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Register a new userSuggestion of Coherent Radio Reflections from an Electron-Beam Induced Particle Cascade
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Testbeam experiment 576 (T576) at the SLAC National Accelerator Laboratory sought to make the first measurement of coherent radio reflections from the ionization produced in the wake of a high-energy particle shower. The >10 GeV electron beam at SLAC End Station A was directed into a large high-density polyethylene target to produce a shower analogous to that produced by an EeV neutrino interaction in ice. Continuous wave (CW) radio was transmitted into the target, and receiving antennas monitored for reflection of the transmitted signal from the ionization left in the wake of the shower. We detail the experiment and report on preliminary hints of a signal consistent with a radio reflection at a significance of 2.36$sigma$. We recommend another test-beam measurement in order to verify the signal.
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We report on the measurement of coherent radio emission from the electron beam sudden appearance at the Telescope Array Electron Light Source facility. This emission was detected by four independent radio detector setups sensitive to frequencies ranging from 50 MHz up to 12.5 GHz. We show that this phenomenon can be understood as a special case of coherent transition radiation by comparing the observed results with simulations. The in-nature application of this signal is given by the emission of cosmic ray or neutrino induced particle cascades traversing different media such as air, rock and ice.
We present the numerical simulations for an electron-beam-driven and loss-cone-driven electron-cyclotron maser (ECM) with different plasma parameters and different magnetic field strengths for a relatively small region and short time-scale in an attempt to interpret the recent discovered intense radio emission from ultracool dwarfs. We find that a large amount of electromagnetic field energy can be effectively released from the beam-driven ECM, which rapidly heats the surrounding plasma. A rapidly developed high-energy tail of electrons in velocity space (resulting from the heating process of the ECM) may produce the radio continuum depending on the initial strength of the external magnetic field and the electron beam current. Both significant linear polarization and circular polarization of electromagnetic waves can be obtained from the simulations. The spectral energy distributions of the simulated radio waves show that harmonics may appear from 10 to 70$ u_{rm pe}$ ($ u_{rm pe}$ is the electron plasma frequency) in the non-relativistic case and from 10 to 600$ u_{rm pe}$ in the relativistic case, which makes it difficult to find the fundamental cyclotron frequency in the observed radio frequencies. A wide frequency band should therefore be covered by future radio observations.
The T2K experiment observes indications of $ u_murightarrow u_e$ appearance in data accumulated with $1.43times10^{20}$ protons on target. Six events pass all selection criteria at the far detector. In a three-flavor neutrino oscillation scenario with $|Delta m_{23}^2|=2.4times10^{-3}$ eV$^2$, $sin^2 2theta_{23}=1$ and $sin^2 2theta_{13}=0$, the expected number of such events is 1.5$pm$0.3(syst.). Under this hypothesis, the probability to observe six or more candidate events is 7$times10^{-3}$, equivalent to 2.5$sigma$ significance. At 90% C.L., the data are consistent with 0.03(0.04)$<sin^2 2theta_{13}<$ 0.28(0.34) for $delta_{rm CP}=0$ and a normal (inverted) hierarchy.
Recent technological advances allowed the coherent optical manipulation of high-energy electron wavepackets with attosecond precision. Here we theoretically investigate the collision of optically-modulated pulsed electron beams with atomic targets and reveal a quantum interference associated with different momentum components of the incident broadband electron pulse, which coherently modulates both the elastic and inelastic scattering cross sections. We show that the quantum interference has a high spatial sensitivity at the level of Angstroms, offering potential applications in high-resolution ultrafast electron microscopy. Our findings are rationalized by a simple model.
Electron-tracking Compton camera, which is a complete Compton camera with tracking Compton scattering electron by a gas micro time projection chamber, is expected to open up MeV gamma-ray astronomy. The technical challenge for achieving several degrees of the point spread function is the precise determination of the electron-recoil direction and the scattering position from track images. We attempted to reconstruct these parameters using convolutional neural networks. Two network models were designed to predict the recoil direction and the scattering position. These models marked 41$~$degrees of the angular resolution and 2.1$~$mm of the position resolution for 75$~$keV electron simulation data in Argon-based gas at 2$~$atm pressure. In addition, the point spread function of ETCC was improved to 15$~$degrees from 22$~$degrees for experimental data of 662$~$keV gamma-ray source. These performances greatly surpassed that using the traditional analysis.
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