This document summarizes a search for Centauro events at the PHENIX experiment at RHIC. It discusses the history and previous searches for Centauro events. The analysis uses PHENIX data from Au+Au collisions at √sNN = 200 GeV to look for anomalous domains with large deviations between the number of charged tracks and photon-like clusters in η-φ phase space bins. A multi-resolution analysis technique is used to identify potential Centauro-like domains and estimate their size and position on an event-by-event basis. Preliminary results are shown for the maximum deviation between charged and neutral particles across bins and in different centrality bins.

1. Search for Centauro EventsSearch for Centauro Events
at RHIC-PHENIXat RHIC-PHENIX
Kensuke Homma / Tomoaki Nakamura
for the PHENIX Collaboration
Hiroshima University
Contents
• History of Centauro Search
• Search Strategy
• Observable and Analysis Method
• Analysis Results
• Summary and Future Plan

2. 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.

3. List of Centauro SearchesList of Centauro Searches
Experiment Collaboration CM Energy Search Region (η,φ)
1980 Mt.
Chacaltaya
Brazil-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)

4. 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

5. Disoriented Chiral CondensateDisoriented Chiral Condensate
Quench Mechanism
K.Rajagopal and F.Wilczek
: Nucl. Phys. B379, 395
(1993)






→




 ⋅
d
u
e
d
u i θτγ5
( ) σφφφ
πσφ
µ
µ HvL ii
i
+−−∂∂=
=
222
4
1
2
1
),(
Chiral transformation Linear sigma model
quench
σ
π
V
σ
π
V
restoration
QCD vacuumDCC
Chiral symmetry breaking
term due to finite masses

6. Search StrategySearch Strategy
If 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:
df
f
dffPyprobabilit
nnn
n
ffraction
2
1
)(:
:
0
0
=
++
=
−+
πππ
π
probability: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.

7. 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.

8. ObservablesObservables
γ
γ
γπ
γπ
φηφη
φηφη
φηδ
NN
NN
NN
NN
A
ch
ch
I
+
∆∆−∆∆
≈
+
∆∆−∆∆
≡∆∆
±
±
)()(
)()(
)(3
Define 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.

9. 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
＝
( － )
( ＋ )
0.7
φ(x)
0.7
ψ(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

10. SignalSignal
DecompositionDecomposition
j : resolution level
k : k-th bin
Cjk : coefficients of φ
Djk : 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

11. QuizQuiz
•Where is an
anomalous
domain?
•What is the
domain size?
Pink dots are distributed
around 0 based on Gaussian
(mean=0, σ=1.0) over 28
bins.
A single domain is hidden
with Gaussian (mean=Nσ, σ=1.0)

12. AnswersAnswers
Nσ=3 j=5
Nσ=2 j=4
Nσ=1 j=3
Nσ=0.5 j=2

13. 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

14. 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]

15. 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

16. 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)

17. 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

18. Level-by-Level Deviation SizeLevel-by-Level Deviation Size⊿η:0.044 0.088 0.175
0.350
⊿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

19. Positive DeviationPositive Deviation
(Centauro Type)(Centauro Type)
pseudo rapidity :η
azimuthalangle:φ[rad]
⊿η=0.175
⊿φ=22.5
pseudo rapidity :η
azimuthalangle:φ[rad]
＋ : charged track = 46
○ : photon-like cluster = 0

20. 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.

21. Back up slidesBack up slides

22. 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
ZDCTotalEnergy
b
to ZDC
spectator
participant
to BBC
Central Arm
Central Arm

23. Normalization per centrality binNormalization per centrality bin
Number of Charged Tracks
NumberofPhoton-likeClusters
Centrality <Nt>+<Ng> Factor
10 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

24. Centrality-by-CentralityCentrality-by-Centrality
Maximum Deviation SizeMaximum Deviation Size
-1.0 -0.5 0 0.5 1.0
Top 10%
100843
events
10-20%
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