Xuan Li 1

Rapidity dependency of azimuthal correlations for pp and dAu

Xuan Li (BNL&SDU)

STAR Collaboration meeting (BNL, Nov 2010)

Xuan Li 2

Outline

• Motivation• Data analysis– cluster finder introduction– π0 like events selection and data & simulation

comparison– Preliminary correlation results

• Summary & To do

Xuan Li 3

Motivation• To probe nuclear gluon density at low x.

Proton gluon density

At a given x, nuclear (mass number A) gluon density ≈ A1/3* nucleon gluon density. And we lack data below x=0.02 for nuclear [Phys. Rev. C70 (2004)044905, hep-ph/0308248].

Can’t increase indefinitely.Saturation?

Fixed Target Experiments

Rapid rise of the gluon density at low-x evident from F2(x)/lnQ2 at fixed x (Prytz relation)

Xuan Li 4

Motivation• How to access low X gluon.

Q2 ~ pT2

s 2EN

ln(tan(2

))

xq xF / z

xF 2E

s

z E

Eq

xg pT

se g

• Large rapidity p production (hp~4) probes asymmetric partonic collisions.

• Mostly high-x valence quark + low-x gluon

• 0.3 < xq< 0.7

• 0.001< xg < 0.1 , this is broad distribution for gluon.

• If we measure two jets, we will limit the measured gluon x range.

Forward di-jets are more sensitive to low x gluon.

Xuan Li 5

Motivation• Test the phase boundary at fixed Q2.

€

ln(1

x)

€

ln(PT2)

Fix PT , look through different x region

τ related to rapidity of produced hadrons.

(Iancu and Venugopalan, hep-ph/0303204)

Fix Pt at forward rapidity π0, and vary the rapidity of associated π0.Vary the Pt to study the boundary.

Xuan Li 6

Motivation

FMS-BEMC(TPC) correlation

Triggering on the forward rapidity π0, the rapidity of the associated π0 is correlated with the soft parton involved in the partonic scattering.

• Provide direct sensitivity to gluon density at 0.001< x < 0.02.

arXiv:0907.3473

PT(FMS)>2.5GeV/c1.5GeV/c<PT(BEMC/TPC)<PT(FMS)

PT(FMS)>2.0GeV/c1.0GeV/c<PT(BEMC/TPC)<PT(FMS)

Xuan Li 7

Motivation

FMS-FMS correlation

Triggering on the forward rapidity π0, the rapidity of the associated π0 is correlated with the soft parton involved in the partonic scattering.

• Provide direct sensitivity to gluon density at 0.001< x < 0.02.

arXiv:1005.2378

Xuan Li 8

Motivation

FMS-EEMC correlation

Triggering on the forward rapidity π0, the rapidity of the associated π0 is correlated with the soft parton involved in the partonic scattering.

• Provide direct sensitivity to gluon density at 0.001< x < 0.02.

?

Xuan Li 9

π0 decay kinematics• Run8 STAR geometry

€

Mγγ = Eγγ 1− Zγγ2 sin

φγγ

2, where Eγγ = E1 + E 2,

Zγγ =E1 − E2

E1 + E2

and φγγ is angle between two photon

momentum vectors. dγγ is the seperation of the two

photons.

π0 decay into 2 photons. Assuming the energy of π0 is 3GeV to 10GeV, then the separation of photons in EEMC is from 25.2cm to 7.6 cm.

Proton (Deuteron)Proton (Gold)

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FMS π0 triggered event• Within the FMS triggered data, selecting events where di-

photon invariant mass is less than 0.2GeV/c2 and Pt is larger than 2.5 GeV/c.

For example, with pp FMS triggered data.

• Primary vertex associated with BBC coincidence requirements.

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Introduction to cluster finder• BEMC (EEMC) geometryEEMC η range [1.08,2.0], BEMC η range [-1,1].

Z

X(Y)

X

Y

ϕ

η

ϕ

η

EEMC BEMC

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Event display• Run 8 pp fms triggered data. Cluster is threshold bounded group

of towers. The energy threshold for the BEMC tower is 70MeV, and for EEMC is ADC pedestal plus 4sigma. Sorting the tower energy, then add in the tower near the high tower to construct cluster.

EEMC BEMC

cluster

cluster

BEMC tower energy depositedwithout energy threshold.

13

EEMC cluster properties in pp data• Single cluster tower multiplicity, energy, η and φ.

pp dAu

1: Tower multiplicity mean

1.84 1.93

2: cluster energy mean

0.93 0.94

3: cluster η mean 1.49 1.57

4 cluster ϕ χ2/ndf 76 406

1 2

34

14

BEMC cluster properties in pp data• Single cluster tower multiplicity, energy, η and φ.

pp dAu

1: Tower multiplicity mean

1.52 1.83

2: cluster energy mean

0.43 0.70

3: cluster η mean 0.02 0.02

4: cluster ϕ χ2/ndf 241 186

15

π0 like event (di-cluster)• PP part for BEMC η>=0 part.

Mass of di-clustersleading tower energy over cluster energy in leading cluster

Zγγ is energy sharing between two clusters

(1) 1.25GeV/c < Pt<2.5GeV/c(2) Fiducial Volume cut, requirecluster detector η in [0,0.9]..

(1) 1.25GeV/c < Pt<2.5GeV/c(2) Fiducial Volume cut, reuirecluster detector η in [0,0.9]. (3) Ratio of leading tower energyover cluster energy > 0.9(4) Zγγ < 0.7

π0 peak in BEMC di-clusters.

16

π0 like event (di-cluster)• PP part for EEMC

Mass of di-clusters Zγγ is energy sharing between two clusters

leading tower energy over cluster energy in leading cluster

(1) 1.25GeV/c < Pt<2.5GeV/c(2) Fiducial Volume cut, requirecluster detector η in [1.1,1.9]..

(1) 1.25GeV/c < Pt<2.5GeV/c(2) Fiducial Volume cut, reuirecluster detector η in [1.1,1.9]. (3) Ratio of leading tower energyover cluster energy > 0.9(4) Zγγ < 0.7

π0 peak in EEMC di-clusters.

17

π0 like event (di-cluster)• dAu part for BEMC η>=0 part.

Mass of di-clustersleading tower energy over cluster energy in leading cluster

Zγγ is energy sharing between two clusters

(1) 1.25GeV/c < Pt<2.5GeV/c(2) Fiducial Volume cut, requirecluster detector η in [0,0.9]..

(1) 1.25GeV/c < Pt<2.5GeV/c(2) Fiducial Volume cut, reuirecluster detector η in [0,0.9]. (3) Ratio of leading tower energyover cluster energy > 0.9(4) Zγγ < 0.7

π0 peak in BEMC di-clusters.

18

π0 like event (di-cluster)• dAu part for EEMC

Mass of di-clustersleading tower energy over cluster energy in leading cluster

Zγγ is energy sharing between two clusters

(1) 1.25GeV/c < Pt<2.5GeV/c(2) Fiducial Volume cut, requirecluster detector η in [1.1,1.9]..

(1) 1.25GeV/c < Pt<2.5GeV/c(2) Fiducial Volume cut, reuirecluster detector η in [1.1,1.9]. (3) Ratio of leading tower energyover cluster energy > 0.9(4) Zγγ < 0.7

π0 peak in EEMC di-clusters.

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π0 events in the EEMC single cluster?• Assuming the tower is zero massed,

• Assuming the leading tower, sub-leading tower as the photon candidates in the EEMC single cluster,

• Dγγ is defined as the separation between the photons which is projected in the EEMC detector.

X

Y

Dγγ

Z

X(Y)

γ1

γ2

Dγγ

€

Ecluster = E i , i

∑r P cluster =

r P i ,

i

∑ i is the tower in the cluster

€

Zγγ =E1 − E2

E1 + E2

, E1 is the leading tower energy and E 2 is

the sub - leading tower energy.

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Simulated π0 decay kinematics• Projection on the EEMC, with the π0 Pt in [1.25GeV/c,

2.5GeV/c] and Zγγ<0.7 cuts.

Dγγ VS η of π0 Dγγ VS Zγγ

Most of the π0 events are in EEMC single clusters.

For FMS π0 events,Cuts on the single cluster is(1) 1.25GeV/c<Pt<2.5GeV/c(2) Zγγ < 0.7

21

π0 like event (single cluster)• PP part for EEMC

Mass of single cluster Leading and sub-leading tower energy over cluster energy

Zγγ is energy sharing between leading two towers.

1.25GeV/c < Pt<2.5GeV/c

(1) 1.25GeV/c < Pt<2.5GeV/c.(2) Ratio of leading plus sub-leading tower energy over cluster energy in [0.5,0.85].(3) Zγγ < 0.65

π0 candidates

22

π0 like event (single cluster)• dAu part for EEMC

Mass of single cluster Leading and sub-leading tower energy over cluster energy

Zγγ is energy sharing between leading two towers.

1.25GeV/c < Pt<2.5GeV/c

(1) 1.25GeV/c < Pt<2.5GeV/c.(2) Ratio of leading plus sub-leading tower energy over cluster energy in [0.5,0.85].(3) Zγγ < 0.65

π0 candidates

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MB data and simulation comparison• EEMC pp MB single cluster simulation.

ratio is Leading and sub-leading tower energy over cluster energy.Zγγ is energy sharing between leading two towers.

Simulation Simulation

Data

Data

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MB data and simulation comparison• EEMC pp MB single cluster propeties.

MB simulationMB data

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MB data and simulation comparison• EEMC pp MB single cluster invariant mass.

(1) 1.25GeV/c < Pt<2.5GeV/c.(2) Ratio of leading plus sub-leading tower energy over cluster energy in [0.5,0.85].(3) Zγγ < 0.65

scale different

Simulation Data

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MB data and simulation comparison• EEMC dAu MB single cluster invariant mass.

(1) 1.25GeV/c < Pt<2.5GeV/c.(2) Ratio of leading plus sub-leading tower energy over cluster energy in [0.5,0.85].(3) Zγγ < 0.65

scale different

Simulation Data

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Azimuthal correlation (FMS-BEMC)• FMS photon pair Pt > 2.5GeV/c and mass<0.2 GeV/c2. BEMC

di-cluster 1.25GeV/c < Pt < 2.5GeV/c and mass<0.2GeV/c2.

Fms triggered pp data Fms triggered dAu dataUnc

orre

cted

Coi

ncid

ence

Pro

babi

lity

(rad

ian

-1 )

Width 0.710 ± 0.030 Width 0.733± 0.041

Xuan Li 28

Azimuthal correlation (FMS-BEMC)• FMS photon pair Pt > 2.0GeV/c and mass<0.2 GeV/c2. BEMC

di-cluster 1.0GeV/c < Pt < 2.0GeV/c and mass<0.2GeV/c2.

Fms triggered pp data Fms triggered dAu dataUnc

orre

cted

Coi

ncid

ence

Pro

babi

lity

(rad

ian

-1 )

Width 0.815 ± 0.019 Width 0.752± 0.031

Xuan Li 29

Azimuthal correlation (FMS-EEMC)• FMS photon pair Pt > 2.5GeV/c and mass<0.2 GeV/c2. EEMC di-

cluster 1.25GeV/c < Pt < 2.5GeV/c and mass<0.2GeV/c2.

Fms triggered pp data Fms triggered dAu data

Unc

orre

cted

Coi

ncid

ence

Pro

babi

lity

(rad

ian

-1 )

Width 0.961 ± 0.127 Width 0.817 ± 0.196

Xuan Li 30

Azimuthal correlation (FMS-EEMC)• FMS photon pair Pt > 2.0GeV/c and mass<0.2 GeV/c2. EEMC di-

cluster 1.0GeV/c < Pt < 2.0GeV/c and mass<0.2GeV/c2.

Fms triggered pp data Fms triggered dAu data

Unc

orre

cted

Coi

ncid

ence

Pro

babi

lity

(rad

ian

-1 )

Width 0.833 ± 0.048 Width 1.032 ± 0.179

Xuan Li 31

Azimuthal correlation (FMS-EEMC)• FMS photon pair Pt > 2.5GeV/c and mass<0.2 GeV/c2. EEMC

single cluster 1.25GeV/c < Pt < 2.5GeV/c and mass<0.2GeV/c2.

Fms triggered pp data Fms triggered dAu dataUnc

orre

cted

Coi

ncid

ence

Pro

babi

lity

(rad

ian

-1 )

Width 0.731 ± 0.021 Width 0.935 ± 0.061

Xuan Li 32

Azimuthal correlation (FMS-EEMC)• FMS photon pair Pt > 2.0GeV/c and mass<0.2 GeV/c2. EEMC

single cluster 1.0GeV/c < Pt < 2.0GeV/c and mass<0.2GeV/c2.

Fms triggered pp data Fms triggered dAu data

Unc

orre

cted

Coi

ncid

ence

Pro

babi

lity

(rad

ian

-1 )

Width 0.840 ± 0.015 Width 1.039 ± 0.053

Xuan Li 33

Summary• To find the 3rd point from FMS-EEMC azimuthal

correlation to approach gluon density at low x.• BEMC di-cluster π0 like correlation results are

consistent with Ermes’s correlation results.• There are π0 like hints in the EEMC tower clusters.

To do• To add in ESMD information to get clearer π0 events. • Need suggestions and help for he ESMD calibration.• Work on the

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Backup

Xuan Li 35

Motivation

FMS-FMS correlation

FMS-EEMC correlation

FMS-BEMC(TPC) correlation

Triggering on the forward rapidity π0, the rapidity of the associated π0 is correlated with the soft parton involved in the partonic scattering.

• Provide direct sensitivity to gluon density at 0.001< x < 0.02.

Xuan Li 36

Event display• Run 8 dAu fms triggered data.

EEMC BEMC

Xuan Li 37

Cluster width definition• BEMC• Unfold the barrel, and put in the Rϕ, Z plane.

Z

X(Y)

R

ϕ

Z

Rϕ

Large width

Small width

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Cluster width definition• EEMC• In xy plane.

X

Y

Large width

Small width

X

Y

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dAu FMS triggered data • FMS di-photon invariant mass.

With FMS photon pair which has mass less than 0.2GeV/c2 and Pt larger than 2.5 GeV/c.

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EEMC cluster property in dAu data• Single cluster tower multiplicity, energy, η and φ.

Xuan Li 41

BEMC cluster property in dAu data• Single cluster tower multiplicity, energy, η and φ.

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π0 like event (single cluster)• EEMC pp fms triggered single cluster mass.

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π0 like event (single cluster)• EEMC dAu fms triggered single cluster mass.

Xuan Li 44

MB data and simulation comparison• EEMC dAu MB single cluster simulation.

ratio is Leading and sub-leading tower energy over cluster energy.Zγγ is energy sharing between leading two towers.

Simulation Simulation

Data

Data