English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Tools annual

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

Positrons beam dump experiments have unique features to search for verynarrow resonances coupled superweakly to $e^+ e^-$ pairs. Due to the continueloss of energy from soft photon bremsstrahlung, in the first few radiationlengths of the dump a positron beam can continuously scan for resonantproduction of new resonances via $e^+$ annihilation off an atomic $e^-$ in thetarget. In the case of a dark photon $A'$ kinetically mixed with the photon,this production mode is of first order in the electromagnetic coupling$\alpha$, and thus parametrically enhanced with respect to the $O(\alpha^2)$$e^+e^- \to \gamma A'$ production mode and to the $O(\alpha^3)$ $A'$bremsstrahlung in $e^--$nucleon scattering so far considered. If the lifetimeis sufficiently long to allow the $A'$ to exit the dump, $A' \to e^+e^-$ decayscould be easily detected and distinguished from backgrounds. We explore theforeseeable sensitivity of the Frascati PADME experiment in searching with thistechnique for the $17\,$MeV dark photon invoked to explain the $^8$Be anomalyin nuclear transitions.

Resonant production of dark photons in positron beam dump experiments