Measurements of jet quenching using semi-inclusive hadron+jet distributions in pp and central Pb-Pb collisions at sNN=5.02 TeV

The ALICE Collaboration reports measurements of the semi-inclusive distribution of charged-particle jets recoiling from a high transverse momentum (high <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>) charged hadron, in <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mi>p</c:mi><c:mi>p</c:mi></c:mrow></c:math> and central Pb-Pb collisions at center-of-mass energy per nucleon–nucleon collision <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mrow><d:msqrt><d:msub><d:mi>s</d:mi><d:mi>NN</d:mi></d:msub></d:msqrt><d:mo>=</d:mo><d:mn>5.02</d:mn></d:mrow></d:math> TeV. The large uncorrelated background in central Pb-Pb collisions is corrected using a data-driven statistical approach which enables precise measurement of recoil jet distributions over a broad range in <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:msub><e:mi>p</e:mi><e:mrow><e:mi mathvariant="normal">T</e:mi><e:mo>,</e:mo><e:mi>ch</e:mi><e:mspace width="4pt"/><e:mi>jet</e:mi></e:mrow></e:msub></e:math> and jet resolution parameter <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"><h:mi>R</h:mi></h:math>. Recoil jet yields are reported for <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"><i:mrow><i:mi>R</i:mi><i:mo>=</i:mo><i:mn>0.2</i:mn></i:mrow></i:math>, 0.4, and 0.5 in the range <j:math xmlns:j="http://www.w3.org/1998/Math/MathML"><j:mrow><j:mn>7</j:mn><j:mo><</j:mo><j:msub><j:mi>p</j:mi><j:mrow><j:mi mathvariant="normal">T</j:mi><j:mo>,</j:mo><j:mi>ch</j:mi><j:mspace width="4pt"/><j:mi>jet</j:mi></j:mrow></j:msub><j:mo><</j:mo><j:mn>140</j:mn></j:mrow><j:mo> </j:mo><j:mrow><j:mi>GeV</j:mi><j:mo>/</j:mo><j:mi>c</j:mi></j:mrow></j:math> and <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"><m:mrow><m:mi>π</m:mi><m:mo>/</m:mo><m:mn>2</m:mn><m:mo><</m:mo><m:mi mathvariant="normal">Δ</m:mi><m:mi>φ</m:mi><m:mo><</m:mo><m:mi>π</m:mi></m:mrow></m:math>, where <o:math xmlns:o="http://www.w3.org/1998/Math/MathML"><o:mrow><o:mi mathvariant="normal">Δ</o:mi><o:mi>φ</o:mi></o:mrow></o:math> is the azimuthal angular separation between hadron trigger and recoil jet. The low-<q:math xmlns:q="http://www.w3.org/1998/Math/MathML"><q:msub><q:mi>p</q:mi><q:mrow><q:mi mathvariant="normal">T</q:mi><q:mo>,</q:mo><q:mi>ch</q:mi><q:mspace width="4pt"/><q:mi>jet</q:mi></q:mrow></q:msub></q:math> reach of the measurement explores unique phase space for studying jet quenching, the interaction of jets with the quark–gluon plasma generated in high-energy nuclear collisions. Comparison of <t:math xmlns:t="http://www.w3.org/1998/Math/MathML"><t:msub><t:mi>p</t:mi><t:mrow><t:mi mathvariant="normal">T</t:mi><t:mo>,</t:mo><t:mi>ch</t:mi><t:mspace width="4pt"/><t:mi>jet</t:mi></t:mrow></t:msub></t:math> distributions from <w:math xmlns:w="http://www.w3.org/1998/Math/MathML"><w:mrow><w:mi>p</w:mi><w:mi>p</w:mi></w:mrow></w:math> and central Pb-Pb collisions probes medium-induced jet energy loss and intra-jet broadening, while comparison of their acoplanarity distributions explores in-medium jet scattering and medium response. The measurements are compared to theoretical calculations incorporating jet quenching.