Bulletin of the American Physical Society
APS April Meeting 2015
Volume 60, Number 4
Saturday–Tuesday, April 11–14, 2015; Baltimore, Maryland
Session M14: General Cosmic Rays |
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Sponsoring Units: DAP Chair: Elizabeth A. Hays, NASA Room: Key 10 |
Sunday, April 12, 2015 3:30PM - 3:42PM |
M14.00001: The Effect of a Maximum Lepton Energy on the Stability of Pions and Cosmic Ray Physics Peter Denton, Danny Marfatia, Thomas Weiler The IceCube experiment has detected astrophysical neutrinos with energies in the 10 TeV to 2 PeV range. Extrapolating the measured power-law spectrum beyond 2 PeV, a few higher energy continuum events and a few events at the Glashow resonance energy of 6.3 PeV are predicted but not observed. Recently, it was postulated that the reason for the apparent energy cutoff in the IceCube neutrino data is because Nature has provided an absolute maximum energy for neutrinos. Since the charged pion decays to leptons, energy cutoffs for the leptons in turn imply that the lifetime and mean free path of the pion increase, eventually reaching absolute stability. We calculate the lifetime of the charged pion under these assumptions and discuss its role in ultra high energy cosmic ray physics. [Preview Abstract] |
Sunday, April 12, 2015 3:42PM - 3:54PM |
M14.00002: ABSTRACT WITHDRAWN |
Sunday, April 12, 2015 3:54PM - 4:06PM |
M14.00003: Geant4-based Simulation Study of Cosmic Ray Showers and the Associated Applications Olesya Sarajlic, Xiaochun He Cosmic ray radiation has galactic origin and consists primarily of protons and a small percentage of heavier nuclei. The primary cosmic ray particles interact with the molecules in the atmosphere and produce showers of secondary particles at about 15 km altitude. A Geant4-based cosmic ray shower simulation is developed to study secondary cosmic ray particle showers in the full range of the Earth's atmosphere. A proper atmospheric air density profile and a full-scale geomagnetic field are implemented in order to precisely simulate the particle interactions in the atmosphere. Preliminary results from this simulation will be presented along with the association applications in the study of the correlation between the cosmic ray flux variation at the sea level and the dynamic weather patterns. [Preview Abstract] |
Sunday, April 12, 2015 4:06PM - 4:18PM |
M14.00004: Geant4 Simulation of Air Showers using Thinning Method Mohammad S. Sabra, John W. Watts, Mark J. Christl Simulation of complete air showers induced by cosmic ray particles becomes prohibitive at extreme energies due to the large number of secondary particles. Computing time of such simulations roughly scales with the energy of the primary cosmic ray particle, and becomes excessively large. To mitigate the problem, only small fraction of particles can be tracked and, then, the whole shower is reconstructed based on this sample. This method is called Thinning. Using this method in Geant4, we have simulated proton and iron air showers at extreme energies (E \textgreater 10$^{\mathrm{16}}$ eV). Secondary particle densities are calculated and compared with the standard simulation program in this field, CORSIKA. [Preview Abstract] |
Sunday, April 12, 2015 4:18PM - 4:30PM |
M14.00005: Radio Emission from particle cascades in the presence of a magnetic field Katharine Mulrey Geomagnetic radiation from air showers is an attractive technique for detecting ultra-high energy cosmic rays. Macroscopic and microscopic models have been developed which qualitatively agreed with field observations. A controlled laboratory experiment at the SLAC National Accelerator Laboratory (SLAC) was designed to test these models. The experiment measures the radio frequency emission from cascades of secondary particles in a dense dielectric medium in the presence of a magnetic field. The cascades were induced by a $\sim$ 4.5 GeV electron beam in a polyethylene target placed in magnetic fields up to $+$/-1000 G. The radio emission beam pattern was sampled in horizontal and vertical polarizations by multiple antennas with a total frequency band of 30-3000MHz. The emission was found to be in good agreement with model predictions, including a Cerenkov-like beam pattern and linear scaling with magnetic field. [Preview Abstract] |
Sunday, April 12, 2015 4:30PM - 4:42PM |
M14.00006: Studying Stratospheric Temperature Variation with Cosmic Ray Measurements Xiaohang Zhang, Xiaochun He The long term stratospheric cooling in recent decades is believed to be equally important as surface warming as evidence of influences of human activities on the climate system. Un- fortunatly, there are some discrepancies among different measurements of stratospheric tem- peratures, which could be partially caused by the limitations of the measurement techniques [1]. It has been known for decades that cosmic ray muon flux is sensitive to stratospheric temperature change. Dorman proposed that this effect could be used to probe the tempera- ture variations in the stratophere [2]. In this talk, a method for reconstructing stratospheric temperature will be discussed. We verify this method by comparing the stratospheric tem- perature measured by radiosonde with the ones derived from cosmic ray measurement at multiple locations around the globe. References [1] David W. J. Thompson, et al., Nature 491 (2012). [2] Dorman L., Cosmic Ray Meteorolgical Effects Nauka, Moscow (1972) [Preview Abstract] |
Sunday, April 12, 2015 4:42PM - 4:54PM |
M14.00007: Correlation of Windspeed and Antarctic Surface Roughness Mark Stockham When electromagnetic waves interact with a media interface the transmitted and reflected portions of the incoming wave depend on the incident angle of the wave and wavelength (as well as the material properties of the media). The roughness of the surface of Antarctica affects the radio frequency signals received by airborne experiments, such as the balloon-borne experiment ANITA (ANtarctic Impulsive Transient Antenna) which observes the reflected radio waves from cosmic ray-induced extensive air showers (EAS). Roughness of a given scale can cause decoherence of the reflected signal and is an important effect to understand when estimating the amplitude of the incoming wave based on the reflected wave. It is challenging to get a survey of surface roughness over many of the areas that these experiments are likely to pass over. Correlating historical wind speed records with statistical roughness as observed by the backscatter of satellite [R\'emy F, Parouty S. \textit{Remote Sensing}. 2009] and airborne experiments operating at different frequencies can possibly be used to predict time-dependent surface roughness with surface wind speed as the input. These correlations will be presented for a variety of areas on the Antarctic ice shelf. [Preview Abstract] |
Sunday, April 12, 2015 4:54PM - 5:06PM |
M14.00008: How did the universe get magnetized? Mikhail Medvedev The origin of the micro-Gauss magnetic fields in the IGM of galaxy clusters is one of the outstanding problem in modern cosmology. We demonstrate that the cluster accretion shocks are naturally and inevitably generate sub-equipartition magnetic fields from scratch in a two-step process. Indeed, accretion shocks accelerate cosmic rays, which further generate magnetic fields via a streaming, Weibel-type plasma instability. We stress that no seed field is needed in this scenario. We develop a self-similar model of a cosmic-ray-modified foreshock and demonstrate that, in contrast to the conventional lore, the generated magnetic fields (i) are large-scale, i.e., can be of the order of the the shock curvature radius, ~tens of kpc or more, hence they are effectively decoupled from dissipation and hence are long-lived on the Hubble time and (ii) are strong enough, i.e., of the order of a fraction of the cosmic ray pressure, to meet observational constraints. We stress that no seed field is needed in this scenario, unlike other shock-related models of the field generation (e.g., via the Bell instability or the Richtmeyer-Meshkov vorticity instability). [Preview Abstract] |
Sunday, April 12, 2015 5:06PM - 5:18PM |
M14.00009: Stokes' Parameters Compared to Astrophysical Magnetic Turbulence Parameters Miriam Forman, Robert Wicks, Sean Oughton, Timothy Horbury Since the divergence of a magnetic field is zero, the Fourier transform of fluctuations $\delta $\textbf{B(k}) must be perpendicular to \textbf{k}, so $\delta $\textbf{B(k}) has components only in the plane perpendicular to \textbf{k}. When there is also a mean field \textbf{B}, the obvious choice of coordinates to describe $\delta $\textbf{B(k}) are the unit vectors \textbf{t }in the direction\textbf{ B x k} and \textbf{p} in the direction \textbf{(Bxk) x k}, called the ``toroidal'' and ``poloidal'' directions, respectively. Oughton, et al. (1997) as elucidated by Wicks et al. (2012) showed that the power spectral tensor P$_{\mathrm{ij}}$(\textbf{k}) of magnetic fluctuations is described by four scalar functions of \textbf{k}, multiplying the tensors \textbf{t:t}, \textbf{p:p}, \textbf{t:p}$+$\textbf{p:t}, and \textbf{t:p}-\textbf{p:t} so that the Hermitian Pij(\textbf{k}) $=$Tor(\textbf{k}) \textbf{t:t }$+$ Pol(\textbf{k}) \textbf{p:p }$+$ C(\textbf{k}) [\textbf{t:p}$+$\textbf{p:t] }$+i$kH(\textbf{k}) [\textbf{t:p}-\textbf{p:t}]. Since the electromagnetic fluctuations $\delta $\textbf{B(k}) and $\delta $\textbf{E(k}) in a beam of light are also perpendicular to their \textbf{k}, the four scalar functions of magnetic turbulence in astrophysics which scatters cosmic rays and allows their acceleration, are analogs of the Stokes' parameters. Using Chandrasekhar's (1960) notation [I,Q,U,V]: I$=$ Tor $+$ Pol $=$Tr(P$_{\mathrm{ij}}$(\textbf{k}); Q$=$Tor-Pol; U$=$C; we speculate that V corresponds to magnetic helicity kH in turbulence. We are studying projections of P$_{\mathrm{ij}}$(\textbf{k}) observed by spacecraft in the solar wind. [Preview Abstract] |
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