1. Oct23-2008 論文セミナー

2. Abstract

3.  Au+Au √s NN =62.4GeV  mid-rapidity, 7 centrality classes  m T spectra  dN/dy  energy dependence (SPS, AGS data)  yield  (anti-Λ)/Λ ratio

4. 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

5. 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

6. experimental setup  Au+Au √s NN =62.4GeV (Run4)  mid-rapidity STAR detector(|y|<0.5)  6.5×10 6 events  7 different centrality classes  # of primary tracks(0-5% ~ 60-80%)  charged particle track : TPC -> PID

7. 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

8. vertex  ex  a<0.5cm  b>2.85cm  c>0.90cm  d>5cm Λ π p b c a d

9. m T spectra & integrated yield  m T 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)

10. m T spectra & integrated yield

11. integrated yield  integrated yield  〈 N part 〉 ← Glauber model  integrated yield / 〈 N part 〉  enhancement of strangeness production as a function of centrality  normalized @ most peripheral bin  same enhancement pattern with SPS experiment  earlier saturation point

12. 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

13. 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