Abstract
The existence of a new force beyond the Standard Model is compelling because it could explain several striking astrophysical observations which fail standard interpretations. We searched for the light vector mediator of this dark force, the U boson, with the KLOE detector at the DAΦNE e+e− collider. Using an integrated luminosity of 1.54 fb−1, we studied the process e+e−→Uγ, with U→e+e−, using radiative return to search for a resonant peak in the dielectron invariant-mass distribution. We did not find evidence for a signal, and set a 90% CL upper limit on the mixing strength between the Standard Model photon and the dark photon, ε2, at 10−6–10−4 in the 5–520 MeV/c2 mass range.
Highlights
The Standard Model (SM) of particle physics has received further confirmation with the discovery of the Higgs boson [1,2,3], there are strong hints of physics it cannot explain, such as neutrino oscillations [4] and the measured anomalous magnetic moment of the muon [5]
The mediator of the new force would be a gauge vector boson, the U boson, referred to as a dark photon or A. It would be produced during Weakly InteractingMassive Particle (WIMP) annihilations, have a mass less than two proton masses, and a leptonic decay channel in order to explain the astrophysical observations recently reported by many experiments [11,12,13,14,15,16,17,18,19,20,21]
We investigated the e+e− → Uγ process by considering the U boson decaying into e+e−
Summary
The Standard Model (SM) of particle physics has received further confirmation with the discovery of the Higgs boson [1,2,3], there are strong hints of physics it cannot explain, such as neutrino oscillations [4] and the measured anomalous magnetic moment of the muon [5]. The mediator of the new force would be a gauge vector boson, the U boson, referred to as a dark photon or A It would be produced during WIMP annihilations, have a mass less than two proton masses, and a leptonic decay channel in order to explain the astrophysical observations recently reported by many experiments [11,12,13,14,15,16,17,18,19,20,21]. The finite-width effects related to s-channel annihilation sub-processes, scattering t-channel and s–t interference are of order of U/mU for the integrated cross section and can be neglected with respect to any potential resonance we would observe; U ∼ 10−7–10−2 MeV for the coupling strengths to which we are sensitive [30]. Using a sample of KLOE data collected during 2004–2005, corresponding to an integrated luminosity of 1.54 fb−1, we derived a new limit on the kinetic mixing parameter, ε2, approaching the dielectron mass threshold
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