Proton to Pion ratio in Jet and Bulk region in Heavy Ion collisions Misha Veldhoen (Utrecht University) For the ALICE collaboration Hard Probes 2012 Cagliari, Italy Measured by the ALICE detector, TeV

Hadronization at high and low p T 1 In A–A collisions, for p T < 6 GeV/c, a significantly enhanced Baryon to Meson ratio is observed. In p—p collisions the dominant particle production mechanism is fragmentation.

Reproducing the Baryon Enhancement One possible hadronization mechanism at p T < 6 GeV is coalescence/recombination. 2 Recombination and Hydro Hydrodynamics Hot matter Baryon p T = 3p T,parton Meson p T = 2p T,parton Hydrodynamic models reproduce the charged particle spectra and ratios for p T < 2 GeV/c. Thermal Recombination arXiv:

Hadronization in Jets What about hadronization in Jets? Several predictions have been made. 3 Shower-Thermal Recombination, (enhanced B/M should be observed in Jets) [Hwa, Yang] Medium effects, MLLA+LPHD formalism [Sapeta, Wiedemann] also predicts enhanced B/M ratio in Jets. We will present a measurement of the p/π ratio in the Jet peak and Bulk region of a di-hadron correlation. Baryon p T =3p T,parton Meson p T =2p T,parton Hard parton Hot matter arXiv: K ± /π ± p(p)/π ± - Ratio p T (GeV/c)

Di-Hadron Correlations 1.4M central (0-10%) Pb—Pb. Associated particles: 1.5 < p T < 4.5 GeV/c, Trigger particles: 5.0 < p T < 10.0 GeV/c. |η| < 0.8. PID using TOF and TPC. Corrections – Mixed event correction (pair acceptance). – Efficiency (tracking and PID) as function of p T and particle species. – No feed-down correction, Λ spectrum in jets not known. 4

Selecting Peak and Bulk Regions Five-dimensional histogram: Peak- and Bulk regions can be selected by integrating over Δϕ and Δη. 5 Bulk Jet = Peak – Bulk Δϕ 0 π Δϕ (rad) Δη Count

Combined PID: TPC and TOF Specific energy loss, Time Projection Chamber (TPC) Time Of Flight (TOF) Good separation between pions, kaons and protons at intermediate p T. π π π p p p K K K 6 t TOF – π (ps) dE/dx – π (a.u.) Count 3.0 < p T < 3.5 GeV/c 3.5 < p T < 4.0 GeV/c 4.0 < p T < 4.5 GeV/c Count t TOF – π (ps) Count t TOF – π (ps)

Combined PID: Peak Shapes p K π p K π p K π Expected PID signals depend on p T and η  Non- Gaussian peak shapes. Generated templates to fit non-Gaussian peaks. 7 Mass Assumption: Pions Mass Assumption: KaonsMass Assumption: Protons dE/dx – p (a.u.) dE/dx – K (a.u.) dE/dx – π (a.u.) Count t TOF – π (ps) Count t TOF – K (ps) Count t TOF – p (ps)

Combined PID: Fit Example I 1.Data, mass assumption: pions. p p K K π π π Kaon and Proton templates subtracted, remaining peak fitted with a function (Gauss+Tail). 3.Final fit, pions (function), kaons and protons (template) t TOF – π (ps) Count dE/dx – π (a.u.) Count t TOF – π (ps) Count t TOF – π (ps)

Combined PID: Fit Example II Slice through the pion peak (TOF). 5.Slice through the proton peak (TPC). t TOF – π (ps) dE/dx – π (a.u.) Count

Proton and Pion Yields in Peak and Bulk Bulk yield normalized to peak region: < Δϕ < 0.52, -0.6 < Δη < 0.6 Correlated and uncorrelated uncertainties shown separately. p T,assoc (GeV/c) 10 1/N trig dN/dp T,assoc (GeV/c) -1 p T,assoc (GeV/c) π π p p Count 1/N trig dN/dp T,assoc (GeV/c) -1 p T,assoc (GeV/c) Count 1/N trig dN/dp T,assoc (GeV/c) -1

p/π Ratio p/π Ratio in Bulk region (-0.52 < Δφ < 0.52 rad, ±0.60 < Δη < ± 1.50) Results not feed-down corrected. 11

p/π Ratio Comparison with feed- down corrected p/π ratio, from inclusive spectra (0-5%), (QM2010 prel.) Inclusive spectra used |y| < 0.5 instead of |η| <

p/π Ratio Comparison with the p/π Ratio in the Jet (Peak – Bulk) (-0.52 < Δφ < 0.52 rad, < Δη < 0.40) Jet ratio not feed- down corrected. Significant difference between Bulk and Jet ratio. 13

p/π Ratio Comparison with Pythia p/π ratio in Jet. (Pythia v6.4.21, default tune) Pythia p/π ratio agrees with measured Pb–Pb p/π ratio in Jet. Particle production in Jet dominated by fragmentation. No evidence for medium modification. 14

Summary and Conclusions p/π Ratios in the Jet and Bulk of a di-hadron correlation were presented. Particles identified using both TPC and TOF. The p/π ratio in Bulk is compatible with the p/π ratio from feed down corrected inclusive spectra in the range 1.5 < p T < 3.0 GeV/c. The p/π ratio in the Jet is compatible with a Pythia curve in the range 2.0 < p T < 4.0 GeV/c. (Pythia v6.4.21, default tune) Our measurement suggests that particle production mechanism in jets is dominated by fragmentation. No evidence for medium modification. 15

BACKUP 16

Fit Quality 17 (Data-Fit)/Data(Data-Fit)/σ stat