13 research outputs found
Measurements of second-harmonic Fourier coefficients from azimuthal anisotropies in p+p, p+Au, d+Au, and He 3 +Au collisions at sNN =200 GeV
Recently, the PHENIX Collaboration has published second- and third-harmonic Fourier coefficients v2 and v3 for midrapidity (|η
Measurement of φ -meson production in Cu+Au collisions at sNN =200 GeV and U+ U collisions at sNN =193 GeV
The PHENIX experiment reports systematic measurements at the Relativistic Heavy Ion Collider of φ-meson production in asymmetric Cu+Au collisions at sNN=200GeV and in U+U collisions at sNN=193GeV. Measurements were performed via the φ→K+K- decay channel at midrapidity |η
Disentangling centrality bias and final-state effects in the production of high- using direct in Au collisions at GeV
International audiencePHENIX presents a simultaneous measurement of the production of direct and in Au collisions at GeV over a range of 7.5 to 18 GeV/ for different event samples selected by event activity, i.e. charged-particle multiplicity detected at forward rapidity. Direct-photon yields are used to empirically estimate the contribution of hard-scattering processes in the different event samples. Using this estimate, the average nuclear-modification factor is , consistent with unity for minimum-bias (MB) Au events. For event classes with moderate event activity, is consistent with the MB value within 5% uncertainty. These results confirm that the previously observed enhancement of high- production found in small-system collisions with low event activity is a result of a bias in interpreting event activity within the Glauber framework. In contrast, for the top 5% of events with the highest event activity, is suppressed by 20% relative to the MB value with a significance of , which may be due to final-state effects
Transverse single-spin asymmetry of midrapidity and mesons in +Au and +Al collisions at 200 GeV
International audiencePresented are the first measurements of the transverse single-spin asymmetries () for neutral pions and eta mesons in +Au and +Al collisions at GeV in the pseudorapidity range 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 + collisions. These measurements show no evidence of additional effects that could potentially arise from the more complex partonic environment present in proton-nucleus collisions
Transverse single-spin asymmetry of charged hadrons at forward and backward rapidity in polarized +, +Al, and +Au collisions at GeV
International audienceReported here are transverse single-spin asymmetries () in the production of charged hadrons as a function of transverse momentum () and Feynman- () in polarized +, +Al, and +Au collisions at GeV. The measurements have been performed at forward and backward rapidity () in + collisions, whereas the +Al and +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 + collisions
Measurement of <math><mi>ϕ</mi></math>-meson production in <math><mrow><mi>Cu</mi><mo>+</mo><mi>Au</mi></mrow></math> collisions at <math><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>200</mn></mrow></math> GeV and <math><mrow><mi mathvariant="normal">U</mi><mo>+</mo><mi mathvariant="normal">U</mi></mrow></math> collisions at <math><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>193</mn></mrow></math> GeV
International audienceThe PHENIX experiment reports systematic measurements at the Relativistic Heavy Ion Collider of ϕ-meson production in asymmetric Cu+Au collisions at sNN=200GeV and in U+U collisions at sNN=193GeV. Measurements were performed via the ϕ→K+K− decay channel at midrapidity |η|<0.35. Features of ϕ-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 ϕ 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 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
Measurement of <math><mi>ϕ</mi></math>-meson production in <math><mrow><mi>Cu</mi><mo>+</mo><mi>Au</mi></mrow></math> collisions at <math><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>200</mn></mrow></math> GeV and <math><mrow><mi mathvariant="normal">U</mi><mo>+</mo><mi mathvariant="normal">U</mi></mrow></math> collisions at <math><mrow><msqrt><msub><mi>s</mi><mrow><mi>N</mi><mi>N</mi></mrow></msub></msqrt><mo>=</mo><mn>193</mn></mrow></math> GeV
International audienceThe PHENIX experiment reports systematic measurements at the Relativistic Heavy Ion Collider of ϕ-meson production in asymmetric Cu+Au collisions at sNN=200GeV and in U+U collisions at sNN=193GeV. Measurements were performed via the ϕ→K+K− decay channel at midrapidity |η|<0.35. Features of ϕ-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 ϕ 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 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
Identified charged-hadron production in Al, HeAu, and CuAu collisions at GeV and in UU collisions at GeV
International audienceThe PHENIX experiment has performed a systematic study of identified charged-hadron (, , , ) production at midrapidity in Al, HeAu, CuAu collisions at GeV and UU collisions at GeV. Identified charged-hadron invariant transverse-momentum () and transverse-mass () spectra are presented and interpreted in terms of radially expanding thermalized systems. The particle ratios of and have been measured in different centrality ranges of large (CuAu, UU) and small (Al, HeAu) collision systems. The values of ratios measured in all considered collision systems were found to be consistent with those measured in collisions. However the values of ratios measured in large collision systems reach the values of , which is times larger than in collisions. These results can be qualitatively understood in terms of the baryon enhancement expected from hadronization by recombination. Identified charged-hadron nuclear-modification factors () are also presented. Enhancement of proton values over meson values was observed in central HeAu, CuAu, and UU collisions. The proton values measured in Al collision system were found to be consistent with values of , , , and mesons, which may indicate that the size of the system produced in Al collisions is too small for recombination to cause a noticeable increase in proton production
Identified charged-hadron production in Al, HeAu, and CuAu collisions at GeV and in UU collisions at GeV
International audienceThe PHENIX experiment has performed a systematic study of identified charged-hadron (, , , ) production at midrapidity in Al, HeAu, CuAu collisions at GeV and UU collisions at GeV. Identified charged-hadron invariant transverse-momentum () and transverse-mass () spectra are presented and interpreted in terms of radially expanding thermalized systems. The particle ratios of and have been measured in different centrality ranges of large (CuAu, UU) and small (Al, HeAu) collision systems. The values of ratios measured in all considered collision systems were found to be consistent with those measured in collisions. However the values of ratios measured in large collision systems reach the values of , which is times larger than in collisions. These results can be qualitatively understood in terms of the baryon enhancement expected from hadronization by recombination. Identified charged-hadron nuclear-modification factors () are also presented. Enhancement of proton values over meson values was observed in central HeAu, CuAu, and UU collisions. The proton values measured in Al collision system were found to be consistent with values of , , , and mesons, which may indicate that the size of the system produced in Al collisions is too small for recombination to cause a noticeable increase in proton production
Highlights from the PHENIX experiment
International audiencePHENIX has performed an extensive study on the evolution of medium effects from small to large systems. PHENIX has continued searching for Quark-Gluon Plasma (QGP) in small systems by measuring collectivity, modification of light hadron and quarkonia production, and jet substructure. In large systems, detailed studies on the property of the QGP have been done using direct photon, -hadron correlation, heavy-flavor electron, and flow with a large statistics of data collected in 2014. This report covers new results from the PHENIX experiment in various collision systems