Multiprocess imaging of nuclear modifications on parton distributions in proton-nucleus collisions

Nuclear modifications to collinear parton distribution functions are conventionally quantified by the ratios <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:msubsup><a:mrow><a:mi>r</a:mi></a:mrow><a:mrow><a:mi>i</a:mi></a:mrow><a:mrow><a:mi mathvariant="normal">A</a:mi></a:mrow></a:msubsup><a:mo stretchy="false">(</a:mo><a:mi>x</a:mi><a:mo>,</a:mo><a:msup><a:mrow><a:mi>Q</a:mi></a:mrow><a:mrow><a:mn>2</a:mn></a:mrow></a:msup><a:mo stretchy="false">)</a:mo><a:mo>=</a:mo><a:msubsup><a:mrow><a:mi>f</a:mi></a:mrow><a:mrow><a:mi>i</a:mi></a:mrow><a:mrow><a:mi mathvariant="normal">A</a:mi><a:mo>,</a:mo><a:mi>proton</a:mi></a:mrow></a:msubsup><a:mo stretchy="false">(</a:mo><a:mi>x</a:mi><a:mo>,</a:mo><a:msup><a:mrow><a:mi>Q</a:mi></a:mrow><a:mrow><a:mn>2</a:mn></a:mrow></a:msup><a:mo stretchy="false">)</a:mo><a:mo>/</a:mo><a:msubsup><a:mrow><a:mi>f</a:mi></a:mrow><a:mrow><a:mi>i</a:mi></a:mrow><a:mrow><a:mtext>proton</a:mtext></a:mrow></a:msubsup><a:mo stretchy="false">(</a:mo><a:mi>x</a:mi><a:mo>,</a:mo><a:msup><a:mrow><a:mi>Q</a:mi></a:mrow><a:mrow><a:mn>2</a:mn></a:mrow></a:msup><a:mo stretchy="false">)</a:mo></a:mrow></a:math>. For a given nucleus <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mi>A</k:mi></k:math>, these ratios generally depend on the parton momentum fraction <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mi>x</m:mi></m:math>, the probing scale <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:msup><o:mi>Q</o:mi><o:mn>2</o:mn></o:msup></o:math>, and the parton species <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"><q:mi>i</q:mi></q:math>. Determining these dependencies relies on a global analysis of diverse experimental data. However, in realistic observables, these dependencies are intricately intertwined, making their extraction challenging. In this paper, we propose a novel approach to effectively image the nuclear modification factors <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"><s:msubsup><s:mi>r</s:mi><s:mi>i</s:mi><s:mi mathvariant="normal">A</s:mi></s:msubsup><s:mo stretchy="false">(</s:mo><s:mi>x</s:mi><s:mo>,</s:mo><s:msup><s:mi>Q</s:mi><s:mn>2</s:mn></s:msup><s:mo stretchy="false">)</s:mo></s:math> at the observable level in proton-nucleus collisions at the Large Hadron Collider. Specifically, through a combined study of <x:math xmlns:x="http://www.w3.org/1998/Math/MathML" display="inline"><x:mi>Z</x:mi></x:math>-boson production, <z:math xmlns:z="http://www.w3.org/1998/Math/MathML" display="inline"><z:mi>Z</z:mi><z:mo>+</z:mo><z:mtext>jet</z:mtext></z:math> production, and <bb:math xmlns:bb="http://www.w3.org/1998/Math/MathML" display="inline"><bb:mi>Z</bb:mi><bb:mo>+</bb:mo><bb:mi>c</bb:mi></bb:math>-jet production, we separately enhance signals arising from light-quark, gluon, and heavy-flavor (charm) distributions in nuclei. This enables us to effectively image the <db:math xmlns:db="http://www.w3.org/1998/Math/MathML" display="inline"><db:msubsup><db:mi>r</db:mi><db:mi>i</db:mi><db:mi mathvariant="normal">A</db:mi></db:msubsup><db:mo stretchy="false">(</db:mo><db:mi>x</db:mi><db:mo>,</db:mo><db:msup><db:mi>Q</db:mi><db:mn>2</db:mn></db:msup><db:mo stretchy="false">)</db:mo></db:math> for specific parton species. The feasibility of this method is validated through perturbative calculations at next-to-leading order in the strong coupling constant, employing three sets of nuclear PDF parametrizations: EPPS21, nCTEQ15, and TUJU19. Future measurements of these observables are expected to provide better-motivated parametrization forms of nuclear PDFs and yield new insights into the detailed partonic structures of nuclei.