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Systematic Effects on (di)muon acceptances

Systematic Effects on (di)muon acceptances. Michele Floris na60 weekly meeting 19/05/05. Outline. Uncertainties in detector or reconstruction parameters can affect dimuon mass distributions and acceptances Density of carbon in absorber Magnetic field(s) Position of ACM magnet

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Systematic Effects on (di)muon acceptances

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  1. Systematic Effects on (di)muon acceptances Michele Floris na60 weekly meeting 19/05/05

  2. Outline • Uncertainties in detector or reconstruction parameters can affect dimuon mass distributions and acceptances • Density of carbon in absorber • Magnetic field(s) • Position of ACM magnet • Beam position • … • A detailed study was done to understand how these reflect on single/di muon distributions Michele Floris - Seminario XVII Ciclo

  3. Simulation details • Input events provided by Genesis • J/Psi  NA50 parametrization • ACM = 4000, PT7 = 900 • Events tracked/reconstructed with different settings • Standard parameters • PDG density for absorber carbon in generation (not in rec.) • ACM = 3980A in gen., ACM = 4000A in rec. • ACM displaced 10cm in gen. (not in rec.) • Different beam position (both in gen. and rec.) Michele Floris - Seminario XVII Ciclo

  4. Cocktail plot with standard parameter h w f J/y peak not properly normalized VT dimuons J/y Irrelevant for these studies (as long as normalization is internally consistent) Michele Floris - Seminario XVII Ciclo

  5. Comparison of mass spectra Standard vsPDG carbon Density MASS SHIFT (energy loss is not properly corrected) Michele Floris - Seminario XVII Ciclo

  6. Systematic check for mass shifts Mass difference wrt to standard parameters Omega Phi JPsi * pdg carbon * Dm/m: -0.0209 -0.0190 -0.0107 Dm/err: -17.4929 -20.9798 -10.9553 * displaced acm * Dm/m: 0.0047 0.0051 0.0054 Dm/err: 4.5272 9.2577 5.6796 * lower acm field * Dm/m: -0.0017 -0.0005 0.0010 Dm/err: -1.7018 -0.6818 1.1260 * different beam center * Dm/m: 0.0021 -0.0004 0.0001 Dm/err: 2.2338 -0.5432 0.1420 Omega Phi JPsi * standard parameters * mass: 0.7799 +- 0.0004 1.0170 +- 0.0004 3.0925 +- 0.0020 sigma: 0.0229 +- 0.0004 0.0250 +- 0.0004 0.0710 +- 0.0019 chi2 : 27.4990 / 7.0000 31.8731 / 8.0000 27.5618 / 27.0000 * pdg carbon * mass: 0.7640 +- 0.0008 0.9980 +- 0.0008 3.0599 +- 0.0022 sigma: 0.0232 +- 0.0007 0.0256 +- 0.0007 0.0692 +- 0.0019 chi2 : 9.7484 / 7.0000 7.0281 / 8.0000 34.7851 / 27.0000 * displaced acm * [...] Big Small but relevant Negligible Michele Floris - Seminario XVII Ciclo

  7. Conclusions so far • PDG carbon density produces a huge shift in mass, not observed in the data • We investigated other effects, but none seems to be able to compensate for it • Is there something else? • Is geant energy loss reliable? • If something is compensating for the mass shift, there may still be a difference in acceptance • Are the acceptances different in the different simulations? • See the following… Michele Floris - Seminario XVII Ciclo

  8. Single muon acceptance std carbon vs pdg carbon Detector effects, such as the material in the absorber, determine the acceptance of the single muon Sizeable difference, big difference at very low p Michele Floris - Seminario XVII Ciclo

  9. Dimuon acceptance • How does this difference reflects in dimuon acceptance (vs pT and mass)? • Definition of acceptance: • hRec/hGen not suitable (also depends on mass shifts, smearing etc.) • If mass shift is compensated difference in acc is still present • hGen(filled only if the particle was rec) / hGen(all) • Probability of a particle of being reconstructed (regardless of reconstructed kinematics) • Unsuited to correct data, useful to compare different simulations • Depends on how the momentum is shared between the two muons for a given mass • Depends on the generator. We used Genesis. • Cannot use an “unphysical” (e.g. flat) generator Michele Floris - Seminario XVII Ciclo

  10. Dimuon acceptance differences • The input distributions (cocktail plot) was the same for all simulations • The difference in acceptance can be extracted comparing histograms of accepted particles filled with generated kinematics rec gen (if rec) Michele Floris - Seminario XVII Ciclo

  11. Comparison 1 (ACM = 3980 A)

  12. Comparison 2 (PDG Carbon)

  13. Single muon kinematics Standard simulation, vt muons Michele Floris - Seminario XVII Ciclo

  14. Comparison 2.b (PDG Carbon cut on single mu) Single mu p > 8 GeV

  15. Dimuon Acceptance Standard PDG Carbon

  16. Dimuon Acceptance – Comparison (mass) 0. < pT < 0.2 GeV 0.2 < pT < 0.4 GeV Standard PDG carbon 0.4 < pT < 0.6 GeV 0.6 < pT < 0.8 GeV Michele Floris - Seminario XVII Ciclo

  17. Dimuon Acceptance – Comparison (mass) 0. < m < 0.2 GeV 0.2 < m < 0.4 GeV Standard PDG carbon 0.4 < m < 0.6 GeV 0.6 < m < 0.8 GeV Michele Floris - Seminario XVII Ciclo

  18. What’s next? • Complete these studies systematically for all MCs • Understand which scenarios are really “realistic” • Systematic error bar on acceptance • Find cuts in single muon acceptance to define a trusted region • Analytical form of the cut • Minimize syst. error Michele Floris - Seminario XVII Ciclo

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