QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. STAR STAR Paul Sorensen Brookhaven National Laboratory for the STAR Collaboration for the STAR Collaboration STAR first measurements of event-by- first measurements of event-by- event event Elliptic Flow Elliptic Flow Fluctuations Fluctuations
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first measurements of event-by-event Elliptic Flow Fluctuations
STAR. first measurements of event-by-event Elliptic Flow Fluctuations. Paul Sorensen Brookhaven National Laboratory for the STAR Collaboration. motivation for this study 1) increase accuracy of v 2 2) gain sensitivity to initial conditions (CGC?) 1 and 2 are needed for estimates - PowerPoint PPT Presentation
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QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
STARSTAR
Paul SorensenBrookhaven National Laboratoryfor the STAR Collaborationfor the STAR Collaboration
STAR
first measurements of event-by-eventfirst measurements of event-by-event
q-vector and v2 related by definition: v2 = cos(2i)=q2,x/√M
sum over particles is a random-walk central-limit-theorem
width depends on• multiplicity: narrows due to failure of CLT at low M• non-flow: broadens gn = cos(n(i- j)) (2-part. correlations)• v2 fluctuations: broadens
J.-Y. Ollitrault nucl-ex/9711003; A.M. Poskanzer and S.A. Voloshin
nucl-ex/9805001
€
q x = Mv
simula
ted q
distrib
utio
n
j
j is observed angle for event j after summing over tracks i
analyzing the multiplicity analyzing the multiplicity dependencedependence
why isn’t it easy: non-flow (g2) broadens the distribution
fluctuations (v2) also broaden the distribution
how do we distinguish between v2 and g2:the width changes have a different dependence on the number of tracks: broadening from v2 scales with √M
analyze the same events sometimes use all tracks, sometimes fewer tracks
fit multiple distributions simultaneously: provides multiple provides multiple equations to solve for the 2 unknownsequations to solve for the 2 unknowns
Sanity checks:– fit to simulated data: do we get back what we put in? Test passed Test passed for for allall input values input values– fit data from combined centrality bins: does v2 increase as it should? Test passedTest passed– sensitivity to assumed shape of v2 distribution? we used a gaussian we used a gaussian and a function that describes the and a function that describes the partpart distribution: only small distribution: only small deviations in mean or rms <15%deviations in mean or rms <15%– fit using 2, 3, or 5 different multiplicities? some differences on range of allowed g2 values
q
simulated dN/dq
QuickTime™ and aTIFF (Uncompressed) decompressor
are needed to see this picture.
STARSTAR
STAR PreliminarySTAR Preliminary
centrality dependence of r.m.s. and mean ((vv22 and and vv22)) for 200 GeV
• using the multiplicity dependence of the |q| distribution we’ve measured v2 fluctuations (v2)
• uncertainty on v2 reduced
v2/v2 (rms/mean) is approximately 36% independent of centrality– agreement with NeXSPheRIO using a QGP EOS– also consistent with phenomenological scaling
v2=0.034*part*(dN/dy)1/3
• new probe for early stages of HI collisions– explore pseudorapidity dependence (v2
1v22 - v2
1v21)
to reveal dynamics beyond geometry– explore sensitivity to CGC– explore sensitivity to EOS (sys. errors on theory?)– explore sensitivity to critical point fluctuations