Introduction of Secondary Vertexing Class for Tagging Beauty - - PowerPoint PPT Presentation

Introduction of Secondary Vertexing Class for Tagging Beauty Electron

MinJung Kweon Physikalisches Institut, Universität Heidelberg

03 Jun 2009, HFE Meeting, GSI

03 June 2009 MinJung Kweon

• Analysis procedure
• HFE electron selection
• single track selection
• e-hi pair selection
• remove photonic e using

e-e veto

• construct secondary vertex

and apply tagging condition

2

Beauty Tagging using Secondary Vertexing

d0 decay length of B hadron primary vertex secondary vertex impact parameter e h1 h2 h3 h4 h5 e, h1, .., hi, .., hn calculate χ2 e, h1, .., hn recalculate χ2 e, ha, hb e, ha

OR

remove maximum χ2 contributor (using KF class) apply tagging condition

）

which is based on:

• long life time (~ 500 μm)
• large mass (~ 5 GeV/c2)

03 June 2009 MinJung Kweon 3

Distinctive Variables for Tagging

• HFE electron requirement
• impact parameter of single tracks
• secondary vertex χ2
• invariant mass of e, ha, hb or e, ha
• signed Lxy= r .pe+h / |pe+h|

d0 primary vertex impact parameter e h1 ha hb h4 h5 pe+h r

{

secondary vertexing class

03 June 2009 MinJung Kweon

• Analysis procedure
• HFE electron selection
• single track selection
• e-hi pair selection
• remove photonic e using

e-e veto(not yet imp.)

• construct secondary vertex

and apply tagging condition

• Output histograms are

separately stored in dedicated tree

4

Implementation as part of HFE package

// instantiate fSECVTX = new AliHFEsecVtx; ... // single track loop for(Int_t itrack = 0; itrack < fESD->GetNumberOfTracks(); itrack++){ if(!fPID->IsSelected(track)) continue; // start pair analysis if (fEnableSECVTX) { ... for(Int_t jtrack = 0; jtrack < fESD->GetNumberOfTracks(); jtrack++){ htrack = fESD->GetTrack(jtrack); ... // single track cut if(!fSECVTX->SingleTrackCut(htrack)) continue; // now you make a e-h pair and store partner info as private member // if it pass a certain cut fSECVTX->AnaPair(track, htrack); } // run secondary vertexing algorithm based on the above e and hadron tracks, // and apply tagging cut fSECVTX->RunSECVTX(track); } }

• HFE
• AliHFEpid
• AliHFEcuts
• ...
• AliHFEsecVtx

03 June 2009 MinJung Kweon 5

Purity and Efficiency (with Preliminary cuts)

2 4 6 8 10 12 14 1 10

2

10

3

10

4

10

right tagged electron wrong tagged electron beauty passed ESD single track cuts

(mc) (GeV/c)

T

p 2 4 6 8 10 12 14 |<0.9) ! |<0.9 + cut)/input b elec.(| !

• tagged. b elec.(|

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

right tagged electron wrong tagged electron beauty passed ESD single track cuts p+p @10 TeV beauty electron triggered event v4-16-Rev-08

• True/False b-Tagging and tagging efficiency (done with beauty triggered sample)
• Understanding on the individual variables should be ahead

﹖

have to understand single track efficiency first

03 June 2009 MinJung Kweon

• Use of reconstructed PID
• Understanding of single track impact parameter cut
• Input PID for tracks constructing KF particle?
• How often the secondary tracks are included in the primary vertex and resulting bias on

primary vertex due to those tracks?

6

Short Term To-Do and Open Issue