Abstract
The existence of a new, photon-like, massive particle, theγ′or dark photon, is postulated in several extensions of the Standard Model. These models are often advocated to explain some recent puzzling astrophysical observations, as well as to solve the so far unexplained deviation between the measured and calculated values of the muon anomaly. Dark photons can be produced ate+e-colliders both in continuum events and in vector meson transitions and can eventually decay into an electron-positron pair. For a proper choice of the parameters of the theory, aγ′can have a relatively long lifetime and can therefore be observed as ane+e-vertex well separated by the primary interaction point. This case is discussed in reference to very high luminositye+e-colliders either in construction or under study in several laboratories in the world. It is shown that a search strategy based on the detection of displaced vertices can be in principle very effective in covering a rather wide and to date unexplored region of the theoretical parameters space.
Highlights
In the Standard Model (SM), interactions among elementary particles are mediated by the vector bosons of the strong, weak, and electromagnetic forces
If the γ is light enough and if its couplings with SM particles are suppressed by a factor ≤10−3 with respect to those of the ordinary photon, it can acquire a relatively long lifetime
This fact can be exploited at e+e− colliders by searching a γ → e+e− decay vertex well separated by the primary production one, in e+e− → γγ events
Summary
In the Standard Model (SM), interactions among elementary particles are mediated by the vector bosons of the strong, weak, and electromagnetic forces. New forces can have escaped detection so far, either if their associated bosons are very heavy or if their couplings to ordinary matter are weak enough The latter case has been advocated, among others, in models which try to explain and reconcile among them several puzzling astrophysical observations performed in recent years [1,2,3,4]. The usage of beams of very small dimensions allows one to obtain a clear γ signal by observing secondary vertices of a well-defined invariant mass, well separated by the beams interaction point In the paper, this case will be discussed for three different possible choices of the machine center-of-mass energy, corresponding, respectively, to the mass of the φ(1020), the J/ψ(1S), and the Υ(4S) mesons.
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