Strange and Multistrange Hadrons v2 From RunV 200GeV Cu Cu Collisions

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Strange and Multi-strange Hadrons v2 From Run-V
200GeV CuCu Collisions
Shusu Shi For group meeting
Many thanks to J.H. Chen, Y. Lu, X.H. Shi
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Overview

• Motivation
• Analysis
• Results
• Summary and outlook

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Motivation

• Study the colliding size dependence of v2.
• Test mass ordering and NQ scaling first observed
  at AuAu collision.
• Test the early thermalization hypothesis at RHIC.
• Study non-flow using Ftpc reaction plane.

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Event and Track Selection
Used events
Centrality bins 10 20 30 40 50 60
140 103 74 53 37 25
1. Reactionplane from FTPC can suppress some of
the non-flow correlation and auto correlation
effects. 2.Comparing the v2 results from FTPC
reactionplane with TPC reactionplane can help us
understand the non-flow effects.
Tracks used for FTPC reaction
plane Primary
tracks 5 lt nFitHits lt 11 0.52 lt
gnHitsFit/gnHitsPoss lt 1.05 0.1 lt pT lt 2.0
GeV/c 2.5lteta lt 4.0
Tracks used for TPC reaction plane
Primary tracks nFitHits gt
16 gnHitsFit/gnHitsPoss gt 0.52
0.15 lt pT lt 2.0 GeV/c
eta lt 1.0 gDcalt2.0
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FTPC and TPC NHitsFit distributions
(a)
(b)
(c)
(d)

• (a) Eta distribution for primary tracks.
  (b) NHitsFit distribution for primary tracks.
• NHitsFit distribution for FTPC tracks (d)
  NHitsFit distribution for TPC tracks.
• (2.5lt h lt4.0)
  (hlt1.0)

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Phi distributions
Phi distributions

• West
• FarWest
• East
• FarEast

(a)
(b)
1. We remove the detector bias by applying phi
weights to the tracks. 2. Phi weights are
generated by inverting the normalized phi
distributions of detected tracks for a large
event sample. 3. Phi weight corrections are done
day by day, centrality by centrality
(c)
(d)
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Shifting Corrections
Equation (1) and (2) define the event flow vector
Q2 and the event plane Angle ?2 (The subscript 2
means we use the second harmonic)
(1)
(2)
If the detector has only minor inefficiency, both
of east reaction plane and west reaction plane
will be flat. In the reality, they are not
because of the severe loss of acceptance at some
places in FTPC Then we need step 2. Apply
shifting method on east reaction plane and west
reaction plane. The shifting method will force
any distribution to be flat. So both of them will
become perfectly flat if you do it correctly.
(n1,2,3,4 )
J.Barrette et al. Phys. Rev. C56 (1997)3254
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Reaction plane distribution
(a) West
(b) East
Red line stands for distributions after weight
correction Black line stands for distributions
after shift correction Correction term up to n
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(a) West East FTPC.
(d) TPC
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Reaction plane resolution for FTPC
(b)
(a)
(a) Distribution of for FTPC (b) Upper
Reaction plane resolution for FTPC
Lower Reaction plane resolution for TPC (The
first bin stands for the resolution of 0-60
centrality)
Resolution of 0-60 centrality FTPC 0.171 /-
0.004 (Using West and East as sub-events). TPC
0.552 /- 0.001
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200GeV CuCu Collisions Resolution

• 0 60 Minibias Events 3.5M
• FTPC 0.17
• TPC 0.552

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V0 Reconstruction
Cuts selection criteria for Ks
Cuts selection criteria for Lamdas
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Distribution of ?S0 invariant mass
? data Blue S B Red B 9 phi bins
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Distribution of ? invariant mass
? data Blue S B Red B 9 phi bins
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Fitting v2 of ?S0 and ?
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?
V2 can be extracted by fit to ltcos(2f)gt
distribution with equation
pt
minv
ltcos(2f)gt
ltsin(2f)gt
signal background background
sig/(sigbgnd) bgnd/(sigbgnd)
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v2 of ?S0 and ? (0-60)
v2TPC results are similar for CuCu 0-60 and
AuAu 0-80 . CuCu v2FTPC increase with pt and
then saturate. v2FTPC lt v2TPC, this indicates
non-flow effect is reduced using FTPC reaction
plane.
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Compare with Sergeis
CuCu 200 GeV ?S0 and ? 20-60 results are from
Sergei and 0-60 results are from Shusu. 0-60
v2 is reasonably smaller than 20-60 v2.
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NQ Scaling in 200Gev CuCu Collisions
Fig1. CuCu 200GeV ?S0 and ? v2 using FTPC
reaction plane i) at low pT, consistent with
mass ordering ii) at intermediate pT, consistent
with particle type dependence, which are first
observed at AuAu 200 GeV.
Fig2. ?S0 and ? v2 is consistent with NQ scaling.
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Combine with v2 of ?
? has sizable v2 with ?S0 and ? . Need full
statistics for ? v2.
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Summary

• Preliminary 200 GeV CuCu ?S0, ? and ? v2.
• 3.5 M events are used. 20 M in total is coming.
• Use FTPC reaction plane to reduce non-flow
  effect.
• v2FTPC is smaller than v2TPC.
• At low pt, v2 is consistent with mass ordering
• At intermediate pt, v2 is consistent with NQ
  scaling.
• ? peak is seen

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?
V2 can be extracted by fit to ltcos(2f)gt
distribution with equation
pt
minv
ltcos(2f)gt
ltsin(2f)gt
signal background background
sig/(sigbgnd) bgnd/(sigbgnd)
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Outlook

• Full statistics (20M) is coming.
• ? v2
• Compare with results from 200Gev AuAu collisions
  v2 /?
• Systematics.