Session R15: Mini-symposium on New Forces at the GeV Scale and Dark Matter I

Search for the dark photon in $\pi^0$ decays

A sample of 17 million fully reconstructed $\pi^0$ Dalitz decays produced in charged kaon decays in flight collected by the NA48/2 experiment at CERN in 2003-04 is analysed to search for the dark photon ($A'$) via the decay chain $\pi^0 \rightarrow \gamma A'$, $A' \rightarrow e^+ e^-$. No dark photon signal is observed, and the most stringent limits on the dark photon mixing parameter in the mass range 9-70 MeV are established. Limitations of the method and possible future directions are discussed.   

Search for dark particles at Belle (II)

We will present a search for the dark photon, $A^\prime$, and the dark Higgs boson, $h^\prime$, in the so-called Higgs-strahlung channel, $e^+e^- \rightarrow A^\prime h'$, with $h^\prime \rightarrow A^\prime A^\prime$. We investigated ten exclusive final-states with $A^\prime \rightarrow e^+e^-$, $\mu^+\mu^-$, or $\pi^+\pi^-$, in the mass ranges $0.1$~GeV/$c^2$~$< m_{A^\prime} < 3.5$~GeV/$c^2$ and $0.2$~GeV/$c^2$~$< m_{h'} < 10.5$~GeV/$c^2$. We also investigated three inclusive final-states, $2(e^+e^-)X$, $2(\mu^+\mu^-)X$, and $(e^+e^-)(\mu^+\mu^-)X$, where $X$ denotes a dark photon candidate detected via missing mass, in the mass ranges $1.1$~GeV/$c^2$~$< m_{A^\prime} < 3.5$~GeV/$c^2$ and $2.2$~GeV/$c^2$~$< m_{h'} < 10.5$~GeV/$c^2$. Using the entire $977\,\mathrm{fb}^{-1}$ data set collected by Belle, we observed no significant signal. We will also discuss prospects for searches for the light dark matter and the dark photon in the radiative decay process at Belle and Belle II.   

Search for low mass vector gauge bosons mediating dark forces at KLOE

Following recent puzzling astrophysical results, searches for a new low-mass neutral vector boson, weakly coupled with SM particles, are being pursued by several different experiments. The KLOE-2 Collaboration is looking for these particles using both continuum events and Dalitz decays of the $\phi$ meson produced at the DA$\Phi$NE $\phi$-factory at the Laboratori Nazionali di Frascati in Italy. No evidence of their existence has been obtained so far and an upper limit in the mass range between 50 MeV and 1000 MeV has been set. Details on different KLOE-2 searches follow: (a.) The U boson can be produced at DA$\Phi$NE through radiative decays of neutral mesons, such as $\phi\to\eta U$, with $U\to\ell^+\ell^-$. The $\eta$ was tagged by three-pion final states, which provide clean signal events. (b.) In the $e^+e^-\to U\gamma$ process the expected U boson cross section can be as high as O(pb) at DA$\Phi$NE energies. The on-shell boson can decay into a lepton pair, giving rise to a $\ell^+\ell^-\gamma$ signal. (c.) We searched for the existence of a higgsstrahlung process in a secluded sector, possibly leading to a U boson and a dark Higgs boson final state. We investigated the case where the dark Higgs is lighter than the U boson and escapes detection, showing up as missing energy.   

Dark photon search at the PHENIX experiment

The \textquotedblleft{}dark photon,\textquotedblright{} a beyond standard model $U(1)$ gauge boson weakly coupled to ordinary photons, is a popular focus of searches for new forces and dark matter at the GeV-scale. Its existence may explain the muon $(g-2)$ anomaly, as measured by the E821 experiment, as well as the excess of high-energy cosmic-ray positrons observed by PAMELA and AMS. The PHENIX experiment at the Relativistic Heavy Ion Collider has performed a direct search for this dark photon candidate appearing within the light meson decays, $\pi^{0},\eta\rightarrow\gamma e^{+}e^{-}$. An upper limit in the coupling between ordinary photons and dark photons in the mass range of 30 to 90 MeV$/c^{2}$ was obtained. The analysis and results will be discussed in this talk.