The first measurement of the dijet transverse momentum balance xj in proton
lead (pPb) collisions at a nucleon-nucleon center-of-mass energy of √sNN= 8.16TeV is
presented. The xj 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 174.6nb−1, were collected with the CMS detector in 2016.
The xj 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 xj 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
