Neutrino Event Reconstruction

1. Neutrino Event Reconstruction Andy Blake Cambridge University September 2003

2. Introduction • Reconstruction software development ongoing at Cambridge. • New version of AtNuReco now in CVS. • AtNuReco is a track/shower reconstruction package developed for use in atmos neutrino analysis. • General principles: (1) track/shower reconstruction should provide first order event separation. (2) concurrent track/shower reconstruction. • This talk reviews status of track/shower reconstruction and introduces work on energy reconstruction.

3. AtNuRecoAlgorithm Strips Tracks Showers Clusters Track Segments 3D Shower Segments 2D Tracks 2D Showers 3D 3D Tracks 3D Showers CandTracks CandShowers

4. Monte Carlo Studies DetSim • 100,000 atmos neutrino events (~250 kT-yrs) • 120,000 beam neutrino events (~200 kT-yrs) • Study track/shower reconstruction + energy reconstruction. Cambridge Demultiplexer Cambridge Reconstruction Standard Reconstruction Analysis

5. Atmos Nu Track Efficiency/Purity

6. Beam Nu Track Efficiency/Purity efficiency purity

7. Track Reconstruction Quality atmos nu events beam nu events

8. Shower Finding in Transition … • Separate into ‘dense’ (EM-like) and ‘diffuse’ (NC-like) showers. • Reconstruct using ‘expanding’ clustering window. • Not complete – only dense showers so far ... shower multiplicity atmos nu events beam nu events diffuse showers high multiplicity – not physical ..?

9. Atmos Nu Shower Efficiency ve CC events NC events

10. Energy Reconstruction For νμ CC events … neutrino energy = muon energy + vertex shower energy Consider muon kinematics in beam events … energy transferred to muon … scattering of muon … … so it’s important to measure the vertex shower as well as the muon.

11. Measuring Muon Energy muon energy resolution: muon angular resolution: ΔE=5% skewed high energy tails (reco efficiency + fake tracks)

12. Measuring Shower Energy shower energy resolution: shower angular resolution: but ΔPz not symmetric ΔE=30% bad scale! suppressed low energy tails (reco efficiency)

13. Measuring Total Energy (1) Try simple addition: all events events with no vertex shower

14. Kinematic Constraints (1) We can constrain reconstruction of beam neutrino energy … μ ν measure muon energy + direction know resolution Neutrinos arrive from Fermilab know about neutrino interactions measure shower energy + direction know resolution powerful constraint for beam neutrinos … try to implement these constraints and improve energy resolution.

15. Kinematic Constraints (2) Maximize likelihood: Xi = measured quantities kinematic quantities ( W = mass of hadronic system Y = momentum transfer to hadronic system Ω = rotation angle ) resolution functions (energy, angle) e.g. probability vs. overall energy e.g. neutrino energy vs. hadronic mass example event: Eν= 3.7GeV Efit = 3.8GeV

16. Measuring Total Energy (2) all events events with no vertex shower Kinematic fit centres the distributions on zero … … but overall resolution still dominated by track/shower resolution.

17. Conclusion • Reconstruction development ongoing at Cambridge. (i) tracks – lower efficiency but better purity. (ii) showers – in active development. • Now looking at reconstruction of kinematic quantities too. (i) constrain ν direction for beam nu analysis. (ii) form p(L/E) for atmos nu analysis. • Reconstruction has come a long way … … but still lots to do!