1. CPPM (IN2P3-CNRS et Université de la Méditerranée), Marseille, France Olivier Leroy, for the Marseille group Trigger meeting, CERN19 April 2004 b-tagging plans in Marseille 1.Introduction and motivations 2.Workplan 3.Reproduce existing results 4.Conclusions and prospects

2. O. Leroy 19 April 2004b-tagging plans in Marseille2 Introduction  We are starting a new activity in CPPM  Aim = best b-flavour tagging, offline and online  No results today, just plans  Subactivities: 1. Offline The starting point is a sample of « offline selected events » Aim = highest tagging power on this sample 2. Online The starting point is a sample of « offline selected and correctly tagged events » Aim = optimize L0xL1xHLT on this sample 3. Tagging strategies Control samples, how to measure mistag rate in data, systematics

3. O. Leroy 19 April 2004b-tagging plans in Marseille3 Motivations  TDR tagging results for Bs: Effi=49.8%, mistag=32.8%, tag power=5.9% Can we tag (even not perfectly) the 50% of Bs currently thrown away ? Same thing for Bd Can we improve the current the mistag rate? A 5% improvement (i.e going from 32.8% to 31.2%) is equivalent to 20% more statistics, i.e 2 years of LHC running over 10 !

4. O. Leroy 19 April 2004b-tagging plans in Marseille4 Workplan 1. Understand and reproduce existing results: reoptimized TDR and LHCb note 2003-115 2. Propose and test news ideas: 1. Offline tagging 1. Opposite Charm Vertex 2. Improved opposite jet charge 3. Same side jet charge 4. Optimal combination of tagging variables 2. Online tagging 1. Write a tagging algorithm running in HLT, with a poor K/pi separation 2. Very well tagged events deserve to be written on tape even without clear Bsignal ?

5. O. Leroy 19 April 2004b-tagging plans in Marseille5 1. Understand and reproduce existing results

6. O. Leroy 19 April 2004b-tagging plans in Marseille6 Tagging vocabulary Same side Bsignal K- K+ Primary vertex Opposite side Btag Lepton from b (-) Opposite charm vertex Koppo Lepton from cascade (+) Ksame Inclusive Btag vertex Effective tagging efficiency: Mistag: Tagging efficiency:

7. O. Leroy 19 April 2004b-tagging plans in Marseille7 Tagging chronology 1. Signal B reconstruction  Usual event selection (e.g. B  K + K - )  Cheated selection using MC truth to increase statistics 2. Remove Signal tracks (e.g. K + and K - ) 3. Loop on remaing tracks and select « taggers »  Long charged tracks  ip/  ip wrt primary vertices  p, pT cuts 4. Choose , e, K 5. Reconstruct inclusive secondary vertex with NO DISTINCTION between B and Charm  Vertex charge = 6. Event sorted in 12 categories and final decision

8. O. Leroy 19 April 2004b-tagging plans in Marseille8 From LHCb note 2003-115 Events sorted in 12 categories, according to available information

9. O. Leroy 19 April 2004b-tagging plans in Marseille9 Reproduce existing results Results compatible with LHCb note 2003-115 (previous slide) DaVinci v9r3, FlavourTagging/v4r7, 1.2M Bs->DsK

10. O. Leroy 19 April 2004b-tagging plans in Marseille10 2. First look at opposite charm vertex

11. O. Leroy 19 April 2004b-tagging plans in Marseille11 Btag vertex resolution Charm contribution clearly visible

12. O. Leroy 19 April 2004b-tagging plans in Marseille12 Conclusions and prospects  Study opposite Charm vertex Is LHCb precise enough to distinguish B from Charm vertex in an inclusive way ? If this is possible, reverse the charge of lepton for those identified to come from the Charm  Opposite jet charge The existing one is discrete and do not use fragmentation tracks Weight tracks with their (p,pT,) Today’s efficiency ~50%. What mistag can we reach with efficiency =100% ?  Build a same side jet charge  Optimize combined tagging result  Tagging algorithm in HLT