1. SQM2004, Cape Town, Sept. 16, 2004 STAR 1 Cronin Effect for the identified particles from 200 GeV d+Au collisions Xiangzhou Cai Shanghai INstitute of Applied Physics (SINAP) Chinese Academy of Sciences for the STAR Collaboration (Presented by Yu-Gang Ma, SINAP) Outline Introduction and Motivations Spectra, fit function and comparison Rcp, R dAu, particle dependence of Cronin effect Summary

2. SQM2004, Cape Town, Sept. 16, 2004 STAR 2 IntroductionAndMotivation

3. STAR 3 Some Definitions Initial-state effect: The effect happens before the hard scattering. Final-state effect: The effect happens after or at the hard scattering. The behavior of the many-body systems we study (such as p-A, A-B collision) can be “calibrated” with a “reference system” like p-B or p-p. Similarly, the central collision can be “calibrated” by the peripheral collision in the following way:

4. SQM2004, Cape Town, Sept. 16, 2004 STAR 4 STAR PHENIX 1)Particle dependence of R AA /R cp and v 2 from Au+Au collisions is observed. How about R AA /R cp in dAu? particle type or mass dependence? (R cp for K s, , ,  and p ). 2) The Cronin effect has been considered as due to initial parton scattering. Should the Cronin effect be influenced by the final state particle formation dynamics? 3) Recombination models predict the particle type dependence of the Rcp at intermediate p T in AuAu collisions. Rcp & v 2 @ 200GeV Au+Au  m  ~1019 MeV/c 2 ; m  ~1116 MeV/c2; m Ks ~498 MeV/c2 PHENIX: PRL91, 182301(03) STAR: PRL92, 052302(04) nucl-ex/0306007 Models: Greco et al, PRC68, 034904(03) Saturation at intermediate p T Baryon and meson difference Baryon Meson

5. SQM2004, Cape Town, Sept. 16, 2004 STAR 5 Analysis details And Spectra of identified particles

6. SQM2004, Cape Town, Sept. 16, 2004 STAR 6 Centrality definition of dAu@200GeV 1)dE/dx identify stable charged particles in a certain momentum range. 2)Unstable particles identified by decay topology or event mixing method. Multiplicity FTPC East in d+Au collisions 40-100% 20-40% 0-20% Three Multiplicity Bins are defined by the Nch per event in FTPC East After cut: ~ 10 Million events STAR Preliminary

7. SQM2004, Cape Town, Sept. 16, 2004 STAR 7 Event Selection: |VertexZ| < 50cm, with Primary vertex found, good run After cuts, # of Events ~ 10M Decay mode: Ks =>  +   - (68.6%)  -    - (99.9%) p + +  -  (63.9%)  =>  +   - (49.1%) K* =>   (100%) Ks, ,  are reconstructed using topology cuts, like decay length, dca- v0-primV Daughter tracks are NOT identified when pt>1.1 GeV/c, but v0 can be identified at much higher pT.  event mixing

8. SQM2004, Cape Town, Sept. 16, 2004 STAR 8 Ks and  are V0 particles: decay length: Ks = 2.69 cm  = 7.89 cm In TPC, neutral Ks and  are reconstructed from charged particles: p, K and  (See above sketch). Topology Cuts (See the right sketch) |vertexZ|<50cm DcaV0: between two daughter tracks < 0.7cm DcaImpact (distance between V0 and Primary vertex) < 0.75 cm (  ), and < 0.6cm (Ks) Decay length (distance between primary vertex and V0 decay point) > 2 cm (Ks and  )  -- p+p+ Ks and  reconstruction & Topology cuts Primary Vertex Ks -- ++ Primary Vertex Decay point DcaV0 Decay len DcaImpact Track 1 Track 2

9. SQM2004, Cape Town, Sept. 16, 2004 STAR 9 Reconstruction of  B Dca Lambda Daughters Dca Xi To Prim Vertex   Decay Length Xi  Reconstruction by the topology of the decay:    +  -  p +  -  Selection by: geometrical cuts dE/dx pid  Efficiency and acceptance correction done using the embedding Monte-Carlo technique Javier Castillo

10. SQM2004, Cape Town, Sept. 16, 2004 STAR 10   K + K - Branching Ratio = 0.49 Both K+ and K- come from the same event Signal K+ and K- come from different event Background Mixed event is supposed to contain everything of significance to the correlation analysis except the correlation itself. Calculate the invariant mass of every possible K + K - pairs and accumulate the signal to reconstruct  in each (y, pt) bin. Event Mixing Method

11. SQM2004, Cape Town, Sept. 16, 2004 STAR 11 Measurements in dAu collisions Mass = 1019.4±0.5MeV/c 2, FWHM=7.3  1.1 MeV/c 2 K + K - pair invariant mass background subtracted  For 40~100% centrality bin at |y|<0.5 and 0.4<p t <1.3GeV/c. Red line is the same-event distribution. Black line is the normalized mixed-event distribution. Invariant mass distribution of  meson

12. SQM2004, Cape Town, Sept. 16, 2004 STAR 12 Invariant mass plots |y|<1 0.4 <pt< 6.0 |y|<1 0.4 <pt< 6.0 |y|<1 0.6 <pt< 5.0 |y|<0.5 0.4 <pt< 1.3  Without background subtraction Ks, ,  : topology cuts;  : event mixing The quality of signals are pretty good.

13. SQM2004, Cape Town, Sept. 16, 2004 STAR 13  Spectra for MinBias  production in dAu  exp fit covering low pt end and power-law fit covering high pt region.  Double exponential fit can reproduce the experimental data better than other two funtions. Comparison of different Fits for  Spectra Double exponential fit: T1: ~300MeV; T2: 1.0~1.5GeV; STAR Preliminary

14. SQM2004, Cape Town, Sept. 16, 2004 STAR 14 Spectra and fits: Ks  p T : 0.4 – 6 GeV/c. cross point: p T ~(2~4)GeV/c 2. With efficiency correction (including vertex efficiency). Statistical errors only. the Lambda spectra are corrected for Xi feeddown. Recombination model may fit spectra well … TT(low pt)+TS(middle pt)+SS(high pt)  double exp fit STAR Preliminary

15. SQM2004, Cape Town, Sept. 16, 2004 STAR 15 Spectra :  k, p The spectra in d+Au collisions are harder than those in p+p collisions STAR Preliminary p+p peripheral central

16. SQM2004, Cape Town, Sept. 16, 2004 STAR 16 dN/dy vs. , Ks, ,  increase with in dAu and AuAu collisions. dAu Minbias STAR Preliminary

17. SQM2004, Cape Town, Sept. 16, 2004 STAR 17 vs. :  shows no dependence of within error bar, but  and  are different. dAu Minbias STAR Preliminary 

18. SQM2004, Cape Town, Sept. 16, 2004 STAR 18 Cronin effect And Recombination model

19. SQM2004, Cape Town, Sept. 16, 2004 STAR 19 Comparison with Recombination Model (I) R.C. Hwa et al., nucl-th/0403001; R.C. Hwa et al., nucl-th/0406066 Recombination model can reproduce the  spectra in d+Au collisions.

20. SQM2004, Cape Town, Sept. 16, 2004 STAR 20 Comparison with Recombination Model (II) R.C. Hwa et al., nucl-th/0403001; R.C. Hwa et al., nucl-th/0406066 Recombination model can reproduce the p spectra in d+Au collisions.

21. SQM2004, Cape Town, Sept. 16, 2004 STAR 21 Rcp of , Ks, ,  @ dAu 200 GeV Mesons (Ks,  ) have the same Rcp for dAu Baryons ( ,  ) have the same Rcp too, but higher than mesons. Particle production at intermediate p T region is dividing by the particle’s type, not the mass. Similar particle dependence has been observed in Au+Au collisions. Such dependence is indicative of hadron formation dynamics such as recombination/coalescence. TTTSSS TTT TTS+TSSSSS STAR:  behaves like mesons, despite of the large mass: ReComb prediction

22. SQM2004, Cape Town, Sept. 16, 2004 STAR 22 R dAu of  comparing with  K p Particle production at intermediate p T region is sorted by the particle’s type, not the mass Low p T, R dAu <1 High p T, R dAu >1 P x ~=1 GeV/c R dAu (p)> R dAu ( , ,K) RdAu of  is closer to that of  and k than that of p STAR Preliminary

23. SQM2004, Cape Town, Sept. 16, 2004 STAR 23 Comparison with pA collision s =27.4GeV P.B Straub,PRL 68, 452(1992) R w/Be at pA collisions W: tungsten Be: beryllium s =38.8GeV the particle dependence has also been observed previously at lower energy. R w/Be : Mesons (2 quarks): Mesons (2 quarks): Kaon and  ~ 1.5; Baryons (3 quarks): Baryons (3 quarks): proton ~ 2.5 Particle-type dependence! ~1.4 ~1.5 ~2.5

24. SQM2004, Cape Town, Sept. 16, 2004 STAR 24 1)Measure the productions for various particles (Ks,   k, p ) in dAu collisions @200GeV. 2)Double exponential function can fit the , Ks,  and  spectra better than others. 3)R dAu and R cp in dAu are grouped into mesons and baryons. It indicates that the particle production is dividing by particle type rather than particle mass. 4)It indicates that the initial parton scattering model alone cannot explain the observed particle dependence. The hadron formation dynamics play an important role. Recombination picture provides a possible hadronization scheme for the particle dependence. Summary

25. SQM2004, Cape Town, Sept. 16, 2004 STAR 25 The End Thank you!