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

Motivation I : Strangeness enhancement 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. 2 Redlich, JPG27 Redlich&Tounsi, 02 From A. Timmins

Motivation II : Cronin effect Cronin effect in p+A, d+Au collision [Cronin1975], seen in nuclear modification factor R AA or R CP < 1 for p T < P x > 1 for p T > P x approach 1 again when p T → 3 p q h A Traditional models [Accardi hep-ph/ ] : Multiple parton/hardon scatterings in initial state Recombination/ Coalescence: [Hwa&Yang 03, 04] Final state effect, modification of hadronization 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.

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

Outline K 0 s, ,  spectra in most central d+Au 200GeV Strangeness enhancement in most central d+Au Baryon enhancement at intermediate p T (  / K 0 s ) Cronin effect, particle type dependence of R dAu in most central d+Au Summary 5

STAR Run 08 d+Au Experiment Setup Time Projection Chamber Forward TPCs 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. 6

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 east Forward TPC (Au side, -3.8<  <-2.8), ‘refMult’ in the right plot  Currently, only the most central (0-20%) events are well defined by East FTPC. 7 STAR Preliminary

Strangeness reconstruction in STAR Strange particles are reconstructed with their secondary TPC tracks through weak decay topology, thanks to TPC full azimuthal coverage. 8 K 0 s, |y|<1 0.4 <pt< 0.6 Λ, |y|<1 0.4 <pt< 0.6 Ξ, |y|<1 0.6 <pt< 1.0 STAR Preliminary

Spectra of K 0 s, Λ, Ξ Λ(Λbar) corrected for weak decay feed-down from Ξ’s Spectra can be fitted with Levy function [Wilk&Wlodarczyk 00], low p T – exponential high p T – power law fitting parameters: percentage of dN/dy from extrapolation at low p T : K 0 s 10% ; Λ 17.5%; Ξ 29% 9 d+Au 200 GeV, 0-20% dN/dynTχ2/ndf K0sK0s 1.21± ± ± /12 Λ0.402± ± ± /10 Ξ0.058± ± ± /5 STAR Preliminary statistical error only

Strangeness enhancement Λ and K 0 s 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 10 dN/dy / relative to pp STAR Preliminary statistical error only for d+Au data Number of Participants N part

Λ/K 0 s Baryon enhancement at intermediate p T at STAR measured with Λ/K 0 s Most central d+Au data is close to peripheral Au+Au 11 STAR Preliminary p+p data is from STAR PRC75

Nuclear modification factor R dAu 12 STAR Preliminary π,K,p data is from STAR, PLB616, 637, statistical error only; φ data is from STAR arXiv: ; p+p K 0 s and Λ is from STAR PRC75 K 0 s agree with charged K at low p T Λ agrees with proton at intermediate p T (2 – 4GeV/c). Particle type (baryon/meson) dependence of R dAu for p T from 2.0 to 4 GeV/c; φ meson R dAu also falls into the meson band, for high statistical φ data, see C. Jena and X. Zhang’s posters

Summary Measured productions for 3 identified particles(K 0 s, , Ξ) in most central (0-20%) d+Au collisions at RHIC Strangeness (K 0 s, , Ξ)  enhancement in central d+Au. Especially, we see Ξ enhancement factor is also large in most central d+Au  /K 0 s 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 ( K 0 s, ,φ vs. p,  ), indicating that the hadronization scheme may have an impact on the Cronin effect 13

backups 14

Comparison of K0 to charged K spectra Good agreement of K 0 s and charged K (from TPC dEdx) spectra at low p T. 15 STAR Preliminary

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