First measurements of N-subjettiness in central Pb-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 2.76 TeV
抄録
<jats:title>A<jats:sc>bstract</jats:sc> </jats:title><jats:p>The ALICE Collaboration reports the first fully-corrected measurements of the <jats:italic>N</jats:italic>-subjettiness observable for track-based jets in heavy-ion collisions. This study is performed using data recorded in pp and Pb-Pb collisions at centre-of-mass energies of <jats:inline-formula><jats:alternatives><jats:tex-math>$$ \sqrt{s} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math></jats:alternatives></jats:inline-formula> = 7 TeV and <jats:inline-formula><jats:alternatives><jats:tex-math>$$ \sqrt{s_{\mathrm{NN}}} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:msub> <mml:mi>s</mml:mi> <mml:mi>NN</mml:mi> </mml:msub> </mml:msqrt> </mml:math></jats:alternatives></jats:inline-formula> = 2<jats:italic>.</jats:italic>76 TeV, respectively. In particular the ratio of 2-subjettiness to 1-subjettiness, <jats:italic>τ</jats:italic><jats:sub>2</jats:sub><jats:italic>/τ</jats:italic><jats:sub>1</jats:sub>, which is sensitive to the rate of two-pronged jet substructure, is presented. Energy loss of jets traversing the strongly interacting medium in heavy-ion collisions is expected to change the rate of two-pronged substructure relative to vacuum. The results are presented for jets with a resolution parameter of <jats:italic>R</jats:italic> = 0<jats:italic>.</jats:italic>4 and charged jet transverse momentum of 40 ≤ <jats:italic>p</jats:italic><jats:sub>T<jats:italic>,</jats:italic>jet</jats:sub> ≤ 60 GeV/<jats:italic>c</jats:italic>, which constitute a larger jet resolution and lower jet transverse momentum interval than previous measurements in heavy-ion collisions. This has been achieved by utilising a semi-inclusive hadron-jet coincidence technique to suppress the larger jet combinatorial background in this kinematic region. No significant modification of the <jats:italic>τ</jats:italic><jats:sub>2</jats:sub><jats:italic>/τ</jats:italic><jats:sub>1</jats:sub> observable for track-based jets in Pb-Pb collisions is observed relative to vacuum PYTHIA6 and PYTHIA8 references at the same collision energy. The measurements of <jats:italic>τ</jats:italic><jats:sub>2</jats:sub><jats:italic>/τ</jats:italic><jats:sub>1</jats:sub>, together with the splitting aperture angle ∆<jats:italic>R</jats:italic>, are also performed in pp collisions at <jats:inline-formula><jats:alternatives><jats:tex-math>$$ \sqrt{s} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math></jats:alternatives></jats:inline-formula> = 7 TeV for inclusive jets. These results are compared with PYTHIA calculations at <jats:inline-formula><jats:alternatives><jats:tex-math>$$ \sqrt{s} $$</jats:tex-math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:mi>s</mml:mi> </mml:msqrt> </mml:math></jats:alternatives></jats:inline-formula> = 7 TeV, in order to validate the model as a vacuum reference for the Pb-Pb centre-of-mass energy. The PYTHIA references for <jats:italic>τ</jats:italic><jats:sub>2</jats:sub><jats:italic>/τ</jats:italic><jats:sub>1</jats:sub> are shifted to larger values compared to the measurement in pp collisions. This hints at a reduction in the rate of two-pronged jets in Pb-Pb collisions compared to pp collisions.</jats:p>
収録刊行物
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- Journal of High Energy Physics
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Journal of High Energy Physics 2021 (10), 2021-10
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