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International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR  Ks,  and  production at 200 GeV d+Au collisions from STAR Xiangzhou Cai,

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Presentation on theme: "International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR  Ks,  and  production at 200 GeV d+Au collisions from STAR Xiangzhou Cai,"— Presentation transcript:

1 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR  Ks,  and  production at 200 GeV d+Au collisions from STAR Xiangzhou Cai, Yugang Ma, Hai Jiang, Jingguo Ma for the STAR Collaboration Shanghai INstitute of Applied Physics University of California, Los Angeles Lawrence Berkeley National Laboratory PAs: Lee Barnby, Xiangzhou Cai, Magali Estienne, Hai Jiang, Camelia Mironov, Lijuan Ruan, Frank Simon, Nu Xu, Haibin Zhang Outline Motivations for measuring Ks, ,  and  Analysis details of dAu analysis (Ks, , , K*, Kink-K) Spectra, fit function and comparison Rcp, R dAu, particle dependence of Cronin effect Summary

2 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR Motivation & Introduction 1) Particle dependence of R AA /Rcp and v2 from Au+Au collisions is observed. How about RAA/Rcp in dAu? particle type or mass dependence? (R cp for K s, , and  ). 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) Transverse momentum production: versus multiplicity  m  ~1019 MeV/c 2 ; m  ~1116 MeV/c2; m Ks ~498 MeV/c2

3 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR dAu 200GeV STAR MuDst P03a: MinBias and Combined Event Trigger ID: 2001 or 2003 Primary Vertex Position: -50cm<z<50cm Track nFitPts: > 15 |eta|: < 1.0 Pt range: 0.1GeV < Pt track < 4.0GeV Data Sets and Event Cuts

4 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR Centrality definition of dAu 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

5 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR 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. ,K*: event mixing  p+p+ Decay point -- Primary Vertex -- -- Decay point

6 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR 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

7 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR   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

8 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR 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. STAR Preliminary

9 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR Acceptance and Efficiency 4 Embedding method:  Generate tracks with certain p T and rapidity distribution. (SimTrack)  Generate Monte-Carlo tracks in STAR geometry (MCTrack) Acceptance =  TPC response simulator generates hits  Monte-Carlo hits are embedded in the real data  Reconstruct the “embedded events” using the same chain as real data production (RecTrack)  Tracking efficiency extraction Efficiency =  Total correction factor Correction = Acceptance * Efficiency*Branching Ratio

10 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR Efficiency Correction of  Ks and   The efficiency increases with Pt and becomes flat  Weak multiplicity dependence. The difference of efficiency correction between different centrality bins is small than the error bars. STAR Preliminary

11 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR  Spectra for MinBias Phi 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 Double exponential fit: T1: ~300MeV; T2: 1.0~1.5GeV; STAR Preliminary

12 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR  production in AuAu and pp  200 GeV  meson production from both AuAu and pp collisions are analysed by Jingguo Ma.  200 GeV  meson production from dAu is necessary for further understanding:   production mechanism  particle dependence of nuclear modification factor

13 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR Spectra and fits p T : 0.4 – 6 GeV/c. With efficiency correction (including vertex efficiency). Statistical errors only. cross point: pT~(2~4)GeV/c2. Recombination model may fit spectra well … TT(low pt)+TS(middle pt)+SS(high pt)  double exp fit STAR Preliminary

14 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR  - +  bar minbias : dN/dy = 0.0268 +- 0.0007  +  bar minbias (inclusive) : dN/dy = 0.339 +- 0.007 If assuming  0   - and  ~ 10%  -, Then feed-down from   ~ 0.056 ( 17% ) Consistent with the feed-down in AuAu ~ 15% Consistent with the feed-down in AuAu ~ 15% (Hui, Magali’s SQM paper)  spectra and feed-down contribution to  STAR Preliminary

15 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR Spectra comparison Different measurements are consistent within STAR! From Camelia

16 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR dN/dy vs. , Ks, ,  increase with in dAu and AuAu collisions. dAu Minbias STAR Preliminary

17 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR vs. :  shows no dependence of within error bar, but  and  are different. dAu Minbias STAR Preliminary

18 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR R cp definition We select three data samples: “Central”: centrality 0-20% “Semi-central”: centrality 20-40% “Peripheral”: centrality 40-100% Then we calculate the ratios Central/Peripheral as function of p T at different rapidities. Rcp = (d 2 N/dp T d  ) cent / (d 2 N/dp T d  ) peri Many corrections and systematics cancel out.

19 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR Rcp of , Ks, ,  Mesons (Ks, K ,  ) have the same Rcp for dAu and AuAu collisions Baryons ( ,  ) have the same Rcp too, but higher than mesons. Recombination/Coalescence model works! Particle production at intermediate p T region is dividing by the particle’s type, not the mass. Recombination/Coalescence model works! They can explain the difference of Rcp between mesons and baryons for both dAu and AuAu. (Z.M.Ko et al., R.C.Hwa et al….) TTTSSS TTT TTS+TSSSSS AuAu 200 GeVdAu 200 GeV STAR:  and K* behave like mesons, despite of the large mass: ReComb prediction

20 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR Nuclear modification factor R dAu The behavior of the many-body systems we study (A-A or d-A) can be “calibrated” with a “simple system” like p-p. Borrowing from “Cronin effect” studies, we compare particle production in d-A to the scaled production in p-p: R dAu = (d 2 N dAu /dp T d  ) / (N coll d 2 N pp /dp T d  ) With N coll being the estimated number of binary collisions as d “goes through” the Au nuclei.

21 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR RdAu RdAu of  is closer to that of p and k than that of p Particle production at intermediate pT region is sorted by the particle’s type, not the mass

22 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR 1)Measure the productions and for various particles (Ks,  ) in dAu collisions 2)Double exponential function can fit the , Ks,  and  spectra better than others, dN/dy scale linearly with the number of charged particles 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 as predicted by the parton recombination/quark coalescence model. 4)R cp plots show no suppression indicating that the suppression in Au+Au maybe arises from additional effects Summary

23 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR The End Thank you!

24 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR From Fragmentation to Recombination With more partons around: multiple parton fragmentation (higher twist) If phase space is filled with partons, recombine/coalesce them into hadrons. Use just the lowest Fock state, i.e. valence quarks: qqq  B qq  M

25 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR Recombination model of Hwa and Yang Nucl-th/0403001, Nucl-th/0404066  + +  - in d+Au P in d+Au

26 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR Spectra and fits Ks yield is lower than TOF_K and kink at the low pt, but the shapes are same. Neutral K* in mt exp fit Charge K* in power-law fit K* from Lijuan, Haibin Kink from Camelia TOF_K from Lijuan

27 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR v 2 Scaling Baryons are pushed further in P T Perfect scaling for all measured hadrons, some deviation for pions (from  decays) P. Sorensen

28 International CCAST Workshop on QCD & RHIC Physics, Aug. 13, 2004 STAR 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 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 also! ~1.4 ~1.5 ~2.5

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