Electron IdentificationElectron Identification

Supriya DasGesellschaft für Schwerionenforschung mbH (GSI)

27th. September, 2007 Supriya Das, CBM Collaboration meeting, Dresden 2

Motivation

Till the last collaboration meeting we had the concept and results from electron identification.

But, the software was standalone i.e. one code for electron identification and pair analysis.

Requirement of self sufficient software to provide identified electrons to be used in further analysis, mixed event generation etc.

Needs to be flexible/user friendly in terms of changing cuts for different detectors, decision of using different cuts for identification ability to select electrons identified by one or more

detectors

Requirement to disentangle the real and MC world.

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SoftwareTask : CbmDileptonAssignPidInput : All arrays from reconstucted data (no MC)Output : 1. Collection of identified tracks (CbmDileptonTrackReal)

Global track index, chi2primary, momentum, isRich, isTrd, isTof 2. Histograms before and after cuts

Constructor contains all default cut values and switchesUser has to provide user defined values in macro (see later)

[ no cut on chi2primary, can be used for secondary electron analyses]

Task : CbmDileptonAssignMCidInput : All reco and mc arraysOutput : 1. Collection of tracks after MC association (CbmDileptonTrackSim) momentum, fakeTrack, fakeRing, MCPdg, MCMotherId, MCMotherPdg 2. Histograms for efficiency, purity, pion,suppression etc.

This collection has one-to-one correspondence with previous one

[ two parameters needed to be supplied, cut on chi – to select primary radial distance – to define RICH acceptance]

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Block diagram of electron id

Reconstructed event

CbmDileptonAssignPid

CbmDileptonTrackReal

Real

CbmDileptonAssignMCid

MC information

CbmDileptonTrackSim

Simulation

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CbmDileptonAssignPid – flow chart

isTRD isTOF

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RichPid – flow chart

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Software (contd.)

• gSystemLoad->(“libDilepton”);

• // Electron id assignment • CbmDileptonAssignPid* taskPid = new CbmDileptonAssignPid(1);

• Float_t aRichCuts[] = {1., 0.4, 0., 130, 21.85, 4.35, 6.17, 0.14}; // Distance, SelectionNN, selection2D, Radial, NHitMean, NHitSigma, RMean, RSigma

• taskPid->SetRichCuts(true, true, aRichCuts); //sMomentum, sSelection (true=NN, false=2D)• • Float_t aTrdCuts[] = {1.5,0.95, 1.1, 21., 0.9}; // Mom, PidLikeLow, PidLikeHigh, PidWkn,

PidAnn• taskPid->SetTrdCuts(true,true,false,false,aTrdCuts); //sLike, sWkn, sAnn• • taskPid->SetTofCuts(true,0.01); //sMomentum, Mass2• • fRun->AddTask(taskPid);• • // MC Association, needed for simulated data stream• CbmDileptonAssignMCid* taskMCid = new CbmDileptonAssignMCid();• fRun->AddTask(taskMCid);

Macro to run the electron id …

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Systematics

• 5 e- and 5 e+ embedded into central UrQMD events for three different beam energies

• Standard and low mass dilepton* set up used• 10,000 events simulated• Standard cuts used for identification• ANN and Wkn methods for TRD are used – Likelihood

needs tuning• Software used from aug07 release

Efficiency = identified true electrons / accepted electronsPion suppression = pions identified as electrons / accepted pions

* thin target, extended MVD and STS, 70% magnetic field

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Identification criteria

Identification by TRD based on statisticalanalyses of total energy loss:

ANN - e > 0.8 Wkn - e > 11 Likelihood – 0.95 < e < 1.1

(any one or combination could be used)

Identification by RICH

Identification by TOF

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Impurities in identified electrons

All : 5.81True e : 5.35Fake : 0.09 : 0.06p : 0.014Others : 0.02

Particles/event

Combined information of RICH+TRD+TOF

Au+Au @ 25 AGeVStandard set up

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Falsely matched pions

Electron ring falsely matched with a nearby pion track

Au+Au @ 25 AGeVStandard set up

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Pions mis-id as electrons

Falsely matched

True

Au+Au @ 25 AGeVStandard set up

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Efficiency of electron identification

Standard set up Low mass dilepton set up

25 AGeV

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Pion suppression

Standard set up Low mass dilepton set up

25 AGeV

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Efficiency

Standard set up Low mass dilepton set up

35 AGeV

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Pion suppression

Standard set up Low mass dilepton set up

35 AGeV

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Efficiency

Standard set up Low mass dilepton set up

15 AGeV

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Pion suppression

Standard set up Low mass dilepton set up

15 AGeV

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Efficiency - energy dependence

Standard set up Low mass dilepton set up

Efficiency from RICH only

Variation of efficiency with energy < 10 %

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Energy dependence (contd.)

Standard set up Low mass dilepton set up

Variation of efficiency with energy < 10 %

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-suppression – energy dependence

Standard set up Low mass dilepton set up

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Comparison between two TRD methods

The cuts need to be optimized to get the best efficiency/ pion suppression factor Likelihood method needs more tuning

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Summary and Outlook

• New, user friendly software for electron identification for di-electron analyses is in place.

• Results from systematic study of this package have been presented Different set ups (standard, low mass dileptons) Different energies Different methods for TRD identification

• Cuts could further be optimized to obtain the best efficiency and pion suppression.

• Study of identification with the compact RICH to be done.

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Summary & outlook (contd.)

• All cuts/switches can be modified from macro – user friendly.

• The collections could be kept in root memory and accessed by the next task / could be stored in an intermediate file for later use (self sufficient, has all information).

• Caveat : Can not provide cut-by-cut efficiencies possible solution : go to subtask level

• All codes are in svn (in the last release) Tasks and other classes in cbmroot/dilepton Macro in cbmroot/macro/dilepton

• Documentation exists in Wiki page, http://cbm-wiki.gsi.de/cgi-bin/view/CbmRoot/CbmReconstruction/#Electron_Identification

CBM-Note in preparation.