SQM2004, Cape Town, Sept. 16, 2004 STAR 1 Cronin Effect for the identified particles from 200 GeV...

SQM2004, Cape Town, Sept. 16, 2004

STARSTAR

1

Cronin Effect for the identified particles from 200 GeV d+Au collisions

Xiangzhou CaiShanghai 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, RdAu, particle dependence of Cronin effect

•Summary


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Introduction Introduction

AAndnd

MotivationMotivation


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Some Definitions

ppinelbinAB

TTpp

inelAB

TTAB NT

dydppdT

dydppNdR

/,)2/(

)2/(2

2

peripheralNdydppNd

centralNdydppNdR

binTT

binTTcp |)/)2/((

|)/)2/((2

2

TpB

TpATBA pdd

pdd

A

BpR

2

2

/ /

/)(

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:


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STAR

PHENIX

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 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 pT in AuAu collisions.

Rcp & v2 @ 200GeV Au+Au

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

PHENIX: PRL91, 182301(03) STAR: PRL92, 052302(04) nucl-ex/0306007Models: Greco et al, PRC68, 034904(03)

Saturation at intermediate pT

Baryon and meson difference

Baryon

Meson


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Analysis details Analysis details

AAndnd

Spectra of identified Spectra of identified particles particles


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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 STAR

Preliminary

Preliminary


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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


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• 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


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Reconstruction of

p

B

Dca L

ambda D

augh

ters

Dca X

i To P

rim V

ertex

Decay L

ength

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


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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


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

K+K- pair invariant mass

background subtracted

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


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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.


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Spectra for MinBias 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 for Spectra

21

)0()0(

)1(2

T

mmt

T

mmt

eaaedy

dN

Double exponential fit:

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

STAR STAR PreliminaryPreliminary


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Spectra and fits: Ks

pT: 0.4 – 6 GeV/c. cross point: pT~(2~4)GeV/c2.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



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Spectra : k, p

• The spectra in d+Au collisions are harder than those in p+p collisions


p+pp+p

p+p

peripheral

central


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dN/dy vs. <Nch>

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

dAu Minbias

STAR Prelim

inary

STAR Prelim

inary


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<Pt> vs. <Nch>

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

dAu Minbias

STAR Preliminary

STAR Preliminary


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Cronin effect Cronin effect

AAnd nd

Recombination modelRecombination model


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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.


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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.


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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 pT 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.

TTTT TSTS SSSS

TTTTTT TTS+TSSTTS+TSS SSSSSS

STAR: behaves like mesons, despite of the large mass: ReComb prediction


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RdAu of comparing with K p

•Particle production at intermediate pT region is sorted by the particle’s type, not the mass

ppinelbindAu

TTpp

ineldAu

TTdAu NT

dydppdT

dydppNdR

/,)2/(

)2/(2

2

• Low pT, RdAu <1 High pT, RdAu >1 Px~=1 GeV/c • RdAu(p)> RdAu(,,K) • RdAu of is closer to that of and k than that of pSTAR STAR

PreliminaryPreliminary


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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

the particle dependence has the particle dependence has also been observed previously also been observed previously at lower energy.at lower energy.

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 dependence!Particle-type dependence!

~1.4

~1.5

~2.5

pA A pp

TpB

TpATBA pdd

pdd

A

BpR

2

2

/ /

/)(


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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) 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.

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.

SummarySummary


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The EndThe End

Thank you!Thank you!

SQM2004, Cape Town, Sept. 16, 2004 STAR 1 Cronin Effect for the identified particles from 200 GeV...

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Transcript of SQM2004, Cape Town, Sept. 16, 2004 STAR 1 Cronin Effect for the identified particles from 200 GeV...