Oct23-2008論文セミナー

Abstract

Abstract

Au+Au √sNN=62.4GeV

mid-rapidity, 7 centrality classes mT spectra dN/dy

energy dependence (SPS, AGS data) yield (anti-Λ)/Λ ratio

Introduction

strange particle production →collision でできた matter の情報

Why 62.4GeV? ->energy scan b/w SPS & RHIC 130,200GeV SPS : baryon dominated RHIC : net-baryon free

hope excitation function の情報 constrains to the thermal model predictions

STAR experiment TPC (|y|<1.8):charged track SVT (|y|<1.) ,SSD (|y|<1.) :primary/secondary vertex SVT ,TPC : dE/dx を使用して PID

experimental setup

Au+Au √sNN=62.4GeV (Run4)

mid-rapidity STAR detector(|y|<0.5) 6.5×106 events 7 different centrality classes

# of primary tracks(0-5% ~ 60-80%)

charged particle track : TPC -> PID

reconstruction

neutral particle reconstruction : V0 decay topology method

K0(s)->π++π-

(anti-)Λ->(anti-)proton+(π+)π-

S/N improvement dE/dx information (daughter tracks) distance of closest approach (b/w daughter

tracks) some topological cuts

vertex

ex a<0.5cm b>2.85cm c>0.90cm d>5cm

Λ

π

p

b

c

a d

mT spectra & integrated yield

mT distribution

corrections geometrical acceptance detector inefficiency anti-proton absorption NOT contained weak decays of multi-strange

particles

fitting assuming flat rapidity distribution (|y|<0.5)

mT spectra & integrated yield

integrated yield integrated yield

〈 Npart 〉 ← Glauber model

integrated yield / 〈 Npart 〉 enhancement of strangeness

production as a function of centrality

normalized @ most peripheral bin

same enhancement pattern with SPS experiment

earlier saturation point

Energy dependence of yield & ratio

yield of mid-rapidity anti-Λ : monotonic increase Λ : constant Λ : different b/w SPS & RHIC

anti-Λ/Λ ratio @RHIC energy ratio~1

conclusions

strange hyperon production @62.4GeV new point in excitation function

integrated yield / ratio relatively smooth behavior with energy non-identical particle ratio に重要 (Λ/π, K/π)

typical strangeness enhancement