Measurement of the angle between jet axes in Pb-Pb collisions at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msqrt> <mml:msub> <mml:mi>s</mml:mi> <mml:mrow> <mml:mi>N</mml:mi> <mml:mi>N</mml:mi> </mml:mrow> </mml:msub> </mml:msqrt> <mml:mo>=</mml:mo> <mml:mn>5.02</mml:mn> </mml:mrow> </mml:math> TeV
Resumen
This paper presents the first measurement of the angle between different jet axes (denoted as <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mi mathvariant="normal">Δ</a:mi> <a:msub> <a:mi>R</a:mi> <a:mi>axis</a:mi> </a:msub> </a:mrow> </a:math> ) in <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mtext>Pb-Pb</c:mtext> </c:math> collisions. The measurement is carried out in the 0–10 % most-central events at <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mrow> <d:msqrt> <d:msub> <d:mi>s</d:mi> <d:mrow> <d:mi>N</d:mi> <d:mi>N</d:mi> </d:mrow> </d:msub> </d:msqrt> <d:mo>=</d:mo> <d:mn>5.02</d:mn> </d:mrow> </d:math> TeV. Jets are assembled by clustering charged particles at midrapidity using the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mrow> <e:mtext>anti-</e:mtext> <e:msub> <e:mi>k</e:mi> <e:mi mathvariant="normal">T</e:mi> </e:msub> </e:mrow> </e:math> algorithm with resolution parameters <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"> <g:mrow> <g:mi>R</g:mi> <g:mo>=</g:mo> <g:mn>0.2</g:mn> </g:mrow> </g:math> and 0.4 and transverse momenta in the intervals <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"> <h:mrow> <h:mn>40</h:mn> <h:mo><</h:mo> <h:msubsup> <h:mi>p</h:mi> <h:mrow> <h:mi mathvariant="normal">T</h:mi> </h:mrow> <h:mrow> <h:mi>ch</h:mi> <h:mspace width="0.16em"/> <h:mi>jet</h:mi> </h:mrow> </h:msubsup> <h:mo><</h:mo> <h:mn>140</h:mn> <h:mspace width="0.28em"/> <h:mi>GeV</h:mi> <h:mo>/</h:mo> <h:mi>c</h:mi> </h:mrow> </h:math> and <l:math xmlns:l="http://www.w3.org/1998/Math/MathML"> <l:mrow> <l:mn>80</l:mn> <l:mo><</l:mo> <l:msubsup> <l:mi>p</l:mi> <l:mrow> <l:mi mathvariant="normal">T</l:mi> </l:mrow> <l:mrow> <l:mi>ch</l:mi> <l:mspace width="0.16em"/> <l:mi>jet</l:mi> </l:mrow> </l:msubsup> <l:mo><</l:mo> <l:mn>140</l:mn> <l:mspace width="0.28em"/> <l:mi>GeV</l:mi> <l:mo>/</l:mo> <l:mi>c</l:mi> </l:mrow> </l:math> , respectively. Measurements at these low transverse momenta enhance the sensitivity to quark-gluon plasma (QGP) effects. A comparison to models implementing various mechanisms of jet energy loss in the QGP suggests that the observed narrowing of the <p:math xmlns:p="http://www.w3.org/1998/Math/MathML"> <p:mtext>Pb-Pb</p:mtext> </p:math> distribution relative to <q:math xmlns:q="http://www.w3.org/1998/Math/MathML"> <q:mrow> <q:mi mathvariant="italic">pp</q:mi> </q:mrow> </q:math> can be explained if quark-initiated jets are more likely to emerge from the medium than gluon-initiated jets. These new measurements disfavor intrajet <s:math xmlns:s="http://www.w3.org/1998/Math/MathML"> <s:msub> <s:mi>p</s:mi> <s:mi mathvariant="normal">T</s:mi> </s:msub> </s:math> broadening as implemented in a simple model calculation with the Baier-Dokshitzer-Mueller-Peigne-Schiff formalism for energy loss in the QGP. The comparison of <u:math xmlns:u="http://www.w3.org/1998/Math/MathML"> <u:mtext>Pb-Pb</u:mtext> </u:math> and <v:math xmlns:v="http://www.w3.org/1998/Math/MathML"> <v:mrow> <v:mi mathvariant="italic">pp</v:mi> </v:mrow> </v:math> collisions shows sensitivity to the angular scale at which the QGP can resolve two independent splittings, favoring mechanisms that incorporate incoherent energy loss.