Systematics of quark/gluon tagging Deepak Kar (for the q/g team in - - PowerPoint PPT Presentation

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Systematics of quark/gluon tagging Deepak Kar (for the q/g team in - - PowerPoint PPT Presentation

Sep 15, 2023 264 likes •502 views

Systematics of quark/gluon tagging Deepak Kar (for the q/g team in Les Houches 2015) Based on: arXiv:1605.04692 and work-in-progress MPI@LHC, Chiapas, Mexico 27th November - 2nd December, 2016 Discriminate between From Quantum Diaries 2

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Systematics of quark/gluon tagging

Deepak Kar (for the q/g team in Les Houches 2015) Based on: arXiv:1605.04692 and work-in-progress MPI@LHC, Chiapas, Mexico 27th November - 2nd December, 2016

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Discriminate between…

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From Quantum Diaries

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Quark/gluon discrimination

  • Ideally: identify quark-initiated or

gluon initiated jets.

  • Is that well defined?

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The study

  • In leading order:

quark radiation ∝ CF, gluon radiation ∝ CA

  • Affected strongly by subleading (perturbative and

non-perturbative) effects

  • Modelled in MC generators, but needs constraining

by data

  • Highlights modelling deficiencies

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Variable

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Generalised angularities:

IRC Safe Used

Define: For hadron colliders:

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ATLAS Result(s)

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  • Eur. Phys. J. C (2014) 74: 3023

ATLAS-CONF-2016-034

Data-MC difference (but very optimistic!) Discriminant composed

  • f different observables
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CMS Result

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CERN-CMS-DP-2016-070

Need MC reweighting to match (data) efficiencies

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Discriminant

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Discriminator:

Gluon rejection for a given quark efficiency Quark rejection for a given gluon efficiency

pq (pg) is the probability distribution for the quark jet (gluon jet) sample as a function

  • f the classifier λ

Δ → 0: no discrimination Δ → 1: perfect discrimination

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Idealised ep collider

  • Useful to understand final state evolution

(ignoring initial state complications)

  • Vary collisions energy (Q), jet radius (R)
  • Look at both hadron and parton level

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Quark: Gluon:

Suppress wide angle radiation

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Hadron Level λLHA

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Good agreement LEP data available Larger spread No data available

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Seperation

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Pythia8 more optimistic, Herwig++ more pessimistic

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Non-Perturbative Effects

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Large effect of hadronisation More difference among MC models as well

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Overall Separation

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Large spread in discrimination power (even more at hadron level)

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Dependance on R

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Separation increases with R (more phase space?)

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Dependance on Q

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Separation increases with Q at parton level (more phase space?)

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Dependance on ⍺S

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No clear trend at parton level, except Herwig++, rest decreases at hadron level

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Proton-proton Results

  • Very preliminary
  • Z+jets (quark

enriched), dijets (gluon enriched)

  • Shown standard jets,

but mMDT /Soft drop effects also looked at

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Hadron Level λLHA

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Decent agreement Larger Difference

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Separation

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Separation

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Pythia more optimistic Opposite trend

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Summary

  • Important physics applications
  • Large effect for generator setting, non-

perturbative/shower effects

  • Need (unfolded) measurements,

specially for gluon processes

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