The LHCb Collaboration measures production of the exotic hadron <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:msub><a:mi>χ</a:mi><a:mrow><a:mi>c</a:mi><a:mn>1</a:mn></a:mrow></a:msub><a:mo stretchy="false">(</a:mo><a:mn>3872</a:mn><a:mo stretchy="false">)</a:mo></a:math> in proton-nucleus collisions for the first time. Comparison with the charmonium state <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mi>ψ</e:mi><e:mrow><e:mo stretchy="false">(</e:mo><e:mn>2</e:mn><e:mi>S</e:mi><e:mo stretchy="false">)</e:mo></e:mrow></e:math> suggests that the exotic <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:msub><i:mi>χ</i:mi><i:mrow><i:mi>c</i:mi><i:mn>1</i:mn></i:mrow></i:msub><i:mo stretchy="false">(</i:mo><i:mn>3872</i:mn><i:mo stretchy="false">)</i:mo></i:math> experiences different dynamics in the nuclear medium than conventional hadrons, and comparison with data from proton-proton collisions indicates that the presence of the nucleus may modify <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:msub><m:mi>χ</m:mi><m:mrow><m:mi>c</m:mi><m:mn>1</m:mn></m:mrow></m:msub><m:mo stretchy="false">(</m:mo><m:mn>3872</m:mn><m:mo stretchy="false">)</m:mo></m:math> production rates. This is the first measurement of the nuclear modification factor of an exotic hadron. © 2024 CERN, for the LHCb Collaboration 2024 CERN