Designing optimal experiments: an application to proton Compton scattering

J. A. Melendez, R. J. Furnstahl, H. W. Grießhammer, J. A. McGovern, D. R. Phillips, M. T. Pratola

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


Interpreting measurements requires a physical theory, but the theory’s accuracy may vary across the experimental domain. To optimize experimental design, and so to ensure that the substantial resources necessary for modern experiments are focused on acquiring the most valuable data, both the theory uncertainty and the expected pattern of experimental errors must be considered. We develop a Bayesian approach to this problem, and apply it to the example of proton Compton scattering. Chiral Effective Field Theory (χEFT) predicts the functional form of the scattering amplitude for this reaction, so that the electromagnetic polarizabilities of the nucleon can be inferred from data. With increasing photon energy, both experimental rates and sensitivities to polarizabilities increase, but the accuracy of χEFT decreases. Our physics-based model of χEFT truncation errors is combined with present knowledge of the polarizabilities and reasonable assumptions about experimental capabilities at HIγS and MAMI to assess the information gain from measuring specific observables at specific kinematics, i.e. to determine the relative amount by which new data are apt to shrink uncertainties. The strongest gains would likely come from new data on the spin observables Σ 2x and Σ2x′ at ω≃ 140 to 200 MeV and 40 ∘ to 120 ∘. These would tightly constrain γE1E1- γE1M2. New data on the differential cross section between 100 and 200 MeV and over a wide angle range will substantially improve constraints on αE1- βM1, γπ and γM1M1- γM1E2. Good signals also exist around 160 MeV for Σ 3 and Σ2z′. Such data will be pivotal in the continuing quest to pin down the scalar polarizabilities and refine understanding of the spin polarizabilities.
Original languageEnglish (US)
JournalThe European Physical Journal A
Issue number3
StatePublished - Feb 27 2021
Externally publishedYes

Bibliographical note

KAUST Repository Item: Exported on 2021-03-25
Acknowledged KAUST grant number(s): C0015, CRG
Acknowledgements: We thank Ian Vernon for useful discussions, and M. Ahmed, E. Downie, G. Feldman, P. P. Martel, as well as the MAMI-A2/CB and Compton@HIγS teams for their patience in discussing experimental constraints. We gratefully acknowledge the stimulating atmosphere created by organizers and participants of the workshops UNCERTAINTY QUANTIFICATION AT THE EXTREMES (ISNET-6) at T.U. Darmstadt (Germany) and BAYESIAN INFERENCE IN SUBATOMIC PHYSICS - A WALLENBERG SYMPOSIUM (ISNET-7) at Chalmers U. (Göteborg, Sweden), which triggered and expanded these investigations. H.W.G. gratefully acknowledges the warm hospitality and financial support of the A2/Crystall Ball Collaboration Meeting 2020 at MAMI (U. Mainz, Germany), of both Ohio University and the Ohio State University, and of the University of Manchester, where part of this work was conducted. The work of R.J.F. and J.A.M. was supported in part by the National Science Foundation under Grant Nos. PHY–1614460 and PHY–1913069 and the NUCLEI SciDAC Collaboration under US Department of Energy MSU subcontract RC107839-OSU. The work of D.R.P. was supported by the US Department of Energy under contract DE-FG02-93ER-40756 and by the ExtreMe Matter Institute EMMI at the GSI Helmholtzzentrum für Schwerionenphysik, Darmstadt, Germany. The work of H.W.G. was supported in part by the US Department of Energy under contract DE-SC0015393, by the High Intensity Gamma-Ray Source HIγS of the Triangle Universities Nuclear Laboratory TUNL in concert with the Department of Physics of Duke University, and by The George Washington University: by the Dean’s Research Chair programme and an Enhanced Faculty Travel Award of the Columbian College of Arts and Sciences; and by the Office of the Vice President for Research and the Dean of the Columbian College of Arts and Sciences. His work was conducted in part at GW’s Campus in the Closet. The work of J.McG. was supported by the UK Science and Technology Facilities Council Grant ST/P004423/1. The work of M.T.P. was supported in part by the King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) under Award No. OSR-2018-CRG7-3800.3.
This publication acknowledges KAUST support, but has no KAUST affiliated authors.

ASJC Scopus subject areas

  • Nuclear and High Energy Physics


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