2018 European Nuclear Physics Conference

Searching for the two γ -decay of the X(17)

4 Sept 2018, 18:10

20m

Fundamental Symmetries

Speaker

Ádám Nagy (Institute for Nuclear Research, Hungarian Academy of Sciences (MTA Atomki), Debrecen Hungary)

Description

Serious efforts have been made to find particles related to dark matter. According to theoretical predictions, a (10 MeV-1 GeV) light particle is expected (hereinafter called X-boson), which mediates the interaction between dark particles. Krasznahorkay et. al. have succesfully investigated the X→e−e+ mode [1]. They excited the EX = 17.6 MeV and EX = 18.15 MeV states of 8Be and measured the angular correlation between the e− and e+ particles emitted during the de-excitation of these states. Signifcant peak-like enhancement of the internal pair creation was observed at large angles, which was interpreted as the creation and decay of an intermediate particle with the mass of m0c2 = 16.70±0.35 (stat)±0.5(sys). The observed anomaly could not be described within conventional nuclear physics [2]. Feng et. al. suggested an explanation assuming a vector gauge boson with a mass of m 0c2 = 16.7 MeV, Jπ = 1+ mediateing a fifth force [3]. According to this interpretation, the X-boson decays with e −e +-pair emission. More recently, Ellwanger and Moretti gave another interpretation of these data [4]: a Jπ=0− pseudo scalar particle was observed. According to the Landau-Yang theorem, the X →γγ decay is allowed only if the X - particle is pseudo scalar. In the case of a vector boson, it is strictly forbidden. In order to be able to choose between the two different scenarios, it was decided to study the X→γγ mode using the 3 He(n, γ)4 He reaction. The γγ -decay of the X-boson might have been observed already by Subbert and Berthollet in the in this reaction [5]. We revisited their experiment and measured the angular correlation of the γ -rays using 12 3”×3” LaBr3 detectors. If a new particle with a mass of 16.7 MeV is created in the decay of the 0− state, and also decays with two γ photons, their angular correlation should peak at an angle of Θ=105o with equal energies. In the talk, the first results of the ongoing X -boson experiments will be presented. [1] A. J. Krasznahorkay et al. ; Phsy. Rev. Lett. 116 , 042501, (2016). [2] X. Zhang, G. A. Miller ; Phys. Lett. B773, 159 , (2017). [3] J. L. Feng et al. ; Phys. Rev. Lett. 117 , 071803, (2016). [4] U. Ellwanger, S. Moretti ; arXiv: 1609.01669v2. [5] M. Subbert , R. Berthollet , Nucl. Phys. A318, 54 (1979).

Selected session

1.) Fundamental Symmetries and Interactions
2.) Nuclear Structure and Dynamics

Presentation materials

Slides

4_EuNPC2018_NagyAdam.pdf