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

相对论重离子碰撞与低能强子物理研讨会 , 2004/8/3-7, 威海

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 (SINAP)University of California, Los Angeles (UCLA)

Lawrence Berkeley National Laboratory (LBNL)

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, Cronin effect and recombination model

•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 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 also necessary for further understanding: production mechanism particle dependence of nuclear modification factor


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

Kaon 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%

STAR Preliminary

Three Multiplicity Bins are defined by the Nch per event in FTPC East

After cut: ~ 10 Million events


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 length

DcaImpact

Track 1

Track 2


STARSTAR

Measurements in dAu collisionsMass = 1019.4±0.5MeV/c2, FWHM=7.31.1 MeV/c2

K+K- pair invariant mass

background subtracted

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.

Invariant mass distribution of meson


STARSTAR

pp collisionsMeasured Mass=1019 MeV/c2, FWHM=7.10.3 MeV/c2

Misidentified KsPhi

K+K- pair invariant mass

background subtracted


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.


STARSTAREfficiency Correction of Ks and

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.

STAR 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 functions.

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;


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 Spectra comparison

Different measurements are consistent within STAR!

From Camelia


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 SQD paper)

spectra and feed-down contribution to


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 model works!Recombination model works!•Recombination modelRecombination model can explain the difference of Rcp between mesons and baryons for both dAu and AuAu. How? nucl-th/0403001, nucl-th/0401001

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 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, PRL, in press


STARSTARRecombination model of Hwa and Yang (contd)

Nucl-th/0404066


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 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 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


STARSTAR

1) Measure productions and <pt> for various particles (Ks, , K*, Kink-K) in dAu collisions;

2) Double exponential function can fit the , Ks, and spectra better than others;

3) dN/dy of scales linearly with number of charged particles;

4) 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.

5) Final state effect based on recombination model works for the spectra and Rcp at dAu collisions;

6) Rcp plots show no suppression indicating that the suppression in Au+Au arises from additional effects.

SummarySummary


STARSTAR

The EndThe End

Thank you!Thank you!


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

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

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