Strangeness production and Cronin effect in d+Au collisions at √s NN = 200 GeV in STAR

1. Strangeness production and Cronin effect in d+Au collisions at √sNN = 200 GeV in STAR Xianglei Zhu (Tsinghua U / UCLA)For the STAR Collaboration

2. Motivation I : Strangeness enhancement From A. Timmins • Strangeness enhancement in A+A collisions at RHIC energy, as a QGP signature (see. A. Timmins’ talk) • d+Au strangeness data will connect peripheral A+A and p+p, supplying the baseline for the study of strangeness enhancement in the deconfined matter. Redlich, JPG27 Redlich&Tounsi, 02

3. h q p A Motivation II : Cronin effect Cronin effect in p+A, d+Aucollision [Cronin1975], seen in nuclear modification factor RAA or RCP • < 1 for pT < Px • > 1 for pT > Px • approach 1 again when pT → • What is the mechanism of Cronin effect? • traditional models: do not explicitly predict particle type dependence, but centrality dependence. • final state models: predict particle species dependence of Cronin effect • Measurements of particle type and centrality dependence of Cronin effect seem helpful to understand the effect. Recombination/Coalescence:[Hwa&Yang 03, 04] Final state effect, modification of hadronization Traditional models [Accardihep-ph/0212148]: Multiple parton/hardon scatterings in initial state

4. Cronin effect in d+Au STAR STAR, PLB637, PLB616 • Cronin effect seen with identified particle RdAu • For 2<pT<5GeV/c, RdAu of proton seems higher than pions. • With topological reconstruction, strange hadrons have good PID up to high pT! Suitable for the study of particle type dependence of Cronin effect.

5. Outline • K0s, L, X spectra in most central d+Au 200GeV • Strangeness enhancement in most central d+Au • Baryon enhancement at intermediate pT (L/ K0s) • Cronin effect, particle type dependence of RdAu in most central d+Au • Summary

6. STAR Run 08 d+Au Experiment Setup Time Projection Chamber • Vertex Position Detector to confine primary vertex within ±30 cm, together with east ZDC as minimum bias trigger • No inner silicon detectors • pion, kaon, proton and electron : identified using ionization energy loss in TPC. Forward TPCs

7. The data set • STAR Run 8 d+Au 200GeV Minimum Bias data • Event Selection: • |VertexZ| < 30cm • ~ 32M events after the cuts. • Centrality definition in d+Au: • Provided by uncorrected # of charged particles @ east Forward TPC (Au side, -3.8<<-2.8),‘refMult’ in theright plot • Currently, only the most central (0-20%) events are well definedby East FTPC. STAR Preliminary

8. Strangeness reconstruction in STAR • Strange particles are reconstructed with their secondary TPC tracks through weak decay topology, thanks to TPC full azimuthal coverage. STAR Preliminary STAR Preliminary STAR Preliminary K0s, |y|<1 0.4 <pt< 0.6 Λ, |y|<1 0.4 <pt< 0.6 Ξ, |y|<1 0.6 <pt< 1.0

9. Spectra of K0s, Λ, Ξ • Λ(Λbar) corrected for weak decay feed-down from Ξ’s • Spectra can be fitted with Levy function [Wilk&Wlodarczyk 00], low pT – exponentialhigh pT – power lawfitting parameters:percentage of dN/dy from extrapolation at low pT:K0s 10% ; Λ 17.5%; Ξ 29% d+Au 200 GeV, 0-20% STAR Preliminary statistical error only

10. Strangeness enhancement statistical error only for d+Au data • Λ and K0s enhancement factor is almost the same in most central d+Au, lie in a trend with peripheral Cu+Cu and Au+Au • Ξ yield is consistent with that from most peripheral Cu+Cu. • strangeness enhancement factor is proportional to the strangeness content in d+Au too STAR Preliminary dN/dy / <Npart> relative to pp Number of Participants Npart

11. Λ/K0s • Baryon enhancement at intermediate pT at STAR measured with Λ/K0s • Most central d+Au data is close to peripheral Au+Au p+p data is from STAR PRC75 STAR Preliminary

12. Nuclear modification factor RdAu • K0s agree with charged K at low pT • Λ agrees with proton at intermediate pT (2 – 4GeV/c). • Particle type (baryon/meson) dependence of RdAu for pT from 2.0 to 4 GeV/c; φ meson RdAu also falls into the meson band, for high statistical φ data, see C. Jena and X. Zhang’s posters STAR Preliminary π,K,p data is from STAR, PLB616, 637, statistical error only; φ data is from STAR arXiv:0809.4737;p+p K0s and Λ is from STAR PRC75

13. Summary • Measured productions for 3 identified particles(K0s, L, Ξ) in most central (0-20%) d+Au collisions at RHIC • Strangeness (K0s, L, Ξ)enhancement in central d+Au. Especially, we see Ξ enhancement factor is also large in most central d+Au • L/K0s ratio in dAu is close to Au+Au most peripheral (60-80%) • d+Au Nuclear modification factor seems to show particle type (baryon/meson) difference(K0s ,,φ vs. p, L), indicating that the hadronization scheme may have an impact on the Cronin effect

14. backups

15. Comparison of K0 to charged K spectra • Good agreement of K0s and charged K (from TPC dEdx) spectra at low pT. STAR Preliminary

16. ~1.4 ~1.5 ~2.5 s =38.8GeV s =27.4GeV RAA in low energy p+A collisions Rw/Be in p+A collisions P.B Straub,PRL 68, 452(1992) W: tungsten Be: beryllium Rw/Be : Mesons (2 quarks): kaon and pion ~ 1.5; Baryons (3 quarks): proton ~ 2.5 Particle-type dependence ??