Far Detector Fiducial Volume Studies

1. Far Detector Fiducial Volume Studies Andy Blake Cambridge University Saturday February 24th 2007

2. Overview • Previous study (doc-db #2467) suggested that the current fiducial • volume can be expanded to produce a modest gain in sensitivity, • without introducing any significant bias. • This talk: • – Comparison of sensitivities for current and expanded fiducial volume. • – Determination of cosmic muon background. current fiducial volume: expanded fiducial volume: R > 0.4 m, Redge > 0.2 m. 4 < trk.vtx.plane < 241 (SM1). 253 < trk.vtx.plane < 466 (SM2). R < √14 m. 0.5 < trk.vtx.z < 14.3 m (SM1). 16.2 < trk.vtx.z < 28.0 m (SM2). Andy Blake, Cambridge University Fiducial Volume Studies, slide 2

3. Oscillation Fit • Calculate sensitivity for expanded fiducial volume. • – Expand the fiducial volume separately in Z and R. • Initial Event Selection. • – Reconstructed muon track (must pass track fitter). • – Apply PID cut. • Mechanics of Oscillation Fit. • – Purely statistical (ignore all systematic errors). • – Fit to overall reconstructed neutrino energy spectrum. • E (GeV) = [ 0, 30 ] (60 bins) + 1 bin overflow. • – Perform oscillation fit on 200 x 200 grid. • m2 (10-3 eV2) = [ 2.0, 4.0 ] , Sin22 = [ 0.8, 1.0 ]. • – True Oscillation Parameters: • m2 = 3 x 10-3 eV2, Sin22 = 1.0. • – True Normalization: 2.5 x 1020 PoTs. • – Simulate 100 experiments at each grid point. • Use both contained vertex and rock interactions. Andy Blake, Cambridge University Fiducial Volume Study, slide 3

4. Expanded Radial Cuts • Standard Cuts: • R < √14 m. • New Cuts: • >20 cm from edge. • >40 cm from coil hole. Andy Blake, Cambridge University Fiducial Volume Studies, slide 4

5. Expanded Z cuts • Standard Cuts: • 0.5 m < trk.vtx.z < 14.3 m (SM1). • 16.2 m < trk.vtx.z < 28.0 m (SM2). • New Cuts: • 4 < trk.vtx.plane < 241 (SM1). • 253 < trk.vtx.plane < 466 (SM2). Andy Blake, Cambridge University Fiducial Volume Studies, slide 5

6. Comments Expanded Radial Cuts. – Gain is small here because standard fiducial cuts are quite tight to begin with (see right). – May gain more with an energy-dependent cut (i.e. expand fiducial volume for clean events). – Should investigate effect of calibration error (and B field error) close to edge of detector. Expanded Longitudinal Cuts. – Standard fiducial cuts are conservative. – Can expand a little in all directions! – Gain is modest, but worth having. Andy Blake, Cambridge University Fiducial Volume Studies, slide 6

7. Cosmic Muon Background Cosmic muon background divided into forward-going and backward-going events: Forward-Going Cosmics Backward-Going Cosmics (reconstructed as forward-going!) Background Rejection: Containment Cuts. Track Direction Cuts. Background Rejection: (Containment Cuts). Track Direction Cuts. Track Timing Cuts. Andy Blake, Cambridge University Fiducial Volume Studies, slide 7

8. Cosmic Background Determination • Cosmic muon background determined using “fake” spill triggers. • – 3.6M fake triggers from data between May’05 and Feb’06. • – Remove LI events, HV trips, coil trips. • – Equivalent to 6 mins live time. • Compare with MC expectation for cosmic muons. • – 50,000 MC cosmic muons processed with Cedar reconstruction. • – Equivalent to 19 hrs live time. • Compare with MC expectation for beam neutrinos and rock muons. • – Normalized to data assuming beam intensity of 2.5e13 PoTs per spill. • – Equivalent to 1e20 PoTs. • Define: • – “Forward-going cosmic” = trk.vtx.y>trk.end.y • – “Backward-going cosmic” = trk.vtx.y<trk.end.y Andy Blake, Cambridge University Fiducial Volume Studies, slide 8

9. Cosmic Background Determination • Event Selection Cuts: • – Reconstructed muon track (must pass track fitter). • – Apply PID cut. • Containment Cuts: • – >20 cm from detector edge. • – >40 cm from centre of coil hole. • – 4 < vertex plane < 241 (SM1). • – 253 < vertex plane < 466 (SM2). • Track Direction Cut: • – cos θ > 0.6. • (where θ = reconstructed angle between muon and neutrino). • Timing Cut. • – Forward timing RMS – Backward timing RMS < 1.66 ns. Andy Blake, Cambridge University Fiducial Volume Studies, slide 9

10. Forward-Going Cosmics (I) DISTANCE FROM VERTEX TO EDGE OF DETECTOR Andy Blake, Cambridge University Fiducial Volume Studies, slide 10

11. Forward-Going Cosmics (II) DISTANCE FROM VERTEX TO FIRST PLANE OF DETECTOR Andy Blake, Cambridge University Fiducial Volume Studies, slide 11

12. Forward-Going Cosmics (III) RECONSTRUCTED ANGLE RELATIVE TO BEAM DIRECTION Andy Blake, Cambridge University Fiducial Volume Studies, slide 12

13. Backward-Going Cosmics (I) DISTANCE FROM VERTEX TO EDGE OF DETECTOR Andy Blake, Cambridge University Fiducial Volume Studies, slide 13

14. Backward-Going Cosmics (II) RECONSTRUCTED ANGLE RELATIVE TO BEAM DIRECTION Andy Blake, Cambridge University Fiducial Volume Studies, slide 14

15. Backward-Going Cosmics (III) FORWARD TIMING RMS – BACKWARD TIMING RMS Andy Blake, Cambridge University Fiducial Volume Studies, slide 15

16. Results Forward-Going Events (VtxY>EndY): Backward-Going Events (EndY>VtxY): Andy Blake, Cambridge University Fiducial Volume Studies, slide 16

17. Cosmic Muon Background Results(standard fiducial volume) Forward-Going Events (VtxY>EndY): Backward-Going Events (EndY>VtxY): Andy Blake, Cambridge University Fiducial Volume Studies, slide 17

18. Cosmic Muon Background Event (I) (Run 31373, Snarl 85401) Andy Blake, Cambridge University Fiducial Volume Studies, slide 18

19. Cosmic Muon Background Event (II) (Run 31373, Snarl 85401) Andy Blake, Cambridge University Fiducial Volume Studies, slide 19

20. Summary • Expanded fiducial volume produces modest gain in sensitivity. • – Expanded Z cut produces the larger gain. • – Expanded R cut produces a small gain, and needs further study. • (e.g. effect of calibration error hasn’t been investigated). • Cosmic muon background should be small. • – MC expectation is ~0.1 events per 1.0e20 PoTs (1 event observed in data). • – No significant increase in background for expanded fiducial volume. Andy Blake, Cambridge University Fiducial Volume Studies, slide 20