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Cosmic Muon Analysis: Current Status

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

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Cosmic Muon Analysis: Current Status

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  1. Cosmic Muon Analysis:Current Status Stuart Mufson, Brian Rebel Argonne March 18, 2005

  2. 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 • 2,640,752 events MC tracks less noisy than in the data

  3. The 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: “bump” “bump” present in data not found in MC data charge ratio MC field map 120 & standard reconstruction data/MC Fit Momentum

  4. The Problem Is this a real physical effect? Almost certainly not. When normal & reverse field data are co-added, the effect vanishes: Normal and reverse field data weighted by live time charge ratio Fit Momentum Even the azimuthal distribution (another manifestation of the problem) of the charge ratio becomes flat when normal/reversefield data are combined Normal and reverse field data weighted by live time charge ratio Azimuth

  5. The 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 data charge ratio charge ratio MC data/MC Fit Momentum Fit Momentum

  6. The Problem No significant differences from map 120  map 201  map 202 field map 201 field map 202 data charge ratio charge ratio MC data/MC Fit Momentum Fit Momentum

  7. zenith  Cos(Zenith Angle) Cut An effective cut that minimizes the “bump” is cos(zenith) = cos( ) < 0.85 ( > 31o) charge ratio cos() cut “bump” “bump” Fit Momentum Fit Momentum field map 202 Events coming from near the zenith contribute substantially to the “bump”

  8. Cos(Zenith Angle) Cut Interestingly, even though the field map does not change the charge ratio significantly, it does flatten the cos(zenith) distribution field map 120 field map 202 data cos() field map 201 charge ratio charge ratio MC cos() field map 202 data/MC cos() cos()

  9. Recent Progress Define the quantity: track strip use fraction = (# double ended strips in the track)/(total # of strips in the track) cut data • data and MC show asymmetry in • track strip use fraction • for low track strip use fraction – • data: systematically incorrect • charge ID • MC: coin flip charge ratio MC Track Strip Use Fraction Cut on events with low track strip use fraction > 0.55

  10. MC Track Strip Use Fraction -- Events data no obvious differences between data events and MC events Charge ID: systematic error Charge ID: coin flip

  11. Track Strip Use Fraction Cut although very suggestive, the track strip use fraction cut only improves low momentum reconstruction somewhat charge ratio all cuts through cos() cut all cuts through cos() cut + track strip use fraction cut Fit Momentum

  12. From South From North charge ID purity Fit Momentum Recent Progress 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

  13. Asymmetry in Charge ID Purity – MC Events

  14. Data Sets – effect of final cuts higher quality MC tracks

  15. Recent Progress cuts: • 1-10 + • cos() cut • track strip fraction cut • impact parameter cut cuts: 1-10 data data charge ratio Fit Momentum Fit Momentum field map 202 • GOOD NEWS: for beam events, charge reconstruction works! • beam events donot 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 ....

  16. Cosmic Rays NOT-SO-GOOD-NEWS: we still do not completely understand charge reconstruction for cosmics (and therefore atmospheric neutrino events) field map 202, all cuts EXCEPT cos() cut charge ratio charge ratio Fit Momentum Azimuth

  17. tracker gives points equal weight, even though field not known as accurately in outer reaches of detector Cosmic 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 we know these events are trouble • Argonne conjecture: to be discussed by Maury (Erik?) • Sergei conjecture: discussed at last collaboration meeting; problems • with tracker

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