Flavor dependence of energy-energy correlators
Liliana Apolinário, R. Kunnawalkam Elayavalli, Nuno Olavo Madureira, Jun-Xing Sheng, Xin-Nian Wang, Z. C. Yang
Abstract
Energy-energy correlators (EECs) within high energy jets serve as a key experimentally accessible quantity to probe the scale and structure of the quark-gluon plasma (QGP) in relativistic heavy-ion collisions. The CMS Collaboration’s first measurement of the modification to the EEC within single inclusive jets in <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:mi>Pb</a:mi> <a:mo>+</a:mo> <a:mi>Pb</a:mi> </a:mrow> </a:math> collisions relative to <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mrow> <c:mi mathvariant="normal">p</c:mi> <c:mo>+</c:mo> <c:mi mathvariant="normal">p</c:mi> </c:mrow> </c:math> collisions reveals a significant enhancement at small angles, which may arise from jet transverse momentum <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"> <g:msub> <g:mi>p</g:mi> <g:mi>T</g:mi> </g:msub> </g:math> selection biases due to jet energy loss. We investigate the dependence of jet EECs on the flavor of the initiating parton. The EEC distribution of a gluon jet is broader and the peak of transition from the perturbative to the nonperturbative regime occurs at a larger angle than that of a quark jet. Such flavor dependence leads to the different EECs for <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:mi>γ</i:mi> </i:math> -jets and single inclusive jets due to their different flavor composition. It is also responsible for a colliding energy dependence of EECs of single inclusive jets at fixed jet energy. We also investigate the impact of flavor composition variation on the <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:msub> <k:mi>p</k:mi> <k:mi>T</k:mi> </k:msub> </k:math> dependence of the jet EEC. We further propose that a change in the gluon jet fraction in <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"> <m:mrow> <m:mi mathvariant="normal">A</m:mi> <m:mo>+</m:mo> <m:mi mathvariant="normal">A</m:mi> </m:mrow> </m:math> collisions compared to <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"> <q:mrow> <q:mi mathvariant="normal">p</q:mi> <q:mo>+</q:mo> <q:mi mathvariant="normal">p</q:mi> </q:mrow> </q:math> can also contribute to a non-negligible enhancement of the medium modified EEC at small angles. Using the model, we predict the reduction of the gluon jet fraction in <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"> <u:mrow> <u:mi mathvariant="normal">A</u:mi> <u:mo>+</u:mo> <u:mi mathvariant="normal">A</u:mi> </u:mrow> </u:math> collisions and estimate its impact on the EEC.