Abstract
Electron beam fixed target experiments such as NA64 and LDMX use missing energy-momentum to detect the production of dark matter and other long-lived states. The most studied production mechanism is dark Bremsstrahlung through a vector mediator. In this work, we explore a complementary source of missing energy-momentum signals: Bremsstrahlung photons can convert to hard vector mesons in exclusive photoproduction processes, which then decay to dark matter or other invisible particles, such as neutrinos. We find that existing NA64 data can improve the leading constraints on invisible light vector meson decays, while a future run of LDMX could improve them by up to 5 orders of magnitude. For the examples of a dark photon and a $U(1{)}_{B}$ gauge boson mediator, accounting for meson decays substantially enhances these experiments' sensitivity, especially to thermal relic dark matter of mass ${m}_{\ensuremath{\chi}}\ensuremath{\gtrsim}0.1\text{ }\text{ }\mathrm{GeV}$.
Highlights
Light dark matter (DM) in the sub-GeV mass range has received a surge of interest over the last decade, triggered by its potential to explain several direct and indirect detection anomalies [1–3], and more generally by its viability as a WIMP-like thermal relic in simple dark sector models
Invisible and radiative decays of light flavorless mesons [12,13] and heavy quarkonia [14–18] into DM have been reconsidered from an effective field theory perspective
II, we describe in greater detail how invisible meson decay can give rise to missing energy/momentum signals at NA64 and PROBING INVISIBLE VECTOR MESON DECAYS WITH THE
Summary
Light dark matter (DM) in the sub-GeV mass range has received a surge of interest over the last decade, triggered by its potential to explain several direct and indirect detection anomalies [1–3], and more generally by its viability as a WIMP-like thermal relic in simple dark sector models Such models generically predict meson decays with missing energy, and several works explored flavor violating decays of B mesons, D mesons, and kaons [4–6], and invisible and radiative decays of light flavorless mesons [4,7] and heavy quarkonia [8–11]. The exclusive production and invisible decay of an energetic meson contributes to this inclusive missing energy signal As a result, such experiments may be used to simultaneously set limits on the invisible branching ratios of all kinematically accessible mesons, potentially strengthening existing constraints by orders of magnitude.
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