New results on the <sup>8</sup>Be anomaly

Krasznahorkay, A.; Csatlós, M.; Csige, L.; Gácsi, Zoltán; Gulyás, J.; Nagy, Antal; Sas, N.J.; Tímár, J.; Tornyi, T.; Vajda, I.

doi:10.1088/1742-6596/1056/1/012028

Cited by 49 publications

(78 citation statements)

References 6 publications

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“…The Atomki Collaboration [1] has recently detected hints of a new light bosonic state, with mass ≃17 MeV, from the measurement of the angle between e þ e − pairs and their invariant mass produced by the 18.15 MeV nuclear transition in the excited state 8 Be Ã [2] (see also Refs. [3][4][5][6]). 1 There have been several studies [7][8][9][10][11][12][13][14][15][16][17][18][19] trying to explain the nature of this new state which mostly focus on a vector boson solution.…”

Section: Introductionmentioning

confidence: 99%

Atomki Anomaly in Family-Dependent U(1)′ Extension of the Standard Model

et al. 2019

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In the context of a gauge invariant, nonanomalous, and family-dependent (nonuniversal) Uð1Þ 0 extension of the Standard Model, wherein a new high-scale mechanism generates masses and couplings for the first two fermion generations and the standard Higgs mechanism does so for the third one, we find solutions to the anomaly observed by the Atomki Collaboration in the decay of excited states of beryllium, in the form of a very light Z 0 state, stemming from the Uð1Þ 0 symmetry breaking, with significant axial couplings so as to evade a variety of low-scale experimental constraints.

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Section: Introductionmentioning

confidence: 99%

Atomki Anomaly in Family-Dependent U(1)′ Extension of the Standard Model

et al. 2019

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“…This allows to set the new limits on the X − e − coupling in the range 1.2 × 10 −4 e 6.8 × 10 −4 , excluding part of the parameter space favored by the Berillium anomaly. The non-observation of the decay A → e + e − allows also to set the new bounds on the mixing strength of photons with dark photons (A ) with a mass 24 MeV.Recently, the search for new light bosons weakly coupled to SM particles was additionally inspired by the observation in the ATOMKI experiment by Krasznahorkay et al [1,2] of a ∼7σ excess of events in the invariant mass distribution of e + e − pairs produced in the nuclear transitions of the excited 8 Be * to its ground state via internal pair creation. It was shown that this anomaly can be interpreted as the emission of a protophobic gauge boson X with a mass of 16.7 MeV decaying into e + e − pair [3,4].…”

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confidence: 99%

Improved limits on a hypothetical X(16.7) boson and a dark photon decaying into e+e− pairs

Banerjee¹,

Bernhard²,

Burtsev³

et al. 2020

Phys. Rev. D

107

103

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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 * nucleus ("Berillium anomaly") are reported. The X boson could be produced in the bremsstrahlung reaction e − Z → e − ZX by a high energy beam of electrons incident on the active target in the NA64 experiment at the CERN SPS and observed through its subsequent decay into e + e − pair. 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 to set the new limits on the X − e − coupling in the range 1.2 × 10 −4 e 6.8 × 10 −4 , excluding part of the parameter space favored by the Berillium anomaly. The non-observation of the decay A → e + e − allows also to set the new bounds on the mixing strength of photons with dark photons (A ) with a mass 24 MeV.Recently, the search for new light bosons weakly coupled to SM particles was additionally inspired by the observation in the ATOMKI experiment by Krasznahorkay et al. [1,2] of a ∼7σ excess of events in the invariant mass distribution of e + e − pairs produced in the nuclear transitions of the excited 8 Be * to its ground state via internal pair creation. It was shown that this anomaly can be interpreted as the emission of a protophobic gauge boson X with a mass of 16.7 MeV decaying into e + e − pair [3,4]. This explanation of the anomaly was found to be consistent with the existing constraints assuming that the X has non-universal coupling to quarks, coupling to electrons in the range 2 × 10 −4 e 1.4 × 10 −3 and lifetime 10 −14 τ X 10 −12 s. It is interesting that a new boson with such relatively large couplings to charged leptons could also resolve the so-called (g µ − 2 ) anomaly, a discrepancy between measured and predicted values of the muon anomalous magnetic moment. This has motivated worldwide efforts towards the experimental searches, see, e.g., Refs. [5,6], and studies of the phenomenological aspects of light vector bosons weakly coupled to quarks and leptons, see, e.g., and also earlier works of Refs. [13][14][15][16]. The latest experimental results from the ATOMKI group show a similar excess of events at approximately the same invariant mass in the nuclear transitions of another nucleus, 4 He [17]. This further increases the importance of independent searches for a new particle X.Another strong motivation to search for new light bosons decaying into e + e − pair comes from the dark matter puzzle. An interesting possibility is that in addition to gravity a new force between the dark sector and visible matter, carried by a new vector boson A , called dark photon, might exist [18,19]. Such A could have a mass

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“…In this respect, results from (g − 2) of the muon are prototypical. Another interesting result which has recently been reported is the one in Krasznahorkay et al [1] (see also [2][3][4][5]), by the Atomki experiment [6]. The latter is a pair spectrometer for measuring multi-polarities of nuclear transitions, specifically, using a multidetector array designed and constructed for the simultaneous measurement of energy and angular correlations of electron-positron pairs, in turn emerging via internal pair creation from a variety of nuclear transitions in various isotopes, such as 16 O, 12 C, and 8 Be.…”

Section: Introductionmentioning

confidence: 63%

New Physics Suggested by Atomki Anomaly

et al. 2019

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We consider several extensions of the Standard Model (SM) which can explain the anomalies observed by the Atomki collaboration in the decay of excited states of Beryllium via a new boson with a mass around 17 MeV yielding e + e − pairs. We show how both spin-0 and 1 solutions are possible and describe the Beyond the SM (BSM) scenarios that can accommodate these. They include BSM frameworks with either an enlarged Higgs, or gauge sector, or both.

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New results on the ⁸Be anomaly

Cited by 49 publications

References 6 publications

Atomki Anomaly in Family-Dependent U(1)′ Extension of the Standard Model

Atomki Anomaly in Family-Dependent U(1)′ Extension of the Standard Model

Improved limits on a hypothetical X(16.7) boson and a dark photon decaying into e+e− pairs

New Physics Suggested by Atomki Anomaly

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New results on the 8Be anomaly

Cited by 49 publications

References 6 publications

Atomki Anomaly in Family-Dependent U(1)′ Extension of the Standard Model

Atomki Anomaly in Family-Dependent U(1)′ Extension of the Standard Model

Improved limits on a hypothetical X(16.7) boson and a dark photon decaying into e+e− pairs

New Physics Suggested by Atomki Anomaly

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Resources

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New results on the ⁸Be anomaly