Systematic study of flow vector fluctuations in sNN=5.02 TeV Pb-Pb collisions

Measurements of the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:msub><a:mi>p</a:mi><a:mi mathvariant="normal">T</a:mi></a:msub></a:math>-dependent flow vector fluctuations in Pb–Pb collisions at <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:msqrt><c:msub><c:mi>s</c:mi><c:mi>NN</c:mi></c:msub></c:msqrt><c:mo>=</c:mo><c:mn>5.02</c:mn><c:mspace width="0.16em"/><c:mi>TeV</c:mi></c:mrow></c:math> using azimuthal correlations with the ALICE experiment at the Large Hadron Collider are presented. A four-particle correlation approach [ALICE Collaboration, ] is used to quantify the effects of flow angle and magnitude fluctuations separately. This paper extends previous studies to additional centrality intervals and provides measurements of the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:msub><e:mi>p</e:mi><e:mi mathvariant="normal">T</e:mi></e:msub></e:math>-dependent flow vector fluctuations at <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:mrow><g:msqrt><g:msub><g:mi>s</g:mi><g:mi>NN</g:mi></g:msub></g:msqrt><g:mo>=</g:mo><g:mn>5.02</g:mn><g:mspace width="0.16em"/><g:mi>TeV</g:mi></g:mrow></g:math> with two-particle correlations. Significant <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"><i:msub><i:mi>p</i:mi><i:mi mathvariant="normal">T</i:mi></i:msub></i:math>-dependent fluctuations of the <k:math xmlns:k="http://www.w3.org/1998/Math/MathML"><k:msub><k:mover accent="true"><k:mi>V</k:mi><k:mo>⃗</k:mo></k:mover><k:mn>2</k:mn></k:msub></k:math> flow vector in Pb–Pb collisions are found across different centrality ranges, with the largest fluctuations of up to <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"><m:mrow><m:mo>∼</m:mo><m:mn>15</m:mn><m:mo>%</m:mo></m:mrow></m:math> being present in the 5% most central collisions. In parallel, no evidence of significant <n:math xmlns:n="http://www.w3.org/1998/Math/MathML"><n:msub><n:mi>p</n:mi><n:mi mathvariant="normal">T</n:mi></n:msub></n:math>-dependent fluctuations of <p:math xmlns:p="http://www.w3.org/1998/Math/MathML"><p:msub><p:mover accent="true"><p:mi>V</p:mi><p:mo>⃗</p:mo></p:mover><p:mn>3</p:mn></p:msub></p:math> or <r:math xmlns:r="http://www.w3.org/1998/Math/MathML"><r:msub><r:mover accent="true"><r:mi>V</r:mi><r:mo>⃗</r:mo></r:mover><r:mn>4</r:mn></r:msub></r:math> is found. Additionally, evidence of flow angle and magnitude fluctuations is observed with more than <t:math xmlns:t="http://www.w3.org/1998/Math/MathML"><t:mrow><t:mn>5</t:mn><t:mi>σ</t:mi></t:mrow></t:math> significance in central collisions. These observations in <u:math xmlns:u="http://www.w3.org/1998/Math/MathML"><u:mtext>Pb–Pb</u:mtext></u:math> collisions indicate where the classical picture of hydrodynamic modeling with a common symmetry plane breaks down. This has implications for hard probes at high <v:math xmlns:v="http://www.w3.org/1998/Math/MathML"><v:msub><v:mi>p</v:mi><v:mi mathvariant="normal">T</v:mi></v:msub></v:math>, which might be biased by <x:math xmlns:x="http://www.w3.org/1998/Math/MathML"><x:msub><x:mi>p</x:mi><x:mi mathvariant="normal">T</x:mi></x:msub></x:math>-dependent flow angle fluctuations of at least 23% in central collisions. Given the presented results, existing theoretical models should be reexamined to improve our understanding of initial conditions, quark–gluon plasma properties, and the dynamic evolution of the created system.