We report the observation of a new structure in the
Λ
0
b
π
+
π
−
spectrum using the full LHCb data set of
p
p
collisions, corresponding to an integrated luminosity of
9
 
 
fb
−
1
, collected at
√
s
=
7
, 8, and 13 TeV. A study of the structure suggests its interpretation as a superposition of two almost degenerate narrow states. The masses and widths of these states are measured to be
m
Λ
b
(
6146
)
0
=
6146.17
±
0.33
±
0.22
±
0.16
 
 
MeV
,
m
Λ
b
(
6152
)
0
=
6152.51
±
0.26
±
0.22
±
0.16
 
 
MeV
,
Γ
Λ
b
(
6146
)
0
=
2.9
±
1.3
±
0.3
 
 
MeV
,
Γ
Λ
b
(
6152
)
0
=
2.1
±
0.8
±
0.3
 
 
MeV
,
with a mass splitting of
Δ
m
=
6.34
±
0.32
±
0.02
 
 
MeV
, where the first uncertainty is statistical, the second systematic. The third uncertainty for the mass measurements derives from the knowledge of the mass of the
Λ
0
b
baryon. The measured masses and widths of these new excited states suggest their possible interpretation as a doublet of
Λ
b
(
1
D
)
0
states.