Post on 31-Jan-2016
description
Partially Contained Atmospheric Neutrino Analysis
Andy Blake + John ChapmanCambridge University
January 2004
ν
νμ
μ
UPWARD-GOING MUONS DOWNWARD-GOING MUONS
“direction” problem “containment” problem
Two Categories of PC Event
main background: stopping muons with mis-reconstructed direction
main background: through-going muons that appear contained
shield helps this analysis
Selecting PC Events(1) CONTAIN DIGITS (2) CONTAIN TRACKS
Cambridge Demultiplexer Cambridge Track Reconstruction
Combine digits in adjacent views+ select events with non-contained
hits beside 1 detector edge
Select tracks with > 8 planes + 1 contained vertex
Select events with hits < 0.5m
from 1 detector edge
bottom vertexcontained
top vertex contained
upward-going candidate
downward-going candidate
Event Rates
( kT yr ) -1 MC atmos MC cosmic data
TOTAL FLUX 400 4,500,000
DIGITS > 9 160 2,500,000 3,900,000
PC DIGITS 90 450,000 550,000
PLANES > 8 50 320,000 380,000
TRACK RECO 25 240,000 240,000
PC TRACKS 15 48,000 43,000
PC UP 7 46,000 41,000
PC DOWN 7 2,100 1,800
200,000 MC events
1,000,000MC events
September 2003r18900-19800(~0.12 kT-yr)
stopping muons
Upward-Going PC Events
Upward-Going Muons – Aim
Track Direction Track Topology
Likelihood Analysis
Upward-Going Muons – Timing (1)
(1) Timing
S
CT U viewV view
1/β = -11/β = +1
• Fit S-CT with time slope ± 1• Calculate RMS for each fit• Consider RMSup - RMSdown
MC atmos 97.2 %
MC cosmic 99.8 %
data 99.1 %
Percentage success rate …
Upward-Going Muons - Timing (2)
Timing appears worse for data
Resolution~ 60cm ~ 2ns
• Can also make use of absolute values of RMS …
Upward-Going Muons - Timing (3)
RMSup / RANGE• RMS from fitting wrong time slope
fit
track
3
1
3
)2( 2
2/
0
2/
0
2
2
RANGE
RMSS
dx
dxxRMS
S
S
0
S
Upward-Going Muons - Timing Cuts
5.2 70 370
• RMSup – RMSdown < -0.2 m• RMSup < 2.0 m• RMSdown > 1.0 m• RMSup / RANGE < 0.5• -1.4 < 1/β < -0.6
• RMSup – RMSdown < 0.0 m
1st pass timing cuts
2nd pass timing cuts
3.6 9
(2 evts)
15
(2 evts)
MC atmos
MC cosmic
data
7.3 46,000 41,000
PC digits / tracks
BKG / SIG ~ 1.0
Upward-going Candidates (1)data events: (1) run 19135, snarl 72302
CRATE 15 !
Upward-Going Candidates (2)data events: (2) run 18902, snarl 36351
NEUTRINO CANDIDATE
Upward-Going Candidates (3)MC events: (1) run 231, snarl 44685
Large Angle Scattering
Eμ = 6 GeV
? ?
? ?
?
?? ?
? ?
Upward-Going Candidates (4)MC events: (1) run 242, snarl 65409
Large Scattering Again !!!
Upward-Going Muons – Showers (1)
(2) Vtx Showers• Mop up remaining hits in event• Calculate distance from each track vertex to centre of hits:
Δ VTX = VTXshw - VTXtrk
• Consider Δ VTXup - Δ VTXdown
MC atmos 89.6 %
MC cosmic 38.1 %
data 45.6 %
Percentage success rate …Δ VTXup
Δ VTXdown
for cosmics, showers are distributed
roughly evenly between track vertices,
but slightly more vertex showers
are found at BOTTOM of track
Upward-Going Muons – Showers (2)
Vertex Shower Reconstruction• showers reconstructed in two passes 1st pass – dense “primary” showers ( ≥ 4 planes, ≥ 10 strips) 2nd pass – diffuse “secondary” showers• select the dense showers• eliminates many “fake” muon showers … … but some still found on steep tracks with multiple strips per plane
Upward-Going Muons - Showers (3)
Δ VTXup
Δ VTX = VTXshw - VTXtrk
Quality Cuts
W
ρ ~ Nstrips / W3
shower vertex position: shower density:
Upward-Going Muons - Shower Cuts
BKG / SIG ~ 40.0• shower planes > 4• Δ VTXup < 0.7 m • density > 5.0 strips plane-3
(kT-yr)-1 MC atmos MC cosmic data
PC UP 7.3 46,000 41,000
UP-GOING SHOWER
3.6 12,000 10,000
DENSE SHOWER
1.4 150 160
QUALITY CUTS
1.0 30(6 evts)
50(6 evts)
Upward-Going Candidatesexample data events
neutrino
Downward-Going PC Events
Downward-Going Muons
• 0.5m containment cut on top track vertex removes 99% through-going muons
• most remaining events are steep muons that sneak between the planes
• remove clean background using trace/direction cuts
track containment
Downward-Going Muons – Direction Cuts
Py/P Pz/P
py/p < 0.9 pz/p > 0.2
Downward-Going Muons –Trace Cuts
TRACE Zextrapolate trackto detector edge + calculate Z component
Trace Z > 6 plns
Next Background LayerRemaining background dominated by very steep muons:
• muons travelling significant distances down a single plane • muons turning back on themselves
Downward-Going Muons –Very Steep Muons
Distances of digits from track vertex
• Combine digits in adjacent views around track vertex
• Calculate distance between track vertex and furthest digits
Charge around track vertex
• Plane with maximum charge close to track vertex
ΔR < 1.1 m Q < 500 PE
Downward-Going Muons –Timing Quality
Steep muon events have poor timing
0.5 < | 1/β | < 1.5
Downward-Going Muons -Containment Cuts
(kT-yr) -1 MC atmos MC cosmic data
PC DOWN 7.2 2,100 1,800
DOWN-GOINGTIMING
5.4 2,100 1,800
ANGLE + TRACE
5.0 200 220
Qmax , ΔR
+ TIMING
3.5 30(6 evts)
70(8 evts)
• Py/P < 0.9• Pz/P > 0.2• Trace Z > 6 plns
• Qmax < 500 PEs• ΔR < 1.1 m• 0.5 < 1/β < 1.5• RMSdown < 2.0 m BKG / SIG ~ 10.0
Downward-Going Candidates
6 MONTE CARLO EVENTS• 3 demux errors• 1 tracking error• 1 missing detector• 1 only just contained
8 DATA EVENTS• 1 demux error• 2 tracking errors• 3 missing detector• 2 coil hole• … 0 neutrinos
Demultiplexing Errorsthese hitsshould be
higher
Tracking Errors
Missing Detector
swallowed by LI ?
Conclusion• Analysis is progressing … … but still need to peel away some more layers of background• Need detailed MC/data comparison e.g. high muon scattering MC timing resolution tracks/showers• Need another round of tagging/fixing
reconstruction errors• … but it’s good that neutrinos can be
extracted from the data!