Reconstruction Issues in Cosmic Ray Muons Maury Goodman/Gavril Giurgiu & Jurgen Reichenbacher

January 6, 2006Maury Goodman2 Monte Carlo Distributions Chi-squared distributions Release 18/14 comparisons Hook events in releases 1.14, 1.16 and 1.18 Maximum analyzable momentum Initial look at Cambridge reconstruction Our concerns about publishing 1099

January 6, 2006Maury Goodman3 R1.14 Monte Carlo, NO CUTS (Problems are more evident before cuts are made) pFit(GeV) Charge ratio Forward Reverse 0.5(Forward+Reverse) pFit(GeV)

January 6, 2006Maury Goodman4 Reconstructed/True charge ratio versus reconstructed/true p in MC pTruth(GeV) True Charge Ratio pTruth(GeV) Reconstructed Charge Ratio pFit(GeV) True Charge ratio pFit(GeV) Charge ratio Forward Reverse pFit(GeV) Low p dip High p randomization

January 6, 2006Maury Goodman5 The low energy dip appears in the Monte Carlo and is a problem with high momentum tracks being reconstructed at low momentum. The problem is worse in the data than the Monte Carlo. (In addition, there are some differences between forward and reverse MC we don’t fully understand.)

January 6, 2006Maury Goodman6 Monte Carlo Alec cut applied: (q/p)/( Sigma q/p ) > 2.5 pFit(GeV) pTrue(GeV) No plane cut 20 planes 60 planes 100 planes 150 planes All plots -> Log z scale -> Vertical tails smaller than they seem High momentum tracks with few planes are reconstructed as low mometum tracks and poor Chi2/ndof ?

pFit(GeV) Mean Chi2/ndof pFit(GeV) Mean Chi2/ndof NO CUTS All cuts + 20 plane cut Bad Chi2 for low reconstructed momentum Monte Carlo Red = positive muons Black = negative muons

January 6, 2006Maury Goodman8 Release 14/18 comparisons 18 data 18.2 MC data 22 p(GeV) Before Alec cut After Alec cut Black 1.14 Blue 1.18

momentum(GeV) charge ratio 20 plane cut 60 plane cut R1.14 data Black: no momentum correction Red: with momentum correction q/p -> q/p ( q/p) Last minute slide “tweak”

January 6, 2006Maury Goodman10 New plot 14 vs 18 Red 1.14 tweak added Blue 1.18 has tweak by default Black 1.14 (no tweak)

January 6, 2006Maury Goodman11 Scanning It would be desirable to have a display package that showed the hits, showed the strips, and showed the fit, that we could use from or at ANL. Why does the on-line display package show such unphysical behavior in the x-y plane?

January 6, 2006Maury Goodman12 Event from Release 16; hit outside the detector

January 6, 2006Maury Goodman13 Rel 1.14 Looks like used a wrong hit (from a brem?) near end of track

January 6, 2006Maury Goodman14 Looks like used a wrong hit (from ???) near end of track)

January 6, 2006Maury Goodman15 Fit to a 3 GeV muon track with a 7 GeV shower Does not fail PhUSE cut. phUse = planeUse = stripUse = digitUse =

January 6, 2006Maury Goodman16 Cambridge Reconstruction Recently John Marshall made available standard ntuples with a new Kalman fitter Only reverse field data exists so far. We need to also reconstruct forward field and Monte Carlo to see if the same problems exist or not. standardCambridge

January 6, 2006Maury Goodman17 Maximum Analyzable Momentum For a muon going through good field, multiple scattering is ~15% of  (1/p)/(1/p) The sagitta for a track with 0 impact parameter is 8 times that for 3.5 m impact Therefore, for muons which “skim” the detector, multiple scattering provides more curvature than bending. This can be quantified as a function of track direction.

January 6, 2006Maury Goodman18 MAM (2) For an infinite cylindrical detector, it should depend only on impact parameter and d(cosz) For a finite detector, it also depends on L Maury, Phil and Tom are all trying to work this out analytically and then apply to the detector This may be part of what the 3.5m 60 plane cut is accomplishing, but it could be made quantitative.

January 6, 2006Maury Goodman19 Concerns about publishing now Using MIC (which might/might not solve the problem) It is a recent circumstance (November 2005) that two separate effects have been identified in the charge ratio analysis: the low energy dip (a charge ratio randomization effect) and previously identified bias(es). We now have a good opportunity to solve the former problem in a more robust analysis, particularly since it appears in the Monte Carlo. It is plausible that the MIC reduces the possibility that hook events contribute to the charge ratio. Reconstruction problems don’t appear to be the motivation for the MIC The analysis reported in note 1099 cannot be repeated in release 1.18, and the reasons for this are not clear. There is strong evidence that some reconstruction issues are much worse in release 1.18 than in release 1.14, with or without the MIC. (maybe the tweak??) Systematic errors should be (and are) being calculated.

January 6, 2006Maury Goodman20 Next Steps Set up scanning in the Monte Carlo Pursue MAM calculation/cut Figure out what the problem with Release 18 is. Finish looking at Cambridge reconstruction.