A
study of the decay <
span id="mml
si1" cla
ss="mathml
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span cla
ss="formulatext
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science?_ob=MathURL&_method=retrieve&_eid=1-
s2.0-S0370269316301022&_mathId=
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ser=111111111&_pii=S0370269316301022&_rdoc=1&_i
ssn=03702693&md5=a27d90cd9ed1c8a9305ee68cb10567d6" title="Clic
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source">D<
sup>0
sup>→K<
sup>&minu
s;
sup>π<
sup>+
sup>μ<
sup>+
sup>μ<
sup>&minu
s;
sup>
span><
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span>
span>
span> i
s performed u
sing data collected by the LHCb detector in proton&nda
sh;proton colli
sion
s at a centre-of-ma
ss energy of 8 TeV, corre
sponding to an integrated lumino
sity of <
span id="mml
si2" cla
ss="mathml
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span cla
ss="formulatext
stixSupport mathImg" data-mathURL="/
science?_ob=MathURL&_method=retrieve&_eid=1-
s2.0-S0370269316301022&_mathId=
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ser=111111111&_pii=S0370269316301022&_rdoc=1&_i
ssn=03702693&md5=aa553350039047030cfe0c9c588b103c" title="Clic
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source">2.0 fb<
sup>&minu
s;1
sup>
span><
span cla
ss="mathContainer hidden"><
span cla
ss="mathCode">
span>
span>
span>. Decay candidate
s with muon pair
s that have an invariant ma
ss in the range <
span id="mml
si102" cla
ss="mathml
src"><
span cla
ss="formulatext
stixSupport mathImg" data-mathURL="/
science?_ob=MathURL&_method=retrieve&_eid=1-
s2.0-S0370269316301022&_mathId=
si102.gif&_u
ser=111111111&_pii=S0370269316301022&_rdoc=1&_i
ssn=03702693&md5=9ca79b3c364a17f07386b953b9201081" title="Clic
k to view the MathML
source">675&nda
sh;875 MeV/c<
sup>2
sup>
span><
span cla
ss="mathContainer hidden"><
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ss="mathCode">
span>
span>
span> are con
sidered. Thi
s region i
s dominated by the <
span id="mml
si11" cla
ss="mathml
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span cla
ss="formulatext
stixSupport mathImg" data-mathURL="/
science?_ob=MathURL&_method=retrieve&_eid=1-
s2.0-S0370269316301022&_mathId=
si11.gif&_u
ser=111111111&_pii=S0370269316301022&_rdoc=1&_i
ssn=03702693&md5=ed6c8ea4c95c2a6afc807fff99e1cc17" title="Clic
k to view the MathML
source">ρ<
sup>0
sup>
span><
span cla
ss="mathContainer hidden"><
span cla
ss="mathCode">
span>
span>
span> and
ω re
sonance
s. The branching fraction in thi
s range i
s mea
sured to be
ss="formula" id="fm0010">
Thi
s i
s the fir
st ob
servation of the decay <
span id="mml
si1" cla
ss="mathml
src"><
span cla
ss="formulatext
stixSupport mathImg" data-mathURL="/
science?_ob=MathURL&_method=retrieve&_eid=1-
s2.0-S0370269316301022&_mathId=
si1.gif&_u
ser=111111111&_pii=S0370269316301022&_rdoc=1&_i
ssn=03702693&md5=a27d90cd9ed1c8a9305ee68cb10567d6" title="Clic
k to view the MathML
source">D<
sup>0
sup>→K<
sup>&minu
s;
sup>π<
sup>+
sup>μ<
sup>+
sup>μ<
sup>&minu
s;
sup>
span><
span cla
ss="mathContainer hidden"><
span cla
ss="mathCode">
span>
span>
span>. It
s branching fraction i
s con
si
stent with the value expected in the Standard Model.