We report the first measurement of the fraction of J/ψ mesons coming from B-meson decay (FB→J/ψ) in p+p collisions at s=510 GeV. The measurement is performed using the forward silicon vertex detector ...and central vertex detector at PHENIX, which provide precise tracking and distance-of-closest-approach determinations, enabling the statistical separation of J/ψ due to B-meson decays from prompt J/ψ. The measured value of FB→J/ψ is 8.1%±2.3%(stat)±1.9%(syst) for J/ψ with transverse momenta 0<pT<5 GeV/c and rapidity 1.2<|y|<2.2. The measured fraction FB→J/ψ at PHENIX is compared to values measured by other experiments at higher center of mass energies and to fixed-order-next-to-leading-logarithm and color-evaporation-model predictions. The bb¯ cross section per unit rapidity dσ/dy(pp→bb¯) extracted from the obtained FB→J/ψ and the PHENIX inclusive J/ψ cross section measured at 200 GeV scaled with color-evaporation-model calculations, at the mean B hadron rapidity y=±1.7 in 510 GeV p+p collisions, is 3.63−1.70+1.92 μb. It is consistent with the fixed-order-next-to-leading-logarithm calculations.
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-overlap 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.
The PHENIX experiment at the Relativistic Heavy Ion Collider measured π0 and η mesons at midrapidity in U+U collisions at sNN=192 GeV in a wide transverse momentum range. Measurements were performed ...in the π0(η)→γγ decay modes. A strong suppression of π0 and η meson production at high transverse momentum was observed in central U+U collisions relative to binary scaled p+p results. Yields of π0 and η mesons measured in U+U collisions show similar suppression pattern to those measured in Au+Au collisions at sNN=200 GeV for similar numbers of participant nucleons. The η/π0 ratios do not show dependence on centrality or transverse momentum and are consistent with previously measured values in hadron-hadron, hadron-nucleus, nucleus-nucleus, and e+e- collisions.
The regularity of pulsar emissions becomes apparent once we reference the pulses’ times of arrivals to the inertial rest frame of the solar system. It follows that errors in the determination of ...Earthʼs position with respect to the solar system barycenter can appear as a time-correlated bias in pulsar-timing residual time series, affecting the searches for low-frequency gravitational waves performed with pulsar-timing arrays. Indeed, recent array data sets yield different gravitational-wave background upper limits and detection statistics when analyzed with different solar system ephemerides. Crucially, the ephemerides do not generally provide usable error representations. In this article, we describe the motivation, construction, and application of a physical model of solar system ephemeris uncertainties, which focuses on the degrees of freedom (Jupiterʼs orbital elements) most relevant to gravitational-wave searches with pulsar-timing arrays. This model, BAYESEPHEM, was used to derive ephemeris-robust results in NANOGravʼs 11 yr stochastic-background search, and it provides a foundation for future searches by NANOGrav and other consortia. The analysis and simulations reported here suggest that ephemeris modeling reduces the gravitational-wave sensitivity of the 11 yr data set and that this degeneracy will vanish with improved ephemerides and with pulsar-timing data sets that extend well beyond a single Jovian orbital period.
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