Observation of Anomalous Internal Pair Creation in ^{8}Be: A Possible Indication of a Light, Neutral Boson.

A J Krasznahorkay,Zs Vajta,J Timár,L Stuhl,T G Tornyi,M Csatlós,A Krasznahorkay,J Gulyás,B M Nyakó,M Hunyadi,T J Ketel,L Csige,I Kuti,Z Gácsi

doi:10.1103/physrevlett.116.042501

A J Krasznahorkay, Zs Vajta + Show 12 more

Open Access

https://doi.org/10.1103/physrevlett.116.042501

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Abstract

Electron-positron angular correlations were measured for the isovector magnetic dipole 17.6MeV (J^{π}=1^{+}, T=1) state→ground state (J^{π}=0^{+}, T=0) and the isoscalar magnetic dipole 18.15MeV (J^{π}=1^{+}, T=0) state→ground state transitions in ^{8}Be. Significant enhancement relative to the internal pair creation was observed at large angles in the angular correlation for the isoscalar transition with a confidence level of >5σ. This observation could possibly be due to nuclear reaction interference effects or might indicate that, in an intermediate step, a neutral isoscalar particle with a mass of 16.70±0.35(stat)±0.5(syst) MeV/c^{2} and J^{π}=1^{+} was created.

Highlights

Electron-positron angular correlations were measured for the isovector magnetic dipole 17.6 MeV (Jπ 1⁄4 1þ, T 1⁄4 1) state → ground state (Jπ 1⁄4 0þ, T 1⁄4 0) and the isoscalar magnetic dipole 18.15 MeV (Jπ 1⁄4 1þ, T 1⁄4 0) state → ground state transitions in 8Be
Significant enhancement relative to the internal pair creation was observed at large angles in the angular correlation for the isoscalar transition with a confidence level of > 5σ
The angular correlation between the eþ and e− emitted in the internal pair creation (IPC) drops rapidly with the separation angle θ [32,33]

Summary

Introduction

Electron-positron angular correlations were measured for the isovector magnetic dipole 17.6 MeV (Jπ 1⁄4 1þ, T 1⁄4 1) state → ground state (Jπ 1⁄4 0þ, T 1⁄4 0) and the isoscalar magnetic dipole 18.15 MeV (Jπ 1⁄4 1þ, T 1⁄4 0) state → ground state transitions in 8Be. For the 17.6 MeV transition we observed a slight deviation from the simulated internal pair conversion correlation (IPCC) curve at angles above 110°, but without any structure, and the deviation could be fully explained by admixing some E1 component typical for the background.

Results

Conclusion