| Article | |
| Title | A new anomaly observed in $^4$He supporting the existence of the hypothetical X17 particle |
| Author(s) | Krasznahorkay, A J (KLTE-ATOMKI) ; Csatlós, M (KLTE-ATOMKI) ; Csige, L (KLTE-ATOMKI) ; Gulyás, J (KLTE-ATOMKI) ; Koszta, M (KLTE-ATOMKI) ; Szihalmi, B (KLTE-ATOMKI) ; Timár, J (KLTE-ATOMKI) ; Firak, D S (Debrecen U.) ; Nagy, Á (Debrecen U.) ; Sas, N J (Debrecen U.) ; Krasznahorkay, A (KLTE-ATOMKI ; CERN) |
| Publication | 2020 |
| Number of pages | 6 |
| In: | J. Phys. : Conf. Ser. 1643 (2020) 012001 |
| In: | International Nuclear Physics Conference 2019, Glasgow, United Kingdom, 29 Jul - 2 Aug 2019, pp.012001 |
| DOI | 10.1088/1742-6596/1643/1/012001 |
| Subject category | Nuclear Physics - Experiment |
| Abstract | Recently, we observed an anomalous peak-like excess of internal $e^+e^-$ pairs at around 140° for the M1 transition depopulating the 18.15 MeV isoscalar $1^+$ state in $^8$Be. The deviation from the theoretical prediction can be described by GEANT simulations assuming the creation and subsequent decay of a new, light boson with a mass of 16.7 MeV/$c^2$. In order to reduce the possible systematic errors from the experimenntal data, we re-investigated the $^8$Be anomaly with an improved setup and confirmed the anomaly within the statistical uncertainties. We also studied the angular correlation of the electron-positron pairs created in the M0 transition depopulating the 21.01 MeV 0$^-$ state in $^4$He, and observed an anomalous excess of $e^+e^-$ pairs at a significantly smaller angle of 115°. Since the transition energy was higher in this case, the observed anomaly could be described by assuming the creation and subsequent decay of the same light particle in the simulations. |
| Copyright/License | CC-BY-3.0 |
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