1. F, Ks, , and X 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 (SINAP)
University of California, Los Angeles (UCLA)
Lawrence Berkeley National Laboratory (LBNL)
Outline
Motivations for measuring Ks,  and f
Analysis details of dAu analysis (Ks, f, L, X, K*, Kink-K)
Spectra, fit function and comparison
Rcp, RdAu, Cronin effect and recombination model
Summary
PAs: Lee Barnby, Xiangzhou Cai, Magali Estienne, Hai Jiang,
Camelia Mironov, Lijuan Ruan, Frank Simon, Nu Xu, Haibin Zhang

2. Motivation & Introduction
1) Particle dependence of RAA/Rcp and v2 from Au+Au collisions is observed. How about RAA/Rcp in dAu? particle type or mass dependence? (Rcp for Ks, , 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: <pT> versus multiplicity
mf~1019 MeV/c2 ; mL~1116 MeV/c2; mKs~498 MeV/c2

3.  production in AuAu and pp
200 GeV f meson production from both AuAu and pp collisions are analysed by Jingguo Ma.
200 GeV f meson production from dAu is also necessary for further understanding:
f production mechanism
particle dependence of nuclear modification factor

4. Data Sets and Event Cuts
dAu 200GeV STAR MuDst P03a:
MinBias and Combined
Event
Trigger ID: or 2003
Primary Vertex Position: -50cm<z<50cm
Track
nFitPts: > 15
|eta|: < 1.0
Kaon Pt range: 0.1GeV < Pttrack < 4.0GeV

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

6. |VertexZ| < 50cm, with Primary vertex found, good run
Event Selection:
|VertexZ| < 50cm, with Primary vertex found, good run
After cuts, # of Events ~ 10M
Decay mode:
Ks =>p + + p (68.6%)
X-  L + p (99.9%)
p+ + p - (63.9%)
=>K + + K - (49.1%)
K* =>K + p (100%)
Ks, L, X 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.
f ,K*: event mixing  p+
Decay point -
Primary Vertex X-

7. Ks and  reconstruction & Topology cuts- - p+ +
Track 1
Decay point
Decay point
Track 2 Ks 
Primary Vertex
Primary Vertex
Ks and  are V0 particles:
decay length: Ks = cm  = 7.89 cm
In TPC, neutral Ks and  are reconstructed from charged particles: p, K and p (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 )
DcaV0
Decay length
DcaImpact

8. K+K- pair invariant mass
Invariant mass distribution of f meson
Phi
For 40~100% centrality bin at |y|<0.5 and 0.4<pt<1.3GeV/c. Red line is the same-event distribution. Black line is the normalized mixed-event distribution.
background subtracted
Measurements in dAu collisions
Mass = ±0.5MeV/c2, FWHM=7.31.1 MeV/c2

9. K+K- pair invariant mass
Misidentified Ks
Phi
background subtracted
pp collisions
Measured Mass=1019 MeV/c2, FWHM=7.10.3 MeV/c2

10. Invariant mass plots Without background subtraction
|y|<1
0.4 <pt< 6.0
|y|<0.5
0.4 <pt< 1.3 f
Without background subtraction
Ks, L, X : topology cuts;
f: event mixing
The quality of signals are pretty good.
|y|<1
0.4 <pt< 6.0
|y|<1
0.6 <pt< 5.0

11. Efficiency Correction of f, Ks and 
STAR Preliminary
The efficiency increases with Pt and becomes flat when Pt is up to 2GeV/c2
The error bar of each efficiency correction is less than 5%.
Weak multiplicity dependence. The difference of efficiency correction between different centrality bins is small than the error.

12. Comparison of different Fits
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 functions.
Double exponential fit:
T1: ~300MeV; T2: 1.0~1.5GeV;

13. Spectra and fits
f double exp fit
pT: 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)

14. Different measurements are consistent within STAR!
Spectra comparison
Different measurements are consistent within STAR!
From Camelia

15. X spectra and feed-down contribution to L
X- + Xbar minbias : dN/dy = ±
L + Lbar minbias (inclusive) : dN/dy = ± 0.007
If assuming X0 ~ X- and  ~ 10% X- ,
Then feed-down from X,  ~ *2.1=
~ ( 17% )
Consistent with the feed-down in AuAu ~ 15% (Hui, Magali’s SQD paper)

16. dN/dy vs. <Nch>
dAu Minbias
f, Ks, L, X increase with <Nch> in dAu and AuAu collisions.

17. <pt> vs. <Nch>
dAu Minbias
<pt>: X shows no dependence of <Nch> within error bar, but f and L are different.

18. Rcp definition Rcp = (d2N/dpTd) cent/ d2N/dpTd) peri
We select three data samples:
“Central”: centrality 0-20%
“Semi-central”: centrality 20-40%
“Peripheral”: centrality %
Then we calculate the ratios Central/Peripheral as function of pT at different rapidities.
Rcp = (d2N/dpTd) cent/ d2N/dpTd) peri
Many corrections and systematics cancel out.

19. Rcp of f, Ks, L, X dAu 200 GeV AuAu 200 GeV TT TS SS TTT TTS+TSS SSS
STAR:  and K* behave like mesons, despite of the large mass: ReComb prediction
Mesons (Ks, K, f) have the same Rcp for dAu and AuAu collisions
Baryons (L, X) have the same Rcp too, but higher than mesons.
Particle production at intermediate pT region is dividing by the particle’s type,
not the mass. Recombination model works!
Recombination model can explain the difference of Rcp between mesons and baryons for both dAu and AuAu. How? nucl-th/ , nucl-th/

20. 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

21. Recombination model of Hwa and Yang
Nucl-th/ , PRL, in press

22. Recombination model of Hwa and Yang (contd)
Nucl-th/

23. v2 Scaling Perfect scaling for all measured hadrons,
P. Sorensen
Perfect scaling for all measured hadrons,
some deviation for pions (from  decays)
P. Sorensen
Baryons are pushed further in PT

24. RdAu = (d2NdAu/dpTd) / (Ncoll d2Npp/dpTd )
Nuclear modification factor RdAu
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:
RdAu = (d2NdAu/dpTd) / (Ncoll d2Npp/dpTd )
With Ncoll being the estimated number of binary collisions as d “goes through” the Au nuclei.

25. 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

26. Comparison with pA collision Particle-type dependence also!
Rw/Be at pA collisions
P.B Straub,PRL 68, 452(1992)
W: tungsten Be: beryllium
~1.4
Rw/Be :
Mesons (2 quarks):
Kaon and p ~ 1.5;
Baryons (3 quarks):
proton ~ 2.5
Particle-type dependence also!
~1.5
~2.5
s =38.8GeV
s =27.4GeV

27. Summary
Measure productions and <pt> for various particles (Ks, f, L, X, K*, Kink-K) in dAu collisions;
Double exponential function can fit the f, Ks, L and X spectra better than others;
dN/dy of f scales linearly with number of charged particles;
RdAu and Rcp in dAu are grouped into mesons and baryons; it indicates particle production is dividing by the particle type rather than particle mass as shown by the parton recombination model.
Final state effect based on recombination model works for the spectra and Rcp at dAu collisions;
Rcp plots show no suppression indicating that the suppression in Au+Au arises from additional effects.

28. The End
Thank you!

29. Spectra and fits Charge K* in power-law fit Kink from Camelia
TOF_K from Lijuan
K* from Lijuan, Haibin
Neutral K* in mt exp fit
Charge K* in power-law fit
Ks yield is lower than TOF_K and kink at the low pt, but the shapes are same.