The first measurement of the dijet transverse momentum balance xjj​ in proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of sNNsNN​ ​ = 8.16 TeV is presented. The xjj​ observable, defined as the ratio of the subleading over leading jet transverse momentum in a dijet pair, is used to search for jet quenching effects. The data, corresponding to an integrated luminosity of 174.6 nb−1−1, were collected with the CMS detector in 2016. The xjj​ distributions and their average values are studied as functions of the charged-particle multiplicity of the events and for various dijet rapidity selections. The latter enables probing hard scattering of partons carrying distinct nucleon momentum fractions x in the proton- and lead-going directions. The former, aided by the high-multiplicity triggers, allows probing for potential jet quenching effects in high-multiplicity events (with up to 400 charged particles), for which collective phenomena consistent with quark-gluon plasma (QGP) droplet formation were previously observed. The ratios of xjj​ distributions for high- to low-multiplicity events are used to quantify the possible medium effects. These ratios are consistent with simulations of the hard-scattering process that do not include QGP production. These measurements set an upper limit on medium-induced energy loss of the subleading jet of 1.26% of its transverse momentum at the 90% confidence level in high multiplicity pPb events.

Search for jet quenching with dijets from high-multiplicity pPb collisions at $\sqrt{{s}_{\text{NN}}}$ = 8.16 TeV

Cavallo, N.;Fabozzi, F.;
2025-01-01

Abstract

The first measurement of the dijet transverse momentum balance xjj​ in proton-lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of sNNsNN​ ​ = 8.16 TeV is presented. The xjj​ observable, defined as the ratio of the subleading over leading jet transverse momentum in a dijet pair, is used to search for jet quenching effects. The data, corresponding to an integrated luminosity of 174.6 nb−1−1, were collected with the CMS detector in 2016. The xjj​ distributions and their average values are studied as functions of the charged-particle multiplicity of the events and for various dijet rapidity selections. The latter enables probing hard scattering of partons carrying distinct nucleon momentum fractions x in the proton- and lead-going directions. The former, aided by the high-multiplicity triggers, allows probing for potential jet quenching effects in high-multiplicity events (with up to 400 charged particles), for which collective phenomena consistent with quark-gluon plasma (QGP) droplet formation were previously observed. The ratios of xjj​ distributions for high- to low-multiplicity events are used to quantify the possible medium effects. These ratios are consistent with simulations of the hard-scattering process that do not include QGP production. These measurements set an upper limit on medium-induced energy loss of the subleading jet of 1.26% of its transverse momentum at the 90% confidence level in high multiplicity pPb events.
2025
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11563/201638
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