Nonperturbative-transverse-momentum effects and evolution in dihadron and direct photon-hadron angular correlations in p+p collisions at s=510 GeV

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Abstract

Dihadron and isolated direct photon-hadron angular correlations are measured in $p+p$ collisions at $\sqrt{s}=510\text{ }\text{ }\mathrm{GeV}$. Correlations of charged hadrons of $0.7<{p}_{T}<10\text{ }\text{ }\mathrm{GeV}/c$ with ${\ensuremath{\pi}}^{0}$ mesons of $4<{p}_{T}<15\text{ }\text{ }\mathrm{GeV}/c$ or isolated direct photons of $7<{p}_{T}<15\text{ }\text{ }\mathrm{GeV}/c$ are used to study nonperturbative effects generated by initial-state partonic transverse momentum and final-state transverse momentum from fragmentation. The nonperturbative behavior is characterized by measuring the out-of-plane transverse momentum component ${p}_{\mathrm{out}}$ perpendicular to the axis of the trigger particle, which is the high-${p}_{T}$ direct photon or ${\ensuremath{\pi}}^{0}$. Nonperturbative evolution effects are extracted from Gaussian fits to the away-side inclusive-charged-hadron yields for different trigger-particle transverse momenta (${p}_{T}^{\mathrm{trig}}$). The Gaussian widths and root mean square of ${p}_{\mathrm{out}}$ are reported as a function of the interaction hard scale ${p}_{T}^{\mathrm{trig}}$ to investigate possible transverse-momentum-dependent evolution differences between the ${\ensuremath{\pi}}^{0}\text{\ensuremath{-}}{\mathrm{h}}^{\ifmmode\pm\else\textpm\fi{}}$ and direct photon-${\mathrm{h}}^{\ifmmode\pm\else\textpm\fi{}}$ correlations and factorization breaking effects. The widths are found to decrease with ${p}_{T}^{\mathrm{trig}}$, which indicates that the Collins-Soper-Sterman soft factor is not driving the evolution with the hard scale in nearly back-to-back dihadron and direct photon-hadron production in $p+p$ collisions. This behavior is in contrast to Drell-Yan and semi-inclusive deep-inelastic scattering measurements.

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