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Azimuthal transverse single-spin asymmetries of inclusive jets and charged pions within jets from polarized-proton collisions at $\sqrt{s} = 500$ GeV

The collaboration
Phys.Rev.D 97 (2018) 032004, 2018.

Abstract
We report the first measurements of transverse single-spin asymmetries for inclusive jet and jet + $\pi^{\pm}$ production at midrapidity from transversely polarized proton-proton collisions at $\sqrt{s} = 500$ GeV. The data were collected in 2011 with the STAR detector sampled from 23 pb$^{-1}$ integrated luminosity with an average beam polarization of 53%. Asymmetries are reported for jets with transverse momenta $6 < p_{T, jet} < 55$ GeV/c and pseudorapidity $|\eta| < 1$. Presented are measurements of the inclusive-jet azimuthal transverse single-spin asymmetry, sensitive to twist-3 initial-state quark-gluon correlators; the Collins asymmetry, sensitive to quark transversity coupled to the polarized Collins fragmentation function; and the first measurement of the "Collins-like" asymmetry, sensitive to linearly polarized gluons. Within the present statistical precision, inclusive-jet and Collins-like asymmetries are small, with the latter allowing the first experimental constraints on gluon linear polarization in a polarized proton. At higher values of jet transverse momenta, we observe the first non-zero Collins asymmetries in polarized-proton collisions, with a statistical significance of greater than $5\sigma$. The results span a range of x similar to results from SIDIS but at much higher $Q^{2}$. The Collins results enable tests of universality and factorization-breaking in the transverse momentum-dependent formulation of perturbative quantum chromodynamics.

• #### Figure 9a

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Inclusive jet asymmetries $A_{UT}^{\sin(\theta_S)}$ as a function of particle-jet $p_T$.

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Inclusive jet asymmetries $A_{UT}^{\sin(\theta_S)}$ as a function of particle-jet $p_T$.

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Collins-like asymmetries as a function of particle-jet $p_T$.

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Collins-like asymmetries as a function of particle-jet $p_T$.

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Collins-like asymmetries as a function of particle-jet $p_T$.

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Collins-like asymmetries as a function of pion $z$.

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Collins-like asymmetries as a function of pion $z$.

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Collins-like asymmetries as a function of pion $z$.

• #### Figure 11a

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Collins-like asymmetries as a function of particle-jet $p_T$ for pions reconstructed with $0.1 < z < 0.3$.

• #### Figure 11b

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Collins-like asymmetries as a function of pion $z$ for jets reconstructed with $6.0 < p_T < 13.8$ GeV/$c$.

• #### Figure 12La

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Collins asymmetries as a function of particle-jet $p_T$.

• #### Figure 12Lb

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Collins asymmetries as a function of particle-jet $p_T$.

• #### Figure 12Lc

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Collins asymmetries as a function of particle-jet $p_T$.

• #### Figure 12Ra

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Collins asymmetries as a function of pion $z$.

• #### Figure 12Rb

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Collins asymmetries as a function of pion $z$.

• #### Figure 12Rc

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Collins asymmetries as a function of pion $z$.

• #### Figure 13a

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Collins asymmetries as a function of pion $j_T$ for jets reconstructed with $22.7 < p_T < 55.0$ GeV/$c$.

• #### Figure 13b

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Collins asymmetries as a function of pion $j_T$ for jets reconstructed with $22.7 < p_T < 55.0$ GeV/$c$.

• #### Figure 13c

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Collins asymmetries as a function of pion $j_T$ for jets reconstructed with $22.7 < p_T < 55.0$ GeV/$c$.

• #### Figure 14

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Collins asymmetries as a function of pion $z$ for jets reconstructed with $22.7 < p_T < 55.0$ GeV/$c$ and \$0...