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Nuclear modification and elliptic flow measurements for mesons at sNN = 200 GeV d+Au and Au+Au

collisions by PHENIX

Dipali Palfor the PHENIX collaboration

Vanderbilt University

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Outline

• Motivation

• meson spectra at different centralities

• Nuclear modification factors for the mesons

• Elliptic flow of the mesons

• Summary and outlook

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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”?

Au + Au @ √sNN = 200 GeV

PHENIX

Motivation: Baryon/meson anomaly

meson has a mass similar to a proton.

Appropriate probe to address the baryon/meson puzzle.

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K+K- measurement in PHENIX

Number of events analyzed:

Spectra: 409 M for TOF

170M for PbSc

Elliptic flow: 800 M

separation in TOF0.3 < p (GeV/c) < 2.5

separation in EMCal: 0.3 < p(GeV/c) < 1.0

Four independent K+K- pairing

TOF – TOF (9% of the total ’s)TOF – PbSc (East) (27% of the total ’s)PbSc(East) – PbSc(East) (9% of the total ’s)PbSc(West) – PbSc(West) (55% of the total’s)

Allows a self-consistent measurement on .

K+K- pairing topology

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meson reconstruction technique

Combinatorial background (CB) is estimated by event mixing.

Normalized to 2(N++.N--), N++ and N– are like sign measured yields.

Signal = Same event - CB

Experimental mass resolution ~ 1 MeV/c2

Better than mass width.

Subtracted spectrum is fitted with Relativistic Breit Wigner convolved with Gaussian mass resolution.

Centroid and width are consistent with PDG.

Number of mesons analyzed Spectra: ~ 44KElliptic flow :~ 180K

<m> = 1.01891 ± 0.00003 (stat) ± 0.00085 (syst) GeV/c2

= 4.22 ± 0.09 (stat) ± 0.506 (syst) MeV/c2

Subtracted spectrum

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• Raw yield extraction N (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: K+K- pair MC through PHENIX simulation chain.– Efficiency: time (experimental run) dependent variations.– Occupancy dependent corrections: Embedding simulated

K+K- pairs into the real data.

Spectra: raw yields to absolutely normalized spectra

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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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meson spectra at different centralities

Talk by A. Kozlov [6(b)]

Poster by D. Pal (158)

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

0.0074 ± 0.0007 ± 0.0020 391 ± 25 ± 50pp

Au

+ A

u @

200

GeV

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Scaling of protons and spectra

Ncoll scaled spectra vs pT compared to protons

Radial Flow at low-pT At intermediate pT, (anti)protons scale with Ncoll

No Ncoll scaling for Baryon/meson effect? Or mass effect?

Quantify nuclear effects by Central-to-peripheral ratios (Rcp) andratio of Au-Au central to pp yields (RAA).

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Two extreme centrality classes show Completely different scales of suppression.

Mesons ( and ) in Au+Au 0 – 10% (most central) are suppressed to the same extent.

They are least (or almost not) suppressedin 60-90% (most peripheral)

Protons are not suppressed anywhere.

Baryons and mesons show a clear difference.

pp

AuAuAA Yield

)Ncoll/Yield(R

What about other centralities?

Suppression of the mesons decreasesfrom central to peripheral.

Two extreme centrality classes show completely different scales of suppression.

Mesons ( and ) in Au+Au 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.

Nuclear modification factors, RAA

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Nuclear modification factor, Rcp

Peripheral

Centralcp )Ncoll/Yield(

)Ncoll/Yield(R

Au + Au collisions show suppressionsfor mesons( and ) and no suppression for the protons and ’s.

d+Au 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 @ √sNN = 200 GeV

Au + Au @ √sNN = 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

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

Peripheral Central

100 – centrality(%)100 – centrality(%)

Peripheral Central

• Reaction plane resolution:sqrtcos2BBCSBBCN

Reaction plane

Extraction of uncorrectedv2 from azimuthal distribution

Reaction plane resolutioncorrection factor

v2 = v2(obs).

v2 measurement in PHENIX

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v2 extraction of

Azimuthal distribution of mesonsFitted with the function:

dN/d()=A [1+2v2(obs)cos2()]

The p1 parameter in the figure is the uncorrected v2.

v2(obs)v2 = R.P. Resolution correction

1.0 < pT (GeV/c) < 1.5 1.5 ≤pT (GeV/c) < 2.0 2.0 ≤pT (GeV/c) < 3.0

v2(obs) = 0.0250 +/- 0.0137v(obs) = 0.0338 +/- 0.0091v2(obs) = 0.0198 +/- 0.0071

Minimum bias Minimum bias Minimum bias

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v2 vs pT

Non-zero v2 observed for mesons

Statistically, it is consistent withother hadrons.

Minimum bias

With present error bar, the quarknumber-scaled meson v2 is

consistent with other hadrons.

Talk by H. Masui, Poster by A. Taranenko (identified hadron v2)

PHENIX Preliminary

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Summary• PHENIX has measured mesons in K+K- decay channel with its full

central arm. K+K- spectra at seven centrality bins have been measured within

1.2 < mT (GeV/c2) < 4.4.

• Nuclear modification factors, Rcp and RAA

in Au-Au collisions exhibits dramatic suppression of ’s like other mesons.

• Rcp in d-Au clearly demonstrate absence of any suppression for the mesons.

• v2 ofhas been measured for the first time. It is non-zero for intermediate pT.

v2 of 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( = A(1+2v2(obs)cos2( – 2)) -- Fit azimuthal distribution of with this function with v2 as a fitting parameter.

• Method 2: v2 (obs) = <cos2(2)> for the 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 ofas: v2(obs) = [NS+B v2(S+B) – NB v2(B)]/NS

S+B = Signal + CB

v2 = v2(obs)/ = Reaction plane resolution = 1/sqrt(2 <cos2(2(BBCS) – 2(BBCN))>)

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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KK in pp collisions: Comparison with STAR