reconstruction issues in cosmic ray muons maury goodman/gavril giurgiu & jurgen reichenbacher

Reconstruction Issuesin Cosmic Ray Muons

Maury Goodman/Gavril Giurgiu & Jurgen Reichenbacher

January 6, 2006 Maury Goodman 2

• 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


R1.14 Monte Carlo, NO CUTS(Problems are more evident before cuts are made)

pFit(GeV)

Cha

rge

ratio

Forward

Reverse

0.5(Forward+Reverse)

pFit(GeV)


Reconstructed/True charge ratioversus reconstructed/true p in MC

pTruth(GeV) pTruth(GeV)

Tru

e C

harg

e R

atio

pTruth(GeV) pTruth(GeV)

Rec

onst

ruct

ed C

harg

e R

atio

pFit(GeV) pFit(GeV)

Tru

e C

harg

e ra

tio

pFit(GeV)

Cha

rge

ratio

Forward

Reverse

pFit(GeV)

Low p dip

High p randomization


• 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.)


Monte CarloAlec cut applied: (q/p)/( Sigmaq/p) > 2.5

pFit(GeV) pFit(GeV) pFit(GeV)

pFit(GeV) pFit(GeV)

pTru

e(G

eV)

pTru

e(G

eV)

pTru

e(G

eV)

pTru

e(G

eV)

pTru

e(G

eV)

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)

Mea

n C

hi2/

ndof

pFit(GeV)M

ean

Chi

2/nd

of

NO CUTS All cuts + 20 plane cut

Bad Chi2 for low reconstructed momentum

Monte Carlo

Red = positive muons Black = negative muons


Release 14/18 comparisons18 data

18.2

MC 14

14 data

2

p(GeV)

Before Alec cut After Alec cut

Black 1.14

Blue 1.18

momentum(GeV)

momentum(GeV)

char

ge r

atio

char

ge r

atio

20 plane cut

60 plane cut

R1.14 data

Black: no momentum correction

Red: with momentum correction q/p -> q/p (1.01 - 0.1 q/p)

Last minute slide

“tweak”


New plot 14 vs 18Red 1.14 tweak added

Blue 1.18 has tweak by default

Black 1.14 (no tweak)


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?


Event from Release 16; hit outside the detector !#@


Rel 1.14

Looks like used a wrong hit (from a brem?) near end of track


Looks like used a wrong hit (from ???) near end of track)


Fit to a 3 GeV muon track with a 7 GeV shower

Does not fail PhUSE cut.phUse = 0.577406planeUse = 0.695652stripUse = 0.223301digitUse = 0.295302


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.

standard Cambridge


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.


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.


Concerns about publishing nowUsing 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.


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.

reconstruction issues in cosmic ray muons maury goodman/gavril giurgiu & jurgen reichenbacher

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