196 Search Results

Reported here are transverse single-spin asymmetries (A_N) in the production of charged hadrons as a function of transverse momentum (pT) and Feynman-x (x_F) in polarized p^↑ + p, p^↑ + Al, and p^↑ + Au collisions at $$\sqrt{^SNN}$$ = 200 GeV. The measurements have been performed at forward and backward rapidity (1.4 < |η| < 2.4) over the range of 1.5 GeV /c < pT < 7.0 GeV /c and 0.04 < |x_F| < 0.2. A nonzero asymmetry is observed for positively charged hadrons at forward rapidity (x_F > 0) in p^↑ + p collisions, whereas the p^↑ + Almore » and p^↑ + Au results show smaller asymmetries. This finding provides new opportunities to investigate the origin of transverse single-spin asymmetries and a tool to study nuclear effects in p + A collisions.« less

We previously published in 2018 a detailed measurement recorded in 2010 for Au+Au collisions at $$\sqrt{^SNN}$$ = 200 GeV of charged two-pion correlation functions in 0%-30% centrality. We found the data to be well described by Bose-Einstein correlation functions stemming from L$$\acute{e}$$vy-stable source distributions. Using a fine transverse momentum binning, we extracted the correlation strength parameter λ, the L$$\acute{e}$$vy index of stability α and the L$$\acute{e}$$vy length scale parameter R as a function of average transverse mass of the pair m_T.

We present measurements of the cross section and double-helicity asymmetry A_LL of directphoton production in $$\vec{p}$$ + $$\vec{p}$$ collisions at $$\sqrt {s}$$ = 510 GeV. The measurements have been performed at midrapidity (|η| < 0.25) with the PHENIX detector at the Relativistic Heavy Ion Collider. At relativistic energies, direct photons are dominantly produced from the initial quark-gluon hard scattering and do not interact via the strong force at leading order. Therefore, at $$\sqrt {s}$$ = 510 GeV, where leading-order-effects dominate, these measurements provide clean and direct access to the gluon helicity in the polarized proton in the gluon-momentum-fraction range 0.02more » < x < 0.08, with direct sensitivity to the sign of the gluon contribution.« less

Presented are the first measurements of the transverse single-spin asymmetries ($$A_N$$) for neutral pions and eta mesons in $$\textit{p}$$ + Au and $$\textit{p}$$ + Al collisions at $$\sqrt{s_{NN}}$$ = 200 GeV in the pseudorapidity range |$$\textit{η}$$| < 0.35 with the PHENIX detector at the Relativistic Heavy Ion Collider. The asymmetries are consistent with zero, similar to those for midrapidity neutral pions and eta mesons produced in $$\textit{p}$$ + $$\textit{p}$$ collisions. These measurements show no evidence of additional effects that could potentially arise from the more complex partonic environment present in proton-nucleus collisions.

Polarized proton-proton collisions provide leading-order access to gluons, presenting an opportunity to constrain gluon spin-momentum correlations within transversely polarized protons and enhance our understanding of the three-dimensional structure of the proton. Midrapidity open-heavy-flavor production at $$\sqrt{s}$$ = 200 GeV is dominated by gluon-gluon fusion, providing heightened sensitivity to gluon dynamics relative to other production channels. Transverse single-spin asymmetries of positrons and electrons from heavy-flavor hadron decays are measured at midrapidity using the PHENIX detector at the Relativistic Heavy Ion Collider. These charge-separated measurements are sensitive to gluon correlators that can in principle be related to gluon orbital angular momentum viamore » model calculations. Explicit constraints on gluon correlators are extracted for two separate models, one of which had not been constrained previously.« less

Recently, the PHENIX Collaboration has published second- and third-harmonic Fourier coefficients v₂ and v₃ for midrapidity (|η|< 0.35 ) charged hadrons in 0%–5% central p+Au, d+Au, and ³He+Au collisions at $$\sqrt{s_{NN}}$$= 200 GeV, utilizing three sets of two-particle correlations for two detector combinations with different pseudorapidity acceptance [Acharya et al., Phys. Rev. C 105, 024901 (2022)]. Here, this paper extends these measurements of v₂ to all centralities in p+Au, d+Au, and ³He+Au collisions, as well as p+p collisions, as a function of transverse momentum (p_T) and event multiplicity. The kinematic dependence of v₂ is quantified as the ratio R ofmore » v₂ between the two detector combinations as a function of event multiplicity for 0.5 < p_T <1 and 2 _T < 2.5 GeV/c. A multiphase-transport (AMPT) model can reproduce the observed v₂ in most-central to midcentral d Au and ³He+Au collisions. However, the AMPT model systematically overestimates the measurements in p+p, p+Au, and peripheral d+Au and ³He+Au collisions, indicating a higher nonflow contribution in the AMPT model than in the experimental data. The AMPT model fails to describe the observed R for 0.5 < p_T < 1 GeV/c , but there is qualitative agreement with the measurements for 2 < p_T < 2.5 GeV/c.« less

Precision studies of simple atoms, such as hydrogen, play an essential role in tests of bound-state QED and determining fundamental constants, such as the Rydberg constant and the proton charge radius. One of the QED predictions is for the Lamb shift of hydrogenic energy levels and, in particular, of the ground state. Here, the value of the 1s Lamb shift in hydrogen and deuterium is required for an accurate determination of the Rydberg constant and the proton charge radius utilizing data from high-resolution spectroscopy of hydrogen and deuterium atoms, as well as for precision tests of bound-state QED. The dominantmore » QED contribution to the uncertainty is due to the α⁸m external-field contributions. We discuss here our recent results on the two- and three-loop contributions, which essentially reduce the theoretical uncertainty. Combined with recent calculations of Laporta on the slope of the Dirac form factor in the three-loop level, our results allow for completion of calculations of α⁸m contributions to the Lamb shift of the ground state in the hydrogen atom.« less

The PHENIX experiment reports systematic measurements at the Relativistic Heavy Ion Collider of φ-meson production in asymmetric Cu + Au collisions at √sNN = 200 GeV and in U + U collisions at √sNN = 193 GeV. Measurements were performed via the φ → K+K− decay channel at midrapidity |η| < 0.35. Features of φmeson 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-overlapmore » size. The elliptic flow of the φ meson in Cu + Au, Au + Au, and U + U collisions scales with second-order-participant eccentricity and the length scale of the nuclearoverlap region (estimated with the number of participating nucleons). At moderate pT , φ-meson production measured in Cu + Au and U + U collisions is consistent with coalescence-model predictions, whereas at high pT the production is in agreement with expectations for in-medium energy loss of parent partons prior to their fragmentation. The elliptic flow for φ mesons measured in Cu + Au and U + U collisions is well described by a (2+1)-dimensional viscous-hydrodynamic model with specific-shear viscosity η/s = 1/4π.« less

We report small nuclear collisions are mainly sensitive to cold-nuclear-matter effects; however, the collective behavior observed in these collisions shows a hint of hot-nuclear-matter effects. The identified-particle spectra, especially the φ mesons which contain strange and antistrange quarks and have a relatively small hadronic-interaction cross section, are a good tool to study these effects. The PHENIX experiment has measured φ mesons in a specific set of small collision systems p+Al, p+Au, and ³He+Au, as well as d+Au at $$\sqrt{s_{NN}}$$=200 GeV. The transverse-momentum spectra and nuclear-modification factors are presented and compared to theoretical-model predictions. The comparisons with different calculations suggest thatmore » quark-gluon plasma may be formed in these small collision systems at $$\sqrt{s_{NN}}$$=200 GeV. However, the volume and the lifetime of the produced medium may be insufficient for observing strangeness-enhancement and jet-quenching effects. The comparison with calculations suggests that the main production mechanisms of φ mesons at midrapidity may be different in p+Al versus p/d/³He+Au collisions at $$\sqrt{s_{NN}}$$=200 GeV. While thermal quark recombination seems to dominate in p/d/³He+Au collisions, fragmentation seems to be the main production mechanism in p+Al collisions.« less

For several decades, the origin of ultra-high-energy cosmic rays (UHECRs) has been an unsolved question of high-energy astrophysics. One approach for solving this puzzle is to correlate UHECRs with high-energy neutrinos, since neutrinos are a direct probe of hadronic interactions of cosmic rays and are not deflected by magnetic fields. In this paper, we present three different approaches for correlating the arrival directions of neutrinos with the arrival directions of UHECRs. The neutrino data are provided by the IceCube Neutrino Observatory and ANTARES, while the UHECR data with energies above ~50 EeV are provided by the Pierre Auger Observatory andmore » the Telescope Array. All experiments provide increased statistics and improved reconstructions with respect to our previous results reported in 2015. The first analysis uses a high-statistics neutrino sample optimized for point-source searches to search for excesses of neutrino clustering in the vicinity of UHECR directions. The second analysis searches for an excess of UHECRs in the direction of the highest-energy neutrinos. The third analysis searches for an excess of pairs of UHECRs and highest-energy neutrinos on different angular scales. None of the analyses have found a significant excess, and previously reported overfluctuations are reduced in significance. Based on these results, we further constrain the neutrino flux spatially correlated with UHECRs.« less