A new preprint recaps developments in establishing the Standard Model prediction for muon g-2 (my own latest recap, with more detail, is in a November 12, 2024 post and shows that the state of the art SM prediction is just 0.2 sigma from the experimental result).
A 2020 "white paper" using a "data driven" model, showing a five sigma discrepancy between theory and experiment was badly wrong, because the data is relied upon was subtly flawed, or understated the uncertainty of its results.
New Lattice QCD calculations which corroborate each other, and some new experimental data to contribute to a data driven model, show that, in fact, it is extremely likely that there is no statistically significant difference between ultra-precise experimental measurements of muon g-2 and the best available calculation of the Standard Model predicted value of it.
[T]he final result for ππ from the Muon g-2 experiment is expected in Spring 2025, preceded by a new Theory White Paper.
A further measurement of ππ is planned at J-PARC@KEK using a very different technique with a compact magnetic ring and low momentum π+. Data-taking should start in 2028 with 2 years of running needed to reach a result with ∼ 2°ΓΈ the uncertainty of Muon g-2.
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Searching for the X17 with the PADME experiment
PADME
Collaboration
•
Venelin Kozhuharov
for the collaboration.
Feb 2, 2025
Abstract
The PADME experiment was originally designed to test dark matter theories
predicting the existence of a ''Dark Sector''
composed of particles that interact with Standard Model ones
exclusively through the exchange of a new, massive mediator.
The confirmation of the X17 anomaly,
observed in nuclear decays at the ATOMKI in Debrecen,
sparked considerable interest in the particle physics community.
If the anomaly arises from the decay of a new state into an e+e−
pair,
the time-reversal symmetry implies that it must be also producible
through e+e− annihilation.
The PADME experiment can rely on the world's only e+ beam with the
appropriate energy for a resonant production of X17.
The collaboration dedicated 2022 data taking
to investigate the X17 anomaly via e+e−→X17→e+e−
reaction,
aiming to probe the particle hypothesis.
An overview of the scientific program of the experiment
and the present status of the search for X17 at PADME are presented.
DOI: https://doi.org/10.22323/1.476.0727
arXiv:2503.01594 (hep-ph)
[Submitted on 3 Mar 2025]
Exploring X17 and dark charges in the context of Standard Model tensions
Antonio Capolupo, Aniello Quaranta, Raoul Serao
We report on recent results, according to which the hyphothetical X17 boson could affect the muon g-2 anomaly and the Lamb Shift. Moreover by considering the kinetic mixing between this new boson and the U(1)Y we establish possible contribution of the X17 to the W mass.
Comments: Proceeding for the conference DICE 2024. To appear on J. Phys. Conf. Series
Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th); Nuclear Theory (nucl-th)
Cite as: arXiv:2503.01594 [hep-ph]
(or arXiv:2503.01594v1 [hep-ph] for this version)
https://doi.org/10.48550/arXiv.2503.01594
"the hyphothetical X17 boson could affect the muon g-2 anomaly" Given that muon g-2 is increasingly appearing to be exactly what the SM predicts it to be (with confirmation improving this spring), the X17 will be increasingly disfavored.
PADME experiment
The dominant limitations in the analysis of PADME RUN III data were identified to be the
precise knowledge of the number of positrons on target and the two cluster events acceptance
systematics. Both can be addressed by selecting a different normalization channel, π+π− → πΎπΎ,
and measure the relative cross section π(π+π− → π+π− )/π(π+π− → πΎπΎ) as a function of√︁ (π ). The
similarity in the topology cancels to high extent the acceptance related effects and the relative ratio
does not suffer from absolute beam flux determination. For precise charged particle identification
and discrimination between π+π− and πΎπΎ final states, a new Micromegas based detector (fig. 3,
right) with a central anode plane and two signal readout planes is foreseen to be placed in front of
the ECal. The necessary 0.5 % uncertainty in the π+π− → πΎπΎ sample will be achieved by collecting
larger number of positrons-on-target per energy scan point. Preliminary estimations indicate that
with the proposed upgrade and six months of data taking PADME will be able to probe the entire
allowed X17 parameter space. A run with the described improvements was scheduled and will take
place in 2025
PADME foresees a new run in 2025 with an upgraded setup which will allow to completely
probe the allowed parameter space for 16.4 MeV ≤ ππ17 ≤ 17.4 MeV
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