1 Aim and Definitions Aim is to formulate

1. Aim and Definitions • Aim is to formulate an efficient selection procedure for π πo decays of the τ • Analysis will optimise: efficiency purity rej. factor Ns=number signal decays in MC sample (2 Nx. BR), ns=number truth-matched candidates selected b=total number of background decays selected Nb= number background decays in sample, nb=number background decays selected • To combine MC will scale to a data sample of (so far) 0. 134 fb-1 of data Mitchell Naisbit Manchester University Elba 2003 1

2. Tau. User Preselection Nano Cuts Input 1 M generic τ+τ- events Mitchell Naisbit Manchester University Elba 2003 2

2. Tau. User Preselection Nano Cuts Input 1 M generic τ+τ- events Level-3 trigger cut Mitchell Naisbit Manchester University Elba 2003 3

2. Tau. User Preselection Nano Cuts Input 1 M generic τ+τ- events Level-3 trigger cut Stream 19 42% pass nanofilter Mitchell Naisbit Manchester University Elba 2003 4

2. Tau. User Preselection Micro Cuts Events input from nanofilter Mitchell Naisbit Manchester University Elba 2003 5

2. Tau. User Preselection Micro Cuts Events Input from nanofilter # tracks even and <8 Mitchell Naisbit Manchester University Elba 2003 6

2. Tau. User Preselection Micro Cuts Events Input from nanofilter # tracks even and <8 Zero net charge Mitchell Naisbit Manchester University Elba 2003 7

2. Tau. User Preselection Micro Cuts Events Input from nanofilter # tracks even and <8 Zero net charge Topology classification 36% pass preselection Mitchell Naisbit Manchester University Elba 2003 8

3. Selection Procedure Selection for data and MC samples: For 1 -1 events backgrounds reduced by tag Selection requirements π PID (pi. LHLoose) π not in e. Micro. Loose Single AWG πo e or μ PID as tag or Signal side Tag side As above for ρ tag Mitchell Naisbit Manchester University Elba 2003 9

4. Monte Carlo truth matching Reconstruction Requirements for signal τ decays recon. π, πo, γA, γB must match back to particle in truth list of same identity π and πo must have same mother which is a true ρ γA and γB must have same mother which is a true πo Mitchell Naisbit Manchester University Elba 2003 10

5. Results – τ+τ- MC Running on 1 M generic τ+τ- events (1) Ns= 508, 200 signal decays (1) Truth codes for selected decays (2) Truth codes for truth-matched candidates ns = 48, 613 (3) Backgrounds (3) btau = 21, 401 Main τ backgrounds are a 1 decays and improperly reconstructed signal decays. Mitchell Naisbit Manchester University Elba 2003 11

5. Results – background MC Analysed MC samples of (hadronic) (leptonic) (photon) Giving scaled results- Ns=61, 385 Mitchell Naisbit ns=5, 872 bτ=2, 585 bother=2, 208 b = bτ + bother = 4, 793 Manchester University Elba 2003 12

5. Results ε = 9. 57 % π = 55. 10 % Main backgrounds • Non-signal τ (a 1) • Improperly reconstructed signal decays • Leptonic (bhabha+FSR) and some hadronic Mitchell Naisbit Manchester University Elba 2003 13

6. Event Parameter Distributions - τ+τ- MC n. Neutrals Ranges from 2 to ~15 n. Charged. Tracks Ranges 0 to ~6 n. Neutrals thrust. Mag Ranges from ~0. 79 to ~0. 99 (but no quantities are of use to eliminate τ) Mitchell Naisbit Manchester University Elba 2003 14

6. Event Parameter Distributions - τ+τ- MC n. Neutrals Ranges from 2 to ~15 n. Charged. Tracks Ranges 0 to ~6 n. Neutrals thrust. Mag Ranges from ~0. 79 to ~0. 99 (but no quantities are of use to eliminate τ) Mitchell Naisbit Manchester University Elba 2003 15

6. Event Parameter Distributions - τ+τ- MC n. Neutrals Ranges from 2 to ~15 n. Charged. Tracks Ranges 0 to ~6 n. Neutrals thrust. Mag Ranges from ~0. 79 to ~0. 99 (but no quantities are of use to eliminate τ) Mitchell Naisbit Manchester University Elba 2003 16

6. Event Parameter Distributions - background MC n. Neutrals cut >~ 12 (hadronics) Mitchell Naisbit n. Charged. Tracks cut all >~ 6 (hadronics) Manchester University Elba 2003 17

6. Event Parameter Distributions - background MC cut <~ 0. 8 (hadronics) cut >~ 0. 99 (leptonics) thrust. Mag Mitchell Naisbit Manchester University Elba 2003 18

7. Efficiency and Purity Optimisation n. Neutrals n. Charged Tracks cut > 6 cut > 12 thrust. Mag cut > 0. 988 cut < 0. 79 Mitchell Naisbit Manchester University Elba 2003 19

8. Invariant Mass Spectrum ε = 9. 57 % ε = 9. 51% π = 55. 10 % π = 65. 52% r ~100% Mitchell Naisbit Manchester University Elba 2003 20

9. Future Work • Finalise Selection Procedure • Complete study into τ + non-τ backgrounds and how to minimise them • Perform fits to the invariant mass spectrum • Implement detector unfolding techniques Mitchell Naisbit Manchester University Elba 2003 21