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

Adare, A.*; Hasegawa, Shoichi   ; Imai, Kenichi; Nagamiya, Shoji; Sako, Hiroyuki   ; Sato, Susumu  ; Tanida, Kiyoshi   ; PHENIX Collaboration*; 462 of others*

Dihadron and isolated direct photon-hadron angular correlations are measured in $$p+p$$ collisions at $$sqrt{s}$$ = 510 GeV. Correlations of charged hadrons of $$0.7 < p_T < 10$$ GeV/$$c$$ with $$pi^0$$ mesons of $$4 < p_T < 15$$ GeV/$$c$$ or isolated direct photons of $$7 < p_T < 15$$ 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 $$p_{rm out}$$ perpendicular to the axis of the trigger particle, which is the high-$$p_T$$ direct photon or $$pi^0$$. Nonperturbative evolution effects are extracted from Gaussian fits to the away-side inclusive-charged-hadron yields for different trigger-particle transverse momenta ($$p_{T}^{rm trig}$$). The Gaussian widths and root mean square of $$p_{rm out}$$ are reported as a function of the interaction hard scale $$p_{T}^{rm trig}$$ to investigate possible transverse-momentum-dependent evolution differences between the $$pi^0$$-$$h^pm$$ and direct photon-$$h^{pm}$$ correlations and factorization breaking effects. The widths are found to decrease with $$p_{T}^{rm trig}$$, 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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Category:Astronomy & Astrophysics

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