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FBS: From Experimental Data to Pole Parameters in a Direct Way (Angle Dependent Continuum Ambiguity and Laurent + Pietarinen Expansion)

Paper published in Few-Body Syst (2018) 59: 96. , 

From Experimental Data to Pole Parameters in a Direct Way (Angle Dependent Continuum Ambiguity and Laurent + Pietarinen Expansion)

A. Švarc, Y. Wunderlich, H. Osmanović, M. Hadžimehmedović, R. Omerović, J. Stahov, V. Kashevarov, K. Nikonov, M. Ostrick, L. Tiator, R. Workman

Few-Body Syst (2018) 59: 96.
DOI: https://doi.org/10.1007/s00601-018-1410-y

This article belongs to the Topical Collection “NSTAR 2017—The International Workshop on the Physics of Excited Nucleons”.

Unconstrained partial-wave amplitudes obtained at discrete energies from fits to complete sets of eight independent observables which are required to uniquely reconstruct reaction amplitudes do not vary smoothly with energy, and are in principle non-unique. We demonstrate how this behavior can be ascribed to the continuum ambiguity. Starting from the spinless scattering case, we demonstrate how an unknown overall phase depending on energy and angle mixes the structures seen in the associated partial-wave amplitudes making the partial wave decomposition non-unique, and illustrate it on a simple toy model. We then apply these principles to pseudo-scalar meson photoproduction and show that the non-uniqueness effect can be removed through a phase rotation generating “up-to-a-phase” unique set of SE partial wave amplitudes. Extracting pole positions from partial wave amplitudes is the next step. Up to now, there was no reliable way to extract pole parameters from SE partial waves, but a new and simple single-channel method (Laurent + Pietarinen expansion) applicable for continuous and discrete data has been recently developed. It is based on applying the Laurent decomposition of partial wave amplitude, and expanding the non-resonant background into a power series of a conformal-mapping, quickly converging power series obtaining the simplest analytic function with well-defined partial wave analytic properties which fits the input. The generalization of this method to multi- channel case is also developed and presented. Unifying both methods in succession, one constructs a model independent procedure to extract pole parameters directly from experimental data without referring to any theoretical model.


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PRC: Connection between angle-dependent phase ambiguities and the uniqueness of the partial-wave decomposition

Paper published in Phys. Rev. C 97, 054611 – Published 21 May 2018

Connection between angle-dependent phase ambiguities and the uniqueness of the partial-wave decomposition 
A. Švarc, Y. Wunderlich, H. Osmanović, M. Hadžimehmedović, R. Omerović, J. Stahov, V. Kashevarov, K. Nikonov, M. Ostrick, L. Tiator, and R. Workman.

DOI:https://doi.org/10.1103/PhysRevC.97.054611

Unconstrained partial -wave amplitudes, obtained at discrete energies from fits to complete sets of eight independent observables, may be used to reconstruct reaction amplitudes. These partial-wave amplitudes do not vary smoothly with energy and are in principle nonunique. We demonstrate how this behavior can be ascribed to the continuum ambiguity. Starting from the spinless scattering case, we show how an unknown overall phase, depending on energy and angle, mixes the structures seen in the associated partial-wave amplitudes. This process is illustrated using a simple toy model. We then apply these principles to pseudoscalar meson photoproduction, showing how the above effect can be removed through a phase rotation, allowing a consistent comparison with model amplitudes. The effect of this phase ambiguity is also considered for Legendre expansions of experimental observables.


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PWA 10 - ATHOS 5 Workshop 2018

The International Workshop on Partial Wave Analyses and Advanced Tools for Hadron Spectroscopy, PWA10/ATHOS5, is a combination of the 10th International Workshop on Pion-Nucleon Partial Wave Analysis and the Interpretation of Baryon Resonances and the 5th Workshop on Partial Wave Analysis Tools for Hadron Spectroscopy. It will take place at the Institute of High Energy Physics, Chinese Academy of Sciences in Beijing, China. Previous editions of this workshop include PWA9/ATHOS4 (U. Bonn, 2017) and PWA8/ATHOS3 (GWU, 2015). 

The aim of the workshop is to bring together experimental and theoretical groups working in hadron spectroscopy for constructive discussions of recent results, open issues and future perspectives of the field. Common issues in meson and baryon spectroscopy related to partial wave analyses and the interpretation of data will be emphasized.

PWA10/ATHOS5 Workshop, Beijing, China, July 16 - 20, 2018.





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PWA Collaboration meeting - Mainz 2018


SFB-S3 Collaboration meeting: Partial Wave Analysis with Analytical Constraints 
Mainz, 05 - 09 March 2018,
A2 Seminarroom, Neubau 1st Floor

TIMETABLE (All talks can be found on the MTZ Collaboration web page):

 Monday, 5 March, 10:00-12:30 
 Michael Ostrick: Opening
 Jugoslav Stahov: PWA with analytical constraints for γ,π and e,e'π 
 Rifat Omerovic: Data binning for PWA of pion photo production data 
 Hedim Osmanovic: First results on SE analysis for γ,π0 

Tuesday, 6 March, 10:00-12:30 
Lothar Tiator: Overview on MAID models
Viktor Kashevarov: EtaMAID2018 for γ,η and γ,η' on proton and neutron
Kirill Nikonov: Dispersion Relations for Eta Photoproduction

Wednesday, 7 March, 10:00-12:30 
Mikhail Gorshteyn: Lecture on Finite Energy Sumrules
Mirza Hadzimehmedovic: Lecture on L+P Expansion Method 
Peter Weidenkaff: PWA at BES and PANDA
Vincent Mathieu: Regge Theory

Thursday, 8 March, 10:00-12:30 
Alfred Svarc: Ambiguities in PWA for Meson Photoproduction
Yannick Wunderlich: Mathematical Aspects of Phase Rotation Ambiguities
Vladimir Pascalutsa: PWA for Compton Scattering on the Proton

Further Aspects: 
Error Analysis and Covariance Matrix Exchange of Mathematica and Fortran programs for Fitting and L+P Method



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PRC: Fixed-t analyticity as a constraint in single-energy partial-wave analyses of meson photoproduction reactions

Paper published in Phys. Rev. C 97.015207 - Published 31 January 2018

Fixed-t analyticity as a constraint in single-energy partial-wave analyses of meson photoproduction reactions
H. Osmanović, M. Hadžimehmedović, R. Omerović, J. Stahov, V. Kashevarov, K. Nikonov, M. Ostrick, L. Tiator, and A. Švarc

DOI:https://doi.org/10.1103/PhysRevC.97.015207

Partial-wave amplitudes of meson photoproduction reactions are an important source of information in baryon spectroscopy. We investigate a new approach in single-energy partial-wave analyses of these reactions. Instead of using a constraint to theoretical models in order to achieve solutions which are continuous in energy, we enforce the analyticity of the amplitudes at fixed values of the Mandelstam variable t. We present an iterative procedure with successive fixed-t amplitude analyses which constrain the single-energy partial-wave analyses and apply this method to the $\gamma p \rightarrow \eta p$. We use pseudodata, generated by the EtaMAID model, to test the method and to analyze ambiguities. Finally, we present an analytically constrained partial-wave analysis using experimental data for four polarization observables recently measured at MAMI and GRAAL in the energy range from threshold to $\sqrt{s}=1.85 GeV$.




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About PWA TUZLA

We are theoretical physicists at Faculty of Natural Sciences and Mathematics - University of Tuzla. Our group is a part of the Mainz - Tuzla - Zagreb Partial Wave Analysis collaboration.

As a part of the MTZ PWA, our results are "above the line" in PDG library.

Related sites

Physics Department >>
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Mainz-Tuzla-Zagreb PWA >>
PDG - Particle Data Group >>
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GWU/SAID Washington >>
Bonn-Gatchina PWA >>
JPac Center Indiana Uni. >>
CLAS Phy. Database >>

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