Azimuthal anisotropy in CuAu
collisions at RHIC-PHENIX
Hiroshi Nakagomi
Univ. of Tsukuba

Jan. 24th 2017

CiRfSE workshop

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Azimuthla anisotropy:Elliptic & triangular flow
Triangular flow v3

Au+Au 200GeV

Ψ3

Ψ2
Elliptic flow v2✓Initial spatial anisotropy εn -> Final momentum anisotropy vn- Converted through hydrodynamic expansion✓v2, v3 are sensitive to initial condition and viscosity of QGP- Theoretically, initial condition and viscosity have uncertainty
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Longitudinal structure
Initial geometry/density

Final momentum anisotropy

arXiv:12004.5814v2

Phys.Lett.B636:299-304
Glauber + Hydro
Au+Au 200GeV✓Similar geometry at whole η-Almost rapidity independent-Used in most models✓Density decrease at higher rapidity
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QGP+hadron fluid

QGP only✓Trapezoidal rapidity dependence- At higher rapidity, smaller energy
density makes smaller v2

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3Longitudinal flow fluctuation ?
atforward/backward
rapidity✓CMS observed flow fluctuation
X2-pc C(⌘a , ⌘b ,)=1+2

Vn (⌘a , ⌘b ) cos(nV n ( ⌘ a , ⌘b )rn (⌘a , ⌘b ) =Vn (⌘a , ⌘b )hvn ( ⌘a )vn (⌘b ) cos(n[=hvn (⌘a )vn (⌘b ) cos(n[)

aabη0n(⌘a )n (⌘a )n (⌘b )])in (⌘b )])i

Phys. Rev. C 92 034911•rn=1 → No flow fluctuation-vn(ηa)=vn(-ηa) & Ψn(ηa)=Ψn(-ηa)=Ψn(ηb)•rn<1 → F/B flow fluctuation-vn(ηa)≠vn(-ηa): εn(ηa)≠εn(-ηa)-Ψn(ηa)≠Ψn(-ηa)≠Ψn(ηb) : Twisted Ψn(η)

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Cu+Au collisions
Initial spatial anisotropy:ε2Collision picture
ε2,Au
ε2,Cu+Au
ε2,Cuε2,Aubeam axis

ε2,Cu✓First asymmetric Cu+Au collisions were operated in 2012
✓Asymmetric initial condition provides-Different Forward/Backward density and geometry-> Rapidity asymmetric vn-> Measurements of vn in asymmetric system could be goodstudy of longitudinal structureJan. 24th 2017

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5Result:η dependence of dN/dη and vn
Charged hadron dN/dη

Charged hadron v2

Charged hadron v3✓Au-going dN/dη > Cu-going dN/dη in Cu+Au collisions-Npart,Au> Npart,Cu→ Larger initial density in Au-going side
✓Au-going vn > Cu-going vn in Cu+Au collisions-Assume rapidity independent event plane-εn,Au> εn,Cu, Npart,Au> Npart,Cu→Asymmetry of vn is caused by geometry or energy density or bothJan. 24th 2017

CiRfSE workshop

6Result:Mid-η vn
Charged hadron v2

Charged hadron v3✓vn is plotted as function of mid-rapidity dN/dη(∝ energy density)- vn ∝ εn , energy density- At same dN/dη bin, the similar pressure gradient is expected.
✓v2 in Cu+Au collisions is always between those in Au+Au and Cu+Cu✓Unlike v2, Cu+Au v3 is consistent with Au+Au v3
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Result:Study of mid-η initial geometry✓Cu+Au v2/ε2 is consistent with Au+Au and Cu+Cu results→MC-Glauber reproduce ε2 well
✓Cu+A v3/ε3 is not consistent with Au+Au results→MC-Glauber might not reproduce ε3 correctlyJan. 24th 2017

CiRfSE workshop

8Result:F/B-η vn✓vn is plotted as function of f/b-rapidity dN/dη- Au-going dN/dη > Cu-going dN/dη✓Au-going side shows larger vn than Cu-going side
→Caused by difference of initial geometries between Au and Cu ?
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CiRfSE workshop

9Result:Study of f/b-η initial geometry for 2nd harmonics
Rapidity dependent ε2
Au

Boost invariant ε2
Cu

AuCu

✓Failed to scaled with rapidity dependence of ε2✓common ε2,Au-going = ε2,Cu-going is favored-F/B asymmetry is caused by dN/dη(initial energy density)
Jan. 24th 2017

CiRfSE workshop

10Result:Study of f/b-η initial geometry for 3rd harmonics
Rapidity dependent ε3
Au

Boost invariant ε3
Cu

AuCu

✓common ε3,Au-going = ε3,Cu-going is favored-F/B asymmetry is caused by dN/dη(initial energy density)✓Like mid-rapidity v3, MC-Glauber can not describe
system size dependence?
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CiRfSE workshop

11Summary
By studying azimuthal anisotropy in Cu+Au
collisions,✓Initial geometry at Forward/Backward iscommon between -4<η<+4✓F/B asymmetry of vn is caused by F/Basymmetry of initial density✓MC-glauber does not describe ε3 wellJan. 24th 2017

CiRfSE workshop

12Result:Study of f/b-η initial density
2Npart,Cu

Npart,Au(Cu)-going

2Npart,Au✓Weighted Npart scaling for CuAu dN/dη- Npart,Au(Cu)-going = wNpart,Au+(2-w)Npart,Cu (2Npart,Cu <Npart,Au(Cu)-going < 2Npart,Au)- Npart,Au and Npart,Cu are participants in Au and Cu, respectively✓Au-going side -> Npart,Au and Npart,Cu , Cu-going side -> Npart,Cu
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Azimuthal anisotropy:elliptic flow
Initial spatial anisotropy:ε2

Momentum anisotropy:v2pyypxxconverted thoughhydrodynamic expansion✓Initial spatial anisotropy ε2 -> Final momentum anisotropy v2- Non-isotropic pressure gradient✓Azimuthal anisotropy is strong probe!
- Clear origin -> initial spatial geometry- Influenced by hydrodynamic expansion

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Theory prediction of F/B asymmetry of εn and vn
Initial geometry
ε2,Backward ε2,midFinal momentum anisotropy v2

ε2,Forward
Pb+Pb 2.76TeV

beam axis
PhysRevC.90.034915✓Event by event, forward/backward vn might be asymmetric- initial participant geometries of the two nuclei would be different- Rapidity independent participant plane for εn and vn- εn,B < εn,Fvn,B < vn,F

➡ Initial geometry has strong rapidity dependenceJan. 24th 2017

CiRfSE workshop

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Event plane method
Event plane(EP) method- one of the flow measurement methods- produced particles are measured with respect to EP- EP is the azimuthal direction most particles are emitted to- observed vn is corrected by EP resolution< cos(n[vn =Res{Elliptic momentx

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Ψ2yφiobsn ]) >obs }n

Ψ3Triangular moment

yφix

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ε2 at F/B rapidity

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ε3 at F/B rapidity

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εn at mid-rapidity

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Initial model dependenceJan. 24th 2017

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