# Presentation: 480783

## Amazing Title Slide

- Reworking the CES Cluster Reconstruction Algorithm
- By: Steve Fedele
- Advisor: Pavel Murat

## Overview

- Tau reconstruction description
- Shortcomings  of old reconstruction algorithm
- Description of new algorithm
- Preliminary results
- The future

- TAU

## Tau reconstruction

- Tau leptons decayeither leptonically or hadronically
- Leptonic: T -> e vv
- Hadronic: T -> Pi v
- Leptonic decay is difficult to identify
- W -> e v
- W -> T v -> e v vv
- Hadronic decay via 2 primary channels
- “1 prong” : T -> Pi+ Pi0 .... v
- “3 prong”: T -> Pi+ Pi+ Pi – Pi0 ... v
- Pi0 decay into 2 photons
- Thus reconstruction of photons allow reconstruction of taus
- Photon reconstruction occurs in CES / Calorimeter

## CES Overview

- CEM : (Electromagnetic Calorimeter) before CHA (Hadronic Calorimeter)
- CES =  Strip Chamber located inside CEM
- Read out from X side (Wire) and Z side (Strip)
- Each channel reads out total ADC counts (charge) deposited on that channel.

- CHA
- CEM
- CES ^

## Reconstruction Goals:
Identify “clusters” on wire and strip side
Match clusters on wire and strip side
From this one can tell
Energy of shower
Location of shower in 2D CES plane

- Identify “clusters” on wire and strip side
- Match clusters on wire and strip side
- From this one can tell
- Energy of shower
- Location of shower in 2D CES plane

_**CES Readout Example**_

## Old Reconstruction Algorithm

- Fixed window algorithm
- Track/Seed based reconstruction
- Fit to standard shower profile obtained from 1985 test beam
- For more details see Riveline's CDF note number 5863

## Windowing method can group two distinct clusters into one
Reduces the ability to resolve close or merged clusters
Such merged clusters occur often in the case of high PT pi0 decay
Track based methods fail on neutral particles, e.g. Pi0s.  
Standard E/P < 2 cut implicitly supresses photon emission

- Reduces the ability to resolve close or merged clusters
- Such merged clusters occur often in the case of high PT pi0 decay
- Track based methods fail on neutral particles, e.g. Pi0s.
- Standard E/P < 2 cut implicitly supresses photon emission

_**Old Algorithm: Issues**_

## The Algorithm
Identify continuous regions of charge
Identify local maxima within regions
Fit to standard cluster shape by varying
Charge Q on individual cluster
Offset DX from maxima position
Note:
Total charge of clusters in region must remain normalized
-0.5 channel < DX < 0.5 channel
Assumptions:
All particles produce same shower profile
Number of clusters = Number of maxima

- Identify continuous regions of charge
- Identify local maxima within regions
- Fit to standard cluster shape by varying
- Charge Q on individual cluster
- Offset DX from maxima position
- Note:
- Total charge of clusters in region must remain normalized
- -0.5 channel < DX < 0.5 channel
- Assumptions:
- All particles produce same shower profile
- Number of clusters = Number of maxima

_**New Algorithm: Description**_

## New Algorithm: Questions

- Is assumption on cluster shape valid?
- What is cluster shape?
- Can we use old Run I cluster shape?
- How do bad channels in CES affect results?
- How to correct for this?

## Readout Corrections

- Two types
- Global : effects of chamber warping – continuous
- Channel specific due to wiring, electronics, etc.
- Correct global effects by looking at Wire/Strip charge vs position
- Gives continuous correction factor
- Different types of bad channels
- Dead
- Noisy
- Identify by obtaining energy spectrum histogram for each channel and comparing it to its neighbor's (factor out continuous problems)
- Details, see CDF Note 7097 (in theaters soon)

## Cluster Shape

- Assume tracks point to “correct” location of cluster
- Cut based on:
- Residual dx/dz < 5cm
- Number merged clusters = 1
- No bad channels in cluster
- Cluster energy > 1GeV
- Plot charge fraction versus offset from track extrapolation point
- Obtain most likely charge vs offset graph (cluster shape graph)
- Details, see CDF Note 7097

## Cluster Shape: Details

- Cluster shape depends on
- Channel width
- Z location (geometry of detector)
- Result: wires and strips have different cluster shape
- Strip shape is scaled by a factor of 1 – cos(θ)/2
- cos(θ) motivated by geometry
- 1⁄2 is experimentally determined

## New Algorithm: In Action

- Correctly resolves merged clusters
- Track based residuals:
- ~15% more events pass cuts
- More events closer to 0 dx
- MC Pi0 Mass Plot promising

## Comparison: Residuals

- Old Residuals:
- Number Events: 7731
- Z RMS: 1.291
- X RMS: 1.612
- New Residuals:
- Number Events: 9058
- Z RMS: 1.256
- X RMS: 1.050

- OLD

- NEW

## Cluster Matching

- Associate wire clusters and strip clusters
- Obtain 2D location of shower in CES plane
- Old Algorithm does not do this
- Algorithm is efficient
- Match 1 cluster on one side with 1 or more clusters on other
- Make total energies as close as possible
- Account for wire/strip gains and dead channels when matching
- Method
- Match strip and wire clusters 1:1 to form showers
- Attempt to add remaining clusters to existing showers
- Proceed in order of decreasing energy
- Allows one to obtain position of non track-based particles
- Needs more testing but early results promising

## Immediate Benefits

- Single pass as opposed to 3
- Reconstruction of clusters is done only within CES
- Allows for tighter cuts
- No radiation supression by E/p < 2 cut
- Instead cut on E/(p + ???)
- Better reconstruction of high PT pi0
- More, cleaner statstics for events that involve decay into neutral particles (LOTS!)
- Makes measurements more accurate, e.g. better measurement of tau mass

## To Do

- Suitable Chi2 function for cluster fitting
- Pi0 and Tau reconstruction code
- Reimplementation
- Debugging
- More tests must be done to eliminate bugs and obtain estimate of algorithm's performance
- Obtain accurate results using reconstruction algorithm to generateinterest

## Summary

- Taus decay into pi0s which decay into photons
- Photon reconstruction essential in tau reconstruction
- Old cluster reconstruction algorithm insufficient for this
- New algorithm resolves merged clusters efficiently and appropriately
- Early results positive
- MC pi0 mass
- Track based residuals
- Still more to do for testing