Abstract

The Dalitz plot analysis technique has become an increasingly important method in heavy flavour physics. The Laura++ fitter has been developed as a flexible tool that can be used for Dalitz plot analyses in different experimental environments. Explicitly designed for three-body decays of heavy-flavoured mesons to spinless final state particles, it is optimised in order to describe all possible resonant or nonresonant contributions, and to accommodate possible CP violation effects. Program summaryProgram title: Laura++Program Files doi:http://dx.doi.org/10.17632/jn266r57nk.1Licensing provisions: Apache License, Version 2.0Programming language:C++Nature of problem: Dalitz-plot analysis of particle decays is an important and increasingly utilised technique in particle physics, in particular in heavy flavour physics. While various software tools have been used for Dalitz plot analyses, these are usually not well optimised and are neither scalable for use with larger samples nor flexible enough to be easily adapted for other analyses.Solution method:Laura++ is a dedicated package for performing Dalitz-plot analysis that is flexible enough both to be used in a range of experimental environments and to describe many possible different decays and types of analyses. It allows analysts to create amplitude models to describe the decay of interest and to use those models either to generate pseudoexperiments or to fit them to data.

Highlights

  • Decays of unstable heavy particles to multibody final states can in general occur through several different intermediate resonances

  • The phase space factors ∆Ω are equal to ∆m′∆θ ′ |J| where the square Dalitz plot (SDP) bin size is given by ∆m′∆θ ′ and the Jacobian of the SDP transformation is that of Eq (28); since equal binning is required, the ratio of phase space factors reduces to a ratio of Jacobians

  • The Laura++ package provides a flexible and optimised framework for Dalitz-plot analysis. While it can be used for the decay of any stable spin-zero particle to any final state containing three stable spin-zero particles, it has until now been most widely used for decays of B or D mesons to three pseudoscalars

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Summary

Introduction

Decays of unstable heavy particles to multibody final states can in general occur through several different intermediate resonances. Many ideas for DP analyses have been proposed, since they provide interesting possibilities to provide insight into hadronic structures, to measure CP violation effects and to test the Standard Model These include methods to determine the angles α, β and γ of the CKM Unitarity Triangle with low theoretical uncertainty from, respectively B0 → π +π −π 0 [48], B0 → Dπ +π − [49,50] and B0 → DK +π − decays [51,52], among many other potential analyses. It has become increasingly important to have a publicly available Dalitz-plot analysis package that is flexible enough both to be used in a range of experimental environments and to describe many possible different decays and types of analyses Such a package should be well validated and have excellent performance characteristics, in particular in terms of speed since complicated amplitude fits can otherwise have unacceptable CPU requirements.

Dalitz-plot analysis formalism
Resonance lineshapes
Angular distributions and Blatt–Weisskopf form factors
Fit fractions
Helicity angle convention
Experimental effects
Implementation of the signal component
Particle definitions and kinematics
Isobar dynamics and resonances
Symmetry
Normalisation of signal model
Signal model and amplitude coefficients
Implementation of efficiency and resolution effects
Efficiency
Resolution
Dalitz-plot distributions
Other discriminating variables
Work flows
Common setup
Toy generation
Fitting
Weighting events
Performance
Binned χ 2 method
Examples
Future developments
Plotting the amplitude
Decay-time-dependent fits
Alternative handling of resolution effects
Non-zero spins
Genetic algorithms
Interface to EvtGen
10. Summary
K -matrix
Implementation details for K -matrix
Pedagogical K -matrix plots
LauArgusPdf
LauChebychevPdf
LauCrystalBallPdf
LauNovosibirskPdf
D.10. LauParametricStepFuncPdf
Findings
D.13. Dalitz-plot-dependent PDFs

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