Minimum Bias Jets and Top

1. Minimum BiasJets and Top W. H. Bell 25/01/2007

2. Overview • Minimum bias – A commissioning analysis • Motivation • Objectives • Possible Triggers • MBTS • Simulation of LVL1 • Trigger bias study • b-jet shapes – A route to top physics

3. Minimum bias - Motivation • Predictions of dN/dη at LHC uncertain • Accurate minimum bias needed for pile-up • Analysis requires • Tracking through SCT and Pixel • Alignment • Commissioning

4. Minimum bias – LHC Predictions σmb approximately 65mb Integrated luminosity of 10pb-1 => 1012 Events

5. Minimum bias – Objectives • Study charged particle multiplicity distributions • Measure dN/dη and momentum spectrum • Extend the pT cutoff below 500MeV • Use the sample for studies of the underlying event

6. Minimum bias - Triggers • Low Luminosity regime: • Random Trigger + online tracking • Minimum Bias Trigger Scintillators (MBTS)

7. MBTS - Introduction 2 segments in η 8 segments in φ 2.0 < η < 3.8 inner η outer η

8. Data Selection • Pythia 6.4 @ 14TeV • Inelastic non-diffractive • Inelastic single and double diffractive • Empty events using particle gun • Data passed through ATLAS Geant simulation and digitization • Generation of MBTS LVL1 containers

9. Inelastic Non-diffractive

10. Single and double diffractive

11. 9 samples of 25ns Shape of pulse comes from cable measurement The pulse is not the charge but a mV signal. Charge from height of central bin MBTS LVL1 – Simulated Signal Taken from non-diffractive data

12. MBTS LVL1 – Inelastic Non-diffractive

13. MBTS LVL1 – Single and double diffractive

14. MBTS LVL1 – Empty Events Empty events

15. MBTS LVL1 – Inelastic Non-diffractive Events All present but <1% in total

16. MBTS LVL1 – Single and double diffractive Events

17. MBTS LVL1 – Empty Events Events

18. Trigger Efficiency – Inelastic Non-diffractive ε

19. Trigger Efficiency – Single and double diffractive ε

20. Minimum bias – Future work • Trigger efficiency plots for tracks • Define good track. • Use track parameters to cut away non-prompt tracks and thus plot dN/dη and dN/dpT • Look at fake rates and extrapolation errors • NSD Selection: energy balance? • Accurate beam gas and beam halo simulation needed • CSC note in preparation

21. Starting from InDetRecExample minPT=75MeV GlobalChi2 Fitter Low Pt Tracking Tracks/Gev GeV From 400 events of single and double diffractive data

22. b-jet Shapes • Jet shapes are sensitive to initial parton • Jet shapes provide a means of selecting b jets from flavour creation • Reduce light jet backgound

23. Jet Shape Study • Starting from: • CDF Note 8370 • DIS HERA event shapes • Using Generator + lhc_jet • lhc_jet provides Midpoint and other algs

24. Generator particles Energy φ η

25. Midpoint Jets Energy φ η

26. Top Physics with ATLAS • σ(pp→ttbar) roughly 830pb (NLO) @ 14TeV • After 1 year low luminosity 8x106 ttbar events • Measure t quark mass to 1GeV • Look for: • ttbar spin correlations • resonances decaying to ttbar • Rare decays • Use to commission the detector

27. Backup

28. MBTS Trigger Distributions Single and double diffractive

29. MBTS Trigger Distributions Non-diffractive