Search for a dark photon in
e
+
e
−
collisions at
B
A
B
AR
The
B
A
B
AR
Collaboration
The following includes supplementary material for the Electronic Physics Auxiliary Publication Service.
Events / ( 0.005 GeV )
21000
22000
23000
Events / ( 0.005 GeV )
21000
22000
23000
= 7.02 GeV
A’
m
(GeV)
ee
m
6.85
6.9
6.95
7
7.05
7.1
7.15
7.2
Data - Bkg
0
500
(GeV)
ee
m
6.85
6.9
6.95
7
7.05
7.1
7.15
7.2
Data - Bkg
0
500
Events / ( 0.003 GeV )
1600
1800
2000
Events / ( 0.003 GeV )
1600
1800
2000
= 6.08 GeV
A’
m
(GeV)
red
m
5.95
6
6.05
6.1
6.15
6.2
Data - Bkg
-100
0
100
(GeV)
red
m
5.95
6
6.05
6.1
6.15
6.2
Data - Bkg
-100
0
100
FIG. 1: Fit to the dielectron mass distribution (left) and the reduced dimuon mass distribution (right) with the most significant
deviations from zero for each channel. The fit is shown as a solid red line, and the background component as a red dashed
line. The difference between the data and the fitted background is shown in the lower panel, together with the fitted signal
component (dashed green curve).
Events / ( 0.0005 GeV )
4000
6000
8000
Events / ( 0.0005 GeV )
4000
6000
8000
= 0.04 GeV
A’
m
(GeV)
ee
m
0.02 0.025 0.03 0.035 0.04 0.045 0.05 0.055 0.06
Data - Bkg
-200
0
200
(GeV)
ee
m
0.02 0.025 0.03 0.035 0.04 0.045 0.05 0.055 0.06
Data - Bkg
-200
0
200
Events / ( 0.001 GeV )
0
500
1000
Events / ( 0.001 GeV )
0
500
1000
= 0.04 GeV
A’
m
(GeV)
red
m
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Data - Bkg
-50
0
50
(GeV)
red
m
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Data - Bkg
-50
0
50
FIG. 2: Example of fit to the dielectron mass distribution (left) and the reduced dimuon mass distribution (right) in the low
mass region. The fit is shown as a solid red line, and the background component as a red dashed line. The difference between
the data and the fitted background is shown in the lower panel, together with the fitted signal component (dashed green curve).
(GeV)
A’
m
0
2
4
6
8
10
) fb
-
e
+
e
→
A’, A’
γ
→
-
e
+
(e
σ
1
10
2
10
Measured limit
Expected limit
σ
1
±
Expected limit
σ
2
±
Expected limit
(GeV)
A’
m
0
2
4
6
8
10
) fb
-
μ
+
μ
→
A’, A’
γ
→
-
e
+
(e
σ
-1
10
1
10
Measured limit
Expected limit
σ
1
±
Expected limit
σ
2
±
Expected limit
FIG. 3: Upper limit (90% CL) on the
e
+
e
−
→
γA
′
,A
′
→
e
+
e
−
(left) and
e
+
e
−
→
γA
′
,A
′
→
μ
+
μ
−
(right) cross-sections as a
function of the dark photon mass, together with the expected limits.
2