f, ks, , and x production at 200 gev d+au collisions from star

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

STARSTAR Ks, and production at 200 GeVd+Au collisions from STAR

Xiangzhou Cai, Yugang Ma, Hai Jiang, Jingguo Mafor 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, RdAu, particle dependence of Cronin effect

•Summary


STARSTAR 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

m~1019 MeV/c2 ; m~1116 MeV/c2; mKs~498 MeV/c2


STARSTAR

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 < Pttrack < 4.0GeV

Data Sets and Event Cuts


STARSTAR 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 STAR

Preliminary

Preliminary


STARSTAR

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+

Decay point

-

Primary Vertex

-

-

Decay point


STARSTAR

• 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+

Ks and reconstruction & Topology cuts

Primary Vertex

Ks

-

+

Primary Vertex

Decay point Decay point

DcaV0

Decay len

DcaImpact

Track 1

Track 2


STARSTAR

K+ K- Branching Ratio = 0.49

Both K+ and K- come from the same eventSignal

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 possibleK+K- pairs and accumulate the signal toreconstruct in each (y, pt) bin.

Event Mixing Method


STARSTAR 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 STAR

Preliminary

Preliminary


STARSTARAcceptance and

Efficiency

4

Embedding method: Generate tracks with certain pT 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

SimTrack

MCTrack

MCTrack

cTrackRe


STARSTAREfficiency Correction of Ks and

The efficiency increases with Pt and becomes flatWeak multiplicity dependence. The difference of efficiency correction between different centrality bins is small than the error bars.

STAR STAR

Preliminary

Preliminary


STARSTAR

Spectra for MinBias Phi production in dAuexp 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

21

)0()0(

)1(2

T

mmt

T

mmt

eaaedy

dN

Double exponential fit:

T1: ~300MeV; T2: 1.0~1.5GeV;

STAR STAR PreliminaryPreliminary


STARSTAR production in AuAu and ppproduction 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


STARSTAR Spectra and fits

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)

double exp fit



STARSTAR

- + 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 Consistent with the feed-down in AuAu ~ 15% AuAu ~ 15% (Hui, Magali’s SQM paper)

spectra and feed-down contribution to



STARSTAR Spectra comparison

Different measurements are consistent within STAR!

From Camelia


STARSTAR dN/dy vs. <Nch>

• , Ks, , increase with <Nch> in dAu and AuAu collisions.

dAu Minbias



STARSTAR <pt> vs. <Nch>

<pt>: shows no dependence of <Nch> within error bar, but and are different.

dAu Minbias



STARSTAR Rcp 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 pT at different rapidities.

Rcp = (d2N/dpTd) cent/ (d2N/dpTd) peri

Many corrections and systematics cancel out.


STARSTAR 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.Particle production at intermediate pT region is dividing by the particle’s

type, not the mass. Recombination/Coalescence model works!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….)

TTTT TSTS SSSS

TTTTTT TTS+TSSTTS+TSS SSSSSS

AuAu 200 GeVdAu 200 GeV

STAR: and K* behave like mesons, despite of the large mass: ReComb prediction


STARSTAR 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.


STARSTAR 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


STARSTAR

1) Measure the productions and <pt> 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) RdAu and Rcp 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) Rcp plots show no suppression indicating that the suppression in Au+Au maybe arises from additional effects

SummarySummary


STARSTAR

The EndThe End

Thank you!Thank you!


STARSTAR 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:

qqqB qqM


STARSTARRecombination model of Hwa and Yang

Nucl-th/0403001, Nucl-th/0404066

++- in d+Au P in d+Au


STARSTAR 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


STARSTAR v2 Scaling

Baryons are pushed further in PT

Perfect scaling for all measured hadrons,some deviation for pions (from decays)

P. Sorensen

P. Sorensen


STARSTAR Comparison with pA collision

s =27.4GeV

P.B Straub,PRL 68, 452(1992)Rw/Be at pA collisions

W: tungsten Be: beryllium

s =38.8GeV

RRw/Bew/Be : : Mesons Mesons (2 quarks):(2 quarks):

Kaon and Kaon and ~ 1.5; ~ 1.5; Baryons Baryons (3 quarks):(3 quarks):

protonproton ~ 2.5 ~ 2.5

Particle-type Particle-type dependence also!dependence also!

~1.4

~1.5

~2.5

f, ks, , and x production at 200 gev d+au collisions from star

Documents