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2015

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Articles 451 - 460 of 460

Full-Text Articles in Astrophysics and Astronomy

Search For Dark Photons From Neutral Meson Decays In P+P And D+ Au Collisions At √Snn =200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Marcus Hohlmann, S. Rembeczki, Phenix Collaboration Jan 2015

Search For Dark Photons From Neutral Meson Decays In P+P And D+ Au Collisions At √Snn =200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Marcus Hohlmann, S. Rembeczki, Phenix Collaboration

Aerospace, Physics, and Space Science Faculty Publications

The standard model (SM) of particle physics is spectacularly successful, yet the measured value of the muon anomalous magnetic moment (g-2)μ deviates from SM calculations by 3.6σ. Several theoretical models attribute this to the existence of a "dark photon," an additional U(1) gauge boson, which is weakly coupled to ordinary photons. The PHENIX experiment at the Relativistic Heavy Ion Collider has searched for a dark photon, U, in π0,η→γe+e- decays and obtained upper limits of O(2×10‐⁶) U-γ mixing at 90% C.L. for the mass range 30< mᵤ < 90 MeV/c². Combined with other experimental limits, the remaining region in the U-γ mixing parameter space that can explain the (g-2)ᵤ deviation from its SM value is nearly completely excluded at the 90% confidence level, with only a small region of 29

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Systematic Study Of Azimuthal Anisotropy In Cu + Cu And Au + Au Collisions At √Snn =62.4 And 200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Klaus Dehmelt, Marcus Hohlmann, S. Rembeczki, Phenix Collaboration Jan 2015

Systematic Study Of Azimuthal Anisotropy In Cu + Cu And Au + Au Collisions At √Snn =62.4 And 200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Klaus Dehmelt, Marcus Hohlmann, S. Rembeczki, Phenix Collaboration

Aerospace, Physics, and Space Science Faculty Publications

We have studied the dependence of azimuthal anisotropy v₂ for inclusive and identified charged hadrons in Au+Au and Cu+Cu collisions on collision energy, species, and centrality. The values of v₂ as a function of transverse momentum pT and centrality in Au+Au collisions at sNN=200 and 62.4 GeV are the same within uncertainties. However, in Cu+Cu collisions we observe a decrease in v₂ values as the collision energy is reduced from 200 to 62.4 GeV. The decrease is larger in the more peripheral collisions. By examining both Au+Au and Cu+Cu collisions we find that v₂ depends both on eccentricity and the …

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Centrality Dependence Of Low-Momentum Direct-Photon Production In Au+Au Collisions At √Snn =200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Marcus Hohlmann, Phenix Collaboration Jan 2015

Centrality Dependence Of Low-Momentum Direct-Photon Production In Au+Au Collisions At √Snn =200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Marcus Hohlmann, Phenix Collaboration

Aerospace, Physics, and Space Science Faculty Publications

The PHENIX experiment at RHIC has measured the centrality dependence of the direct photon yield from Au+Au collisions at √sNN=200 GeV down to pT=0.4 GeV/c. Photons are detected via photon conversions to e+e- pairs and an improved technique is applied that minimizes the systematic uncertainties that usually limit direct photon measurements, in particular at low pT. We find an excess of direct photons above the Ncoll-scaled yield measured in p+p collisions. This excess yield is well described by an exponential distribution with an inverse slope of about 240MeV/c in the pT range 0.6-2.0 GeV/c. While the shape of the pT …

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Φ Meson Production In D + Au Collisions At √Snn =200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Marcus Hohlmann, S. Rembeczki, Phenix Collaboration Jan 2015

Φ Meson Production In D + Au Collisions At √Snn =200 Gev, Andrew Marshall Adare, Gyöngyi Baksay, László A. Baksay, Marcus Hohlmann, S. Rembeczki, Phenix Collaboration

Aerospace, Physics, and Space Science Faculty Publications

The PHENIX Collaboration has measured φ meson production in d+Au collisions at √sNN=200 GeV using the dimuon and dielectron decay channels. The φ meson is measured in the forward (backward) d-going (Au-going) direction, 1.2 < y < 2.2 (-2.2 < y < -1.2) in the transverse-momentum (pT) range from 1-7 GeV/c and at midrapidity │y│< 0.35 in the pT range below 7 GeV/c. The φ meson invariant yields and nuclear-modification factors as a function of pT, rapidity, and centrality are reported. An enhancement of φ meson production is observed in the Au-going direction, while suppression is seen in the d-going direction, and no modification is observed at midrapidity relative to the yield in p+p collisions scaled by the number of binary collisions. Similar behavior was previously observed for inclusive charged hadrons and open heavy flavor, indicating similar cold-nuclear-matter effects.

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Koi-3158: The Oldest Known System Of Terrestrial-Size Planets, Tiago L. Campante, Darin A. Ragozzine Jan 2015

Koi-3158: The Oldest Known System Of Terrestrial-Size Planets, Tiago L. Campante, Darin A. Ragozzine

Aerospace, Physics, and Space Science Faculty Publications

The first discoveries of exoplanets around Sun-like stars have fueled efforts to find ever smaller worlds evocative of Earth and other terrestrial planets in the Solar System. While gas-giant planets appear to form preferentially around metal-rich stars, small planets (with radii less than four Earth radii) can form under a wide range of metallicities. This implies that small, including Earth-size, planets may have readily formed at earlier epochs in the Universe's history when metals were far less abundant. We report Kepler spacecraft observations of KOI-3158, a metal-poor Sun-like star from the old population of the Galactic thick disk, which hosts …

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Koi-3158: The Oldest Known System Of Terrestrial-Size Planets, Tiago L. Campante, Darin A. Ragozzine Jan 2015

Koi-3158: The Oldest Known System Of Terrestrial-Size Planets, Tiago L. Campante, Darin A. Ragozzine

Aerospace, Physics, and Space Science Faculty Publications

The first discoveries of exoplanets around Sun-like stars have fueled efforts to find ever smaller worlds evocative of Earth and other terrestrial planets in the Solar System. While gas-giant planets appear to form preferentially around metal-rich stars, small planets (with radii less than four Earth radii) can form under a wide range of metallicities. This implies that small, including Earth-size, planets may have readily formed at earlier epochs in the Universe's history when metals were far less abundant. We report Kepler spacecraft observations of KOI-3158, a metal-poor Sun-like star from the old population of the Galactic thick disk, which hosts …

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The Effect Of Direct Electron-Positron Pair Production On Relativistic Feedback Rates, Igor B. Vodopiyanov, Joseph R. Dwyer, Eric S. Cramer, R. J. Lucia, Hamid K. Rassoul Jan 2015

The Effect Of Direct Electron-Positron Pair Production On Relativistic Feedback Rates, Igor B. Vodopiyanov, Joseph R. Dwyer, Eric S. Cramer, R. J. Lucia, Hamid K. Rassoul

Aerospace, Physics, and Space Science Faculty Publications

Runaway electron avalanches developing in thunderclouds in high electric field become self-sustaining due to relativistic feedback via the production of backward propagating positrons and backscattered X-rays. To date, only positrons created from pair production by gamma rays interacting with the air have been considered. In contrast, direct electron-positron pair production, also known as "trident process," occurs from the interaction of energetic runaway electrons with atomic nuclei, and so it does not require the generation of a gamma ray mediator. The positrons produced in this process contribute to relativistic feedback and become especially important when the feedback factor value approaches unity. …

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Quantum Tests Of The Einstein Equivalence Principle With The Ste-Quest Space Mission, Brett Altschul, Quentin G. Bailey, Luc Blanchet, Kai Bongs, Philippe Bouyer, Luigi Cacciapuoti, Et Al. Jan 2015

Quantum Tests Of The Einstein Equivalence Principle With The Ste-Quest Space Mission, Brett Altschul, Quentin G. Bailey, Luc Blanchet, Kai Bongs, Philippe Bouyer, Luigi Cacciapuoti, Et Al.

Publications

We present in detail the scientific objectives in fundamental physics of the Space–Time Explorer and QUantum Equivalence Space Test (STE–QUEST) space mission. STE–QUEST was pre-selected by the European Space Agency together with four other missions for the cosmic vision M3 launch opportunity planned around 2024. It carries out tests of different aspects of the Einstein Equivalence Principle using atomic clocks, matter wave interferometry and long distance time/frequency links, providing fascinating science at the interface between quantum mechanics and gravitation that cannot be achieved, at that level of precision, in ground experiments. We especially emphasize the specific strong interest of performing …

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Exploring How Social Media Can Be Used To Promote Space Awareness: A Case Study Of The Yuri's Night Web 2.0, Alan Steinberg, Jeffrey Alles, Ryan L. Kobrick Jan 2015

Exploring How Social Media Can Be Used To Promote Space Awareness: A Case Study Of The Yuri's Night Web 2.0, Alan Steinberg, Jeffrey Alles, Ryan L. Kobrick

Publications

Despite the importance of social media as an inexpensive and efficient means of communication, it is not clear to what degree space advocacy groups are making a strong organized effort to use the resources available to them. Moreover, there is no previous literature that specifically examines the use of social media tools by space organizations. This study seeks to start a larger dialog regarding how the space advocacy community can make use of these tools to promote their mission. Using a case study approach, this article focuses specifically on the organization of Yuri’s Night to explore how this group is …

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Characterization Of The Ligo Detectors During Their Sixth Science Run, Tiffany Summerscales, Ligo Collaboration Jan 2015

Characterization Of The Ligo Detectors During Their Sixth Science Run, Tiffany Summerscales, Ligo Collaboration

Faculty Publications

In 2009–2010, the Laser Interferometer Gravitational-Wave Observatory (LIGO) operated together with international partners Virgo and GEO600 as a network to search for gravitational waves (GWs) of astrophysical origin. The sensitivity of these detectors was limited by a combination of noise sources inherent to the instrumental design and its environment, often localized in time or frequency, that couple into the GW readout. Here we review the performance of the LIGO instruments during this epoch, the work done to characterize the detectors and their data, and the effect that transient and continuous noise artefacts have on the sensitivity of LIGO to a …

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