The workshop “Shedding light on X17” brings together scientists looking for the existence of a possible new light particle, often referred to as X17. This hypothetical particle can explain the resonant structure observed at  $$\sim $$  <math> <mo>∼</mo> </math>   17 MeV in the invariant mass of electron-positron pairs, produced after excitation of nuclei such as  $$^8\hbox {Be}$$  <math> <mrow> <msup> <mrow></mrow> <mn>8</mn> </msup> <mtext>Be</mtext> </mrow> </math>   and  $$^4\hbox {He}$$  <math> <mrow> <msup> <mrow></mrow> <mn>4</mn> </msup> <mtext>He</mtext> </mrow> </math>   by means of proton beams at the Atomki Laboratory in Debrecen. The purpose of the workshop is to discuss implications of this anomaly, in particular theoretical interpretations as well as present and future experiments aiming at confirming the result and/or at providing experimental evidence for its interpretation.

United States

Daniele Alves

Italy

Daniele Barducci

Gianluca Cavoto

France

Luc Darmé

Spain

Luigi Delle Rose

Germany

Luca Doria

Jonathan Feng

André Frankenthal

Ashot Gasparian

United Kingdom

Evgueni Goudzovski

Carlo Gustavino

Egypt

Shaaban Khalil

Bulgaria

Venelin Kozhuharov

Hungary

Attila Krasznahorkay

Tommaso Marchi

Manuel Meucci

Gerald Miller

Stefano Moretti

Marco Nardecchia

Enrico Nardi

Czechia

Hugo Natal da Luz

Giovanni Organtini

Switzerland

Angela Papa

Ann-Kathrin Perrevoort

Vlasios Petousis

Gabriele Piperno

Mauro Raggi

Francesco Renga

Patrick Schwendimann

Rudolf Sýkora

Claudio Toni

Paolo Valente

Cecilia Voena

Cheuk-Yin Wong

Xilin Zhang

Shedding light on X17: community report

Photon-like particles are predicted in many extensions of the Standard Model. They have interactions similar to the photon, are vector bosons, and can be produced together with photons. The present paper proposes a search for such particles in the <math id="M2"><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>-</mo></mrow></msup><mo>→</mo><mi>U</mi><mi>γ</mi></math> process in a positron-on-target experiment, exploiting the positron beam of the DA<math id="M3"><mrow><mi>Φ</mi></mrow></math>NE linac at the Laboratori Nazionali di Frascati, INFN. In one year of running a sensitivity in the relative interaction strength down to ~10−6 is achievable, in the mass region from 2.5 <math id="M4"><mtext>MeV</mtext><mo>&lt;</mo><msub><mrow><mi>M</mi></mrow><mrow><mi>U</mi></mrow></msub><mo>&lt;</mo><mn>20</mn></math> MeV. The proposed experimental setup and the analysis technique are discussed.

Proposal to Search for a Dark Photon in Positron on Target Collisions at DA NE Linac