Energy Flow Technique and *where I am

Lily

Have been looking at the technique developed by Mark Hodgkinson, Rob Duxfield of Sheffield. Here is a summary.

*Last slide is RE: hadronic W reconstruction

There are currently 2 calibration schemes use by the jet group:

•The standard ‘H1-style’: calibrates cells in jets to the jet energy scale

•Local hadron style: calibrates cells to the hadron scale- no correction in place yet.

•In rel 12, local hadron weights are applied for eflow. This results in an improvement in linearity and a comparable sigma compared with local hadron jets.

•Improvement is expected to be less in r13 (better local hadron jets)

•H1 style calibration is currently better than local hadron

In rel 12:

• Need to run eflow on ESDs- cells in hadronic topo clusters

• Standard Jet finder is run on eflow objects instead of caloclusters or towers

• Can run on ESD in RecExCommon with eflowJobOptions to create AOD containing eflow jet collections, I.e

Eflow4ConeParticleJets - Cone 0.4 with eflow objects as input

• In rel 13, should be able to just run eflowJoboptions on AOD as part of analysis job

Running eflow: current situation:

Current jet calibration schemes:

At low Pt (<~140GeV) the Inner Detector has significantly better resolution than the

calorimeters, so tracking can be used to improve jet resolution:

Can also use E(calo)/P(track) to check calorimeter calibration.

Cluster-level method (simple way):

• Match tracks to clusters

• For lowish Pt: use energy measurement from track to get expected energy deposit in calorimeter Eexp and sigma (Eexp)

• Ecalo - Eexp = Eunexpected

• Compare Eunexpected with sigma(Eexp) [which is = sigma(Ecalo)] and possibly away cluster

How does it work?

What is it good for?

*

* ATLAS TDR: SINGLE PIONS, ETA=0

Cell-level method (complex way):

• Devise an ordering method to remove cells using Monte Carlo

• Use this method to remove cells until Ecalo - Eexp

• Use cell-based weights to calibrate remaining cluster energy

How does it work?

Notes:

• Tracks must have >1 pixel hit

• Separate electrons from pions using the ratio of TRT hits: (number of high threshold hits)/(number of total hits). Electrons have mean ratio ~2.5, pions ~0.7

Weighted mean energy density for all cells in layer

More detail- Cell based method

• Cells are classified by (a) calorimeter region and (b) distance from track axis

• Compare energy distribution relative to track axis with that of Monte Carlo (single pions)

• Extrapolate track axis to form ‘shower axis’ in calorimeter

• Look at a very small region around track axis (comparable with error on track extrapolation)

• Weight cells around track axis according to their distance from the axis

• Descriptive plots courtesy of Rob Duxfield on following slides…

More detail- Cell based methodThe following plots show a cluster formed by a neutron and pion overlapping, and the pion

has been identified as having first interaction in the 2nd layer of the LAr calorimeter:

Plots are Energy density in eta-phi space

More detail- Cell based methodThe energy of the cluster is subtracted, beginning with the EM core and continuing ordered in

energy density, until the subtracted energy = expected energy from tracking.

Plots are Energy density in eta-phi space

More detail- Cell based methodThe remaining cluster, with its heart removed, is discarded.

.

SUM-UP: Calo Energy is replaced with Track Energy

Does it work?

Sigma=0.1775+/-0.0072

Does it work?

Sigma=0.1775+/-0.0072

Sigma=0.1625+/-0.0062

Does it work?

Sigma= 0.1775+/-0.0072

Sigma= 0.1625+/-0.0062

Sigma= 0.1382+/-0.0051

YES*this is all for rel 11 with local hadron cell weights

Latest results:

Barcelona workshop: J1 sample okay, but J2 sample had worse sigma with eflow jets than with H1 topocluster jets..

Problem found to be due to:

•Double counting effect-> too much energy in reconstructed jets.

•Introduced new parameter:

•If Ecluster <(Eexpected-(k2 *sigmaexpected)) the use cluster energy, NOT track energy

•E/P must used cluster which is matched & contains 95% of Energy in 0.4 cone around track

More Information:

All the information in these slides was gathered from talks given by Mark Hodgkinson and Rob Duxfield from Sheffield, and from very helpful emails from Mark Hodgkinson.

The talks are attached to the UCLttH wiki page:

•Cell based method: RD_eflow_dec05

•Latest Results: MH_14-03-07

•Everything else: go to Indico jetEtMiss page and search for Mark Hodgkinson

Jobs for Lily:

• Practise eflow using any old ESD sample at UCL

• Make 12.0.6 HG5 0570,0571 ESDs using panda as they don’t currently exist. (As far as I can tell)

•Or…how long until we get rel 13 standard production datsets?

More Stuff I’m doing now:Our reconstruction of the hadronic W

•Currently wjjTool defines correctly reconstructed W if

•Two combined light jets have mass within 30GeV of W mass

•Both these jets have a W as their parent

•My problems and worries:

•Found that matching these ‘reco correct’ Ws to gen Ws (as I did for plots shown last week) was producing a lot of events where the reco W clearly does not correspond to the gen W:

Have put in WdR match, indexing and playing with GenParticle iterator .

Can we check for certain that the two light jets come from the *same* W ?