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Searching for the X17 with the PADME experiment

V. Kozhuharov

TL;DR

PADME tests the X17 anomaly by exploiting resonant production in $e^+e^-$ annihilation to search for a light vector mediator coupling to Standard Model particles; it combines missing-mass techniques, energy scans around $M_{X17}$, and detector upgrades to probe previously inaccessible regions of the $M_{X17}$–$g_{ve}$ parameter space; the results and projections indicate that, with a dedicated 2025 run and upgrades, PADME can either discover or robustly constrain the X17 in the range $16.4~\mathrm{MeV} \le M_{X17} \le 17.4~\mathrm{MeV}$, informing the dark sector hypothesis and clarifying ATOMKI results.

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 $e^+e^- \to X17 \to e^+e^-$ 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.

Searching for the X17 with the PADME experiment

TL;DR

PADME tests the X17 anomaly by exploiting resonant production in annihilation to search for a light vector mediator coupling to Standard Model particles; it combines missing-mass techniques, energy scans around , and detector upgrades to probe previously inaccessible regions of the – parameter space; the results and projections indicate that, with a dedicated 2025 run and upgrades, PADME can either discover or robustly constrain the X17 in the range , informing the dark sector hypothesis and clarifying ATOMKI results.

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 pair,the time-reversal symmetry implies that it must be also producible through 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 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.

Paper Structure

This paper contains 4 sections, 2 equations, 3 figures.

Table of Contents

  1. Introduction
  2. The PADME experiment at LNF-INFN
  3. Searching for new light particles
  4. Conclusions

Figures (3)

  • Figure 1: A sketch of the PADME experiment together with the DA$\Phi$NE accelerator complex. The DHSTB001 dipole magnet deflects the positrons to BTFEH1 while DHSTB002 directs them towards the PADME target.
  • Figure 2: Left: A summary of the PADME runs taken at different beam energy, measured by monitoring the dipole magnet current and by Hall probes. Right: Expected rate of the reconstructed two cluster events in the case of a presence of a new state with mass $M_{X_{17}} = 16.8~\mathrm{MeV}$ with coupling $g_{ve} = 0.8\times 10^{-3}$.
  • Figure 3: Left:Preliminary estimation of the PADME sensitivity (90% CL limits) to the X17 parameter space with RUN III data. Excluded regions by KLOE Anastasi:2015qla and NA64 NA64:2019auh are also presented. Right: A sketch of the new PADME Micromegas chamber to discriminate between charged and neutral 2 cluster final states and to provide measurement of the charged particle directions.