Search for Centauro Events Search for Centauro Events at RHIC-PHENIXat RHIC-PHENIX

Kensuke Homma / Tomoaki Nakamurafor the PHENIX Collaboration

Hiroshima University

Contents

• History of Centauro Search

• Search Strategy

• Observable and Analysis Method

• Analysis Results

• Summary and Future Plan

Centauro / Anti Centauro EventCentauro / Anti Centauro Event

Cosmic ray experiments

• Brazil-Japan collaboration in Bolivia Y.Fujimoto and S.Hasegawa, Phys. Rep. 65, 151 (1980)

• JACEE J.J.Lord and Iwai, Paper No. 515, International Conference on High Energy Physics, Dallas (1992)

O : Photon, + : Charged Particle

Anti Centauro

This is an anomalous domain based on isospin symmetry.

List of Centauro SearchesList of Centauro Searches

Experiment Collaboration CM Energy Search Region (η,φ) 1980 Mt.

ChacaltayaBrazil-Japan √s 1.7 TeV≧ ------------

1992 Balloon JACEE ------------ 5.0<η<9.0⊿φ<2π

1982 SPPS UA5 √s=540 GeV |η|<5.0

1983 SPPS UA1 √s=540 GeV |η|<3.1

1986 SPPS UA5 √s=900 GeV |η|<5.0

1996 TEVATRON CDF √s=1.8 TeV |η|<4.2, , φ<2π⊿1997 TEVATRON MINIMAX √s=1.8 TeV 3.4<η<4.2

1998 SPS WA98 √s=3.5 TeV (Pb+Pb) 2.80<η< 3.75⊿φ<π

2001 RHIC PHENIX √s=39.4 TeV (Run2 Au+Au)

|η| < 0.35⊿φ<1/2π (×2 arm)

PHENIX Experiment at Run2PHENIX Experiment at Run2

Using Magnetic Field-off data

Gamma-like Cluster (Electro-Magnetic Calorimeter)

Charged Track (BBC Z-Vertex, Drift Chamber and Pad Chamber1)

|η| < 0.35

⊿φ < π/2 in each arm

Disoriented Chiral CondensateDisoriented Chiral Condensate

Quench Mechanism

K.Rajagopal and F.Wilczek : Nucl. Phys. B379, 395 (1993)

→

⋅

d

ue

d

u i θτγ5 ( ) σφφφ

πσφ

µµ HvL ii

i

+−−∂∂=

=222

4

1

2

1

),(Chiral transformation Linear sigma model

quench

σ

π

V

σ

π

Vrestoration

QCD vacuumDCC

Chiral symmetry breaking term due to finite masses

Search StrategySearch StrategyIf every event could contain largely deviated domains on isospin symmetry and most of domains per event could be detected within a limited detector acceptance, we would be able to discuss anomaly based on the probability distribution by the statistical treatment like:

dff

dffPyprobabilit

nnn

nffraction

2

1)(:

:0

0

=

++=

−+ πππ

π

pro

bab

ilit

y :

P(f

)

fraction : f

DCC (Centauro type)

No DCC (binomial)

However, we do not know domain information on the numbers and sizes a priory, and our detector acceptance is very limited. Therefore we need to search for rare events containing anomalous domain like cosmic ray experiments rather than the simple statistical treatment.

We search for a most largely deviated domain per event by looking at differences between number of charged and gamma clusters by changing regions of interest as we do by eyes, because we don’t know what the size is and where the position is.

For example, we want to pick up this domain. We must do this search in several million events.

ObservablesObservables

γ

γ

γπ

γπ

φηφη

φηφηφηδ

NN

NN

NN

NNA

ch

ch

I

+∆∆−∆∆

≈

+∆∆−∆∆

≡∆∆±

±

)()(

)()()(

3Define an asymmetry between number of charged tracks and neutral clusters in event-by-event base as a function of subdivided η-φ phase spaces normalized by one standard deviation for a given multiplicity class.

δAI3

Domain Size

Deviation Size

Domain Position

η,φ

Domain size and domain position of largely deviated regions can be obtained at the same time by using Multi Resolution Analysis (MRA) technique.

Multi Resolution Analysis (MRA)Multi Resolution Analysis (MRA)

Wavelet function

Scaling function

Level j-1 : 2j-1 bins Level j : 2j bins

φ(2x) = 1/√2 {φ(x) + ψ(x) }φ(2x-1) = 1/√2 {φ(x) - ψ(x) }

-0.7

＝

(－ )

(＋ )

0.7φ(x)

0.7ψ(x)

x

x

-1

1

1

φ(2x-1)

x-1

1

1

φ(2x)

x

-0.7

Total number of bins is 2j

Level j represents a resolution level

Signal Signal DecompositionDecomposition

j : resolution levelk : k-th bin Cjk : coefficients of φDjk : coefficients of ψ

Signal

φ ψ

k k+

+

+

+

22 20j=4

j=3

j=2

j=1

j=0

Cjk

Djk

24/2j→ Domain Size

k → Domain Position

Cjk → Deviation Size

Djk → used to pick up k

Look for a maximum Djk per event

QuizQuiz

•Where is an anomalous domain?

•What is the domain size?

Pink dots are distributedaround 0 based on Gaussian(mean=0, σ=1.0) over 28 bins.

A single domain is hiddenwith Gaussian (mean=Nσ, σ=1.0)

AnswersAnswersNσ=3 j=5

Nσ=2 j=4

Nσ=1 j=3

Nσ=0.5 j=2

eta (j=4)phi(j=4)

C

1) projection on eta

2) projection on phi

1) projection on phi

2) projection on eta

Domain C:AI3= ~20 x 8bins(η, φ)=(3, 7) (jη , jφ)=(3, 2)

A B

Result:Correct

(η,φ)=(3,7)

(jη,jφ)=(3,2)

Result:Wrong

(η,φ)=(7,1)

(jη,jφ)=(2,4)

Example of 2-D MRA by DjkmaxExample of 2-D MRA by Djkmax

Select a domain with larger Djkmax in the second projection

Data Analysis (East Arm)Data Analysis (East Arm)

• Magnetic Field-off

• Minimum bias 818,507 events

number of charged tracks > 0

number of photon-like clusters >0

• Charged Track

BBC Z-Vertex, Drift Chamber and

Pad Chamber1 associated straight-line track

• Photon-like Cluster

Cluster of Electro-Magnetic Calorimeter

1) Photon cluster shower shape

2) Time of flight of photon

3) Not associated with charged track

4) dead and hot channels are rejected

Number of Selected Charged Track

Number of Selected Photon-like Clusters

[uncorrected]

[uncorrected]

Baseline fluctuationsBaseline fluctuations Binomial sample

Produce hit maps (28 x 28 bins in η−φ) per short run segment for γ clusters and charged tracks respectively from real data to reproduce inefficient area of the detector as realistic as possible.

Randomly distribute γ clusters and charged tracks to all η−φ space, but if there is no entry in the hit map, discard the cluster or track until # of accepted clusters and tracks coincide with those observed in a given real event.

η

φ

η

φ

Map for charged tracks

Map for γ clusters

W/O hit map With hit map

Example of binomial distributionExample of binomial distribution

DC component of Nch-Nγ per event is subtracted in advance before the 2D MRA. This gives almost symmetric shape in the maximum deviation distribution, even if the slope in the correlation plot is different from one, unless a given hit map biases partial phase space.

(Nch, Nγ)=(200,100)

Maximum Deviation SizeMaximum Deviation Size

Maximum Deviation Size (A.U.)

• PHENIX magnetic field-off data

Au+Au 200 GeV

818,507 events

East Arm [uncorrected]

• Binomial sample with hit map

100 times larger statistics

using same multiplicity-set

Level-by-Level Deviation Size Level-by-Level Deviation Size ⊿

η:

0.

044

　0.

088

　

0.17

5

0.35

0 　

⊿φ :　　 2.813° 　 　 5.625°　　　 11.25° 　　　 22.50° 　 45.00°

[East Arm, uncorrected]

-1.0 -0.5 0 0.5 1.0 -1.0 -0.5 0 0.5 1.0-1.0 -0.5 0 0.5 1.0-1.0 -0.5 0 0.5 1.0-1.0 -0.5 0 0.5 1.0

-- Data --Binomial

Positive DeviationPositive Deviation(Centauro Type)(Centauro Type)

pseudo rapidity :η

azim

uth

al a

ngl

e :φ

[rad

]

⊿η=0.175

⊿φ

=22

.5

pseudo rapidity :η

azim

uth

al a

ngl

e :φ

[rad

]

＋ : charged track = 46

○ : photon-like cluster = 0

Summary and Future PlanSummary and Future Plan

• We have demonstrated two dimensional multi-resolution analysis on the asymmetry between the number of the charged tracks and γ-like clusters in the η-φ phase space.

• Detector biases will be more rigorously studied.• We will set a reasonably tight significance level to

define the degree of anomaly based on realistic physical models with normal fluctuations.

• We will measure signal to background ratios above the significance level .

• We will discuss characters of those events such as centrality dependence and azimuthal correlation with respect to reaction plane.

Back up slidesBack up slides

Centrality DeterminationCentrality Determination • Event characterization in terms of impact

parameter (b) in Au+Au collisions.– Large : peripheral collision– Small : central collision

• Coincidence between BBC and ZDC.– Determine collision centrality.– 92 % of inelastic cross section can be

seen.• Extract variables using Glauber Model

– Number of participants (N_part). • Number of nucleons participate in a

collision. • Represents centrality.• Related with soft physics.

– Number of binary collisions (N_binary).

• Number of Nucleon-Nucleon collisions.

• Related with hard physics.• Incoherent sum of N-N collisions

becomes a baseline for A-A collisions.

peripheral central

BBC Charge Sum

ZD

C T

ota

l En

erg

y

bto ZDC

spectator

participant

to BBC

Central Arm

Central Arm

Normalization per centrality binNormalization per centrality bin

Number of Charged Tracks

Nu

mb

er o

f P

ho

ton

-lik

e C

lus

ters

Centrality <Nt>+<Ng> Factor10 0-10% 221.5 0.067 9 10-20% 158.3 0.079 8 20-30% 109.2 0.096 7 30-40% 72.36 0.118 6 40-50% 44.92 0.149 5 50-60% 25.88 0.196 4 60-70% 13.87 0.269 3 70-80% 7.744 0.360 2 80-90% 5.319 0.434 1 90-94% 4.223 0.487

><+>< γNNch/1

Correlation between Nch vs. Nγ

[uncorrected]Normalization factor

per centrality

Centrality-by-Centrality Centrality-by-Centrality Maximum Deviation SizeMaximum Deviation Size

-1.0 -0.5 0 0.5 1.0

Top 10%

100843 events10-20%

101585

20-30%

98416

30-40%

98673

40-50%

98898

50-60%

98685

60-70%

92970

70-80%

68048

80-90%

42529

90-94%

5589

-1.0 -0.5 0 0.5 1.0

-- Data --Binomial