Z mass shift in MC release 17Z mass shift in MC release 17

Comparing release 16 and 17Comparing release 16 and 17

Peter Kluit

Muon week 15 November MCP/MATF meeting 9 November 2011

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IntroductionIntroduction

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A Z mass shift has been reported in MCP in MC release 17Several studies are ongoing: latest is from Nayanka BolnetSee MATF 26 october https://indico.cern.ch/conferenceDisplay.py?confId=160046Here I try to localize and pin down further the problem for the Muon Spectrometer (there is also an ID problem see 4 Nov ID Tracking weekly https://indico.cern.ch/conferenceDisplay.py?confId=161459)

MC release 16 mc10_7TeV.106047.PythiaZmumu_no_filter.recon.ESD.e574_s933_s946_r1652MC release 17 mc11_7TeV.106047.PythiaZmumu_no_filter.recon.ESD.e815_s1272_s1274_r2730

Z muon muons selection 2 MuidCB muons with pT > 20 GeVTruth matching uses the ID hit truth matching (p after FSR)

The MC truth for Z mass:The MC truth for Z mass:

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Fit is with Egge function: using the truth momentum for massConclusion: NO mass shift Rel16-17 at “generator” level < 5 MeV

The CB resolution pTrue/p CB The CB resolution pTrue/p CB – 1– 1

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Fit is with double gaussian and common mean: Conclusion: dp/p shift Rel17 is -1.4 10-3 (q<0) (140 MeV@Z)

The CB resolution pTrue/p CB The CB resolution pTrue/p CB – 1– 1

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Fit is with double gaussian and common mean: Conclusion: dp/p shift Rel17 is -1.8 10-3 (q>0) (180 MeV@Z)

The SA resolution pTrue/p SA The SA resolution pTrue/p SA – 1– 1

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Fit is with double gaussian and common mean: Conclusion: dp/p shift Rel17 is -2.0 10-3 (q<0) (200 MeV@Z)

The SA resolution pTrue/p SA The SA resolution pTrue/p SA – 1– 1

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Fit is with double gaussian and common mean: Conclusion: dp/p shift Rel17 is -1.8 10-3 (q<0) (180 MeV@Z)

The ME resolution pTrue/p The ME resolution pTrue/p ME – 1ME – 1

track at Muon Entrytrack at Muon Entry

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Fit is with double gaussian and common mean: Conclusion: dp/p shift Rel17 is -4.0 10-3 (q<0) (400 MeV@Z)

The ME resolution pTrue/p The ME resolution pTrue/p ME – 1ME – 1

track at Muon Entrytrack at Muon Entry

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Fit is with double gaussian and common mean: Conclusion: dp/p shift Rel17 is -4.0 10-3 (q<0) (400 MeV@Z)

The ME resolution pTrue/p The ME resolution pTrue/p ME – 1ME – 1

track at Muon Entry: Eta track at Muon Entry: Eta dependencedependence

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Momenta are shifted upward (so too high) by 200-600 MeV

Note that this shift is localized: ONLY in the Muon System

What happens between IP and Muon Entry?

The Eloss between IP and The Eloss between IP and Muon Entry in Simulation Muon Entry in Simulation

truthtruth

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Very small changes in Eloss…and irrelevant for the shift reported on slide 10

Conclusion; the issue is in the simulation & reco of the Muon System

The Eloss between the first The Eloss between the first and last hit in Muon Systemand last hit in Muon System

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Small changes in Eloss ~ 50 MeVCannot be the cause

The ME resolution pTrue/p The ME resolution pTrue/p ME – 1ME – 1

track at Muon Entry Z prime sample track at Muon Entry Z prime sample release 17release 17

Dinos his sampleDinos his sample

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Conclusion: dp/p shift Z prime Rel17 is ALSO -4.0 10-3 (q><0)

The B field integral: between The B field integral: between the first and last hit in Muon the first and last hit in Muon

SystemSystem

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Some observations:

The Integrated Bfield used in the reconstruction looks very symmetric in rel 17Checked logfiles in Dinos mc11 production: “asymmetric map is loaded”. I don’t understand this….More symmetric than in rel 16

Changes wrt 16 are significantMaybe a B field issue?

ConclusionsConclusions

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We have in mc 11 a major upward shift in the momentum in the Muon System of 200-700 MeV for Z’s.NB: Release 16 is OK

For Z and Z prime the dp/p shift is similar -4 per mille.

A simple “Muon System E loss problem” is not very likely.

The cause can only be in the simulation & reconstruction in the Muon System. The generator is very similar.

Possible causes: - configuration problems that make that one picks up an inconsistent B field map e.g.- Or … a muon tracking precision problem in G4?- Or …

Configuration issues?Configuration issues?

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In the simulation a field map was used with current 20400: Thanks Laurent

However we see during the reconstruction of the simulated data:Thanks Dinos, Felix and Niels:Py:AutoConfiguration WARNING BField current in input file differs from GEO version!! Field is configured due to GEO version

Py:AutoConfiguration INFO Trying to guess magnetic field status from geometryVersion.Py:AutoConfiguration INFO Toroid current fm GEO PK 20500.000000Py:AutoConfiguration INFO Toroid current from input file metadata PK 20500.000000

Note that this fits perfectly with the observations!

But… in the reconstruction it looks like a current of 20400 is used.Puzzling!