Chapter 3
Phenomenology of the Massive Dark
Photon
The phenomenology of the massive dark photon is discussed in terms of its interaction
with the SM particles, as given by Eq. (1.5):
L = −εeJ
μ A
μ ,
(3.1)
where J
μ is the electromagnetic current. The strength of this interaction is modulated
by the parameter ε. The parameter space for the experimental searches is given by
the mass of the dark photon m A and the mixing parameter ε.
3.1 Production, Decays and Detection
Because the current in Eq. (3.1) is the same as the usual electromagnetic current, dark
photons A
can be produced like ordinary photons. The main production mechanisms
are (Fig. 3.1):
– Bremsstrahlung: The incoming electron scatters off the target nuclei (Z), goes
off-shell and can thus emit the dark photon: e
− Z → e
− ZA
;
– Annihilation: An electron-positron pair annihilates into an ordinary and a dark
photon: e
− e
+
→ γ A
– Meson decays: A meson M (it being a π
0
η, or a K or a D) decays as M → γ A
;
– Drell-Yan: A quark-antiquark pair annihilates into the dark photon, which then
decays into a lepton pair (or hadrons): q¯ q → A
(→
+
− or h
+ h
−
).
Different experiments use different production mechanisms and, sometime, more
than one simultaneously.
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021
M. Fabbrichesi et al., The Physics of the Dark Photon,
SpringerBriefs in Physics, https://doi.org/10.1007/978-3-030-62519-1_3
47