# Presentation: 461066

## Jet Reconstruction and Calibration in Athena

- US ATLAS Software Workshop
- BNL, 27/08/03
- Ambreesh Gupta, for the JetRec Group
- University of Chicago
- Outline:
-  Jet Reconstruction Setup and Algorithms
-  Jet Calibration
-  Some Highlights from JetRec Meeting in Barcelona.

## Jet Physics at Hadron Colliders

- Final state partons produce
- a collimated jet of particles.

- An ideal algorithm will map
- jets with final state partons.

- Jet algorithms sensitive to
- experimental and theoretical uncertainty.

## The Steps of Jet Measurement

- Jet Measurement can be broadly divided in three steps

- Jet Reconstruction

- Energy Calibration

- Flavor Identification

- Energy deposit in the calorimeter is clustered by Jet reconstruction algorithms, e.g Cone and Kt.

- Energy of a Jet is calibrated for non-compensation,
- dead material, magnetic field, etc.

- b-tag, -tag, etc.

## Jet Algorithms

- Jet algorithms have two steps
- Clustering hadrons, calorimeter tower etc.,
- for “nearness”
- Nearness in Angle     =>   Cone Algorithm
- Nearness in Momentum  =>  Kt Algorithm
- Recombination Scheme is the momentum
- addition rule for the set of particles that
- have been identified with a jet.

-  4-vector addition
-  Snow mass scheme
-  . . .

## Jet Reconstruction Packages

## Writing Multiple Jets to the N-tuple

- CaloTower ProtoJet

- Truth Particle ProtoJet

- Cone Algorithm
- Seed less Cone

- Pre-Cluster

- Kt Algorithm

- Split-Merge

- ParticleInJet

- CBNT

- All algorithms can be
- configured to run in
- the same job

- Multiple algorithm
- output can be stored
- with different names

## Jet Samples Used

- The results reported use the following two samples
- - Multi-jet sample produced with different Pt cut values
-   ( 35,70,.., 540 GeV)
- -SUSY data challenge sample. Run 002315.

## Comparing Jet Multiplicity

- Number of Jets

- _Comparing Jet Multiplicity_

- Mean = 6.0

- Mean = 5.6

- Mean = 5.7

## Comparing Jet Transverse Energy

- Transverse Energy

- _Comparing Jet Transverse Energy_

- Mean = 114 GeV

- Mean = 118 GeV

- Mean = 126 GeV

## Reconstructed jet energy

- In bins if true energy at
- eight energy points.
- Good fits to gaussians.

## Jet Energy Calibration 

- _Jet Energy Calibration _

- To account for non-compensation, dead material etc.,
- - H1 scheme (Implemented by Frank Paige)
- - Sampling based corrections (in development)

## Navigating Composite Objects

- energy correction, the navigating the composition of Jet needed.

- _Navigating Composite Objects_

## H1 Calibration

-  H1 Strategy: EM showers are much denser than hadronic ones.
-    Weight high E cell with EM scale and low E cell with hadronic scale.
-  H1 weights derived from di-jet samples. Same weights improve
-    missing Et resolution.

## Jet Calibration: Further developments

- Further studies to develop tools for calculating and storing weights.
-   - requires reading large number (~100K) of jets
-   - calculate weights (interface to a minimizer)
-   - store the weights to be accessed for calibration.
- Sampling based weights
-    - calculated in different eta region of the detector.
-    - first set of weights obtained. Not yet in accessible in Athena.

## Sampling based Correction

## Evolution of JetRec: Barcelona Meeting

-  Since, the last JetRec working group meeting in Tucson (Aug
-    2001),  a lot of progress  made in Jet reconstruction software.
-  Another working group meeting was held in Barcelona ( July
-    2003 ) to review the RTF recommendations. Attended by
-    Present: Frank Merritt, Tom LeCompte, Peter Loch, Srini
-                  Rajagopalan, Martine Bosman.
-     By Phone: F. Paige, D. Cavalli, S. Resconi, D. Rousseau, A. Gupta,
-                  S. George, P. Calafiura.
-   Initial draft of meeting report can be found at JetRec meetings
-     minutes web-page ( date: 30th of July)

## Barcelona Meeting: Highlights

-  EnergyCluster class will replace the existing ProtoJet class.
-   The nature of abstraction remains the same, as far as Jet
-    algorithms are concerned, but it conforms to the general Athena
-    reconstruction setup and hence will utilize common services.
-  The Jet Data Objects will conform to the general Athena scheme
-    to navigate composite objects.
-  Associating information with Jets, e.g, tracks in jet, will be
-    provided by extending the present Jet class interface with the
-    help of a templated method for the type of association requested.

## Summary

-  Jet Reconstruction packages are in fully functional state.
-  There have been various user feedback using dc1 dataset
-     – bugs hunted and fixed.
-  With the availability of “noise” and “pileup”, a more realistic
-    test of jet algorithms possible.
-  RTF recommendations reviewed at Barcelona meeting.
-    Structural changes proposed to conform with general Athena
-    reconstruction setup.