54
3 Phenomenology of the Massive Dark Photon
to dark photons, dark Higgs bosons, heavy neutral leptons, axion-like particles,
and many other proposed feebly-interacting particles [47]. FASER and FASER2
aim to collect 150 fb
−1 and 3000 fb
−1 of integrated luminosity, respectively.
– HPS at Jefferson Laboratory (JLab): The HPS experiment [27], proposed at an
electron beam-dump at CEBAF electron beam (2.2–6.6 GeV, up to 500 nA), search
for visible (A
→ e
+ e
− ) dark photon (prompt and displaced) decays produced via
Bremsstrahlung production in a thin W target. The experiment makes use of the
200 nA electron beam available in Hall-B at Jefferson Lab.
– SeaQuest at Fermilab (FNAL): will search for visible dark photon decays A
→
e
+ e
− at the 120 GeV main injector proton beamline at FNAL [26]. It plans to
accumulate approximately 10
18 protons-on-target by 2024.
– MAGIX or Beam Dump Experiment at MESA, Mainz: The MESA accelerator
is a continuous wave linac that will be able to provide an electron beam of
E max = 155 MeV energy and up to 1 mA current [29]. The MAGIX detector
is a twin arm dipole spectrometer placed around a gas target and will search for
search for visible (A
→ e
+ e
− ) dark photon (prompt and displaced) decays produced via Bremsstrahlung production [30]. The possibility of a beam dump setup
experiment is also under study. Timeline: targeted operations in 2021–2022 and 2
years of data taking.
– Experiments at a future e
+ e
− circular collider, FCC-ee: a powerful technique
to be exploited at experiments running at a future e
+ e
− circular collider is the
radiative return, e
+ e
−
→ A
γ, A
→ μ
+
μ
− . The results obtained in [32] have been
rescaled to the integrated luminosities of 150 fb
−1 at
√
s = 90 GeV and 5 ab
−1 at
√
s = 250 GeV, as in [48].
– ATLAS/CMS at the high-luminosity phase at the LHC and at a future pp circular
collider: at pp colliders the dark photon can be produced via a Drell-Yan process,
pp → A
→ e
+ e
−
, μ
+
μ
− . The physics reach of ATLAS/CMS like experiments
have been computed for
√
s = 14 TeV and 3 ab
−1 and
√
s = 100 TeV, 3 ab
−1 [31].
– ATLAS/CMS at a possible LHeC collider in the LHC tunnel and a future FCCeh circular collider: At the LHeC (FCC-eh) a 7 TeV (50 TeV) a proton beam
collides with a 60 GeV electron beam achieving a center-of-mass energy of 1.3 TeV
(3.5 TeV) and a total integrate luminosity of 1 ab
−1 (3 ab
−1 ). At eh colliders the
main production process for the dark photon is the deep inelastic scattering e
−
+
parton → e
− parton A
, with A
→ charged fermions [33].
3.3.2 Constraints for m A > 1 MeV with A Decays
to Invisible Final States
Different constraints apply in the case of massive dark photon going into invisible
final states in the mass region m A > 1 MeV. In this case techniques like missing
momentum, missing energy, and missing mass are used in order to identify a possible
massive dark photon decaying into invisible final states.
3 Phenomenology of the Massive Dark Photon
to dark photons, dark Higgs bosons, heavy neutral leptons, axion-like particles,
and many other proposed feebly-interacting particles [47]. FASER and FASER2
aim to collect 150 fb
−1 and 3000 fb
−1 of integrated luminosity, respectively.
– HPS at Jefferson Laboratory (JLab): The HPS experiment [27], proposed at an
electron beam-dump at CEBAF electron beam (2.2–6.6 GeV, up to 500 nA), search
for visible (A
→ e
+ e
− ) dark photon (prompt and displaced) decays produced via
Bremsstrahlung production in a thin W target. The experiment makes use of the
200 nA electron beam available in Hall-B at Jefferson Lab.
– SeaQuest at Fermilab (FNAL): will search for visible dark photon decays A
→
e
+ e
− at the 120 GeV main injector proton beamline at FNAL [26]. It plans to
accumulate approximately 10
18 protons-on-target by 2024.
– MAGIX or Beam Dump Experiment at MESA, Mainz: The MESA accelerator
is a continuous wave linac that will be able to provide an electron beam of
E max = 155 MeV energy and up to 1 mA current [29]. The MAGIX detector
is a twin arm dipole spectrometer placed around a gas target and will search for
search for visible (A
→ e
+ e
− ) dark photon (prompt and displaced) decays produced via Bremsstrahlung production [30]. The possibility of a beam dump setup
experiment is also under study. Timeline: targeted operations in 2021–2022 and 2
years of data taking.
– Experiments at a future e
+ e
− circular collider, FCC-ee: a powerful technique
to be exploited at experiments running at a future e
+ e
− circular collider is the
radiative return, e
+ e
−
→ A
γ, A
→ μ
+
μ
− . The results obtained in [32] have been
rescaled to the integrated luminosities of 150 fb
−1 at
√
s = 90 GeV and 5 ab
−1 at
√
s = 250 GeV, as in [48].
– ATLAS/CMS at the high-luminosity phase at the LHC and at a future pp circular
collider: at pp colliders the dark photon can be produced via a Drell-Yan process,
pp → A
→ e
+ e
−
, μ
+
μ
− . The physics reach of ATLAS/CMS like experiments
have been computed for
√
s = 14 TeV and 3 ab
−1 and
√
s = 100 TeV, 3 ab
−1 [31].
– ATLAS/CMS at a possible LHeC collider in the LHC tunnel and a future FCCeh circular collider: At the LHeC (FCC-eh) a 7 TeV (50 TeV) a proton beam
collides with a 60 GeV electron beam achieving a center-of-mass energy of 1.3 TeV
(3.5 TeV) and a total integrate luminosity of 1 ab
−1 (3 ab
−1 ). At eh colliders the
main production process for the dark photon is the deep inelastic scattering e
−
+
parton → e
− parton A
, with A
→ charged fermions [33].
3.3.2 Constraints for m A > 1 MeV with A Decays
to Invisible Final States
Different constraints apply in the case of massive dark photon going into invisible
final states in the mass region m A > 1 MeV. In this case techniques like missing
momentum, missing energy, and missing mass are used in order to identify a possible
massive dark photon decaying into invisible final states.