Phenomenological study of the angle between jet axes in heavy-ion collisions

This paper presents a phenomenological study on the angle between the standard and winner-take-all (WTA) jet axes <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mo>(</a:mo><a:mi mathvariant="normal">Δ</a:mi><a:msubsup><a:mi>R</a:mi><a:mrow><a:mi>axis</a:mi></a:mrow><a:mrow><a:mi>WTA</a:mi><a:mtext>–</a:mtext><a:mi>Std</a:mi></a:mrow></a:msubsup><a:mo>)</a:mo></a:mrow></a:math> in high-energy nuclear collisions. The <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mi>p</c:mi><c:mo>+</c:mo><c:mi>p</c:mi></c:mrow></c:math> baseline is provided by the 8 event generator. The in-medium jet propagation is simulated by the linear Boltzmann transport () model, which considers both the elastic and inelastic jet-medium interactions. Our theoretical results calculated by the model show that the <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mrow><d:mi mathvariant="normal">Δ</d:mi><d:msubsup><d:mi>R</d:mi><d:mrow><d:mi>axis</d:mi></d:mrow><d:mrow><d:mi>WTA</d:mi><d:mtext>–</d:mtext><d:mi>Std</d:mi></d:mrow></d:msubsup></d:mrow></d:math> distribution in <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:mrow><f:mi>Pb</f:mi><f:mo>+</f:mo><f:mi>Pb</f:mi></f:mrow></f:math> at <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:mrow><g:msqrt><g:mi>s</g:mi></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> is narrower than that in <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"><i:mrow><i:mi>p</i:mi><i:mo>+</i:mo><i:mi>p</i:mi></i:mrow></i:math>, which agrees well with the recent ALICE measurements. The narrowing of <j:math xmlns:j="http://www.w3.org/1998/Math/MathML"><j:mrow><j:mi mathvariant="normal">Δ</j:mi><j:msubsup><j:mi>R</j:mi><j:mrow><j:mi>axis</j:mi></j:mrow><j:mrow><j:mi>WTA</j:mi><j:mtext>–</j:mtext><j:mi>Std</j:mi></j:mrow></j:msubsup></j:mrow></j:math>, which seems to violate the nature of intrajet broadening due to jet quenching, may be attributed to the influence of “selection bias.” However, the physical details still need to be fully understood. Utilizing a matching-jet method to track the jet evolution in the QGP to remove the selection bias in the Monte Carlo simulations, we observe that the <l:math xmlns:l="http://www.w3.org/1998/Math/MathML"><l:mrow><l:mi mathvariant="normal">Δ</l:mi><l:msubsup><l:mi>R</l:mi><l:mrow><l:mi>axis</l:mi></l:mrow><l:mrow><l:mi>WTA</l:mi><l:mtext>–</l:mtext><l:mi>Std</l:mi></l:mrow></l:msubsup></l:mrow></l:math> distribution becomes broader due to the jet-medium interactions. At the same time, by rescaling the quark- and gluon-jet fractions in <n:math xmlns:n="http://www.w3.org/1998/Math/MathML"><n:mrow><n:mi>Pb</n:mi><n:mo>+</n:mo><n:mi>Pb</n:mi></n:mrow></n:math> collisions to be the same as that in <o:math xmlns:o="http://www.w3.org/1998/Math/MathML"><o:mrow><o:mi>p</o:mi><o:mo>+</o:mo><o:mi>p</o:mi></o:mrow></o:math>, we find that the fraction change may not significantly influence the modification pattern of jet <p:math xmlns:p="http://www.w3.org/1998/Math/MathML"><p:mrow><p:mi mathvariant="normal">Δ</p:mi><p:msubsup><p:mi>R</p:mi><p:mrow><p:mi>axis</p:mi></p:mrow><p:mrow><p:mi>WTA</p:mi><p:mtext>–</p:mtext><p:mi>Std</p:mi></p:mrow></p:msubsup></p:mrow></p:math>. On the other hand, the selected jet sample in <r:math xmlns:r="http://www.w3.org/1998/Math/MathML"><r:mrow><r:mi mathvariant="normal">A</r:mi><r:mo>+</r:mo><r:mi mathvariant="normal">A</r:mi></r:mrow></r:math> collisions has a significantly narrower initial <u:math xmlns:u="http://www.w3.org/1998/Math/MathML"><u:mrow><u:mi mathvariant="normal">Δ</u:mi><u:msubsup><u:mi>R</u:mi><u:mrow><u:mi>axis</u:mi></u:mrow><u:mrow><u:mi>WTA</u:mi><u:mtext>–</u:mtext><u:mi>Std</u:mi></u:mrow></u:msubsup></u:mrow></u:math> distribution than the <w:math xmlns:w="http://www.w3.org/1998/Math/MathML"><w:mrow><w:mi>p</w:mi><w:mo>+</w:mo><w:mi>p</w:mi></w:mrow></w:math> baseline, and such a biased comparison between <x:math xmlns:x="http://www.w3.org/1998/Math/MathML"><x:mrow><x:mi>p</x:mi><x:mo>+</x:mo><x:mi>p</x:mi></x:mrow></x:math> and <y:math xmlns:y="http://www.w3.org/1998/Math/MathML"><y:mrow><y:mi mathvariant="normal">A</y:mi><y:mo>+</y:mo><y:mi mathvariant="normal">A</y:mi></y:mrow></y:math> conceals the actual intrajet broadening effect in the experimental measurements. The investigations presented in this paper will deepen our understanding of the relationship between the actual intrajet modifications in the QGP and the experimental observations.