Air Fluorescence Technique Research Articles

The History of Air Fluorescence

I describe the history of the use of the air-fluorescence technique in UHECR physics.

The Unreasonable Effectiveness of the Air-Fluorescence Technique in Determining the EAS Shower Maximum

We review all existing air-fluorescence measurements of the elongation rate of extensive air showers (slope of mean EAS shower maximum Xmax vs. log of shower energy E) above 1017 eV. We find remarkable agreement for all current and historic experiments over a 30 yr period for the energy range from 1017 to 3 × 1018 eV. The mean elongation rate in this energy interval is near 80 g/cm2/decade. Above this energy, experiments in the Northern hemisphere are in good agreement with an average elongation rate of 48 ± 10 g/cm2/decade while Southern hemisphere experiments have a flatter elongation rate of 26 ± 2 g/cm2/decade. We point out that, given the agreement at lower energies, possible systematic reasons for this difference are unlikely. Given this, the world elongation rate data alone may indicate a composition difference of UHECR in the Northern and Southern hemisphere and thus a diversity of UHECR sources in the Northern and Southern sky.

Intensity of muon bundles according to the NEVOD-DECOR cosmic ray experiment

Data of NEVOD-DECOR experiment on investigations of inclined cosmic ray muon bundles for a long time period (May 2012 – May 2020) are presented. Their comparison with the results of calculations based on simulations of extensive air shower hadron and muon components is carried out. The analysis showed that the observed intensity of muon bundles at primary particle energies of about 1018 eV and higher can be compatible with the expectation only under the assumption of an extremely heavy mass composition of cosmic rays. On the contrary, measurements of the depth of the shower maximum in the atmosphere in the experiments using air fluorescence technique, favour a light mass composition of primary cosmic rays at these energies.

Atmospheric monitor for Telescope Array experiment

The atmospheric monitoring is very important for the observation of air shower by air fluorescence technique. In the Telescope Array (TA) experiment, LIDAR (LIght Detection And Ranging) system and CLF (Central Laser Facility) system have been used for the measurement of atmospheric transparency. The LIDAR system is located in the southeast of TA site. The CLF is located in the center of the TA site. The usefulness of the CLF and LIDAR systems is demonstrated by analyzing the time variation of atmospheric transparency with the systems. The two atmospheric monitor systems are complementary. Therefore, monitoring efficiency is advanced by a new LIDAR system that was installed at CLF system. Clouds are observed with CCD camera, IR camera and eye scan visual check. In addition, we have also measured atmospheric parameters at the ground level using several weather systems.

Ultra-high energy cosmic rays: Setting the stage

The history of ultra-high energy cosmic ray physics is reviewed from the post-war era of arrays such as Volcano Ranch, Haverah Park and Akeno to the development of air-fluorescence and current hybrid arrays. The aim of this paper is to present the background information needed for a better understanding of the current issues in this field that are discussed in much greater depth in the rest of this conference. a. Pre-history: the discovery of cosmic radiation and the study of its penetrating power. This led to great debates between Millikan and Compton about the kinds of particles that composed it. The discovery of the latitude effect followed by the East-West effect conclusively proved that the majority of the cosmic ray particles were positively charged (protons and nuclei). b. Ancient history: the discovery that high energy cosmic radiation produced extensive air showers and that much of the cosmic radiation on the surface was the result of secondary processes in the atmosphere. This was also the era when the presence of very high energy particles in the primary radiation was clearly demonstrated (by B. Rossi, P. Auger and others). c. Middle Ages: the post-war development of large area surface detectors covering areas up to 10km 2 coming from the pioneering work of B. Rossi., J. Linsley and others. d. Renaissance: the development of fully calorimetric techniques based on air-fluorescence (by the Fly's Eye group, based on earlier work of J. Keuffel, K. Greisen and others) and the extension of ground arrays to 100km 2 (AGASA). e. Modern times: the refinement of air-fluorescence techniques (HiRes) and the construction of hybrid air-fluorescence/surface array detectors of unprecedented scale (Pierre Auger Observatory (PAO), Telescope Array (TA)). 2. POST-WAR DEVELOPMENTS

A parameterization of cosmic ray shower profiles based on shower width

Cosmic ray (CR) air showers, detected via the air fluorescence technique, are reconstructed in part using functions that parameterize the longitudinal profile of each shower. The profile parameterization yields the position of shower maximum, Xmax in gm cm−2, which is sensitive to the incident CR particle type: e.g. p, C/N/O, Fe or γ. The integral of the profile is directly related to the shower energy. The Pierre Auger fluorescence reconstruction uses the Gaisser–Hillas (GH) four-parameter form [5]. The HiRes group has used both the Gaisser–Hillas form and a three-parameter Gaussian in age form [7]. Historically analytic shower theory suggested yet other forms; the best known is a three-parameter form popularized by Greisen [6]. Our work now uses the shower full width half-maximum, fwhm, and shower asymmetry parameter, f, to unify the parameterization of all three profile functions. Furthermore, shower profiles expressed in terms of the new parameters: fwhm, f, have correlations greatly reduced over e.g. Gaisser–Hillas parameters X0, λ. This allows shower profile reconstructions to add constraints (if needed) on the mostly uncorrelated parameters fwhm, f.

Measurement of the flux of ultra high energy cosmic rays by the stereo technique

The High Resolution Fly’s Eye (HiRes) experiment has measured the flux of ultrahigh energy cosmic rays using the stereoscopic air fluorescence technique. The HiRes experiment consists of two detectors that observe cosmic ray showers via the fluorescence light they emit. HiRes data can be analyzed in monocular mode, where each detector is treated separately, or in stereoscopic mode where they are considered together. Using the monocular mode the HiRes collaboration measured the cosmic ray spectrum and made the first observation of the Greisen–Zatsepin–Kuzmin cutoff. In this paper we present the cosmic ray spectrum measured by the stereoscopic technique. Good agreement is found with the monocular spectrum in all details.

Atmospheric Monitoring for the Pierre Auger Observatory

The monitoring of atmospheric transparency plays a key role in the reconstruction of ultra high energy cosmic rays with the air fluorescence technique. A review of the instruments (LIDARs, Central Laser Facility, Aerosol Phase Function Monitor) for the detection and characterization of cloud and aerosol parameters in the Pierre Auger Observatory is given.

The FLASH thick-target experiment

A key assumption in the reconstruction of extensive air showers using the air fluorescence technique is that fluorescence is proportional to energy deposition at all depths in the shower. This ansatz, along with the supposition that particle distribution and energy loss can be well modeled by modern shower simulation software, must be thoroughly verified. We report here the results of the first direct measurement of air fluorescence yield as a function of shower depth, as performed in the thick-target phase of the FLASH (FLuorescence in Air from SHowers) experimental program at the SLAC Final-Focus Test Beam facility. We compare observed fluorescence light yields as a function of shower depth to concurrently measured charged particle yields, to the energy deposition predictions of the EGS and GEANT software packages, and to empirical energy-deposition models. We also examine the extent to which the relative yield versus shower depth is independent of wavelength within the fluorescence spectrum. We find the proportionality hypothesis to be well supported by the data, validating the use of fluorescence profiles in the study of ultra high energy cosmic rays.

Fluorescence in air excited by electrons from a 90Sr source

The air fluorescence technique is used to observe ultra-high energy cosmic rays (UHECRs). In this technique, fluorescence from air excited by electrons within an extensive air shower (EAS) under various pressure and temperature conditions is detected by a telescope. The primary energy of the UHECR is estimated from the amount of fluorescence. Since ground-based experiments, such as Fly's Eye, HiRes, Auger, Telescope Array, are carried out at high altitudes, the effects of water vapor may be negligible and the photon yields in dry air, which we have measured and reported so far, will be applicable. However, in case of space-based experiments such as JEM-EUSO, most events will be observed above the sea. Photon yields in moist air are measured with a 90Sr β source and compared to those in dry air at wavelengths of 337, 358 and 391 nm. The presence of water vapor considerably reduces the photon yield. The decrease in the photon yield in moist air should be taken into account to interpret the longitudinal development of EASs near the sea surface, although the effects around the shower maximum for most showers might be small.

On the fluctuations of the fluorescence photon yield of electrons in extensive air showers for different atmospheric conditions

The air fluorescence technique has long been used to detect extensive air showers and to reconstruct its geometry and energy. The fluorescence photon yield of an electron in air is of main importance in the reconstruction procedure. Several experiments are trying to measure in detail the dependency of the yield with energy. In this work we discuss the calculation of the fluorescence yield convoluted with the energy spectrum of particles in the shower as a function of age. We study the fluctuations of the yield resultant from different atmospheric conditions. We calculate the fluorescence yield as a function of height for the US Standard model and for the winter and summer conditions of the Auger Observatory in Argentine. Using the relation between average X max and energy we calculate the fluctuations between winter and summer seasons as a function of energy for proton and iron nuclei as primary particles. The influences of this fluctuation in the energy error as a function of energy are also discussed.

SIMULATIONS OF RADIO EMISSION FROM COSMIC RAY AIR SHOWERS

Radio emission from cosmic ray air showers has the potential to become an additional, cost-effective observing technique for cosmic ray research, being largely complementary to the well-established particle detector and air fluorescence techniques. We present Monte Carlo simulations of radio emission from extensive air showers in the scheme of coherent geosynchrotron radiation from electron-positron pairs gyrating in the earth's magnetic field. Preliminary results of our simulations are the predicted frequency, primary particle energy, shower zenith angle, shower azimuth angle and polarization dependence of the radio emission. These properties can be directly related to data measured by LOPES and other experiments.

Universality of electron distributions in high-energy air showers—Description of Cherenkov light production

The shower simulation code CORSIKA has been used to investigate the electron energy and angular distributions in high-energy showers. Based on the universality of both distributions, we develop an analytical description of Cherenkov light emission in extensive air showers, which provides the total number and angular distribution of photons. The parameterisation can be used e.g. to calculate the contribution of direct and scattered Cherenkov light to shower profiles measured with the air fluorescence technique.

New measurement on photon yields from air and the application to the energy estimation of primary cosmic rays

The air fluorescence technique is used to detect ultrahigh-energy cosmic rays (UHECR), and to estimate their energy. Of fundamental importance is the photon yield due to excitation by electrons, in air of various densities and temperatures. After our previous report, the experiment has been continued using a 90Sr β source to study the pressure dependence of photon yields for radiation in nitrogen and dry air. The photon yields in 15 wave bands between 300nm and 430nm have been determined. The total photon yield between 300nm and 406nm (used in most experiments) in air excited by a 0.85MeV electron is 3.81±0.13 (±13% systematics) photons per meter at 1013hPa and 20°C. The air density and temperature dependencies of 15 wave bands are given for application to UHECR observations.

Energy estimation of UHE cosmic rays using the atmospheric fluorescence technique

We use the CORSIKA air shower simulation program to review the method for assigning energies to ultra-high energy cosmic rays viewed with the air fluorescence technique. This technique uses the atmosphere as a calorimeter, and we determine the corrections that must be made to the calorimetric energy to yield the primary cosmic-ray energy.

Monitoring DC anode current of a grounded-cathode photomultiplier tube

Abstract The Pierre Auger Observatories (PAO) for the highest energy cosmic rays will make use of both the Cherenkov and Air Fluorescence techniques. Surface Detectors (SD) and Fluorescence Detectors (FD) will have to operate in a desert-type environment during at least 15 years. In order to avoid dust deposition, due to electrostatics, and other practical inconveniences derived from biasing the cathode with a negative potential, the 15 000 PMTs of the FD will operate in the grounded cathode configuration. Despite the fact that the anodes will remain at high voltage with respect to ground, the DC anode current, which varies with background light, will have to be recorded. We have developed a current monitoring system based on a novel optocoupled feedback circuit that allows sensitive, linear, and temperature-independent measurements of the DC anode current. A distinctive feature of this circuit is that it uses optical coupling between passive components at high voltage and active components near the ground potential. This represents a substantial improvement over classical solutions which require the supply of power to an active circuit at high voltage. We report on the first tests performed with both active and passive biasing networks which demonstrate the validity of this new method.