arXiv subjects

J. Burns

Publications and source records attributed to J. Burns.

32 records · Page 2Linked to original sources

arXiv2011

Measurement of double-spin asymmetries associated with deeply virtual Compton scattering on a transversely polarized hydrogen target

Double-spin asymmetries in exclusive electroproduction of real photons from a transversely polarized hydrogen target are measured with respect to the product of target polarization with beam helicity and beam charge, and with respect to the product of target polarization with beam helicity alone. The asymmetries arise from the deeply virtual Compton scattering process and its interference with the Bethe--Heitler process. They are related to the real part of the same combination of Compton form factors as that determining the previously published transverse target single-spin asymmetries through the imaginary part. The results for the double-spin asymmetries are found to be compatible with zero within the uncertainties of the measurement, and are not incompatible with the predictions of the only available GPD-based calculation.

hep-ex↗

arXiv2011

Multidimensional Study of Hadronization in Nuclei

Hadron multiplicities in semi-inclusive deep-inelastic scattering were measured on neon, krypton and xenon targets relative to deuterium at an electron(positron)-beam energy of 27.6 GeV at HERMES. These ratios were determined as a function of the virtual-photon energy nu, its virtuality Q2, the fractional hadron energy z and the transverse hadron momentum with respect to the virtual-photon direction pt . Dependences were analysed separately for positively and negatively charged pions and kaons as well as protons and antiprotons in a two-dimensional representation. Compared to the one-dimensional dependences, some new features were observed. In particular, when z > 0.4 positive kaons do not show the strong monotonic rise of the multiplicity ratio with nu as exhibited by pions and negative kaons. Protons were found to behave very differently from the other hadrons.

hep-ex↗

arXiv2011

A Radio Observatory on the Lunar Surface for Solar studies (ROLSS)

By volume, more than 99% of the solar system has not been imaged at radio frequencies. Almost all of this space (the solar wind) can be traversed by fast electrons producing radio emissions at frequencies lower than the terrestrial ionospheric cutoff, which prevents observation from the ground. To date, radio astronomy-capable space missions consist of one or a few satellites, typically far from each other, which measure total power from the radio sources, but cannot produce images with useful angular resolution. To produce such images, we require arrays of antennas distributed over many wavelengths (hundreds of meters to kilometers) to permit aperture synthesis imaging. Such arrays could be free-flying arrays of microsatellites or antennas laid out on the lunar surface. In this white paper, we present the lunar option. If such an array were in place by 2020, it would provide context for observations during Solar Probe Plus perihelion passes. Studies of the lunar ionosphere's density and time variability are also important goals. This white paper applies to the Solar and Heliospheric Physics study panel.

astro-ph.SR↗

arXiv2011

Inclusive Measurements of Inelastic Electron and Positron Scattering from Unpolarized Hydrogen and Deuterium Targets

Results of inclusive measurements of inelastic electron and positron scattering from unpolarized protons and deuterons at the HERMES experiment are presented. The structure functions $F_2^p$ and $F_2^d$ are determined using a parameterization of existing data for the longitudinal-to-transverse virtual-photon absorption cross-section ratio. The HERMES results provide data in the ranges $0.006\leq x\leq 0.9$ and 0.1 GeV$^2\leq Q^2\leq$ 20 GeV$^2$, covering the transition region between the perturbative and the non-perturbative regimes of QCD in a so-far largely unexplored kinematic region. They are in agreement with existing world data in the region of overlap. The measured cross sections are used, in combination with data from other experiments, to perform fits to the photon-nucleon cross section using the functional form of the ALLM model. The deuteron-to-proton cross-section ratio is also determined.

hep-ex↗

arXiv2011

Measurement of azimuthal asymmetries associated with deeply virtual Compton scattering on a longitudinally polarized deuterium target

Azimuthal asymmetries in exclusive electroproduction of a real photon from a longitudinally polarized deuterium target are measured with respect to target polarization alone and with respect to target polarization combined with beam helicity and/or beam charge. The asymmetries appear in the distribution of the real photons in the azimuthal angle $ϕ$ around the virtual photon direction, relative to the lepton scattering plane. The asymmetries arise from the deeply virtual Compton scattering process and its interference with the Bethe-Heitler process. The results for the beam-charge and beam-helicity asymmetries from a tensor polarized deuterium target with vanishing vector polarization are shown to be compatible with those from an unpolarized deuterium target, which is expected for incoherent scattering dominant at larger momentum transfer. Furthermore, the results for the single target-spin asymmetry and for the double-spin asymmetry are found to be compatible with the corresponding asymmetries previously measured on a hydrogen target. For coherent scattering on the deuteron at small momentum transfer to the target, these findings imply that the tensor contribution to the cross section is small. Furthermore, the tensor asymmetry is found to be compatible with zero.

hep-ex↗

arXiv2011

Ratios of Helicity Amplitudes for Exclusive rho-0 Electroproduction

Exclusive rho^0-meson electroproduction is studied in the HERMES experiment, using a 27.6 GeV longitudinally polarized electron/positron beam and unpolarized hydrogen and deuterium targets in the kinematic region 0.5 GeV^2 < Q^2 < 7.0 GeV^2, 3.0 GeV < W < 6.3 GeV, and -t' < 0.4 GeV^2. Real and imaginary parts of the ratios of the natural-parity-exchange helicity amplitudes T_{11} (γ^*_T --> ρ_T), T_{01} (γ^*_T --> ρ_L), T_{10} (γ^*_L --> ρ_T), and T_{1-1} (γ^*_{-T} -->ρ_T) to T_{00} (γ^*_L --> ρ_L) are extracted from the data. For the unnatural-parity-exchange amplitude U_{11}, the ratio |U_{11}/T_{00}| is obtained. The Q^2 and t' dependences of these ratios are presented and compared with perturbative QCD predictions.

hep-ex↗

arXiv2010

Effects of transversity in deep-inelastic scattering by polarized protons

Single-spin asymmetries for pions and charged kaons are measured in semi-inclusive deep-inelastic scattering of positrons and electrons off a transversely nuclear-polarized hydrogen target. The dependence of the cross section on the azimuthal angles of the target polarization (phi_S)and the produced hadron (phi) is found to have a substantial sin(phi+phi_S) modulation for the production of pi+, pi- and K+. This Fourier component can be interpreted in terms of non-zero transversity distribution functions and non-zero favored and disfavored Collins fragmentation functions with opposite sign. For pi0 and K- production the amplitude of this Fourier component is consistent with zero.

hep-ex↗

arXiv2010

Exclusive Leptoproduction of Real Photons on a Longitudinally Polarised Hydrogen Target

Polarisation asymmetries are measured for the hard exclusive leptoproduction of real photons from a longitudinally polarised hydrogen target. These asymmetries arise from the deeply virtual Compton scattering and Bethe-Heitler processes. From the data are extracted two asymmetries in the azimuthal distribution of produced real photons about the direction of the exchanged virtual photon: A_UL with respect to the target polarisation and A_LL with respect to the product of the beam and target polarisations. Results for both asymmetries are compared to the predictions from a generalised parton distribution model. The sin(phi) and cos(0*phi) amplitudes observed respectively for the A_UL and A_LL asymmetries are compatible with the sizeable predictions from the model. Unexpectedly, a sin(2*phi) modulation in the A_UL asymmetry with a magnitude similar to that of the sin(phi) modulation is observed.

hep-ex↗

arXiv2009

Cosmological Studies With A Large-Area X-ray Telescope

A moderate investment of observing time with the International X-ray Observatory to study high-redshift galaxy clusters detected in future large-scale surveys, will provide cosmological measurements of fundamental importance. IXO observations, combined with lensing follow-up, will measure the perturbation growth factor from z=0-2 with an accuracy comparable to, or possibly better than, that expected from observations of cosmic shear with JDEM, and redshift-space distortions with EUCLID. The growth of structure data derived from clusters will significantly improve our knowledge of the dark energy equation of state and will aid in constraining non-GR models for cosmic acceleration. IXO observations of the largest, dynamically relaxed clusters will provide a powerful, independent measurement of the cosmological expansion history using the apparent f_gas(z) trend. Systematic and statistical errors from this technique are competitive with SNIa and BAO studies, making the test extremely useful for improving the accuracy and reliability of the geometric cosmological measurements planned for LSST and JDEM. Only by employing a range of powerful, independent approaches, including those discussed here, can robust answers to puzzles as profound as the origin of cosmic acceleration be expected.

astro-ph.CO↗

arXiv2009

A Proposal for a Renewed Research Emphasis in Astrophysical and Celestial Dynamics

Given the impressive investment by the nation in observational Astronomy and Astrophysics facilities coming on line now and in the near future, we advocate for an increased investment in applied and fundamental research on Astrophysical and Celestial Dynamics (ACD). Specifically we call for a) continued and expanded support for applied research in ACD, b) creation of support for fundamental research in ACD and its subfields, and c) the creation of a unified program to help scientists coordinate and collaborate in their research in these fields. The benefits of this proposal are threefold. First, it will enable researchers to interpret and understand the implications of newly observed phenomena that will invariably arise from new facilities and surveys. Second, research on fundamentals will foster connections between specialists, leveraging advances found in one sub-field and making them available to others. Third, a coordinated approach for applied and fundamental research in ACD will help academic institutions in the United States to produce future researchers trained and knowledgeable in essential subfields such as Mathematical Celestial Mechanics and able to continue its advancement in conjunction with the increase in observations.

astro-ph.CO↗

arXiv2009

Clusters and Large-Scale Structure: the Synchrotron Keys

For over four decades, synchrotron-radiating sources have played a series of pathfinding roles in the study of galaxy clusters and large scale structure. Such sources are uniquely sensitive to the turbulence and shock structures of large-scale environments, and their cosmic rays and magnetic fields often play important dynamic and thermodynamic roles. They provide essential complements to studies at other wavebands. Over the next decade, they will fill essential gaps in both cluster astrophysics and the cosmological growth of structure in the universe, especially where the signatures of shocks and turbulence, or even the underlying thermal plasma itself, are otherwise undetectable. Simultaneously, synchrotron studies offer a unique tool for exploring the fundamental question of the origins of cosmic magnetic fields. This work will be based on the new generation of m/cm-wave radio telescopes now in construction, as well as major advances in the sophistication of 3-D MHD simulations.

astro-ph.CO↗

arXiv2007

Radio Wavelength Observatories within the Exploration Architecture

Observations at radio wavelengths address key problems in astrophysics, astrobiology, and lunar structure including the first light in the Universe (the Epoch of Reionization), the presence of magnetic fields around extrasolar planets, particle acceleration mechanisms, and the structure of the lunar ionosphere. Moreover, achieving the performance needed to address these scientific questions demands observations at wavelengths longer than those that penetrate the Earth's ionosphere, observations in extremely "radio quiet" locations such as the Moon's far side, or both. We describe a series of lunar-based radio wavelength interferometers of increasing capability. The Radio Observatory for Lunar Sortie Science (ROLSS) is an array designed to be deployed during the first lunar sorties (or even before via robotic rovers) and addressing particle acceleration and the lunar ionosphere. Future arrays would be larger, more capable, and deployed as experience is gained in working on the lunar surface.

astro-ph↗

arXiv2002

A Universal Temperature Profile for Galaxy Clusters

We investigate the predicted present-day temperature profiles of the hot, X-ray emitting gas in galaxy clusters for two cosmological models - a current best-guess LCDM model and standard cold dark matter (SCDM). Our numerically-simulated "catalogs" of clusters are derived from high-resolution (15/h kpc) simulations which make use of a sophisticated, Eulerian-based, Adaptive Mesh-Refinement (AMR) code that faithfully captures the shocks which are essential for correctly modelling cluster temperatures. We show that the temperature structure on Mpc-scales is highly complex and non-isothermal. However, the temperature profiles of the simulated LCDM and SCDM clusters are remarkably similar and drop-off as $T +AFw-propto (1+-r/a_x)^{-+AFw-delta}$ where $a_x +AFw-sim r_{vir}/1.5$ and $+AFw-delta +AFw-sim 1.6$. This decrease is in good agreement with the observational results of Markevitch et al.(1998) but diverges, primarily in the innermost regions, from their fit which assumes a polytropic equation of state. Our result is also in good agreement with a recent sample of clusters observed by BeppoSAX though there is some indication of missing physics at small radii ($r<0.2 r_{vir}$). We discuss the interpretation of our results and make predictions for new x-ray observations that will extend to larger radii than previously possible. Finally, we show that, for $r>0.2 r_{vir}$, our universal temperature profile is consistent with our most recent simulations which include both radiative cooling and supernovae feedback.

astro-ph↗

arXiv2001

The Power Supply System of the CLEO III Silicon Detector

The CLEO III detector has recently commenced data taking at the Cornell electron Storage Ring (CESR). One important component of this detector is a 4 layer double-sided silicon tracker with 93% solid angle coverage. This detector ranges in size and number of readout channels between the LEP and LHC silicon detectors. In order to reach the detector performance goals of signal-to-noise ratios greater than 15:1 low noise front-end electronics together with highly regulated low noise power supplies were used. In this paper we describe the low-noise power supply system and associated monitoring and safety features used by the CLEO III silicon tracker.

hep-ex↗