cosmic muon analysis: current status
DESCRIPTION
Cosmic Muon Analysis: Current Status. Stuart Mufson, Brian Rebel Argonne March 18, 2005. Data Sets. Run files processed at Indiana with R1.14 forward field data: December 2003 – April 2004 analysis with field map 202 3,931,684 events MC files processed at Indiana field map 201 - PowerPoint PPT PresentationTRANSCRIPT
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Cosmic Muon Analysis:Current Status
Stuart Mufson, Brian Rebel
Argonne
March 18, 2005
(Mufson&Rebel)
Data SetsData Sets
•Run files processed at Indiana with R1.14
forward field data: December 2003 – April 2004 analysis with field map 202 3,931,684 events
• MC files processed at Indiana
field map 201 2,640,752 events
Fraction Remaining
cut data MC
no cuts 1.0 1.0
1. plane cut 0.759 0.763
2. length cut 0.755 0.758
3. passed fit cut 0.752 0.757
4. uv asymmetry cu5. t
0.746 0.755
5. reduced χ2 cut 0.706 0.737
6. end points cut 0.704 0.736
7. fiducial dz,dr cut 0.688 0.720
8. track-like cut 0.687 0.720
9. double-ended strip cut
0.687 0.720
10. consistent timing, dcos(y) cut
0.687 0.720
MC tracks less noisy than in the data
(Mufson&Rebel)
The ProblemThe Problem
There are many manifestations of the cosmic muon problem. The most physically obvious:
When we plotted the +/- ratio for cosmic muons as a function of their reconstructed momentum, we found the following structure:
Fit Momentum
data
MC
data/MC
field map 120 & standard reconstructionch
arge
rat
io
“bump”
“bump” present in data not found in MC
/
2.5qp
q p
(Mufson&Rebel)
The ProblemThe Problem
Is this a real physical effect? Almost certainly not. When normal & reverse field data are co-added, the effect vanishes:
char
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atio
Normal and reverse field data weighted by live time
Fit Momentum
char
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atio
Normal and reverse field data weighted by live time
Azimuth
Even the azimuthal distribution (another manifestation of the problem) of the charge ratio becomes flat when normal/reversefield data are combined
(Mufson&Rebel)
The ProblemThe Problem
Since reversing the field makes the effect go away, Mufson/Rebel suspect that the magnetic field plays an important role. So far, map improvements have not had a dramatic effect.
field map 120 field map 201
Fit Momentum Fit Momentum
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atio
char
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data
MC
data/MC
(Mufson&Rebel)
The ProblemThe Problem
No significant differences from map 120 map 201 map 202
field map 201 field map 202
Fit Momentum Fit Momentum
char
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atio
char
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data
MC
data/MC
(Mufson&Rebel)
Cos(Zenith Angle) CutCos(Zenith Angle) Cut
An effective cut that minimizes the “bump” is cos(zenith) = cos( ) < 0.85 ( > 31o)
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cos()
zenith
Fit Momentum Fit Momentumfield map 202
“bump” “bump”
cut
Events coming from near the zenith contribute substantially to the “bump”
(Mufson&Rebel)
Interestingly, even though the field map does not change the charge ratio significantly, it does flatten the cos(zenith) distribution
field map 202
field map 201
field map 120
cos()
cos()
cos()
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field map 202
cos()
char
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atio
Cos(Zenith Angle) CutCos(Zenith Angle) Cut
data
MC
data/MC
(Mufson&Rebel)
Recent ProgressRecent Progress
Define the quantity:
track strip use fraction = (# double ended strips in the track)/(total # of strips in the track)
char
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atio
data
MC
cut
data and MC show asymmetry in track strip use fraction
for low track strip use fraction – • data: systematically incorrect charge ID• MC: coin flip
Track Strip Use Fraction
Cut on events with low track strip use fraction > 0.55
(Mufson&Rebel)
Track Strip Use Fraction -- Events
Track Strip Use Fraction -- Events
data MC
no obvious differences between data events and MC events
Charge ID: coin flip
Charge ID: systematic error
(Mufson&Rebel)
although very suggestive, the track strip use fraction cut only improves low momentum reconstruction somewhat
Track Strip Use Fraction Cut
Track Strip Use Fraction Cut
Fit Momentum
char
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atio
all cuts through cos() cut
all cuts through cos() cut + track strip use fraction cut
(Mufson&Rebel)
Recent ProgressRecent Progress
Fit Momentum
char
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D p
uri
ty
From NorthFrom South
While studying MC events, we noticed an asymmetry in the charge ID purity between events coming from the north and events coming from the south
all cuts through cos() cut + track strip use fraction cut
With very high probability, these are all events in the outer part of the detector.
Cut on impact parameter < 3.0 m
(Mufson&Rebel)
Asymmetry in Charge ID Purity – MC Events
Asymmetry in Charge ID Purity – MC Events
(Mufson&Rebel)
Data Sets – effect of final cuts
Data Sets – effect of final cuts
Fraction Remaining
cut data MC
no cuts 1.0 1.0
1. plane cut 0.759 0.763
2. length cut 0.755 0.758
3. passed fit cut 0.752 0.757
4. uv asymmetry cut 0.746 0.755
5. reduced χ2 cut 0.706 0.737
6. end points cut 0.704 0.736
7. fiducial dz,dr cut 0.688 0.720
8. track-like cut 0.687 0.720
9. double-ended strip cut
0.687 0.720
10. consistent timing, dcos(y) cut
0.687 0.720
Fraction Remaining
cut data MC
11. track strip use fraction
0.503 0.499
12. impact parameter 0.406 0.402
13.
0.151 0.178
14. cos() 0.104 0.131
qp
qp
higher quality MC tracks
(Mufson&Rebel)
field map 202
Recent ProgressRecent Progress
Fit Momentum Fit Momentum
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datadata
cuts: 1-10
• 1-10 +• cos() cut• track strip fraction cut• impact parameter cut
cuts:
GOOD NEWS: for beam events, charge reconstruction works!• beam events do not come from near the zenith (zenith angle cut)• need a track quality cut like the track strip fraction cut (optimized for lower momentum events with showers)• need a fiducial volume cut (impact parameter cut)
And it will get better ....
(Mufson&Rebel)
Cosmic RaysCosmic Rays
NOT-SO-GOOD-NEWS: we still do not completely understand charge reconstruction for cosmics (and therefore atmospheric neutrino events)
Fit Momentum Azimuth
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field map 202, all cuts EXCEPT cos() cut
(Mufson&Rebel)
Cosmic RaysCosmic Rays
• Jeff Nelson conjecture: we know the field most poorly in the outer parts of the detector; the tracker gives all track points equal weight
tracker gives points equal weight, even though field not known as accurately in outer reaches of detector
we know these events are trouble
• Argonne conjecture: to be discussed by Maury (Erik?)
• Sergei conjecture: discussed at last collaboration meeting; problems with tracker