Chih-Ching Chen

Measurement of Pressure Dependent Fluorescence Yield of Air: Calibration Factor for UHECR Detectors

In a test experiment at the Final Focus Test Beam of the Stanford Linear Accelerator Center, the fluorescence yield of 28.5 GeV electrons in air and nitrogen was measured. The measured photon yields between 300 and 400 nm at 1 atm and 29 deg C are Y(760 Torr, air) = 4.42 +/- 0.73 and Y(760 Torr, nitrogen) = 29.2 +/- 4.8 photons per electron per meter. Assuming that the fluorescence yield is proportional to the energy deposition of a charged particle traveling through air, good agreement with measurements at lower particle energies is observed.

Air fluorescence measurements in the spectral range 300-420 nm using a 28.5-GeV electron beam

Abstract Measurements are reported of the yield and spectrum of fluorescence, excited by a 28.5xa0GeV electron beam, in air at a range of pressures of interest to ultra-high energy cosmic ray detectors. The wavelength range was 300–420xa0nm. System calibration has been performed using Rayleigh scattering of a nitrogen laser beam. In atmospheric pressure dry air at 304xa0K the total yield is 20.8xa0±xa01.6 photons per MeV.

Performance of two Askaryan Radio Array stations and first results in the search for ultrahigh energy neutrinos

Ultrahigh energy neutrinos are interesting messenger particles since, if detected, they can transmit nexclusive information about ultrahigh energy processes in the Universe. These particles, with energies nabove 1016 eV, interact very rarely. Therefore, detectors that instrument several gigatons of matter are nneeded to discover them. The ARA detector is currently being constructed at the South Pole. It is designed nto use the Askaryan effect, the emission of radio waves from neutrino-induced cascades in the South Pole nice, to detect neutrino interactions at very high energies. With antennas distributed among 37 widely nseparated stations in the ice, such interactions can be observed in a volume of several hundred cubic nkilometers. Currently three deep ARA stations are deployed in the ice, of which two have been taking data nsince the beginning of 2013. In this article, the ARA detector “as built” and calibrations are described. Data nreduction methods used to distinguish the rare radio signals from overwhelming backgrounds of thermal nand anthropogenic origin are presented. Using data from only two stations over a short exposure time of n10 months, a neutrino flux limit of 1.5 × 10−6 GeV=cm2=s=sr is calculated for a particle energy of n1018 eV, which offers promise for the full ARA detector.

First Constraints on the Ultra-High Energy Neutrino Flux from a Prototype Station of the Askaryan Radio Array

Abstract The Askaryan Radio Array (ARA) is an ultra-high energy ( > 10 17 xa0eV) cosmic neutrino detector in phased construction near the south pole. ARA searches for radio Cherenkov emission from particle cascades induced by neutrino interactions in the ice using radio frequency antennas ( ∼ 150 - 800 xa0MHz) deployed at a design depth of 200xa0m in the Antarctic ice. A prototype ARA Testbed station was deployed at ∼ 30 xa0m depth in the 2010–2011 season and the first three full ARA stations were deployed in the 2011–2012 and 2012–2013 seasons. We present the first neutrino search with ARA using data taken in 2011 and 2012 with the ARA Testbed and the resulting constraints on the neutrino flux from 10 17 - 10 21 xa0eV.

Comparison of air fluorescence and ionization measurements of EM shower depth profiles: Test of a UHECR detector technique

Measurements are reported on the fluorescence of air as a function of depth in electromagnetic showers initiated by bunches of 28.5 GeV electrons. The light yield is compared with the expected and observed depth profiles of ionization in the showers. It validates the use of atmospheric fluorescence profiles in measuring ultra high energy cosmic rays.

Near-Field Effects of Cherenkov Radiation Induced By Ultra High Energy Cosmic Neutrinos

The radio approach for detecting the ultra-high energy cosmic neutrinos has become a mature field. The Cherenkov signals in radio detection are originated from the charge excess of particle showers due to Askaryan effect. The conventional way of calculating the Cherenkov pulses by making Fraunhofer approximation fails when the sizes of the elongated showers become comparable with the detection distances. We present a calculation method of Cherenkov pulses based on the finite-difference time-domain (FDTD) method, and attain a satisfying effeciency via the GPU- acceleration. Our method provides a straightforward way of the near field calculation, which would be important for ultra high energy particle showers, especailly the electromagnetic showers induced by the high energy leptons produced in the neutrino charge current interactions.

The Strategy of Discrimination between Flavors for Detection of Cosmogenic Neutrinos

Abstract We propose a new method to identify flavors of ultra high energy cosmic neutrinos. Energy loss of leptons in matter provides important informations for the detection of neutrinos originated from high energy astrophysical sources. 50 years ago, Askaryan proposed to detect Cherenkov signals by radio wave from the negative charge excess of particle showers. The theory of Cherenkov pulses with Fraunhofer approximation was widely studied in the past two decades. However, at high energies or for high density materials, electromagnetic shower should be elongated due to the Landau-Pomeranchuck-Migdal (LPM) effect. As such the standard Fraunhofer approximation ceases to be valid when the distance between the shower and the detector becomes comparable with the shower length. We have performed Monte Carlo simulations recently to investigate this regime based on the finite-difference time-domain (FDTD) method, and modified time domain integration method. In this work, we adopt the deduced relationship between the radio signal and the cascade development profile to investigate its implication to lepton signatures. Our method provides a straightforward technique to identify the neutrino flavor through the detected Cherenkov signals.

DISTINGUISHABILITY OF NEUTRINO FLAVORS THROUGH THEIR DIFFERENT SHOWER CHARACTERISTICS

We propose a new flavor identification method to distinguish mu and tau type ultra high energy cosmic neutrinos (UHECN). Energy loss of leptons in matter is an important information for the detection of neutrinos originated from high energy astrophysical sources. 50 years ago, Askaryan proposed to detect Cherenkov radiowave signals emitted from the negative charge excess of neutrino-induced particle shower. The theory of Cherenkov radiation under Fraunhofer approximation has been widely studied in the past two decades. However, at high energies or for high density materials, electromagnetic shower should be elongated due to the Landau-Pomeranchuck-Migdal (LPM) effect. As such the standard Fraunhofer approximation ceases to be valid when the distance between the shower and the detector becomes comparable with the shower length. Monte Carlo simulations have been performed recently to investigate this regime. Here we adopt the deduced relationship between the radio signal and the cascade development profile to investigate its implication to lepton signatures. Our method provides a straightforward technique to identify the neutrino flavor through the detected Cherenkov signals.

Constraints on the ultra-high-energy neutrino flux from Gamma-Ray bursts from a prototype station of the Askaryan radio array

Abstract We report on a search for ultra-high-energy (UHE) neutrinos from gamma-ray bursts (GRBs) in the data set collected by the Testbed station of the Askaryan Radio Array (ARA) in 2011 and 2012. From 57 selected GRBs, we observed no events that survive our cuts, which is consistent with 0.12 expected background events. Using NeuCosmA as a numerical GRB reference emission model, we estimate upper limits on the prompt UHE GRB neutrino fluence and quasi-diffuse flux from 10 7 to 10 10 GeV. This is the first limit on the prompt UHE GRB neutrino quasi-diffuse flux above 10 7 GeV.

CHERENKOV RADIATION INDUCED BY COSMOGENIC NEUTRINOS IN NEAR-FIELD

The radio technique of cosmogenic neutrino detection, which relies on the Cherenkov signals coherently emitted from the particle showers in dense medium, has now become a mature field. We present an alternative approach to calculate such Cherenkov pulse by a numerical code based on the finite difference time-domain (FDTD) method that does not rely on the far-field approximation. We show that for a shower elongated by the LPM (Landau-Pomeranchuk-Migdal) effect and thus with a multi-peak structure, the generated Cherenkov signal will always be a bipolar and asymmetric waveform in the near-field regime regardless of the specific variations of the multi-peak structure, which makes it a generic and distinctive feature. This should provide an important characteristic signature for the identification of ultra-high energy cosmogenic neutrinos.