Banerjee, D;
Bernhard, J;
Burtsev, VE;
Chumakov, AG;
Cooke, D;
Crivelli, P;
Depero, E;
... Ulloa, P; + view all
(2020)
Improved limits on a hypothetical X (16.7) boson and a dark photon decaying into e⁺e⁻ pairs.
Physical Review D
, 101
(7)
, Article 071101(R). 10.1103/PhysRevD.101.071101.
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Abstract
The improved results on a direct search for a new X ( 16.7 MeV ) boson that could explain the anomalous excess of e + e − pairs observed in the decays of the excited 8 Be ∗ nuclei (“Berillium or X17 anomaly”) are reported. Interestingly, new recent results in the nuclear transitions of another nucleus, 4 He , seems to support this anomaly spurring the need for an independent measurement. If the X boson exists, it could be produced in the bremsstrahlung reaction e − Z → e − Z X by a high energy beam of electrons incident on the active target in the NA64 experiment at the CERN Super Proton Synchrotron and observed through its subsequent decay into e + e − pairs. No evidence for such decays was found from the combined analysis of the data samples with total statistics corresponding to 8.4 × 10 10 electrons on target collected in 2017 and 2018. This allows one to set new limits on the X − e − coupling in the range 1.2 × 10 − 4 ≲ ε e ≲ 6.8 × 10 − 4 , excluding part of the parameter space favored by the X17 anomaly, and setting new bounds on the mixing strength of photons with dark photons ( A ′ ) with a mass ≲ 24 MeV . For the 2018 run, the setup was optimized to probe the region of parameter space characterized by a large coupling ε . This allowed a significant improvement in sensitivity despite a relatively modest increase in statistics.
| Type: | Article |
|---|---|
| Title: | Improved limits on a hypothetical X (16.7) boson and a dark photon decaying into e⁺e⁻ pairs |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1103/PhysRevD.101.071101 |
| Publisher version: | https://doi.org/10.1103/PhysRevD.101.071101 |
| Language: | English |
| Additional information: | Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license (https://creativecommons.org/licenses/by/4.0/). Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10098783 |
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