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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