Measurement of the groomed jet radius and momentum splitting fraction in pp and Pb$-$Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV

Acharya, Shreyasi; Adamova, Dagmar; Adler, Alexander; Aglieri Rinella, Gianluca; Agnello, Michelangelo; Agrawal, Neelima; Ahammed, Zubayer; Ahmad, Shakeel; Ahn, Sang Un; Ahuja, Ishaan

doi:10.1103/PhysRevLett.128.102001

Measurement of the groomed jet radius and momentum splitting fraction in pp and Pb $-$ Pb collisions at $\sqrt{s_{NN}} = 5.02$ TeV

Collaborations

Jul 27, 2021

18 pages

Published in:

Phys.Rev.Lett. 128 (2022) 10, 102001

Published: Mar 7, 2022

e-Print:

2107.12984 [nucl-ex]

DOI:

10.1103/PhysRevLett.128.102001 (publication)

Report number:

CERN-EP-2021-151

Experiments:

CERN-LHC-ALICE

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Abstract: (APS)

This article presents groomed jet substructure measurements in

p p

and

Pb - Pb

collisions at

\sqrt{s_{N N}} = 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,

z_{g}

, and the (scaled) groomed jet radius,

θ_{g}

. Charged-particle jets are reconstructed at midrapidity using the anti-

k_{T}

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

θ_{g}

distribution in

Pb - Pb

collisions compared to

p p

collisions is seen, which provides direct evidence of the modification of the angular structure of jets in the quark-gluon plasma. No significant modification of the

z_{g}

distribution in

Pb - Pb

collisions compared to

p p

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 quark-gluon plasma.

Note:

18 pages, 3 captioned figures, authors from page 13, published version, figures at http://alice-publications.web.cern.ch/node/7293

parton: splitting
quark gluon: plasma
jet: quenching
model: jet
coherence: effect
background: fluctuation
jet: energy loss
charged particle: jet
heavy ion: scattering
jet: momentum

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