The atomic nucleus is composed of two different kinds of fermions: protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority of fermions (usually neutrons) to have a higher average momentum. Our high-energy electron-scattering measurements using (12)C, (27)Al, (56)Fe, and (208)Pb targets show that even in heavy, neutron-rich nuclei, short-range interactions between the fermions form correlated high-momentum neutron-proton pairs. Thus, in neutron-rich nuclei, protons have a greater probability than neutrons to have momentum greater than the Fermi momentum. This finding has implications ranging from nuclear few-body systems to neutron stars and may also be observable experimentally in two-spin-state, ultracold atomic gas systems.

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Transverse momentum distributions and yields for π ± , K ± , p and p in p + p collisions at √ s = 200 and 62.4 GeV at midrapidity are measured by the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC). These data provide important baseline spectra for comparisons with identified particle spectra in heavy ion collisions at RHIC. We present the inverse slope parameter Tinv, mean transverse momentum pT and yield per unit rapidity dN/dy at each energy, and compare them to other measurements at different √ s in p + p and p + p collisions. We also present the scaling properties such as mT scaling, xT scaling on the pT spectra between different energies. To discuss the mechanism of the particle production in p + p collisions, the measured spectra are compared to nextto-leading-order or next-to-leading-logarithmic perturbative quantum chromodynamics calculations.

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A. Adare, 13 S. Afanasiev, 31 C. Aidala, 40, 44, 45