In advance of more targeted tests, data from pion decays rule out a vector X17 boson and strongly constrain an axial-vector X17 boson. In the end, the ATOMKI claim will be discredited.
We derive constraints on the couplings of light vector particles to all first-generation Standard Model fermions using leptonic decays of the charged pion, π+→e+νeXμ. In models where the net charge to which Xμ couples to is not conserved, no lepton helicity flip is required for the decay to happen, enhancing the decay rate by factors of O(m4π/m2em2X). A past search at the SINDRUM-I spectrometer severely constrains this possibility. In the context of the hypothesized 17 MeV particle proposed to explain anomalous 8Be, 4He, and 12C nuclear transitions claimed by the ATOMKI experiment, this limit rules out vector-boson explanations and poses strong limits on axial-vector ones.
Matheus Hostert, Maxim Pospelov, "Pion decay constraints on exotic 17 MeV vector bosons" arXiv:2306.15077 (June 26, 2023).
1 comment:
conclusion
from the conclusion
If the evidence for X(17) persists in the data and
shows up also in other experimental setups, such as at
the Montreal X17 [65] and new JEDI [66] projects, it
would be worthwhile to reconsider a π+ → e+νeXee
search in modern experimental setups. To that end, a
search at the PIONEER experiment at PSI could be
performed, albeit with limited tracking capabilities [67].
An alternative would be to consider kaon factories as
a secondary source of pions. The modern photon ve-
toes and tracking capabilities of NA62 could help reject
backgrounds and extend these types of searches to low
Xee masses. We note that with the hadronic beam at
NA62, the number of pion and kaon decays are compa-
rable. Even with a down-scaled trigger, NA62 may be
well poised to perform such a search alongside other ex-
otic channels like K+ → e+νXee. A persistent X(17)
anomaly would also motivate a new set of π− capture
experiments that would move the suggested anomaly to
smaller angles (∼ 16 degrees) and be free from nuclear
uncertainties [68]. Finally, muon decays could also pro-
vide further insight. Previous studies show that the
Mu3e experiment at PSI can be sensitive to QV
e ε cou-
plings as low as 10−4 by searching for resonances in
μ+ → e+νμνe(X → e+e−) [69].
ACKNOWLEDGMENTS
so far the experiments are still under way
and not axial-vector ones
and this paper said the same
arXiv:2212.06453 (hep-ph)
[Submitted on 13 Dec 2022 (v1), last revised 6 Jun 2023 (this version, v2)]
An updated view on the ATOMKI nuclear anomalies
Daniele Barducci, Claudio Toni
Our conclusions identify the axial vector state as the most promising candidate, while other spin/parity assignments seems disfavored for a combined explanation. Intriguingly, an axial vector state can also simultaneously accommodate other experimental anomalies, {\emph{i.e.}} the KTeV anomaly in π0→e+e− decay while being compatible with the conflicting measurements of the anomalous magnetic moment of the electron (g−2)e and other constraints on the electron couplings of the X boson. The PADME experiment will completely cover the relevant region of the parameter space, thus allowing for a strong test of the existence of the X particle.
axial-vector still being held up from the last one
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