K*0 analysis in Pb-Pb collision at √sNN = 2.76 TeV

Subhash SinghaNISER, Bhubaneswar

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India-ALICE Collaboration Meeting27-28 April 2013

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Outline:

--- Motivation

--- Data Sets and analysis detail

--- Mass/Width as a function of pT

--- Systematic error extraction

--- Corrected pT spectra

--- Particle ratio: K*0/K-

--- Summary

Re-scattering

time

Re-generation

Kinetic freeze out

Lifetime of resonances are comparable to the lifetime of fireball sensitive to the properties of the medium.

Re-scattering and re-generation:

K*0/K

Centrality

Qualitative plot

(K*0/K)AA and (K*0/K)pp re-scattering / re-generation effects.

Lifetime(fm/c)

K*0 4

ϕ 45

Motivation

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Data Sets: Pb-Pb/AOD04990 Good Runs with No V-drift problems

Data Set

00 to 20 ===> 3.05627e+0620 to 40 ===> 3.04396e+0640 to 60 ===> 3.04714e+0660 to 80 ===> 3.06153e+0600 to 80 ===> 1.22089e+07

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Event, Track and PID selection

Track Selection: --- pT > 0.15 GeV/c.--- |η| < 0.8--- |(DCA)r (pT)| < 0.018 + 0.035pT -1.01

--- |(DCA)z|< 2 cm--- ITS and TPC refits.--- min cluster in TPC: 70--- max Chi-square in TPC: 4--- Kπ pair rapidity |y|< 0.5

PID Selection: |Nσ| < 2.0 (using TPC only)Decay Channel:

K*0 K+ π- , K- π+ (BR: 66%)

Event Selection: Physics Selections, |vZ| < 10 cm

Centrality Selection: using V0M

Standard 2010 track quality cuts with filterbit 32

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K*0 Signal extraction: Event Mixing (EM) and Like Sign (LS) distributions

Kπ invariant mass distribution

Background estimated using:

Event mixing techniqueLike Sign technique

Event mixing:

Number of mixed events = 510 bins in Z vertex (-10, 10)10 bins in centrality (0,100)12 bins in event plane angle (0,2π)

Like Sign:

€

NK*0 = NK1

+π 1− +N

K1−π 1

+ − R × NK1

+π i− +N

K1−π i

+ +NK i

+π 1−

i

∑ +NK i

−π 1+

⎛

⎝ ⎜

⎞

⎠ ⎟

€

NK*0 = NK1

+π 1− +N

K1−π 1

+ − 2 × NK1

+π 1+ × N

K1−π 1

−

R Normalization factor

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Example of K*0 Signal extraction

0.8 < pT < 1.2 GeV/c2 0.8 < pT < 1.2 GeV/c2

The combinatorial background is normalized in the invariant mass region (1.1, 1.3) GeV/c2

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0.8 < pT < 1.2 GeV/c2 0.8 < pT < 1.2 GeV/c2

Where

After combinatorial background subtraction, signal is fitted with a p-wave relativistic Breit Wigner function

Example of K*0 Signal extraction

Mass(M0) and width(Γ0) extractedfrom fit parameters

BW

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Mass of K*0 as a function of pT

Mass consistent with PDG value

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Width of K*0 as a function of pT

Width consistent to PDG value

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Mass and Width of K*0: comparison with MC

Mass and width consistent with MC HIJING simulations

K* signal in MC HIJING

0-20%

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List of Systematic checks:

Varying fitting ranges

Varying normalization regions

Varying residual backgrounds (poly2 vs. poly3)

Keeping free width vs. fixed PDG width

Varying Non Rel. BW and Rel. BW

Track Selections (10% constant as a function of pT)

PID : N sigma cuts

Material Budget. (1% constant as a function of pT)

Centrality Selection

Like Sign Method (consistency check)

Sources of systematic uncertainty

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Sources of systematic uncertainty in K*0 yield

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Sources of uncorrelated systematic uncertainty in K*0 yield

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pT Spectra of K*0: Tsallis Levy Fit

dN/dy and <pT> calculated usingdata in the measured region andfit in the extrapolation region.

€

1

Nevt

d2N

dpTdy=

A

T(m +T)× pT × exp(

− pT2 +m2 −m

T)

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pT Spectra of K*0: Boltzmann Gibbs Blast Wave Fit

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<pT> of K*0

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<pT> of ϕ, K*0 with π, K, p-bar

Increasing mass

<pT>ϕ ~ <pT>K*0 ~ <pT>pbar

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Particle ratio: K*0/K- vs Npart

K*0/K- ratio vs Npart hadronic rescattering for central collisions(?)

Log scale on Y-axis

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Particle ratio: K*0/K- vs √sNN

(K*0/K-)AA < (K*/K-)pp hadronic recattering (?)

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Particle ratio: K*0/K- vs (dN/dη) 1/3

K*0/K- vs (dN/dη)1/3 effect of size of the fireball (?)

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Summary:

-- Mass and width of K*0 consistent with PDG value.

-- <pT>ϕ ~ <pT>K*0 ~ <pT>pbar

-- K*0/K- ratio vs Npart hadronic rescattering for

central collisions(?)

-- (K*0/K-)AA < (K*/K-)pp hadronic recattering in AA

collision.

-- K*0/K- vs (dN/dη)1/3 effect of size of the fireball(?).

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Back Up Slides

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Correlated and uncorrelated errors

Eratio= Echeck/YdefEratio= √(E2check- E2

def)/Ydef

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Sources of uncorrelated systematic uncertainty in K*0 yield

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pT Spectra of K*0: Blast Wave predictions (0-20%)

Integral of BW function = 19.88Integral of K* = 15.22

Blast wave parameters:=========================================================beta_max = 0.878514<beta> = 0.644618 +- 0.002296 (e+ = 0.002262, e- = -0.002292)T = 0.096984 +- 0.002141 (e+ = 0.002103, e- = -0.002047)n = 0.725690 +- 0.011371 (e+ = 0.011362, e- = -0.011364)chi2 = 57.718817ndf = 124.000000=========================================================

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K*0 /K as a function of pT

Kaon

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K*0 and K spectra

Since the pT binning of Kaon and K*0 spectra are different, I have takenthe Kaon yields using the fit function Boltzmann Gibbs Blast Wave.

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K*0 (pT)/K(pT)

Linear scale Log scale

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K*0 (p*T)/K(pT)

p*T = pT (MK/MK*)

Linear scale Log scale

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After mass correction for radial flow

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K*0 BGBW model with parameters taking from Kaon

K*0 and K spectra: With BGBW model

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Comparison with preliminary analysis

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Comparison: K*0 Spectra

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K*0 : Mass/Width : Material Budget productions

Mat. Budg. Productions:LHC10h9 Pb-Pb Hijing (137366), 25 K events, +7% material

LHC10h10 Pb-Pb Hijing (137366), 25 K events, -7% material

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K*0 Signals

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K*0 signals : BW Fits (TPC analysis) 0-20%

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K*0 signals : BW Fits (TPC analysis) 20-40%

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K*0 signals : BW Fits (TPC analysis) 40-60%

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K*0 signals : BW Fits (TPC analysis) 60-80%

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Efficiency x Acceptance

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Efficiency x Acceptance

Production: LHC10a11a_bis/ESDs

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Efficiency of K* with different event and track selections

(0.3-5.0) in 0.5 GeV step

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(0.3-5.0) in 0.4 GeV step

Efficiency of K* with different pT combinations

Efficiency of K* and anti-K*

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Looking at K* and anti-K* separately

0-20%0-20%

0-20%An example:Comparison K+ π- and K- π+ distributions

Difference ~ 2%

K*/anti-K* signals : 0-80%

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K* Anti-K*

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Other plots