3.3 Limits on the Parameters ε and m A
53
[GeV]
A'
m
3
−
10
2
−
10
1
−
10
1
1 0
2
10
3
10
ε
9
−
10
8
−
10
7
−
10
6
−
10
5
−
10
4
−
10
3
−
10
2
−
10
N A 6 2 - d u m
p
MESA
APEX
SHiP
SeaQuest
HPS
F A S E R 2
F A S E R
AWAKE
++
NA64(e)
Belle II
(dotted)
-1
(solid), 300 fb
-1
LHCb: 15 fb
FCC-ee, 90 GeV
FCC-ee, 250 GeV
F C C -h h
H L -L H C
LHeC (dashed)
FCC-eh (solid)
*
Be
8
Fig. 3.4 Colored curves are projections for existing and proposed experiments on the massive
dark photon for m A > 1 MeV: Belle-II [20] at SuperKEKb; LHCb upgrade [21, 22] at the LHC;
NA62 in dump mode [23] and NA64(e) ++ [24] at the SPS; FASER and FASER2 [25] at the
LHC; SeaQuest [26] at Fermilab; HPS [27] at JLAB; an NA64-like experiment at AWAKE [28],
and an experiment dedicated to dark photon searches at MESA [29, 30]. For masses above 10 GeV
projections obtained for ATLAS/CMS during the high luminosity phase of the LHC (HL-LHC [31])
and for experiments running at a future FCC-ee [32], LHeC/FCC-eh [33], and FCC-hh [31] are also
shown. The vertical red line shows the allowed range of couplings of a new gauge boson X to
electrons that could explain the 8 Be anomaly [34, 35]. The existing limits are shown as gray areas.
The bottom plot is revised from [36]
– NA62
++ or NA62 in dump mode at the SPS, CERN, will search for a multitude
of feebly-interacting particles, including dark photon, decaying into visible final
states and possibly emerging from the interactions of 400 GeV proton beam with
a dump. NA62 aims to collect approximately 10
18 protons-on-target in 2021–
2024 [23].
– NA64(e)
++ at the SPS, CERN, is the upgrade of the existing NA64(e) experiment. It
aims to collect about 5 × 10
12 electrons-on-target after the CERN Long Shutdown
2 [24].
– NA64-like experiment at AWAKE, CERN: progress in the coming years in protondriven plasma wake-field acceleration of electrons at the AWAKE facility at CERN
could allow an NA64-like experiment be served by a high-intensity high energy
primary electron beam for search for dark photons in visible final states [28].
The sensitivity plot has been obtained assuming ∼10
16 electrons-on-target with
an energy of 50 GeV.
– FASER and FASER2 at the LHC, CERN: FASER [25] is being installed in a service
tunnel of the LHC located along the beam collision axis, 480 m downstream from
the ATLAS interaction point. At this location, FASER (and possibly its larger successor FASER2) will enhance the LHC discovery potential by providing sensitivity
53
[GeV]
A'
m
3
−
10
2
−
10
1
−
10
1
1 0
2
10
3
10
ε
9
−
10
8
−
10
7
−
10
6
−
10
5
−
10
4
−
10
3
−
10
2
−
10
N A 6 2 - d u m
p
MESA
APEX
SHiP
SeaQuest
HPS
F A S E R 2
F A S E R
AWAKE
++
NA64(e)
Belle II
(dotted)
-1
(solid), 300 fb
-1
LHCb: 15 fb
FCC-ee, 90 GeV
FCC-ee, 250 GeV
F C C -h h
H L -L H C
LHeC (dashed)
FCC-eh (solid)
*
Be
8
Fig. 3.4 Colored curves are projections for existing and proposed experiments on the massive
dark photon for m A > 1 MeV: Belle-II [20] at SuperKEKb; LHCb upgrade [21, 22] at the LHC;
NA62 in dump mode [23] and NA64(e) ++ [24] at the SPS; FASER and FASER2 [25] at the
LHC; SeaQuest [26] at Fermilab; HPS [27] at JLAB; an NA64-like experiment at AWAKE [28],
and an experiment dedicated to dark photon searches at MESA [29, 30]. For masses above 10 GeV
projections obtained for ATLAS/CMS during the high luminosity phase of the LHC (HL-LHC [31])
and for experiments running at a future FCC-ee [32], LHeC/FCC-eh [33], and FCC-hh [31] are also
shown. The vertical red line shows the allowed range of couplings of a new gauge boson X to
electrons that could explain the 8 Be anomaly [34, 35]. The existing limits are shown as gray areas.
The bottom plot is revised from [36]
– NA62
++ or NA62 in dump mode at the SPS, CERN, will search for a multitude
of feebly-interacting particles, including dark photon, decaying into visible final
states and possibly emerging from the interactions of 400 GeV proton beam with
a dump. NA62 aims to collect approximately 10
18 protons-on-target in 2021–
2024 [23].
– NA64(e)
++ at the SPS, CERN, is the upgrade of the existing NA64(e) experiment. It
aims to collect about 5 × 10
12 electrons-on-target after the CERN Long Shutdown
2 [24].
– NA64-like experiment at AWAKE, CERN: progress in the coming years in protondriven plasma wake-field acceleration of electrons at the AWAKE facility at CERN
could allow an NA64-like experiment be served by a high-intensity high energy
primary electron beam for search for dark photons in visible final states [28].
The sensitivity plot has been obtained assuming ∼10
16 electrons-on-target with
an energy of 50 GeV.
– FASER and FASER2 at the LHC, CERN: FASER [25] is being installed in a service
tunnel of the LHC located along the beam collision axis, 480 m downstream from
the ATLAS interaction point. At this location, FASER (and possibly its larger successor FASER2) will enhance the LHC discovery potential by providing sensitivity