Measurement of the groomed jet radius and momentum splitting fraction in pp and PbPb collisions at sNN=5.02 TeV

Phys.Rev.Lett. 128 (2022) 102001, 2022.

Abstract
This article presents groomed jet substructure measurements in pp and PbPb collisions at sNN=5.02 TeV with the ALICE detector. The Soft Drop grooming algorithm provides access to the hard parton splittings inside a jet by removing soft wide-angle radiation. We report the groomed jet momentum splitting fraction, zg, and the (scaled) groomed jet radius, θg. Charged-particle jets are reconstructed at midrapidity using the anti-kT algorithm with resolution parameters R=0.2 and R=0.4. In heavy-ion collisions, the large underlying event poses a challenge for the reconstruction of groomed jet observables, since fluctuations in the background can cause groomed parton splittings to be misidentified. By using strong grooming conditions to reduce this background, we report these observables fully corrected for detector effects and background fluctuations for the first time. A narrowing of the θg distribution in PbPb collisions compared to pp collisions is seen, which provides direct evidence of the modification of the angular structure of jets in the quarkgluon plasma. No significant modification of the zg distribution in PbPb collisions compared to pp collisions is observed. These results are compared with a variety of theoretical models of jet quenching, and provide constraints on jet energy-loss mechanisms and coherence effects in the quarkgluon plasma.

  • Table 1

    Figure 2 (left)

    10.17182/hepdata.128137.v1/t1

    Groomed jet momentum splitting fraction zg in pp collisions. 60<pT,chjet<80GeV/c, Soft Drop zcut=0.2,β=0. Note: The first bin corresponds...

  • Table 2

    Figure 2 (left)

    10.17182/hepdata.128137.v1/t2

    Groomed jet momentum splitting fraction zg in Pb-Pb collisions. 60<pT,chjet<80GeV/c, Soft Drop zcut=0.2,β=0. Note: The first bin corresponds...

  • Table 3

    Figure 2 (left)

    10.17182/hepdata.128137.v1/t3

    Groomed jet momentum splitting fraction zg ratio of Pb-Pb to pp collisions. 60<pT,chjet<80GeV/c, Soft Drop zcut=0.2,β=0. Note:...

  • Table 13

    Figure 2 (right) in Ref. [Public Note]

    10.17182/hepdata.128137.v1/t4

    Groomed jet momentum splitting fraction zg in pp collisions. 80<pT,chjet<100GeV/c, Soft Drop zcut=0.2,β=0. Note: The first bin corresponds...

  • Table 14

    Figure 2 (right) in Ref. [Public Note]

    10.17182/hepdata.128137.v1/t5

    Groomed jet momentum splitting fraction zg in Pb-Pb collisions. 80<pT,chjet<100GeV/c, Soft Drop zcut=0.2,β=0. Note: The first bin corresponds...

  • Table 15

    Figure 2 (right) in Ref. [Public Note]

    10.17182/hepdata.128137.v1/t6

    Groomed jet momentum splitting fraction zg ratio of Pb-Pb to pp collisions. 80<pT,chjet<100GeV/c, Soft Drop zcut=0.2,β=0. Note:...

  • Table 7

    Figure 3 (left)

    10.17182/hepdata.128137.v1/t7

    Groomed jet radius (scaled) θg in pp collisions. 60<pT,chjet<80GeV/c, Soft Drop zcut=0.2,β=0. Note: The first bin corresponds to...

  • Table 8

    Figure 3 (left)

    10.17182/hepdata.128137.v1/t8

    Groomed jet radius (scaled) θg in Pb-Pb collisions. 60<pT,chjet<80GeV/c, Soft Drop zcut=0.2,β=0. Note: The first bin corresponds to...

  • Table 9

    Figure 3 (left)

    10.17182/hepdata.128137.v1/t9

    Groomed jet radius (scaled) θg ratio of Pb-Pb to pp collisions. 60<pT,chjet<80GeV/c, Soft Drop zcut=0.2,β=0. Note: The...

  • Table 4

    Figure 2 (right)

    10.17182/hepdata.128137.v1/t10

    Groomed jet momentum splitting fraction zg in pp collisions. 60<pT,chjet<80GeV/c, Soft Drop zcut=0.2,β=0. Note: The first bin corresponds...

  • Table 5

    Figure 2 (right)

    10.17182/hepdata.128137.v1/t11

    Groomed jet momentum splitting fraction zg in Pb-Pb collisions. 60<pT,chjet<80GeV/c, Soft Drop zcut=0.2,β=0. Note: The first bin corresponds...

  • Table 6

    Figure 2 (right)

    10.17182/hepdata.128137.v1/t12

    Groomed jet momentum splitting fraction zg ratio of Pb-Pb to pp collisions. 60<pT,chjet<80GeV/c, Soft Drop zcut=0.2,β=0. Note:...

  • Table 10

    Figure 3 (right)

    10.17182/hepdata.128137.v1/t13

    Groomed jet radius (scaled) θg in pp collisions. 60<pT,chjet<80GeV/c, Soft Drop zcut=0.2,β=0. Note: The first bin corresponds to...

  • Table 11

    Figure 3 (right)

    10.17182/hepdata.128137.v1/t14

    Groomed jet radius (scaled) θg in Pb-Pb collisions. 60<pT,chjet<80GeV/c, Soft Drop zcut=0.2,β=0. Note: The first bin corresponds to...

  • Table 12

    Figure 3 (right)

    10.17182/hepdata.128137.v1/t15

    Groomed jet radius (scaled) θg ratio of Pb-Pb to pp collisions. 60<pT,chjet<80GeV/c, Soft Drop zcut=0.2,β=0. Note: The...

  • Table 16

    Figure 5 (right) in Ref. [Public Note]

    10.17182/hepdata.128137.v1/t16

    Groomed jet radius (scaled) θg in pp collisions. 60<pT,chjet<80GeV/c, Soft Drop zcut=0.4,β=0. Note: The first bin corresponds to...

  • Table 17

    Figure 5 (right) in Ref. [Public Note]

    10.17182/hepdata.128137.v1/t17

    Groomed jet radius (scaled) θg in Pb-Pb collisions. 60<pT,chjet<80GeV/c, Soft Drop zcut=0.4,β=0. Note: The first bin corresponds to...

  • Table 18

    Figure 5 (right) in Ref. [Public Note]

    10.17182/hepdata.128137.v1/t18

    Groomed jet radius (scaled) θg ratio of Pb-Pb to pp collisions. 60<pT,chjet<80GeV/c, Soft Drop zcut=0.4,β=0. Note: The...

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