The	  η	  dependence	  of	  charged	  par/cle	  v2	  measurements	  	  using	  the	  Silicon	  Vertex	  detector	  at	  RHIC-­‐PHENIX	  *,+!% *(( )$!& '%$#!"Hiroshi	  Nakagomi	  for	  the	  PHENIX	  Collabora7on	  (Univ.	  of	  Tsukuba)	Measurement	  of	  v2	  using	  standalone	  VTX	  	  tracking	  	  	  	Introduc/on	&11!.

(0 /	  In	  heavy-­‐ion	  collisions,	  measurement	  of	  azimuthal	  anisotropy	  in	  emiFed	  par7cle	  $%(/momentum	  distribu7on	  is	  a-	  .one	  of	  the	  important	  themes	  for	  the	  inves7ga7on	  of	  Quark	  Gluon	  Plasma	  (QGP).	  For	  this	  measurements,	  we	  need	  to	  be	  able	  to	  measure	  the	  reference	  reac7on/event	  planes	  direc7on	  with	  good	  accuracy.	  	  	  	  In	  2011	  the	  Silicon	  Vertex	  detector	  (VTX)	  was	  installed	  in	  the	  RHIC-­‐PHENIX	  experiment.	  The	  VTX	  is	  composed	  of	  four	  layers,	  in	  which	  the	  inner	  two	  layers	  are	  built	  with	  pixel	  detectors	  and	  the	  outer	  two	  layers	  are	  built	  with	  strip	  detectors.	  The	  VTX	  can	  reconstruct	  charged	  par7cle	  tracks	  and	  iden7fy	  hadrons	  that	  include	  c/b-­‐quark.	  The	  reac7on	  plane	  reconstructed	  using	  the	  VTX	  is	  expected	  to	  have	  good	  resolu7on	  due	  to	  the	  wide	  eta	  acceptance	  of	  the	  detector,	  -­‐1	  to	  +1.	  	

In	  the	  following	  all	  plots	  ,	  	
  ü Use	  standalone	  VTX	  tracking.	  
ü Two	  types	  of	  systema7c	  error	  bars	  	  	  	  	  	  -­‐	  TypeA:track	  cut	  and	  RP	  varia7ons	  and	  sin	  term	  	  	  	  	  	  	  -­‐	  TypeB:diﬀerence	  to	  the	  ppg132	  point	  at	  1GeV/c	pT	  dependence	  of	  v2	  	  （|η|<0.5)	

pppg1320.20.2Systematic Error TypeB:)6(/5+4*0.2Systematic Error TypeA

9:7780.220 ~ 30 %30 ~ 40 %40 ~ 50 %50 ~ 60 %0.150.150.150.10.10.10.10.050.050.050.050.15

3$0'(*-.-,#1# 23

v2/(&*+!
(,*Silicon	  Vertex	  detector	.
,*+)'*(%&&'$#!""PHENIX	  	  detectors	p0000.511.5000.511.5p [GeV/c]
T0.1 20-30 %00.511.5p [GeV/c]η	  dependence	  of	  v2	p00.10.511.5p [GeV/c]

T0.1 30-40 %0p [GeV/c]

T40-50 %0.1

T50-60 %0.25<pt<1.0 [GeV/c]Systematic Error TypeASystematic Error TypeB0.080.080.080.060.060.060.060.040.040.040.040.020.020.020.02v20.08

ü Inner	  two	  layers:	  pixel	  layer	  ü Outer	  two	  layers:	  strip	  layer	0Central	  arms	
  Δη=0.7	  BBC	  North	
  Δη=0.8	  BBC	  South	  Δη=0.8	  VTX	  	
  Δη=2.4	 Wider	  η	  region!!	

-­‐1.2	 -­‐0.35	 0.35	 1.2	3.1	VTX	  is	  expected	  good	  Event	  Plane	  resolu7on	  !!	

η	3.9	<cos2(Ψ２((S)-­‐Ψ２(N)	  )>	BBC0.2

0<cos2(Ψ２((VTX0.5η)-­‐Ψ２(BBCSN)	  )>	1000.150.150.150.150.150.150.150.150.150.150.1	0.10.10.10.10.10.10.10.10.10.10.10.10.05	0.050.050.050.050.050.050.050.050.050.050.050.050000000

0000

0100 050100 050100 050100 050100 05012!

-2100 0-1050100 050100 050100 050100 0

502

!

-2

-10

5010012!

-2.54% !"%!"!54%!"!5!"$(!"!(!"!(!"$'!"!#!"!#!"$%!"!'!"!'!"$-1.5-16-7839-7:;!"!&!"!&!"!(-24Phys.	  Rev.	  C72,	  051901(R)	  (2005)	Systematic Error TypeB!"!%!"!% !"!'!""#$%&#'()'(#*"+,"-.
!"!$!"!$!"!%/01231045678#8598(95:734!
!"!5!"!5!
!

!"#$-0.500.5

!

$"#1

%1.5%"#2&2.5&"#'32 **+,-./01FIG. 3: Elliptic flow as a function of transverse momentum(v2 (pT )) for charged hadrons with 0 < η < 1.5 for the mostcentral 50% of the 200 GeV Au+Au inelastic cross section.
2 bars.
The one sigma 2statistical errors are shown as the errorThe gray boxes represent the systematic errors (90% C.L.).
The data points are located at the average pT position withina pT bin whose size is given by the horizontal error bars. Thecurve2 shows a calculation from hydrodynamics [24].

ü I	  compared	  our	  v 	  with	  PHOBOS’s	  v 	  .	  	  	  	  	  	  -­‐	  	  consistent	  within	  systema7c	  error.	  
ü I	  aFached	  v 	  measured	  in	  STAR.	  

-­‐4	-­‐2	

0	7!"!(!"!(v2{EP}STAR	6!"!#!"!#η	2	
4	<8=>?-@A7:;v2{LYZ}v2{PHOBOS}!"!'5!"!'4!"!&!"!&3!"!%!"!%centrality	  10-­‐40%	  0.15<pT	  <2.0	  [GeV/c]	  	  	2!"!$!"!$!1!"!5!"!5/7:+;5<%1#!""#$%&#'()'(-3-2-10
1η	?-@A7:;spectrometer, the transverse momentum dependence of!"!(!"!(!
=258>+;5<%1#!""#$%&#'()'(the flow strength v2 (pT ) can be measured. This isPhys.	  
Rev.	  C	  77	  (2008)	  54901	  	!"!#!"!#shown in Figure 3 for the top 0 − 50% centrality forFIG.
3: (Colorv2 curvefor charged hadrons from the Lee-Yang Zero Product Generating Functiotracks averaged over therange0 < η <online)1.5. The!"!' as a function of pseudorapidity. Both sets of data have beethe Event-Plane method (open circles),√shows the prediction of 0.15a hydrodynamicalmodel [24]. Asto 2.0 GeV/c and centrality from 10 to 40% of sNN = 200 GeV Au + Au collisions. For compa!"!&!"!&previously observed [2],(10–40%)
the v2 risespT increasesand shown.
[35]as(crosses)are alsoThe error bars are shown only for the statistical uncertaintieat pT above 1.5 GeV/c tends to flatten out well below!"!%!"!%the hydrodynamic curve.
!"!$In these analyses, the reaction plane is determinedin sub-events that are at different pseudorapidities from!
>'>%!
%'those where the v2 is measured. This should significantly
dTreduce the contribution of any non-flow effects to themeasured v2 , particularly those due to short-range correFIG. 4: Elliptic flow as a function of pseudorapidity (v2 (η))
lations. Comparisons of the v2 (pT ) result to the reactionfor charged hadrons from 200-GeV Au+Au collisions for theplane and cumulant methods results from reference [5],three different centrality classes described in the text, rangingaveraged over a similar centrality range, show that ourfrom peripheral to central (25 − 50%, 15 − 25%, 3 − 15%)from top to bottom. The triangles are the results fromresult is most consistent with the one obtained with thethe hit-based method, and the circles are from the trackfour particle cumulant method [25], suggesting that our0.2 (a)4th Poly. fitbasedmethod.
Theopencircles
arethe track-based resultstrack-based methodology is indeed largely immune to0-4

2ü VTX	  	  South	  side	  and	  North	  side	  Event	  Plane	  resolu7on	  is	  beFer	  than	  BBC.	  	  	  	  	  	  -­‐	  We	  can	  use	  Event	  Plane	  reconstructed	  by	  VTX.	  
ü We	  prepare	  various	  	  types	  of	  Event	  Planes.	  
ü v2	  	  is	  measured	  by	  standalone	  VTX	  tracking	  in	  p <1[GeV/c].	  	  	  	  	  	  -­‐	  Standalone	  tracking	  	  can	  be	  used	  for	  2-­‐p	  method	  and	  measurement	  of	  	  	  	  	  	  	  	  	  	  higher	  harmonics	  azimuthal	  anisotropy.	  
ü Consistent	  with	  PHOBOS’s	  result	  within	  systema7c	  error.	  

centrality[%]	100 01PHOBOS	  	  	  	  	  mean	  v2	  	  	  	  ・centrality	  25-­‐60%	  ・0<pT	20-60% 0.25<pT<1[GeV/c]

v20.15500Conclusion	  &	  Outlook	centrality[%]	0.1500.1

0-­‐3<η<-­‐2.5	  	  	  -­‐2.5<η<-­‐2.	  	  	  -­‐2<η<-­‐1.5	  	  	  	  -­‐1.5<η<-­‐1.	  	  -­‐1.<η<-­‐0.5	  	  -­‐0.5<η<0.	  	  	  	  0.<η<0.5	  	  	  	  0.5<η<1.	  	  	  	  	  1.<η<1.5	  	  	  	  	  1.5<η<2.	  	  	  	  	  2.<η<2.5	  	  	  	  	  2.5<η<3.	  
0.15	-1Comparison	  with	  PHOBOS	  v2	  /	  STAR	  v2	p0.02ü Divide	  VTX	  with	  0.5	  η	  slice.	  	  	  	  	  	  	  -­‐	  reconstruct	  	  12	  types	  of	  Event	  Plane.	  
ü Plot	  correla7on	  of	  	  each	  η	  slice	  plane	  	  	  	  	  	  	  and	  BBC	  S+N	  plane	  0.180-2!"!)VTX	  0.5	  η-­‐slice	  vs	  BBC	  S+N	  Correla7on	

p60

!

2

ü In	  the	  above	  centrality	  bins,	  η	  dependenc	  of	  v2	  	  looks	  ﬂat.	  	  	0.06VTX	  Event	  Plane	  resolu7on	  	  is	  beFer	  than	  BBC	  !!	

4010.04VTX:delta eta=12000!"$)VTX:delta eta=10-10.08South	  and	  North	  Correla7on	0.3-20Systematic Error TypeAEvent	  Plane	  Correla/on	  	

p0v2 (%)-­‐3.1	

-­‐3.9	BBC	  North	CNT	BBC	  	  South	VTX	VTX	  η	  coverage	  region	p

34