Phys. Rev. C 98, 054903 (2018) Production of $\pi^0$ and $\eta$ mesons has been measured at midrapidity in
Cu$+$Au collisions at $\sqrt{s_{_{NN}}}$=200 GeV. Measurements were performed
in ...$\pi^0(\eta)\rightarrow\gamma\gamma$ decay channel in the 1(2)-20 GeV/$c$
transverse momentum range. A strong suppression is observed for $\pi^0$ and
$\eta$ meson production at high transverse momentum in central Cu$+$Au
collisions relative to the $p$$+$$p$ results scaled by the number of
nucleon-nucleon collisions. In central collisions the suppression is similar to
Au$+$Au with comparable nuclear overlap. The $\eta/\pi^0$ ratio measured as a
function of transverse momentum is consistent with $m_T$-scaling
parameterization down to $p_T=$2 GeV/$c$, its asymptotic value is constant and
consistent with Au$+$Au and $p$$+$$p$ and does not show any significant
dependence on collision centrality. Similar results were obtained in
hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions as well as in
$e^+e^-$ collisions in a range of collision energies $\sqrt{s_{_{NN}}}=$3--1800
GeV. This suggests that the quark-gluon-plasma medium produced in Cu$+$Cu
collisions either does not affect the jet fragmentation into light mesons or it
affects the $\pi^0$ and $\eta$ the same way.
The PHENIX experiment reports systematic measurements at the Relativistic Heavy Ion Collider of \(\phi\)-meson production in asymmetric Cu\(+\)Au collisions at \(\sqrt{s_{_{NN}}}\)=200 GeV and in ...U\(+\)U collisions at \(\sqrt{s_{_{NN}}}\)=193 GeV. Measurements were performed via the \(\phi\rightarrow K^{+}K^{-}\) decay channel at midrapidity \(|\eta|<0.35\). Features of \(\phi\)-meson production measured in Cu\(+\)Cu, Cu\(+\)Au, Au\(+\)Au, and U\(+\)U collisions were found to not depend on the collision geometry, which was expected because the yields are averaged over the azimuthal angle and follow the expected scaling with nuclear-overlap size. The elliptic flow of the \(\phi\) meson in Cu\(+\)Au, Au\(+\)Au, and U\(+\)U collisions scales with second-order-participant eccentricity and the length scale of the nuclear-overlap region (estimated with the number of participating nucleons). At moderate \(p_T\), \(\phi\)-meson production measured in Cu\(+\)Au and U\(+\)U collisions is consistent with coalescence-model predictions, whereas at high \(p_T\) the production is in agreement with expectations for in-medium energy loss of parent partons prior to their fragmentation. The elliptic flow for \(\phi\) mesons measured in Cu\(+\)Au and U\(+\)U collisions is well described by a (2+1)D viscous-hydrodynamic model with specific-shear viscosity \(\eta/s=1/4\pi\).
Phys. Rev. D 98, 032007 (2018) We have measured the cross section and single spin asymmetries from forward
$W^{\pm}\rightarrow\mu^{\pm}\nu$ production in longitudinally polarized
$p$$+$$p$ collisions ...at $\sqrt{s}=510$ GeV using the PHENIX detector at the
Relativistic Heavy Ion Collider. The cross sections are consistent with
previous measurements at this collision energy, while the most forward and
backward longitudinal single spin asymmetries provide new insights into the sea
quark helicities in the proton. The charge of the W bosons provides a natural
flavor separation of the participating partons.
We describe a method for non-parametric regression which combines regression trees with radial basis function networks. The method is similar to that of Kubat, who was first to suggest such a ...combination, but has some significant improvements. We demonstrate the features of the new method, compare its performance with other methods on DELVE data sets and apply it to a real world problem involving the classification of soybean plants from digital images.
Phys. Rev. D 95, 112001 (2017) The cross section and transverse single-spin asymmetries of $\mu^{-}$ and
$\mu^{+}$ from open heavy-flavor decays in polarized $p$+$p$ collisions at
$\sqrt{s}=200$ GeV ...were measured by the PHENIX experiment during 2012 at the
Relativistic Heavy Ion Collider. Because heavy-flavor production is dominated
by gluon-gluon interactions at $\sqrt{s}=200$ GeV, these measurements offer a
unique opportunity to obtain information on the trigluon correlation functions.
The measurements are performed at forward and backward rapidity ($1.4<|y|<2.0$)
over the transverse momentum range of $1.25<p_T<7$ GeV/$c$ for the cross
section and $1.25<p_T<5$ GeV/$c$ for the asymmetry measurements. The obtained
cross section is compared to a fixed-order-plus-next-to-leading-log
perturbative-quantum-chromodynamics calculation. The asymmetry results are
consistent with zero within uncertainties, and a model calculation based on
twist-3 three-gluon correlations agrees with the data.
