Eta and etaprime photoproduction on the nucleon with the isobar model EtaMAID2018

L. Tiator, M. Gorchtein, V. L. Kashevarov, K. Nikonov, M. Ostrick, M. Hadžimehmedović, R. Omerović, H. Osmanović, J. Stahov, A. Švarc
The European Physical Journal A

Received 13 July 2018,  Accepted 20 October 2018.  First Online 06 December 2018
DOI https://doi.org/10.1140/epja/i2018-12643-x 
Publisher Name Springer Berlin Heidelberg
Print ISSN 1434-6001 Online ISSN 1434-601X

The isobar model EtaMAID has been updated with new and high precision data for 𝜂 and 𝜂′ photoproduction on protons and neutrons from MAMI, ELSA, GRAAL and CLAS. The background is described in a recently developed Regge cut model, and for the resonance part the whole list of nucleon resonances has been investigated with 21 𝑁∗ states contributing to 𝜂 photoproduction and 12 𝑁∗ states contributing to 𝜂′ photoproduction. A new approach is discussed to avoid double counting in the overlap region of Regge and resonances. A comparison is done among four newly updated partial waves analyses for observables and partial waves. Finally, the possibility of a narrow resonance near 𝑊=1900 MeV is discussed, that would be able to explain unexpected energy and angular dependence of observables in 𝑝(𝛾,𝜂′)𝑝 near 𝜂′ threshold.

Read More

Role of angle-dependent phase rotations of reaction amplitudes in η photoproduction on protons

A. Švarc, H. Osmanović, M. Hadžimehmedović, R. Omerović, J. Stahov, M. Gorchteyn, V. Kashevarov, K. Nikonov, M. Ostrick, and L. Tiator
Phys. Rev. C 98, 045206 – Published 19 October 2018

Received 20 July 2018
DOI: https://doi.org/10.1103/PhysRevC.98.045206 

It was recently proved that the invariance of observables with respect to angle-dependent phase rotations of reaction amplitudes mixes multipoles, changing also their relative strength [A. Švarc et al., Phys. Rev. C 97, 054611 (2018)]. Modern partial wave analyses (PWAs) in η photoproduction on protons in the center-of-mass energy range 1.5≤W≤2.0 GeV, either energy-dependent (ED) or single-energy (SE) ones, do not take this effect into consideration. It is commonly accepted that all PWAs give very similar results for the E0+ multipole, but notable differences in this and all other partial waves still remain. In this paper we demonstrate that once these phase rotations are properly taken into account, all ED and SE partial wave analysis in η photoproduction become almost identical for the dominant E0+ multipole, and the agreement among all other multipoles becomes much better. We also show that measured observables are almost equally well reproduced in all PWAs, and the remaining differences among multipoles can be attributed solely to the difference in predictions for unmeasured observables. So, new measurements are needed.

Read More

PWA 10 - ATHOS 5 Workshop 2018

PWA10/ATHOS4 Workshop, Beijing 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 took 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.

In behalf of PWA Tuzla group, Hedim Osmanović and Mirza Hadžimehmedović attended the PWA10/ATHOS4 Workshop. Victor Kashevarov talk from University of Mainz,  a member of Maniz-Tuzla-Zagreb collaboration gave his talk too.  Presentation from their talks can be found on official page of Workshop, or on links below:

Hedim Osmanović - Model Independent Partial Wave Analysis for $π^0$ Photoproduction
Mirza Hadžimehmedović - Pole parameters from etaphotoproduction data using L+P method
Viktor Kashevarov - EtaMAID-2018 for η and η' photoproduction on nucleons

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

Workshop homepage-->

Read More

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. , First Online: 08 June 2018

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.

Read More

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.

Read More

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

Read More

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 $\sqrt{s}=1.85 GeV$.

Read More