Measurement of angular correlations in low-energy internally-created e−e+ pairs using Timepix3 pixel detectors

AbstraktAbstract

We report on measurements of electron–positron pairs internally created in excited 16O∗ nuclei, as detected using Timepix3 pixel detectors. Such experiments, complemented with simulation efforts, form a basis for our long-term programme to remeasure the so-called ATOMKI anomaly, i.e., the discrepancy in the pair-opening-angle distribution between theoretical expectation and experimental findings for 8Be and 4He nuclei. Emphasis is placed on studying the ability of the setup, comprising of three Timepix3 detectors surrounding the target, to reconstruct the vertices of e−e+ pairs and the angle between each-pair members. The 16O∗ nucleus, created by transmutation of fluorine upon bombardment with protons tuned to populate the 6.05-MeV (first excited) oxygen state, is a convenient means of producing copious amounts of pairs via the E0 deexcitation. The high yield suits the testing purposes and compensates the disadvantage that thus-created particles are of significantly lower energies than in reactions supposedly displaying the anomaly, to be eventually studied. Items such as multiple scattering in the detector material, gamma-background suppression and geometric limitations are discussed.

We report on measurements of electron–positron pairs internally created in excited 16O∗ nuclei, as detected using Timepix3 pixel detectors. Such experiments, complemented with simulation efforts, form a basis for our long-term programme to remeasure the so-called ATOMKI anomaly, i.e., the discrepancy in the pair-opening-angle distribution between theoretical expectation and experimental findings for 8Be and 4He nuclei. Emphasis is placed on studying the ability of the setup, comprising of three Timepix3 detectors surrounding the target, to reconstruct the vertices of e−e+ pairs and the angle between each-pair members. The 16O∗ nucleus, created by transmutation of fluorine upon bombardment with protons tuned to populate the 6.05-MeV (first excited) oxygen state, is a convenient means of producing copious amounts of pairs via the E0 deexcitation. The high yield suits the testing purposes and compensates the disadvantage that thus-created particles are of significantly lower energies than in reactions supposedly displaying the anomaly, to be eventually studied. Items such as multiple scattering in the detector material, gamma-background suppression and geometric limitations are discussed.