A study of the decay
mmlsi1" class="mathmlsrc">mulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0370269316301022&_mathId=si1.gif&_user=111111111&_pii=S0370269316301022&_rdoc=1&_issn=03702693&md5=a27d90cd9ed1c8a9305ee68cb10567d6" title="Click to view the MathML source">D0→K−π+μ+μ−mathContainer hidden">mathCode"><math altimg="si1.gif" overflow="scroll"><msup><mrow><mi>Dmi>mrow><mrow><mn>0mn>mrow>msup><mo stretchy="false">→mo><msup><mrow><mi>Kmi>mrow><mrow><mo>−mo>mrow>msup><msup><mrow><mi>πmi>mrow><mrow><mo>+mo>mrow>msup><msup><mrow><mi>μmi>mrow><mrow><mo>+mo>mrow>msup><msup><mrow><mi>μmi>mrow><mrow><mo>−mo>mrow>msup>math> is perfor
med using data collected by the LHCb detector in proton–proton collisions at a centre-of-
mass energy of 8 TeV, corresponding to an integrated lu
minosity of
mmlsi2" class="mathmlsrc">mulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0370269316301022&_mathId=si2.gif&_user=111111111&_pii=S0370269316301022&_rdoc=1&_issn=03702693&md5=aa553350039047030cfe0c9c588b103c" title="Click to view the MathML source">2.0 fb−1mathContainer hidden">mathCode"><math altimg="si2.gif" overflow="scroll"><mn>2.0mn><msup><mrow><mtext> fbmtext>mrow><mrow><mo>−mo><mn>1mn>mrow>msup>math>. Decay candidates with
muon pairs that have an invariant
mass in the range
mmlsi102" class="mathmlsrc">mulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0370269316301022&_mathId=si102.gif&_user=111111111&_pii=S0370269316301022&_rdoc=1&_issn=03702693&md5=9ca79b3c364a17f07386b953b9201081" title="Click to view the MathML source">675–875 MeV/c2mathContainer hidden">mathCode"><math altimg="si102.gif" overflow="scroll"><mn>675mn><mtext>–mtext><mn>875mn><mtext> MeVmtext><mo stretchy="false">/mo><msup><mrow><mi>cmi>mrow><mrow><mn>2mn>mrow>msup>math> are considered. This region is do
minated by the
mmlsi11" class="mathmlsrc">mulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0370269316301022&_mathId=si11.gif&_user=111111111&_pii=S0370269316301022&_rdoc=1&_issn=03702693&md5=ed6c8ea4c95c2a6afc807fff99e1cc17" title="Click to view the MathML source">ρ0mathContainer hidden">mathCode"><math altimg="si11.gif" overflow="scroll"><msup><mrow><mi>ρmi>mrow><mrow><mn>0mn>mrow>msup>math> and
m>ωm> resonances. The branching fraction in this range is
measured to be
This is the first observation of the decay
mmlsi1" class="mathmlsrc">mulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0370269316301022&_mathId=si1.gif&_user=111111111&_pii=S0370269316301022&_rdoc=1&_issn=03702693&md5=a27d90cd9ed1c8a9305ee68cb10567d6" title="Click to view the MathML source">D0→K−π+μ+μ−mathContainer hidden">mathCode"><math altimg="si1.gif" overflow="scroll"><msup><mrow><mi>Dmi>mrow><mrow><mn>0mn>mrow>msup><mo stretchy="false">→mo><msup><mrow><mi>Kmi>mrow><mrow><mo>−mo>mrow>msup><msup><mrow><mi>πmi>mrow><mrow><mo>+mo>mrow>msup><msup><mrow><mi>μmi>mrow><mrow><mo>+mo>mrow>msup><msup><mrow><mi>μmi>mrow><mrow><mo>−mo>mrow>msup>math>. Its branching fraction is consistent with the value expected in the Standard Model.