# Presentation: 322791

## Search for Centauro Events at RHIC-PHENIX

**Search for Centauro Events ****at 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**

## Centauro / 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.**

**Notes:**
In the 1970's high energy cosmic ray experiments observed anomalous events that have a large asymmetry between the number of charged and $\gamma$ clusters. 

## List 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) |

**Notes:**
This is a list of Centauro searches. There are some approaches of searching for Centauro events after the report from cosmic ray experiment but, its candidate have never been observed in the past accelerator experiments. RHIC is the most high energy accelerator with respect to total center of mass energy. We perform this Centauro search by using PHENIX detector at RHIC. 

## PHENIX 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**

**Notes:**
This is the PHENIX detector. This detector has a two arm structure, each of which covers 90 degree in azimuth and $\pm$ 0.35 in pseudo rapidity, and it can detect charged tracks and $\gamma$ clusters in the same phase space. We count charged track by using Drift Chamber and Pad Chamber1, and count gamma-like cluster by using Electro Magnetic Calorimeter which is not associated charged track.

## Disoriented Chiral Condensate

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

**Chiral transformation**

**Linear sigma model**

**quench**

**restoration**

**QCD vacuum**

**DCC**

**Chiral symmetry breaking term due to finite masses**

**Notes:**
These events, named "Centauro Event", could be explained by a generation of disoriented chiral condensates (DCC) at the chiral phase transition based on effective theories of QCD (explained by linear sigma model) . As a result, domains with large fluctuations in the neutral to charged pion ratio could be created event-by-event. In this perspective, such an event is a signature of the chiral symmetry restoration. 

## Search 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:**

**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.**

**Notes:**
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:
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 domains like cosmic ray experiments rather than the statistical treatment above.

## 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.

**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.**

**Notes:**
We search for a most largely deviated domain per event  by looking at differences between number of charged and gamma-like 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.

## Observables

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

***δA******I3***

**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)

**Total number of bins is 2****j**
**Level j represents a resolution level**

## Signal Decomposition

-  **j      : resolution level**
**k      : k-th bin **
**Cjk  : coefficients of φ**
**Djk  : coefficients of ψ**

**2****4****/2****j****→ Domain Size**
**k     → Domain Position**
**Cjk → Deviation Size**
**Djk → used to pick up ****k**

**Look for a maximum Djk per event **

## Quiz

**Where is an anomalous domain?**
**What is the domain size?**

- Pink dots are distributed
- around 0 based on Gaussian
- (mean=0, =1.0) over 28 bins.
- A single domain is hidden
- with Gaussian (mean=N, =1.0)

## Answers

- N=3     j=5

- N=2     j=4

- N=1     j=3

- N=0.5  j=2

## Example of 2-D MRA by Djkmax

- 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
- (, )=(3, 7)
-  (j ,  j)=(3, 2)

- A

- B

- Result:Correct
- (,)=(3,7)
- (j,j)=(3,2)

- Result:Wrong
- (,)=(7,1)
- (j,j)=(2,4)

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

**Select a domain with larger Djkmax in the second projection**

## 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**

## Baseline fluctuations

_**Binomial sample**_
- Produce hit maps (28 x 28 bins in ) per short run segment for  clusters and charged tracks respectively from real data to reproduce inefficient area of the detector as realistic as possible.
- Randomly distribute  clusters and charged tracks to all  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.

- 

- 

- 

- 

**Map for charged tracks**

**Map for ******** clusters**

## Example of binomial distribution

**Example of binomial distribution**

- DC component of Nch-N 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, N)=(200,100)

## Maximum Deviation Size  

**Maximum 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 

**⊿****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

## Positive Deviation(Centauro Type)

**+ ****: charged track         = 46**
**○ ****: photon-like cluster = 0**

## Summary 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 slides

## Centrality 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.

## Normalization per centrality bin

**Number of Charged Tracks**

**Number of Photon-like Clusters**

-      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

**Correlation between Nch vs. N******

- [uncorrected]

**Normalization factor**
**per centrality**

## Centrality-by-Centrality Maximum Deviation Size

**Centrality-by-Centrality Maximum Deviation Size**

-       -1.0       -0.5        0         0.5       1.0

-       -1.0       -0.5        0         0.5       1.0

- -- Data    --Binomial