Far Detector Fiducial Volume Studies

Far Detector Fiducial Volume Studies

Andy BlakeCambridge University

Saturday February 24th 2007

Overview

Andy Blake, Cambridge University Fiducial Volume Studies, slide 2

• 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.

R < √14 m.

0.5 < trk.vtx.z < 14.3 m (SM1).16.2 < trk.vtx.z < 28.0 m (SM2).

R > 0.4 m, Redge > 0.2 m.

4 < trk.vtx.plane < 241 (SM1).253 < trk.vtx.plane < 466 (SM2).

current fiducial volume: expanded fiducial volume:

Oscillation Fit

Andy Blake, Cambridge University Fiducial Volume Study, slide 3

• 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.

Expanded Radial Cuts


• Standard Cuts:

R < √14 m.

• New Cuts:

>20 cm from edge. >40 cm from coil hole.

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).

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.

Cosmic Muon Background


Forward-Going Cosmics Backward-Going Cosmics

Cosmic muon background divided into forward-going and backward-going events:

Background Rejection: Containment Cuts. Track Direction Cuts.

(reconstructed as forward-going!)

Background Rejection: (Containment Cuts). Track Direction Cuts. Track Timing Cuts.

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

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.

Forward-Going Cosmics (I)


DISTANCE FROM VERTEX TO EDGE OF DETECTOR

Forward-Going Cosmics (II)


DISTANCE FROM VERTEX TO FIRST PLANE OF DETECTOR

Forward-Going Cosmics (III)


RECONSTRUCTED ANGLE RELATIVE TO BEAM DIRECTION

Backward-Going Cosmics (I)


DISTANCE FROM VERTEX TO EDGE OF DETECTOR

Backward-Going Cosmics (II)


RECONSTRUCTED ANGLE RELATIVE TO BEAM DIRECTION

Backward-Going Cosmics (III)


FORWARD TIMING RMS – BACKWARD TIMING RMS

Results


MC Beam Neutrinos

MC Rock Muons

MC Cosmic Muons

Data

Event Selection 200.4 ± 0.5 103.4 ± 0.7 44.8 ± 0.5 48

Containment Cuts 171.1 ± 0.4 0.5 ± 0.1 4.3 ± 0.1 4

Direction Cuts 169.5 ± 0.4 0.3 ± 0.0 0.7 ± 0.1 1

Timing Cuts 169.4 ± 0.4 0.3 ± 0.0 0.1 ± 0.0 1

Total 282.4 ± 0.5 0.6 ± 0.1 0.1 ± 0.0 1

Event Selection 134.1 ± 0.4 60.2 ± 0.6 52.5 ± 0.7 67

Containment cuts 114.8 ± 0.3 0.4 ± 0.1 3.3 ± 0.1 3

Direction Cuts 113.0 ± 0.3 0.3 ± 0.0 0.0 ± 0.0 0

Forward-Going Events (VtxY>EndY):

Backward-Going Events (EndY>VtxY):

Cosmic Muon Background Results (standard fiducial volume)


MC Beam Neutrinos

MC Rock Muons

MC Cosmic Muons

Data

Event Selection 200.4 ± 0.5 103.4 ± 0.7 44.8 ± 0.5 48

Containment Cuts 152.0 ± 0.4 0.3 ± 0.0 2.7 ± 0.1 3

Direction Cuts 150.7 ± 0.4 0.3 ± 0.0 0.6 ± 0.1 1

Timing Cuts 150.6 ± 0.4 0.3 ± 0.0 0.1 ± 0.0 1

Total 252.2 ± 0.5 0.6 ± 0.0 0.1 ± 0.0 1

Event Selection 134.1 ± 0.4 60.2 ± 0.6 52.5 ± 0.7 67

Containment cuts 103.1 ± 0.3 0.4 ± 0.1 1.5 ± 0.1 1

Direction Cuts 101.6 ± 0.3 0.3 ± 0.0 0.0 ± 0.0 0

Forward-Going Events (VtxY>EndY):

Backward-Going Events (EndY>VtxY):

Cosmic Muon Background Event (I) (Run 31373, Snarl 85401)


Cosmic Muon Background Event (II) (Run 31373, Snarl 85401)


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.

Far Detector Fiducial Volume Studies

Documents

Transcript of Far Detector Fiducial Volume Studies