Nuclear modification and elliptic flow measurements for f mesons at sNN 200 GeV d Au and Au Au colli

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Nuclear modification and elliptic flow
measurements for f mesons at ?sNN 200 GeV dAu
and AuAu collisions by PHENIX
Dipali Pal for the PHENIX collaboration Vanderbilt
University
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Outline

• Motivation
• f meson spectra at different centralities
• Nuclear modification factors for the f mesons
• Elliptic flow of the f mesons
• Summary and outlook

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Motivation Baryon/meson anomaly
Au Au _at_ vsNN 200 GeV

• Baryon/meson puzzle
• ? Scaling properties of yields
• ? Different suppression
• ? Elliptic flow
• Quark number scaling of the elliptic flow
  parameter v2
• Mass effect or baryon/meson effect?

PHENIX

• f meson has a mass similar to a proton.
• Appropriate probe to address the baryon/meson
  puzzle.

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f ? KK- measurement in PHENIX
Number of events analyzed Spectra 409 M for
TOF 170M for PbSc Elliptic flow
800 M
p/K separation in TOF 0.3 lt p (GeV/c) lt 2.5 p/K
separation in EMCal 0.3 lt p(GeV/c) lt 1.0
KK- pairing topology
Four independent KK- pairing TOF TOF (9
of the total fs) TOF PbSc (East) (27 of the
total fs) PbSc(East) PbSc(East) (9 of the
total fs) PbSc(West) PbSc(West) (55 of the
total fs) ? Allows a self-consistent
measurement on f.

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f meson reconstruction technique
ltmgt 1.01891 0.00003 (stat) 0.00085 (syst)
GeV/c2 G 4.22 0.09 (stat) 0.506 (syst)
MeV/c2
Subtracted spectrum
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Spectra raw yields to absolutely normalized
spectra

• Raw yield extraction
• ? Nf (rec) (mT) Same event (mT) CB(mT)
• Yield is extracted by integrating the
  subtracted mass spectrum over a fixed mass window
  of 5 MeV with respect to the centroid.
• ? Optimized signal and S/B ratio.
• Corrections
• Acceptance KK- pair MC through PHENIX
  simulation chain.
• Efficiency time (experimental run) dependent
  variations.
• Occupancy dependent corrections Embedding
  simulated f?KK- pairs into the real data.

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Minimum-bias spectra

• Excellent agreement between the subsystems
• Understanding of the systematics.
• Run4 result is consistent with Run2.

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f meson spectra at different centralities
Centrality dN/dy T (MeV)
MB 1.08 0.04 0.20 388 5
27 0-10 3.80 0.30 0.72 372
11 26 10-20 2.32 0.16 0.44
394 10 27 20 30 1.62 0.11 0.31
397 10 28 30 40 0.95 0.07
0.18 401 10 28 40 50 0.75
0.04 0.13 377 8 26 50 60 0.35
0.03 0.06 392 12 27 60 90
0.11 0.01 0.02 348 11 24
Au Au _at_ 200 GeV
pp
0.0074 0.0007 0.0020 391
25 50

• Talk by A. Kozlov 6(b)
• Poster by D. Pal (158)

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Scaling of protons and f spectra
Ncoll scaled f spectra vs pT compared to
protons

• Radial Flow at low-pT
• At intermediate pT, (anti)protons
• scale with Ncoll
• No Ncoll scaling for f
• Baryon/meson effect? Or mass effect?

Quantify nuclear effects by Central-to-peripheral
ratios (Rcp) and ratio of Au-Au central to pp
yields (RAA).
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Nuclear modification factors, RAA

• Two extreme centrality classes show
• Completely different scales of suppression.
• Mesons (f and p0) in AuAu 0 10
• (most central) are suppressed to the
• same extent.
• They are least (or almost not) suppressed
• in 60-90 (most peripheral)
• Protons are not suppressed anywhere.
• ? Baryons and mesons show a clear
• difference.

Two extreme centrality classes show completely
different scales of suppression. Mesons (f and
p0) in AuAu 0 10 (most central) are
suppressed to the same extent. They are least
(or almost not) suppressed in 60-90 (most
peripheral) Suppression of mesons increases
from peripheral to central. Protons are not
suppressed anywhere. ? Baryons and mesons show
a clear difference.
Suppression of the mesons decreases from central
to peripheral.
What about other centralities?
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Nuclear modification factor, Rcp
Au Au _at_ vsNN 200 GeV

• Au Au collisions show suppressions
• for mesons(f and p0) and no suppression for the
  protons and Ls.
• dAu collisions (cold nuclear matter) shows no
  suppression for baryons or mesons.
• The anomalous meson suppression is a property of
  the hot and dense matter.

d Au _at_ vsNN 200 GeV
Poster by D. Pal (158), D. Mukhopadhyay (154)
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Elliptic Flow of baryons and mesons
At low pT hydro works remarkably well Above 2
GeV/c a split between mesons and
baryons Universal behavior in flow per quark
expected from recombination Need to measure v2
of f
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v2 measurement in PHENIX
Reaction plane Extraction of uncorrected v2 from
azimuthal distribution Reaction plane
resolution correction factor 1/D. v2
v2(obs).1/D
100 centrality()
100 centrality()
? Peripheral Central ?
? Peripheral Central ?

• Event reaction plane is determined by beam beam
  counter -- BBC South and BBC north

• Reaction plane resolution
• D sqrt(2 ltcos2(?2(BBCS)-?2(BBCN))gt)

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v2 extraction of f
Azimuthal distribution of f mesons Fitted with
the function dN/d(f-Y2)A 12v2(obs)cos2(f-Y)
The p1 parameter in the figure is the uncorrected
v2.
v2(obs) v2
R.P. Resolution correction
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v2 vs pT
Minimum bias
PHENIX Preliminary

• Non-zero v2 observed for f mesons
• Statistically, it is consistent with
• other hadrons.

With present error bar, the quark number-scaled f
meson v2 is consistent with other hadrons.
Talk by H. Masui, Poster by A. Taranenko
(identified hadron v2)
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Summary

• PHENIX has measured f mesons in KK- decay
  channel with its full central arm.
• f?KK- spectra at seven centrality bins have
  been measured within 1.2 lt mT (GeV/c2) lt 4.4.
• Nuclear modification factors, Rcp and RAA
• in Au-Au collisions exhibits dramatic
  suppression of fs like other mesons.
• Rcp in d-Au clearly demonstrate absence of any
  suppression for the f mesons.
• v2 of f has been measured for the first time. It
  is non-zero for intermediate pT.
• v2 of f scaled with number of quark follows
  universal quark number scaling within statistical
  errors.

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Outlook

Considerable improvements expected over the next
few months - A factor of 4 increase in
statistics for spectra analysis finer pT bins
and a wider range - Measurement of v2 as a
function of centrality - Fine tuning of the
cuts and additional statistics for elliptic flow
analysis may enable us to increase statistical
significance of the v2 signal.
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Backup slides
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v2 analysis methods

• Method 1
• dN/d(f-Y2) A(12v2(obs)cos2(f Y2))
• -- Fit azimuthal distribution of f with this
  function with v2 as a fitting parameter.
• Method 2
• v2 (obs) ltcos2(f-Y2)gt for the f mesons.
• Methods 1 and 2 are mathematically
  equivalent.
• Method 3
• Mesure v2 from the azimuthal distributions of
  the same event and CB and then extract
  uncorrected v2 of f as
• v2(obs) NSB v2(SB) NB v2(B)/NS
• SB Signal CB
• v2 v2(obs)/D
• Reaction plane resolution
• 1/sqrt(2 ltcos2(Y2(BBCS) Y2(BBCN))gt)

Three methods have extracted the same v2 value
for Phi mesons. Method 1 has been applied to the
full statistics of the data.
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f?KK in pp collisions Comparison with STAR