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Constraints on the omega pi form factor from analyticity and unitarity

Ananthanarayan, B and Caprini, Irinel and Kubis, Bastian (2016) Constraints on the omega pi form factor from analyticity and unitarity. In: INTERNATIONAL JOURNAL OF MODERN PHYSICS A, 31 (14-15).

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Official URL: http://dx.doi.org/10.1142/S0217751X16300209


Form factors are important low-energy quantities and an accurate knowledge of these sheds light on the strong interactions. A variety of methods based on general principles have been developed to use information known in different energy regimes to constrain them in regions where experimental information needs to be tested precisely. Here we review our recent work on the electromagnetic omega pi form factor in a model-independent framework known as the method of unitarity bounds, partly motivated by the discrepancies noted recently between the theoretical calculations of the form factor based on dispersion relations and certain experimental data measured from the decay omega -> pi(0)gamma*. We have applied a modified dispersive formalism, which uses as input the discontinuity of the omega pi form factor calculated by unitarity below the omega pi threshold and an integral constraint on the square of its modulus above this threshold. The latter constraint was obtained by exploiting unitarity and the positivity of the spectral function of a QCD correlator, computed on the spacelike axis by operator product expansion and perturbative QCD. An alternative constraint is obtained by using data available at higher energies for evaluating an integral of the modulus squared with a suitable weight function. From these conditions we derived upper and lower bounds on the modulus of the omega pi form factor in the region below the omega pi threshold. The results confirm the existence of a disagreement between dispersion theory and experimental data on the omega pi form factor around 0.6 GeV, including those from NA60 published in 2016.

Item Type: Journal Article
Additional Information: Copyright for this article belongas to the WORLD SCIENTIFIC PUBL CO PTE LTD, 5 TOH TUCK LINK, SINGAPORE 596224, SINGAPORE
Keywords: Meson transition form factors; dispersion relations; analyticity and unitarity
Department/Centre: Division of Physical & Mathematical Sciences > Centre for High Energy Physics
Date Deposited: 24 Aug 2016 09:56
Last Modified: 24 Aug 2016 09:56
URI: http://eprints.iisc.ac.in/id/eprint/54280

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