Nuclear modification of

transverse momentum spectra of

identified particles in Pb-Pb collisions at

√sNN= 2.76 TeV with ALICE

Simone SchuchmannGoethe-University of Frankfurt

International School of Nuclear Physics Probing the Extremes of Matter with Heavy Ions 2012, Erice

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 2

Outline

● Motivation

● L and K0s

– Reconstruction

– Nuclear modification factors: RCP and RAA

– Comparison to unidentified

charged particles and p(p), p+;-,K+;- RAA

● Conclusions

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 3

Outline

Sub-detectors of interest in this talk: ALICE TPC and ITS

● Motivation

● L and K0s

– Reconstruction

– Nuclear modification factors: RCP and RAA

– Comparison to unidentified

charged particles and p(p), p+;-,K+;- RAA

● Conclusions

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 4

Motivation I

● Why looking at high pT?– Diagnostic potential to probe the created medium via :

● the measurement of yields and particle ratios● comparison between AA and pp collisions

→ Parton energy loss and modified fragmentation pattern as a measure of the medium influence

● Charged particle RAA:– Strong suppression in Pb-Pb collisions

compared to pp around pT = 6-8 GeV/c– Rise towards high pT

● → Identified particles?● → Baryons versus mesons?

DEg > DEq > DEQ ? arXiv: 1208.2711v1

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 5

Motivation II

● Baryon to meson enhancement for light flavoured particles at low to intermediate pT

● No centrality dependence at high pT

● What is the effect on RCP and RAA?

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 6

Motivation III

● Baryon to meson enhancement likely to be a bulk effect (M.Veldhoen, arXiv:1207.7195)

● Particle production in jets seems not to be affected by medium (A. Ortiz Velasquez,QM12)

● What is the effect on RCP and RAA?

PYTHIA pp

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 7

Motivation III

● Baryon to meson enhancement likely to be a bulk effect (M.Veldhoen, arXiv:1207.7195)

● Particle production in jets seems not to be affected by medium (A. Ortiz Velasquez,QM12)

● What is the effect on RCP and RAA? Wiedemann et al. arXiv: 0707.3494v1

contradicts? →

= pp

PYTHIA pp

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 8

Motivation IV

● Note that

p(AA) / p(AA) > p(pp) / p(pp)

RAA(p) > RAA(p)

● Is this the case?

Wiedemann et al. arXiv: 0707.3494v1

= pp

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 9

Measurement of identified particles

Measurement of identified particles at high pT:

● L and K0s: secondary vertex analysis of V0 decays

– Reconstruction via weak decay products:

K0s p+ p- L p- p

= Invariant mass analysis

→ Identification via topological track reconstruction

→ no PID necessary

● p(p), p+;-,K+;-: identification via relative energy loss dE/dx in the TPC

L

p -

p

primary vertex

secondary vertex

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 10

K0s and L Analysis

Fit of the background

Function: polynomial of 1st or 2nd order Function: Gaussian + polynomial of 1st order

Fit of the peak for mass and resolution extraction

22/05/2011

22/05/2011

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 11

RCP

: comparison K0s – charged

● RCP of charged kaons match the K0

s RCPat low pT

● RCP similar for charged particles and K0

s

● Strong suppression of K0s at

high pT

RCP=dN central /dpTdN periph/dpT

⋅⟨N coll ⟩ periph⟨N coll ⟩central

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 12

RCP

: K0s and L

● Low pT: L enhanced over K0s

(baryon to meson enhance-ment) up to pT = 8 GeV/c

● High pT :

– RCP for L and K0s

compatible– Similar to RCP of

charged particles

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 13

RAA

: peripheral L and K0s

RAA=dN AA/dpTdN pp/dpT

⋅ 1⟨N coll ⟩AA

● Low pT:

– L enhanced over suppressed K0

s

● High pT :

– L and K0s are

suppressed similarly

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 14

RAA

: central vs peripheral

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 15

RAA

: comparison to charged

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Identified charged particles: p,p,K

● Separation of particles at relativistic rise not perfect → need for statistical PID● → Extract particle fractions via

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 17

RAA: p,p,K versus L and K0s

● Low pT: RAA of protons exceeds the pions, kaons → qualitative similar to L, K0s

● High pT: RAA ~ 0.12 at pT = 6 GeV/c. Universal behaviour at higher pT within systematics

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 18

RAA: p,p,K versus L and K0s

● … same picture for peripheral collisions

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 19

RAA: flavour independence at high-pT (?)

● No significant difference between baryons and mesons at high pT● → no indication for different gluon and quark energy loss, or modified

fragmentation in medium

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 20

RAA: flavour independence at high-pT (?)

● No significant difference between baryons and mesons at high pT● → no indication for different gluon and quark energy loss, or modified

fragmentation in medium● … also no significant difference for charmed

hadrons observed● Is this understood: DEg > DEq > DEQ ?

17.09.2012 Simone Schuchmann, Goethe-Universität Frankfurt 21

Summary

● L, K0s, p(p), p+;-, K+;- RCP, RAA measured in Pb-Pb and pp at √sNN= 2.76 TeV up

to pT = 16 - 20 GeV/c.

● Strong suppression observed at high pT (pT > 8 GeV/c):

– p(p),p+;-,K+;-, L and K0s compatible

● At lower pT (pT < 5 GeV/c):

– p and p, L and K0s different in RAA ( RCP):

→ Baryon to meson enhancement● No indication for parton type dependence of energy loss at high pT observed in

ALICE so far