Electron and muon reconstruction in single lepton tT events

(Analysis Note 2005-024) (short!) update of previous session new definition of some observables less sensititive to Pile-Up effects updated all results in discussion with referees ... focus on main updated items

Jorgen D’Hondt (Vrije Universiteit Brussel)on behalf of also S.Lowette and J.Heyninck

PRS General Meeting, CERN, 6th of December 2005

Referees : Anne-Sylvie Giolo-Nicollerat, Martin Grünewald

6th of December 2005 Jorgen D'Hondt (Vrije Universiteit Brussel) 2

Illustration

Select correctlepton

Used 5.41fb-1 of ttbar events

6th of December 2005 Jorgen D'Hondt (Vrije Universiteit Brussel) 3

Classifying the reconstructed lepton

non-W-like

Classify the reconstructed objects identified as leptons in two categories via the Monte Carlo truth information. Determine for each lepton candidate in the final state.

distribution of the R of all reconstructed lepton candidates (e/) in the final state robustness against the used metric was checked: () versus ()

R=0.2 → where one distribution goes up on top of the background

non-W-likeW-like

0.2Takes into account double counted reconstructed electron candidates

6th of December 2005 Jorgen D'Hondt (Vrije Universiteit Brussel) 4

Differentiating the two classessensitive observables

6th of December 2005 Jorgen D'Hondt (Vrije Universiteit Brussel) 5

Observables for the W→ decay

Eiso

iso

log(pTiso)

log(pT)

SZ

• Distribution on the left• Likelihood Ratio S/(S+B) on the right

2.0 GeV (PU)

6th of December 2005 Jorgen D'Hondt (Vrije Universiteit Brussel) 6

Observables for the W→ee decay

Eiso

iso

log(pTiso)

log(pT)

SZ

• Distribution on the left• Likelihood Ratio S/(S+B) on the right

Same tendencies for electrons and muons, as expected

3.6 GeV (PU)

6th of December 2005 Jorgen D'Hondt (Vrije Universiteit Brussel) 7

Combined Likelihood Ratio Variable

linear scale

logarithmic scale

muons electrons

Second bump has disappeared due to new definitions

Correct lepton is the one with the highest Combined LR value

6th of December 2005 Jorgen D'Hondt (Vrije Universiteit Brussel) 8

Comparing with other methods

muons electronscut on the LR-value andscan this LR-cut

Event selection efficiency of the Likelihood Ratio method much less sensitive to Pile-Up effects, which can reach 4% when using a sequential cut based approach.

6th of December 2005 Jorgen D'Hondt (Vrije Universiteit Brussel) 9

Pile-Up influence on observables

about 0.5GeV effect

no effect

6th of December 2005 Jorgen D'Hondt (Vrije Universiteit Brussel) 10

Energy deposits in the calorimeter

Jet clustering algorithms usually start from the collection of calorimeter deposits, but also the lepton creates these deposits and can radiate photons. These calorimeter deposits should be removed before performing the jet clustering algorithm.

It can be seen that there is an asymmetry between the deposits in and , due to the magnetic field along the z-direction. The deposits around the chosen lepton within an asymmetric cone of opening 0.1rad in and 0.05rad in should be removed.

muon electron

Plots have changed due to the propagation of the lepton to the calorimeter surface

Pile-Up included

6th of December 2005 Jorgen D'Hondt (Vrije Universiteit Brussel) 11

Outlook in use cases

Update of previous presented studies (PRS meeting November)

Variable created which differentiates W-like and non-W-like leptons

also differentiates between fake electrons or muons several sensitive observables are combined with a Likelihood Ratio method it was shown that one can increase the event selection efficiency (wrt.HLT) the definition of some variables were updated (= simplified)

Comments from referees were implemented and discussed thoroughly in the updating process

thanks to both Anne-Sylvie and Martin for their constructive and valuable comments