  Collective behavior has been observed in high-energy heavy-ion collisions for
several decades. Collectivity is driven by the high particle multiplicities
that are produced in these collisions. At the CERN Large Hadron Collider (LHC),
features of collectivity have also been seen in high-multiplicity proton-proton
collisions that can attain particle multiplicities comparable to peripheral
Pb-Pb collisions. One of the possible signatures of collective behavior is the
decrease of femtoscopic radii extracted from pion and kaon pairs emitted from
high-multiplicity collisions with increasing pair transverse momentum. This
decrease can be described in terms of an approximate transverse mass scaling.
In the present work, femtoscopic analyses are carried out by the ALICE
Collaboration on charged pion and kaon pairs produced in pp collisions at
$\sqrt{s}=13$ TeV from the LHC to study possible collectivity in pp collisions.
The event-shape analysis method based on transverse sphericity is used to
select for spherical versus jet-like events, and the effects of this selection
on the femtoscopic radii for both charged pion and kaon pairs are studied. This
is the first time this selection method has been applied to charged kaon pairs.
An approximate transverse-mass scaling of the radii is found in all
multiplicity ranges studied when the difference in the Lorentz boost for pions
and kaons is taken into account. This observation does not support the
hypothesis of collective expansion of hot and dense matter that should only
occur in high-multiplicity events. A possible alternate explanation of the
present results is based on a scenario of common emission conditions for pions
and kaons in pp collisions for the multiplicity ranges studied.
