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

） Beauty Tagging using Secondary Vertexing decay length of B hadron • Analysis procedure secondary vertex • HFE electron selection e h 1 • single track selection h 2 • e-h i pair selection h 3 • remove photonic e using h 4 e-e veto d 0 h 5 • construct secondary vertex and apply tagging condition which is based on: - long life time (~ 500 μ m) primary vertex - large mass (~ 5 GeV/c 2 ) impact parameter remove maximum χ 2 contributor (using KF class) OR e, h 1 , .., h i , .., h n e, h 1 , .., h n e, h a , h b e, h a calculate χ 2 recalculate χ 2 apply tagging condition MinJung Kweon 03 June 2009 2

Distinctive Variables for Tagging p e+h e h 1 h a r h b h 4 d 0 h 5 • HFE electron requirement • impact parameter of single tracks primary vertex impact parameter { • secondary vertex χ 2 • secondary vertexing class invariant mass of e, h a , h b or e, h a • signed L xy = r .p e+h / |p e+h | MinJung Kweon 03 June 2009 3

Implementation as part of HFE package • HFE • AliHFEpid • AliHFEcuts • ... • AliHFEsecVtx • Analysis procedure // instantiate fSECVTX = new AliHFEsecVtx ; ... • HFE electron selection // single track loop for(Int_t itrack = 0; itrack < fESD->GetNumberOfTracks(); itrack++){ if(!fPID->IsSelected(track)) continue; • single track selection // start pair analysis if (fEnableSECVTX) { • e-h i pair selection ... for(Int_t jtrack = 0; jtrack < fESD->GetNumberOfTracks(); jtrack++){ • remove photonic e using htrack = fESD->GetTrack(jtrack); ... e-e veto(not yet imp.) // single track cut if(!fSECVTX->SingleTrackCut(htrack)) continue; // now you make a e-h pair and store partner info as private member • construct secondary vertex // if it pass a certain cut fSECVTX->AnaPair(track, htrack); and apply tagging condition } // run secondary vertexing algorithm based on the above e and hadron tracks, • Output histograms are // and apply tagging cut fSECVTX->RunSECVTX(track); separately stored in dedicated } } tree MinJung Kweon 03 June 2009 4

Purity and Efficiency (with Preliminary cuts) • True/False b-Tagging and tagging efficiency (done with beauty triggered sample) 1 |<0.9) right tagged electron right tagged electron wrong tagged electron wrong tagged electron 0.9 4 ! 10 beauty passed ESD single track cuts |<0.9 + cut)/input b elec.(| beauty passed ESD single track cuts 0.8 p+p @10 TeV 0.7 3 ﹖ 10 beauty electron triggered event 0.6 v4-16-Rev-08 0.5 2 10 0.4 ! tagged. b elec.(| 0.3 10 0.2 0.1 1 0 0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14 p (mc) (GeV/c) T have to understand single track efficiency first • Understanding on the individual variables should be ahead MinJung Kweon 03 June 2009 5

Short Term To-Do and Open Issue • 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? MinJung Kweon 03 June 2009 6