1. Selection cuts on Bs→ with FTK F. Crescioli, P. Giannetti, M. Dell'Orso, G. Punzi, G. Volpi 2/5/2006

2. F. Crescioli2/5/2006 Bs->mumu with FTK Brief summary Summary ● Generated signal and background sample with low Pt level 1 cut ● Reconstructed tracks with FTK ● Cross section and standard distribution checks ● First attempt to analyze data proposing a “draft” selection strategy

3. F. Crescioli2/5/2006 Bs->mumu with FTK Signal sample generation Signal sample ● Athena 10.0.6 ● PythiaB as generator (QCD in Pythia msel=1) ● Based on example Bs→μμ jobOption from PythiaB (see next slide) ● ~25k events with single muon level 1 cut, Pt>2GeV and |η| < 2.5 σ(Bs)*(acceptance of generation cuts) = 3.62μb

4. F. Crescioli2/5/2006 Bs->mumu with FTK jobOption description Signal sample ● Kinematic parameters ckin 3 15 ckin 9 -3.5 ckin 10 3.5 ckin 11 -3.5 ckin 12 3.5 ● Other cuts by PythiaB cutbq [0. 102.5 and 10. 2.5] lvl1cut [1. 2. 2.5] Pt hat > 15 GeV for hard interaction |η|<3.5 for final state partons Cut on b quark. Pt > 10 |η|<2.5 LVL1 trigger like cut One muon of Pt > 2 GeV |η|<2.5

5. F. Crescioli2/5/2006 Bs->mumu with FTK Cross sections check Compare results Our cross sections = Rome PYTHIA samples cross section with same cuts at generation (two muons with Pt>6 GeV and |η|<2.5) (N. Nikitine talk at CERN ATLAS B-physics and B-trigger meeting, 22 March 2006) Bs cross section multiplied by Bs→μμ acceptance with pT>6 GeV |η|<2.5 (both muons) σ(Bs)*α = 0.42μb @ Rome PYTHIA samples σ(Bs)*α = 0.52μb @ Our generation process (400 events)

6. F. Crescioli2/5/2006 Bs->mumu with FTK Signal sample tracks reconstruction and analysis Signal sample ● All events processed with ftksim 0.7.1 ● Matched reconstructed tracks with MC truth using the same program used to compute efficiencies in previous talks ● Selected the events with two muon tracks in the barrel region |η|<1

7. F. Crescioli2/5/2006 Bs->mumu with FTK Reconstructed muon tracks Signal sample Pt spectrum of the two highest Pt muons in the event Impact parameter of the two muons

8. F. Crescioli2/5/2006 Bs->mumu with FTK Reconstructed Bs from muons Signal sample Extrapolated secondary vertex on the x-y plane of the two muons Calculated Bs impact parameter Vector pointing the secondary vertex on x-y plane from the center of detector Bs Pt-vector reconstructed from the two muons Secondary vertex x y

9. F. Crescioli2/5/2006 Bs->mumu with FTK Reconstructed Bs from muons Signal sample Invariant mass spectrum of the Bs candidate Impact parameter of the Bs candidate

10. F. Crescioli2/5/2006 Bs->mumu with FTK Selection cuts on signal Cuts ● One muon Pt > 6GeV |η|<1 (level 1 base cut, all efficiencies are computed wrt this selection) ● Second muon |η|<1 and various Pt thresholds (2,3,4,5,6 GeV) ● Impact parameter d(μ)>100μm for both muons ● Impact parameter of reconstruced Bs d(Bs) < 100μm ● Mass of reconstructed Bs between 4.8 GeV and 6 GeV

11. F. Crescioli2/5/2006 Bs->mumu with FTK Selection cuts on signal Cuts Cut on invariant mass 4.8 GeV < M(μμ) < 6 GeV Cut on impact parameter for both muons d(μ) > 100μm Cut on reconstructed Bs impact parameter |d(Bs)| < 100μm

12. F. Crescioli2/5/2006 Bs->mumu with FTK Selection cuts on signal Cuts Pt cut on both muons..Fixed cut at 6 GeV for leading muon, efficiency shown as a function of second muon Pt cut Efficiency is computed wrt events passing lvl1 single muon selection (Pt>6GeV) and with both muons in the barrel region (|η|<1)

13. F. Crescioli2/5/2006 Bs->mumu with FTK Background sample generation Background sample ● Athena 10.0.6 ● PythiaB as generator ● Based on example bb→μμX jobOption from PythiaB (see next slide) ● ~5k events with two muon level 1 cut, Pt>3GeV and |η| < 2.5 σ(Bs)*(acceptance of generation cuts) = 0.43μb

14. F. Crescioli2/5/2006 Bs->mumu with FTK jobOption description Background sample ● Kinematic parameters ckin 3 6 ● Other cuts by PythiaB cutbq [7. 4.5 and 7. 2.5] lvl1cut [1. 3. 2.5] lvl2cut [1. 13. 3. 2.5] Pt hat > 6 GeV for hard interaction Cut on b quark. Pt > 7 |η|<2.5 LVL1 trigger like cut Two muon of Pt > 3 GeV |η|<2.5

15. F. Crescioli2/5/2006 Bs->mumu with FTK Reconstruction Background sample Same reconstruction chain as the signal sample

16. F. Crescioli2/5/2006 Bs->mumu with FTK Reconstruction Background sample Same reconstruction chain as the signal sample

17. F. Crescioli2/5/2006 Bs->mumu with FTK Conclusions ● First attempt on signal and background generation, reconstruction and analysis seems to work ● Results are compatible with what is expected ● Need to better undestand signal and background generation biases (kinematics and other options, as of now left unchanged from PythiaB example jobOptions) ● Discuss an optimized selection strategy, this one was just a test for the tools