Abstract:
Angular correlations between heavy quarks provide a unique probe of the quark-gluon plasma created in ultrarelativistic heavy-ion collisions. Results are presented of a measurement of the azimuthal angle correlations between muons originating from semileptonic decays of heavy quarks produced in 5.02 TeV <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> and <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>p</c:mi><c:mi>p</c:mi></c:math> collisions at the LHC. The muons are measured with transverse momenta and pseudorapidities satisfying <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mrow><e:msubsup><e:mrow><e:mi>p</e:mi></e:mrow><e:mrow><e:mi mathvariant="normal">T</e:mi></e:mrow><e:mrow><e:mi>μ</e:mi></e:mrow></e:msubsup><e:mo>></e:mo><e:mn>4</e:mn><e:mtext> </e:mtext><e:mtext> </e:mtext><e:mi>GeV</e:mi></e:mrow></e:math> and <h:math xmlns:h="http://www.w3.org/1998/Math/MathML" display="inline"><h:mrow><h:mo stretchy="false">|</h:mo><h:msup><h:mrow><h:mi>η</h:mi></h:mrow><h:mrow><h:mi>μ</h:mi></h:mrow></h:msup><h:mo stretchy="false">|</h:mo><h:mo><</h:mo><h:mn>2.4</h:mn></h:mrow></h:math>, respectively. The distributions of azimuthal angle separation <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"><l:mi mathvariant="normal">Δ</l:mi><l:mi>ϕ</l:mi></l:math> for muon pairs having pseudorapidity separation <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"><o:mrow><o:mo stretchy="false">|</o:mo><o:mi mathvariant="normal">Δ</o:mi><o:mi>η</o:mi><o:mo stretchy="false">|</o:mo><o:mo>></o:mo><o:mn>0.8</o:mn></o:mrow></o:math>, are measured in different <t:math xmlns:t="http://www.w3.org/1998/Math/MathML" display="inline"><t:mi>Pb</t:mi><t:mo>+</t:mo><t:mi>Pb</t:mi></t:math> centrality intervals and compared to the same distribution measured in <v:math xmlns:v="http://www.w3.org/1998/Math/MathML" display="inline"><v:mi>p</v:mi><v:mi>p</v:mi></v:math> collisions at the same center-of-mass energy. Results are presented separately for muon pairs with opposite-sign charges, same-sign charges, and all pairs. A clear peak is observed in all <x:math xmlns:x="http://www.w3.org/1998/Math/MathML" display="inline"><x:mi mathvariant="normal">Δ</x:mi><x:mi>ϕ</x:mi></x:math> distributions at <ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline"><ab:mrow><ab:mi mathvariant="normal">Δ</ab:mi><ab:mi>ϕ</ab:mi><ab:mo>∼</ab:mo><ab:mi>π</ab:mi></ab:mrow></ab:math>, consistent with the parent heavy-quark pairs being produced via hard-scattering processes. The widths of that peak, characterized using Cauchy-Lorentz fits to the <db:math xmlns:db="http://www.w3.org/1998/Math/MathML" display="inline"><db:mi mathvariant="normal">Δ</db:mi><db:mi>ϕ</db:mi></db:math> distributions, are found to not vary significantly as a function of <gb:math xmlns:gb="http://www.w3.org/1998/Math/MathML" display="inline"><gb:mi>Pb</gb:mi><gb:mo>+</gb:mo><gb:mi>Pb</gb:mi></gb:math> collision centrality and are similar for <ib:math xmlns:ib="http://www.w3.org/1998/Math/MathML" display="inline"><ib:mi>p</ib:mi><ib:mi>p</ib:mi></ib:math> and <kb:math xmlns:kb="http://www.w3.org/1998/Math/MathML" display="inline"><kb:mi>Pb</kb:mi><kb:mo>+</kb:mo><kb:mi>Pb</kb:mi></kb:math> collisions. This observation will provide important constraints on theoretical descriptions of heavy-quark interactions with the quark-gluon plasma. © 2024 CERN, for the ATLAS Collaboration 2024 CERN
Tópico:
High-Energy Particle Collisions Research
