Introduction

This Tuple Tool implements IBackgroundInfo to give detailed information about how a candidate was (mis)constructed. The following is taken from the doxygen page for IBackgroundInfo, and was written by Vladimir Grigorov.


IBackgroundInfo

Returns the background category for a reconstructed candidate Particle.

Many thanks go to all the users who tested this tool, but especially to Luis Fernandez, Patrick Koppenburg and Jeremie Borel for their assistance in the design and extensive help in ironing out bugs.

Conditions:

  1. all final-state particles used to form the candidate are matched to decay products of the same true MC particle (not necessarily the signal)
  2. all final-state MC particles originating from the true MC particle defined in A are matched to particles used to form the candidate (except photons generated by PHOTOS); in case the decay descriptor of the true MC particle defined in A corresponds to an inclusive decay, "all final-state MC particles" only include the particles required in this (semi-)inclusivei decay.
  3. all final-state particles used to form the candidate are correctly identified, i.e. have been assigned their correct (true) mass
  4. the true MC particle defined in A is a signal decay according to the decay descriptor, or the head of a decay chain which differs from the signal decay chain only by the presence or absence of intermediate resonances but has other otherwise the same head, same final state particles and same topology.
  5. the true MC particle defined in A is a signal decay according to the decay descriptor, and all intermediate states of this decay are correctly reconstructed (as listed in the decay descriptor)
  6. the true MC particle defined in A has a mass which does not exceed the mass of the head of the decay descriptor by more than 100 MeV/c2 (tunable parameter)
  7. at least one final-state particle used to form the candidate is a ghost
  8. final-state particles used to form the candidate are matched to true particles from at least two different collisions (pileup)
  9. at least one final-state particles used to form the candidate is matched to a true decay product of a b-hadron (following mother-daughter relationships all the way through)
  10. at least one final-state particles used to form the candidate is matched to a true decay product of a c-hadron (following mother-daughter relationships all the way through)
  11. at least two final state daughters are matched to the same MCParticle.
  12. at least one final state daughter is matched to an MCParticle which is the MCMother of an MCParticle matched to another final state daughter.
  13. at least one final state daugher is associated to an MCParticle from the primary vertex
  14. every final state daughter is associated to an MCParticle from the same primary vertex

Categories:

  • 0: Signal !G && !K && !L && A && B && C && D && E
  • 10: Quasi-signal !G && !K && !L && A && B && C && D && !E
  • 20: Phys. back. (full rec.) !G && !K && !L && A && B && C && !D
  • 30: Reflection (mis-ID) !G && !K && !L && A && B && !C
  • 40: Phys. back. (part. rec.) !G && !K && !L && A && !B && !(C && F)
  • 50: Low-mass background !G && !K && !L && A && !B && C && F
  • 60: Ghost G
  • 63: Clone !G && K
  • 66: Hierarchy !G && !K && L
  • 70: FromPV !G && !K && !L && M
  • 80: AllFromSamePV !G && !K && !L && N
  • 100: Pileup/FromDifferentPV !G && !K && !L && !A && H
  • 110: bb event !G && !K && !L && !A && !H && I
  • 120: cc event !G && !K && !L && !A && !H && !I && J
  • 130: light-flavour event !G && !K && !L && !A && !H && !I && !J

Examples:

  1. A reconstructed Bs -> (Ds -> KKpi) pi decay could be categorized as signal with respect to the decay descriptor {[[B_s0]nos -> (D_s- => K+ K- pi-) pi+]cc, [[B_s0]os -> (D_s+ => K- K+ pi+) pi-]cc} even if the MC truth indicates a Bs -> (Ds -> (phi -> KK) pi) pi decay.
  2. A reconstructed Bd -> K mumu should not be categorized as a signal with respect to the decay descriptor {[[B0]nos -> (J/psi(1S) -> mu+ mu- {,gamma} {,gamma}) (K*(892)0 -> K+ pi-)]cc, [[B0]os -> (J/psi(1S) -> mu+ mu- {,gamma} {,gamma}) (K*(892)~0 -> K- pi+)]cc} no matter what the MC truth indicates.
  3. A reconstructed Bd -> K mumu should not be categorized as a signal with respect to the decay descriptor {[[B0]nos -> mu+ mu- (K*(892)0 -> K+ pi-)]cc, [[B0]os -> mu- mu+ (K*(892)~0 -> K- pi+)]cc} if the MC truth indicates a Bd -> K* J/psi(mumu) decay.
  4. A reconstructed Bs -> mu+mu- candidate matched to a true J/psi -> mu+mu- decay (could happen if the sidebands around the Bs are very large) and a reconstructed Bd -> K+K- matched to a true Bs -> K+K- are both classified as fully-reconstructed physics background.
  5. A reconstructed Bs -> (Ds -> KKpi) pi candidate matched to a a true Bd -> (D- -> Kpipi) pi decay (mis-ID of one of the pions from the D- as a kaon) is classified as a reflection.
  6. A reconstructed B- -> (D0 -> K-pi+) pi- candidate matched to to the K-,pi+ and pi- of a true Lambda_b -> (Lambda_c -> p K-pi+) pi- is classified as a partially-reconstructed physics background.
  7. A reconstructed Bs -> (Ds -> KKpi) pi+ candidate with all 4 tracks matched to the true final state particles of a true Bs -> (Bs ->KKpi) pi+pi0 decay is classified as a low-mass background.

Please note that there are now three additional categories:

  • FromPV : The candidate particle has at least one final state daughter which comes directly from the primary vertex or a short lived resonance, and the event is not a pileup.
  • AllFromSamePV : The candidate particle's final state daughters all come from the same PV, or from short lived resonances from the same PV.
  • Clone : two final-state Particles are associated to the same MC Particle.
  • Hierarchy : a final state particle has an associated MCParticle which is also the original mother of the MCParticle associated to one of the other final state particles.

Author
Vladimir Gligorov
Date
2009-05-11
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Topic revision: r2 - 2013-03-26 - JackWimberley
 
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