The solutions for the vector and

Fig: Muller, Schlichting, Sharma, PRL 117 142301 (2016)

B→

Goal : Search for signals of CME & suppress flow driven background Voloshin, PRC 70 (2004) 057901

Prithwish Tribedy, QM 2017, Chicago


31

v2

Δγ

B-field driven

0

v2

Δγ

If Background dominates

All Bkg

B-field

Total

Δγ ~0

v ~02

min

Δγmax

v2,max

Chatterjee, Tribedy PRC 92, 011902 (2015)

v2

Δγ

If B-field dominates

All Bkg

B-fieldTotal

Δγ ~0

v ≠02

Δγmax

0min

v2,max

Signal and background of CME

v2

Δγ

0

Voloshin PRC 70 (2004) 057901, Schlichting, Pratt, PRC 83 014913 (2011), Wang PRC 81 064902 (2010),Bzdak, Koch, Liao PRC 83 014905 (2011)

Flow driven

3

Signal & Backgrounds of charge separation

HBT, Coulomb

Flowing resonance

Charge conservation

Momentum conservation

v2

Background

Charge separation(central-events)

�a,b =�cos(�a1 + �b

2�2�2)�

Δγ→0, v2→0

(γOS − γSS)Background ≈ v2{2}N

≥ 0


31

v2

Δγ

B-field driven

0

v2

Δγ


All Bkg

B-field

Total

Δγ ~0

v ~02

min

Δγmax

v2,max


v2

Δγ


All Bkg

B-fieldTotal

Δγ ~0

v ≠02

Δγmax

0min

v2,max


v2

Δγ

0


Flow driven

4


HBT, Coulomb

Flowing resonance

Charge conservation


v2

Background

Magnetic fieldSignal

Ψ2


�a,b =�cos(�a1 + �b

2�2�2)�

Δγ→0, v2→0

Δγ→0, v2 ≠ 0


≥ 0

≈ ⟨B2cos(2(ΨB−Ψ2))⟩


31

v2

Δγ

B-field driven

0

v2

Δγ


All Bkg

B-field

Total

Δγ ~0

v ~02

min

Δγmax

v2,max


v2

Δγ


All Bkg

B-fieldTotal

Δγ ~0

v ≠02

Δγmax

0min

v2,max


v2

Δγ

0


Flow driven

5


HBT, Coulomb

Flowing resonance

Charge conservation


v2

Background


Ψ2


�a,b =�cos(�a1 + �b

2�2�2)�


≥ 0

≈ ⟨B2cos(2(ΨB−Ψ2))⟩

Strategy : look for vanishing Δγ when v2 is still non-zero

Δγ→0, v2→0

Δγ→0, v2 ≠ 0

Prithwish Tribedy, QM 2017, Chicago 6

Analysis details

— Data Set used : U+U 193 GeV (Year 2012), Au+Au 200 GeV (Year 2011), p+Au 200 GeV (Year 2015)

— Acceptance cuts : 0<φ<2π, |η|<1, pT > 0.2 GeV/c

— Centrality : Time Projection Chamber & Zero Degree Calorimeter

0.1

1

10

100

1000

10000

0 100 200 300 400 500 600 700 800

U+U 193 GeV

Entri

es

Refmult

Min-bias0-2%2-4%4-6%6-8%8-10%

1

10

100

1000

10000

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

U+U 193 GeV

Entri

es

ZDCUnAttenuated (East+West)

Min-bias8-10

6-84-62-40-2

Uncorrected multiplicity in |η|<0.5

Multiplicity binning Spectator binning

Neutron response of ZDCs

Centrality Selection

12

0.1

1

10

100

1000

10000

0 100 200 300 400 500 600 700 800

U+U 193 GeV

Entri

es

Refmult

Min-bias0-2%2-4%4-6%6-8%8-10%

-Method 1 (using RefmultCorr)

1

10

100

1000

10000

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

U+U 193 GeV

Entri

es


Min-bias8-10

6-84-62-40-2

-Method 2 (using ZDCs)


12

0.1

1

10

100

1000

10000

0 100 200 300 400 500 600 700 800

U+U 193 GeV

Entri

es

Refmult

Min-bias0-2%2-4%4-6%6-8%8-10%


1

10

100

1000

10000

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

U+U 193 GeV

Entri

es


Min-bias8-10

6-84-62-40-2



12

0.1

1

10

100

1000

10000

0 100 200 300 400 500 600 700 800

U+U 193 GeV

Entri

es

Refmult

Min-bias0-2%2-4%4-6%6-8%8-10%


1

10

100

1000

10000

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

U+U 193 GeV

Entri

esZDCUnAttenuated (East+West)

Min-bias8-10

6-84-62-40-2



12

0.1

1

10

100

1000

10000

0 100 200 300 400 500 600 700 800

U+U 193 GeV

Entri

es

Refmult

Min-bias0-2%2-4%4-6%6-8%8-10%


1

10

100

1000

10000

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

U+U 193 GeV

Entri

es


Min-bias8-10

6-84-62-40-2



12

0.1

1

10

100

1000

10000

0 100 200 300 400 500 600 700 800

U+U 193 GeV

Entri

es

Refmult

Min-bias0-2%2-4%4-6%6-8%8-10%


1

10

100

1000

10000

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

U+U 193 GeV

Entri

es


Min-bias8-10

6-84-62-40-2


STAR preliminary

STAR preliminary


12

0.1

1

10

100

1000

10000

0 100 200 300 400 500 600 700 800

U+U 193 GeV

Entri

es

Refmult

Min-bias0-2%2-4%4-6%6-8%8-10%


1

10

100

1000

10000

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

U+U 193 GeV

Entri

es


Min-bias8-10

6-84-62-40-2


8

Body-Tip (0-1%)

Body-Tip Collisions (U+U)

Different trend than conventional centrality binning

0.026

0.027

0.028

0.029U+U 193 GeV

0-1%

v 2 {

2}

-0.1

0

0.1

0.2

0 1 2 3 4 5

(γO

S -γSS

) × 1

04

|L-R| bin

STAR preliminary

STAR preliminary

STAR preliminary

Binning in spectator asymmetry → independent from centrality binning

Body-Tip

0

0.1

0.2

0.3

0.4

0.02 0.03 0.04U+U 193 GeV

(γO

S -γSS

) × 1

04

v2 {2}

Global-DataBody-Tip

Asymmetry percentile %


γab– v2 correlation plot (multiplicity & spectators)

14

Observations in 0-10%:

• Strong correlation linear in central events : universal curve

Dominance of fluctuations of participants and spectators

0 0.05

0.1 0.15

0.2 0.25

0.3 0.35

0.4

0.025 0.035 0.045

U+U 193 GeV 0-10%∆η>0.025

(γO

S -γSS

) × 1

04

v2 {2}

RefMult binningZDC binning

7

0

0.1

0.2

0.3

0.4

0 0.01 0.02 0.03 0.04

U+U 193 GeV

(γO

S -γSS

) × 1

04

v2 {2}

Multiplicity binningSpectator binning

Results : Central and Ultra-central Collisions

U+U Au+Au

0

0.5

1

0 0.01 0.02 0.03 0.04 0.05

Au+Au 200 GeV

(γO

S -γSS

) × 1

04v2 {2}

Run 4 (0909.1717)Run 7 (1302.3802)Run 11 Cumulant (0-1%)

STAR preliminary

STAR preliminary



14




0 0.05

0.1 0.15

0.2 0.25

0.3 0.35

0.4

0.025 0.035 0.045

U+U 193 GeV 0-10%∆η>0.025

(γO

S -γSS

) × 1

04

v2 {2}


8

0

0.1

0.2

0.3

0.4

0 0.01 0.02 0.03 0.04

U+U 193 GeV

(γO

S -γSS

) × 1

04

v2 {2}


Results : Central and Ultra-central Collisions

U+U Au+Au

0

0.5

1

0 0.01 0.02 0.03 0.04 0.05

Au+Au 200 GeV

(γO

S -γSS

) × 1

04v2 {2}

Run 4 (0909.1717)Run 7 (1302.3802)Run 11 Cumulant (0-1%)

STAR preliminary

STAR preliminary

Data :- Show vanishing charge separation for non-zero values of v2 {2}- Show linear growth with v2 {2}- Show larger v2 {2} offset (Δγ=0) for U+U than Au+Au


Data

0

0.1

0.2

0.3

0.4

0 0.01 0.02 0.03 0.04

U+U 193 GeV

(γO

S -γSS

) × 1

04

v2 {2}



14




0 0.05

0.1 0.15

0.2 0.25

0.3 0.35

0.4

0.025 0.035 0.045

U+U 193 GeV 0-10%∆η>0.025

(γO

S -γSS

) × 1

04

v2 {2}


STAR preliminary

Central and Ultra-central Collisions


Components of LPV correlator

0

0.01

0.02

0.03

0 100 200 300 400

U+U 193 GeV

(γO

S -γSS

)× N

part

Npart

TotalLong-rangeShort-range

STAR preliminary

MC-Glauber

Projected B-fieldData

0

5

10

15

20

0 100 200 300 400-⟨ B2 c

os(2

(ΨB

- Ψ2)

) ⟩ [

fm-4

]

Npart

U+U 193 GeV


0

0.01

0.02

0.03

0 100 200 300 400

U+U 193 GeV

(γO

S -γSS

)× N

part

Npart


STAR preliminary

MC-Glauber


0

5

10

15

20

0 100 200 300 400-⟨ B2 c

os(2

(ΨB

- Ψ2)

) ⟩ [

fm-4

]

Npart

U+U 193 GeV

Ψ2

B

0<Ψ2<2π0<Ψ2<2π 0<ΨB<2π

BB

10

Data

MC-Glauber


0

0.01

0.02

0.03

0 100 200 300 400

U+U 193 GeV

(γO

S -γSS

)× N

part

Npart


STAR preliminary

MC-Glauber


0

5

10

15

20

0 100 200 300 400-⟨ B2 c

os(2

(ΨB

- Ψ2)

) ⟩ [

fm-4

]

Npart

U+U 193 GeV


0

0.01

0.02

0.03

0 100 200 300 400

U+U 193 GeV

(γO

S -γSS

)× N

part

Npart


STAR preliminary

MC-Glauber


0

5

10

15

20

0 100 200 300 400-⟨ B2 c

os(2

(ΨB

- Ψ2)

) ⟩ [

fm-4

]

Npart

U+U 193 GeV

Ψ2

B

0<Ψ2<2π0<Ψ2<2π 0<ΨB<2π

BB

Projected B-field

0

1

2

3

4

5

0 0.05 0.1 0.15

U+U 193 GeV0-10 %

-⟨|eB

2 |cos

(2(Ψ

B-Ψ

2)) ⟩

(fm

)-4

Ellipticity ε2


Chatterjee, Tribedy, PRC 92, 011902 (2015)

0

0.1

0.2

0.3

0.4

0 0.01 0.02 0.03 0.04

U+U 193 GeV

(γO

S -γSS

) × 1

04

v2 {2}



14




0 0.05

0.1 0.15

0.2 0.25

0.3 0.35

0.4

0.025 0.035 0.045

U+U 193 GeV 0-10%∆η>0.025

(γO

S -γSS

) × 1

04

v2 {2}


STAR preliminary

Projected B-field vs ε2 can provide a natural explanation to the data


{x,y}=〈x〉, 〈y〉


Data

0

0.1

0.2

0.3

0.4

0 0.01 0.02 0.03 0.04

U+U 193 GeV

(γO

S -γSS

) × 1

04

v2 {2}



14




0 0.05

0.1 0.15

0.2 0.25

0.3 0.35

0.4

0.025 0.035 0.045

U+U 193 GeV 0-10%∆η>0.025

(γO

S -γSS

) × 1

04

v2 {2}


STAR preliminary

We need to see if a background model can explain data


STAR preliminary

Data & Background expectations

∆γBackground = (γOS − γSS)Background ≈ v2{2}N

0

0.005

0.01

0.015

0.02

0 0.02 0.04

0-20%(Background-model)

U+U 193 GeV

∆γ

× N

part

v2 {2}

Data∆γ ∝ v2 /Npart

⇒ ∆γBackground ×N ≈ v2{2}


Body-Tip (0-1%)


STAR preliminary

STAR preliminary


0.026

0.027

0.028

0.029

U+U 193 GeV0-1%v 2

{2}

-0.1

0

0.1

0.2

0 20 40 60 80 100

(γO

S -γSS

) × 1

04

Symmetry Percentile %

Provides a way to trigger even smaller v2 {2}

8

Body-Tip (0-1%)



0.026

0.027

0.028

0.029U+U 193 GeV

0-1%

v 2 {

2}

-0.1

0

0.1

0.2

0 1 2 3 4 5

(γO

S -γSS

) × 1

04

|L-R| bin

STAR preliminary

STAR preliminary

STAR preliminary


Body-Tip

0

0.1

0.2

0.3

0.4

0.02 0.03 0.04U+U 193 GeV

(γO

S -γSS

) × 1

04

v2 {2}

Global-DataBody-Tip


Chatterjee, Tribedy, PRC 92, 011902 (2015)


Body-Tip (0-1%)



STAR preliminary

STAR preliminary

STAR preliminary


Body-Tip

0

0.1

0.2

0.3

0.4

0.02 0.03 0.04U+U 193 GeV

(γO

S -γSS

) × 1

04

v2 {2}

Global-DataBody-Tip

8

Body-Tip (0-1%)



0.026

0.027

0.028

0.029U+U 193 GeV

0-1%

v 2 {

2}

-0.1

0

0.1

0.2

0 1 2 3 4 5

(γO

S -γSS

) × 1

04

|L-R| bin

STAR preliminary

STAR preliminary

STAR preliminary


Body-Tip

0

0.1

0.2

0.3

0.4

0.02 0.03 0.04U+U 193 GeV

(γO

S -γSS

) × 1

04

v2 {2}

Global-DataBody-Tip


0.026

0.027

0.028

0.029

U+U 193 GeV0-1%v 2

{2}

-0.1

0

0.1

0.2

0 20 40 60 80 100

(γO

S -γSS

) × 1

04

Symmetry Percentile %

Provides a way to trigger even smaller v2 {2}

-0.43±0.03 +(17±1)xv2

-2.9±0.1 +(93±4)xv2


31

v2

Δγ

B-field driven

0

v2

Δγ


All Bkg

B-field

Total

Δγ ~0

v ~02

min

Δγmax

v2,max


v2

Δγ


All Bkg

B-fieldTotal

Δγ ~0

v ≠02

Δγmax

0min

v2,max


v2

Δγ

0


Flow driven

14


HBT, Coulomb

Flowing resonance

Charge conservation


v2

Background


Ψ2


�a,b =�cos(�a1 + �b

2�2�2)�

Δγ→0, v2→0

Δγ→0, v2 ≠ 0

Jet-fragmentation Ψ2 ?


Anatomy of three-particle correlationsSearch of early time charge separation → should be long-range in Δη

STAR preliminary

-0.002

-0.001

0

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8

(All-charge) U+U 193 GeV (30-40%)

⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt

∆η12

fitShort-range-positive

Residualpedestal

C112(∆η12) = A+

SRe−(∆η)2/2σ2

SR −A−

IRe−(∆η)2/2σ2

IR +ALR


t

z

Δη1

τ3τ2τ1

Δη

2Δη

3

-

--

+

++



Short-range-positive

Short-range limit : C112 = ⟨cos(φ1(η1)+φ2(η2)−2φ3)⟩ ≥ 0∆φ → 0,∆η → 0 :

STAR preliminary

-0.002

-0.001

0

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8


⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt

∆η12


Residualpedestal

C112(∆η12) = A+

SRe−(∆η)2/2σ2

SR −A−

IRe−(∆η)2/2σ2

IR +ALR


t

z

Δη1

τ3τ2τ1

Δη

2Δη

3

-

--

+

++



ResidualShort-range-positive

Short-range limit : C112 = ⟨cos(φ1(η1)+φ2(η2)−2φ3)⟩ ≥ 0∆φ → 0,∆η → 0 :

STAR preliminary

-0.002

-0.001

0

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8


⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt

∆η12


Residualpedestal

C112(∆η12) = A+

SRe−(∆η)2/2σ2

SR −A−

IRe−(∆η)2/2σ2

IR +ALR


t

z

Δη1

τ3τ2τ1

Δη

2Δη

3

-

--

+

++


-0.002

0

0.002

0.004

0.4 0.8 1.2 1.6

70-80%

U+U 193 GeV

opposite-sign

∆η12

-0.001

0

0.001 30-40%

U+U 193 GeV

opposite-sign

⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt


Residual

-0.0002-0.0001

0 0.0001 0.0002 0-5%

U+U 193 GeV

opposite-sign

-0.002

0

0.002

0.4 0.8 1.2 1.6

70-80%

U+U 193 GeV

same-sign

∆η12

-0.003

-0.001

0.001 30-40%

U+U 193 GeV

same-sign

⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt


Residual

-0.0004-0.0002

0 0.0002 0-5%

U+U 193 GeV

same-sign

18

Comparison between U+U centralities

STAR preliminary STAR preliminary

Opposite-signSame-sign

Peripheral

Central

Very different trend between central and peripheral events


ResidualShort-range-positive

Comparison between U+U centralities

STAR preliminary

STAR preliminary

Central

Peripheral

-0.004

-0.002

0

0 0.4 0.8 1.2 1.6

70-80%

U+U 193 GeV

∆η12

-0.004

-0.002

030-40%

U+U 193 GeV

⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt

opposite-signsame-sign

-0.004

-0.002

00-5%

U+U 193 GeV

0

0.001

0.002

0.003

0 0.4 0.8 1.2 1.6

70-80%

U+U 193 GeV

∆η12

0

0.001

0.002

0.003

30-40%

U+U 193 GeV

⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt


0

0.001

0.002

0.003

0-5%

U+U 193 GeV


Centrality dependence of charge separation

STAR preliminary

�a,b � �cos((�a1 + �b

2 � 2�3))�v2{2} � �� = �OS��SS

After short-range-positive subtraction, Δγ → 0 for small & large Npart

Short-range positive component: Likely HBT, Coulomb & jet-fragmentation in peripheral eventsOnly HBT, Coulomb in central events.

Residual component:May still have short-range backgrounds in mid-central events

Charge separation :

STAR preliminary

Widths of different componentsMagnitudes of different components

0.01

0.1

1

10

0 100 200 300 400

U+U 193 GeV

σ∆η

Npart

Short-range-positiveResidual

0

0.01

0.02

0.03

0 100 200 300 400 500

U+U 193 GeV

∆γ

× N

part

Npart

TotalResidual



Opposite-signSame-signComparison between U+U and p+Au

STAR preliminary

STAR preliminary

p+A

Peripheral

Central

A+A

A+A

Min-bias

p+Au data are consistent with peripheral U+U

-0.002

0

0.002

0.004

0.4 0.8 1.2 1.60-100% p+Au 200 GeV

opposite-sign

∆η12


Residual

-0.002

0

0.002

0.004

70-80% U+U 193 GeV

opposite-sign

⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt

-0.001

0

0.001

30-40% U+U 193 GeV

opposite-sign

-0.002

0

0.002

0.004

0.4 0.8 1.2 1.60-100% p+Au 200 GeV

same-sign

∆η12


Residual

-0.002

0

0.002

0.004 70-80% U+U 193 GeV

same-sign

⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt

-0.002

0

0.002 30-40% U+U 193 GeVsame-sign



Comparison between U+U and p+Au

STAR preliminary

STAR preliminary

Short-range subtracted component vanishes in p+Au

p+A

Peripheral

Central

A+A

A+A

Min-bias

Residual

-0.004

-0.002

0

0 0.4 0.8 1.2 1.6

0-100% p+Au 200 GeV

∆η12

-0.004

-0.002

070-80% U+U 193 GeV

⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt


-0.004

-0.002

030-40% U+U 193 GeV

0

0.001

0.002

0.003

0 0.4 0.8 1.2 1.6

0-100% p+Au 200 GeV

U+U 193 GeV

∆η12

0

0.001

0.002

0.003

70-80% U+U 200 GeV

U+U 193 GeV

⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt

0

0.001

0.002

0.003

30-40% U+U 200 GeV

U+U 193 GeV




0

0.01

0.02

0.03

0 100 200 300 400

U+U 193 GeV

(γO

S -γSS

)× N

part

Npart


STAR preliminary

MC-Glauber


0

5

10

15

20

0 100 200 300 400-⟨ B2 c

os(2

(ΨB

- Ψ2)

) ⟩ [

fm-4

]

Npart

U+U 193 GeV

Ψ2

B

0<Ψ2<2π0<Ψ2<2π 0<ΨB<2π

BB

23

Data (short-range-positive subtracted)


Ultra-Central A+A

STAR preliminary

-0.002

0

0 0.4 0.8 1.2 1.6

0-100% p+Au 200 GeV

∆η12

-0.002

070-80% U+U 193 GeV

⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt -0.002

00-1% U+U 193 GeV


-0.002

0

0 0.4 0.8 1.2 1.6

0-100% p+Au 200 GeV

∆η12

-0.002

070-80% U+U 193 GeV

⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt -0.002

00-1% U+U 193 GeV


-0.002

0

0 0.4 0.8 1.2 1.6

0-100% p+Au 200 GeV

∆η12

-0.002

070-80% U+U 193 GeV

⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt -0.002

00-1% U+U 193 GeV


Projected B-field in A+A

0

5

10

15

20

0 100 200 300 400-⟨ B2 c

os(2

(ΨB

- Ψ2)

) ⟩ [

fm-4

]

Npart

U+U 193 GeV

{x,y}=〈x〉, 〈y〉

MC-Glauber Chatterjee, Tribedy,

PRC 92, 011902 (2015)



0

0.01

0.02

0.03

0 100 200 300 400

U+U 193 GeV

(γO

S -γSS

)× N

part

Npart


STAR preliminary

MC-Glauber


0

5

10

15

20

0 100 200 300 400-⟨ B2 c

os(2

(ΨB

- Ψ2)

) ⟩ [

fm-4

]

Npart

U+U 193 GeV

Ψ2

B

0<Ψ2<2π0<Ψ2<2π 0<ΨB<2π

BB

24


Ultra-Central A+A

STAR preliminary

-0.002

0

0 0.4 0.8 1.2 1.6

0-100% p+Au 200 GeV

∆η12

-0.002

070-80% U+U 193 GeV

⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt -0.002

00-1% U+U 193 GeV


-0.002

0

0 0.4 0.8 1.2 1.6

0-100% p+Au 200 GeV

∆η12

-0.002

070-80% U+U 193 GeV

⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt -0.002

00-1% U+U 193 GeV


-0.002

0

0 0.4 0.8 1.2 1.6

0-100% p+Au 200 GeV

∆η12

-0.002

070-80% U+U 193 GeV

⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt -0.002

00-1% U+U 193 GeV



0

0.01

0.02

0.03

0 100 200 300 400

U+U 193 GeV

(γO

S -γSS

)× N

part

Npart


STAR preliminary

MC-Glauber


0

5

10

15

20

0 100 200 300 400-⟨ B2 c

os(2

(ΨB

- Ψ2)

) ⟩ [

fm-4

]

Npart

U+U 193 GeV

Ψ2

B

0<Ψ2<2π0<Ψ2<2π 0<ΨB<2π

BB


0

5

10

15

20

0 100 200 300 400-⟨ B2 c

os(2

(ΨB

- Ψ2)

) ⟩ [

fm-4

]

Npart

U+U 193 GeV

{x,y}=〈x〉, 〈y〉

Peripheral A+A



PRC 92, 011902 (2015)



0

0.01

0.02

0.03

0 100 200 300 400

U+U 193 GeV

(γO

S -γSS

)× N

part

Npart


STAR preliminary

MC-Glauber


0

5

10

15

20

0 100 200 300 400-⟨ B2 c

os(2

(ΨB

- Ψ2)

) ⟩ [

fm-4

]

Npart

U+U 193 GeV

Ψ2

B

0<Ψ2<2π0<Ψ2<2π 0<ΨB<2π

BB


0

0.01

0.02

0.03

0 100 200 300 400

U+U 193 GeV

(γO

S -γSS

)× N

part

Npart


STAR preliminary

MC-Glauber


0

5

10

15

20

0 100 200 300 400-⟨ B2 c

os(2

(ΨB

- Ψ2)

) ⟩ [

fm-4

]

Npart

U+U 193 GeV

Ψ2

B

0<Ψ2<2π0<Ψ2<2π 0<ΨB<2π

BB

25



Ultra-Central A+APeripheral A+ABelmont, J.L. Nagle 1610.07964

p+A

0<Ψ2<2π

B

STAR preliminary-0.002

0

0 0.4 0.8 1.2 1.6

0-100% p+Au 200 GeV

∆η12

-0.002

070-80% U+U 193 GeV

⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt -0.002

00-1% U+U 193 GeV


0

5

10

15

20

0 100 200 300 400-⟨ B2 c

os(2

(ΨB

- Ψ2)

) ⟩ [

fm-4

]

Npart

U+U 193 GeV

{x,y}=〈x〉, 〈y〉



PRC 92, 011902 (2015)

https://arxiv.org/find/nucl-th/1/au:+Belmont_R/0/1/0/all/0/1

https://arxiv.org/find/nucl-th/1/au:+Nagle_J/0/1/0/all/0/1



0

0.01

0.02

0.03

0 100 200 300 400

U+U 193 GeV

(γO

S -γSS

)× N

part

Npart


STAR preliminary

MC-Glauber


0

5

10

15

20

0 100 200 300 400-⟨ B2 c

os(2

(ΨB

- Ψ2)

) ⟩ [

fm-4

]

Npart

U+U 193 GeV

Ψ2

B

0<Ψ2<2π0<Ψ2<2π 0<ΨB<2π

BB


0

0.01

0.02

0.03

0 100 200 300 400

U+U 193 GeV

(γO

S -γSS

)× N

part

Npart


STAR preliminary

MC-Glauber


0

5

10

15

20

0 100 200 300 400-⟨ B2 c

os(2

(ΨB

- Ψ2)

) ⟩ [

fm-4

]

Npart

U+U 193 GeV

Ψ2

B

0<Ψ2<2π0<Ψ2<2π 0<ΨB<2π

BB

26



Ultra-Central A+APeripheral A+AShort-range-positive

component subtracted charge separation vanishes the same

way as projected B-field

Belmont, J.L. Nagle 1610.07964

p+A

0<Ψ2<2π

B


0

0 0.4 0.8 1.2 1.6

0-100% p+Au 200 GeV

∆η12

-0.002

070-80% U+U 193 GeV

⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt -0.002

00-1% U+U 193 GeV


0

5

10

15

20

0 100 200 300 400-⟨ B2 c

os(2

(ΨB

- Ψ2)

) ⟩ [

fm-4

]

Npart

U+U 193 GeV

{x,y}=〈x〉, 〈y〉

Terra Ignota (Need Isobars)



PRC 92, 011902 (2015)




— Ultra-central U+U and Au+Au show Δγ ~0, v2≠0

• Δγ vs v2 consistent with B-field vs ε2, constrain for background models of charge separation

—Short-range-positive component (ASR) subtracted charge separation vanishes in central & peripheral events

— p+Au data show no ASR subtracted charge separation, consistent to peripheral A+A

• ASR subtracted signal follow projected B-field in central, peripheral A+A & in p+Au

27

Summary

Current data helped to disentangle signal/background in the limits of vanishing projected B-field. Isobar collisions at RHIC will help clarify the origin of charge separation in the regime of finite B-field.

0

0.2

0.4

0 0.02 0.04

∆γ

× 10

4

v2 {2}


U+UAu+A

uSTAR preliminary

STAR preliminary

-40

-20

0

0 0.4 0.8 1.2 1.6

p+Au 200 GeV

C11

2 ×

Npa

rt

×

104

∆η12


-40

-20

0

0 0.4 0.8 1.2 1.6

U+U 193 GeV (70-80%)

C11

2 ×

Npa

rt

×

104

∆η12


STAR preliminary

+

+

+


backup slides

28



0

0.01

0.02

0.03

0 100 200 300 400

U+U 193 GeV

(γO

S -γSS

)× N

part

Npart


STAR preliminary

MC-Glauber


0

5

10

15

20

0 100 200 300 400-⟨ B2 c

os(2

(ΨB

- Ψ2)

) ⟩ [

fm-4

]

Npart

U+U 193 GeV

Ψ2

B

0<Ψ2<2π0<Ψ2<2π 0<ΨB<2π

BB


0

0.01

0.02

0.03

0 100 200 300 400

U+U 193 GeV

(γO

S -γSS

)× N

part

Npart


STAR preliminary

MC-Glauber


0

5

10

15

20

0 100 200 300 400-⟨ B2 c

os(2

(ΨB

- Ψ2)

) ⟩ [

fm-4

]

Npart

U+U 193 GeV

Ψ2

B

0<Ψ2<2π0<Ψ2<2π 0<ΨB<2π

BB

29



Ultra-Central A+APeripheral A+AShort-range-positive

component subtracted charge separation vanishes the same

way as projected B-field

Belmont, J.L. Nagle 1610.07964

p+A

0<Ψ2<2π

B


0

0 0.4 0.8 1.2 1.6

0-100% p+Au 200 GeV

∆η12

-0.002

070-80% U+U 193 GeV

⟨cos

(φ1

+ φ 2

- 2φ

3)⟩ ×

Npa

rt -0.002

00-1% U+U 193 GeV


Terra Ignota (Need Isobars)


0

0.4

0.8

1.2

0 100 200 300 400

U+U 193 GeV

Y/⟨Y⟩ m

ax

Npart

Y=-⟨ B2 cos(2(ΨB - Ψ2)) ⟩Y=v2 {2}




Outlook for Isobar collisions at RHIC

Zr +Zr Ru +Ru Au +Au

Idea is to change B-field without changing background

Single collision in IP-Glasma model (b=0)

Ru4496

Ru4496+ Zr40

96Zr40

96+

Different B-field with same flow background is expected √s =200 GeV

% Most central0 20 40 60 80

part

* N

γ∆

0

0.01

0.02

Ru+RuZr+Zr

(a)

= 200 GeVNNs

80% bgprojection with 1.2B events

% Most central0 20 40 60 80

(Ru+

Ru

- Zr+

Zr)

γ∆

Rel

. dif.

in

0.1−

0.05−

0

0.05

0.1 = 200 GeVNNs

(b)

)2∈ from σ rel. dif. (5γ∆

rel. dif. (case 1)2∈ rel. dif. (case 2)2∈

3.5 weeks of running with about 1.2 B events can provide about 5σ confidence of signal/bkg.

Gang Wang, QCD Chirality workshop ‘2016, Deng et al PRC 94, 041901 (2016), Skokov et al, 1608.00982

31

v2

Δγ

B-field driven

0

v2

Δγ


All Bkg

B-field

Total

Δγ ~0

v ~02

min

Δγmax

v2,max


v2

Δγ


All Bkg

B-fieldTotal

Δγ ~0

v ≠02

Δγmax

0min

v2,max


v2

Δγ

0


Flow driven

Documents

Disentangling ﬂow and signals of Chiral Magnetic Effect in ... · A 661 (2012) S110–S113 12/02/16 Time-Projection Chamber (used for this analysis) STAR Detector a,b v 2{2}2 =