More Like this

1. Search for point sources of ultra-high-energy photons with the Telescope Array surface detector

   https://doi.org/10.1093/mnras/stz3618  

   Abbasi, R.U. ( February 2020 , Monthly notices of the Royal Astronomical Society)

   Ultra-high-energy (UHE) photons are an important tool for studying the high-energy Universe. A plausible source of photons with exa-eV (EeV) energy is provided by UHE cosmic rays (UHECRs) undergoing the Greisen–Zatsepin–Kuzmin process (Greisen 1966; Zatsepin & Kuzmin 1966) or pair production process (Blumenthal 1970) on a cosmic background radiation. In this context, the EeV photons can be a probe of both UHECR mass composition and the distribution of their sources (Gelmini, Kalashev & Semikoz 2008; Hooper, Taylor & Sarkar 2011). At the same time, the possible flux of photons produced by UHE protons in the vicinity of their sources by pion photoproduction or inelastic nuclear collisions would be noticeable only for relatively near sources, as the attenuation length of UHE photons is smaller than that of UHE protons; see, for example, Bhattacharjee & Sigl (2000) for a review. There also exists a class of so-called top-down models of UHECR generation that efficiently produce the UHE photons, for instance by the decay of heavy dark-matter particles (Berezinsky, Kachelriess & Vilenkin 1997; Kuzmin & Rubakov 1998) or by the radiation from cosmic strings (Berezinsky, Blasi & Vilenkin 1998). The search for the UHE photons was shown to be the most sensitive method of indirect detection of heavy dark matter (Kalashev & Kuznetsov 2016, 2017; Kuznetsov 2017; Kachelriess, Kalashev & Kuznetsov 2018; Alcantara, Anchordoqui & Soriano 2019). Another fundamental physics scenario that could be tested with UHE photons (Fairbairn, Rashba & Troitsky 2011) is the photon mixing with axion-like particles (Raffelt & Stodolsky 1988), which could be responsible for the correlation of UHECR events with BL Lac type objects observed by the High Resolution Fly’s Eye (HiRes) experiment (Gorbunov et al. 2004; Abbasi et al. 2006). In most of these scenarios, a clustering of photon arrival directions, rather than diffuse distribution, is expected, so point-source searches can be a suitable test for photon - axion-like particle mixing models. Finally, UHE photons could also be used as a probe for the models of Lorentz-invariance violation (Coleman & Glashow 1999; Galaverni & Sigl 2008; Maccione, Liberati & Sigl 2010; Rubtsov, Satunin & Sibiryakov 2012, 2014). The Telescope Array (TA; Tokuno et al. 2012; Abu-Zayyad et al. 2013c) is the largest cosmic ray experiment in the Northern Hemisphere. It is located at 39.3° N, 112.9° W in Utah, USA. The observatory includes a surface detector array (SD) and 38 fluorescence telescopes grouped into three stations. The SD consists of 507 stations that contain plastic scintillators, each with an area of 3 m2 (SD stations). The stations are placed in the square grid with 1.2 km spacing and cover an area of ∼700 km2. The TA SD is capable of detecting extensive air showers (EASs) in the atmosphere caused by cosmic particles of EeV and higher energies. The TA SD has been operating since 2008 May. A hadron-induced EAS significantly differs from an EAS induced by a photon because the depth of the shower maximum Xmax for a photon shower is larger, and a photon shower contains fewer muons and has a more curved front (see Risse & Homola 2007 for a review). The TA SD stations are sensitive to both muon and electromagnetic components of the shower and therefore can be triggered by both hadron-induced and photon-induced EAS events. In the present study, we use 9 yr of TA SD data for a blind search for point sources of UHE photons. We utilize the statistics of the SD data, which benefit from a high duty cycle. The full Monte Carlo (MC) simulation of proton-induced and photon-induced EAS events allows us to perform the photon search up to the highest accessible energies, E ≳ 1020 eV. As the main tool for the present photon search, we use a multivariate analysis based on a number of SD parameters that make it possible to distinguish between photon and hadron primaries. While searches for diffuse UHE photons were performed by several EAS experiments, including Haverah Park (Ave et al. 2000), AGASA (Shinozaki et al. 2002; Risse et al. 2005), Yakutsk (Rubtsov et al. 2006; Glushkov et al. 2007, 2010), Pierre Auger (Abraham et al. 2007, 2008a; Bleve 2016; Aab et al. 2017c) and TA (Abu-Zayyad et al. 2013b; Abbasi et al. 2019a), the search for point sources of UHE photons has been done only by the Pierre Auger Observatory (Aab et al. 2014, 2017a). The latter searches were based on hybrid data and were limited to the 1017.3 < E < 1018.5 eV energy range. In the present paper, we use the TA SD data alone. We perform the searches in five energy ranges: E > 1018, E > 1018.5, E > 1019, E > 1019.5 and E > 1020 eV. We find no significant evidence of photon point sources in all energy ranges and we set the point-source flux upper limits from each direction in the TA field of view (FOV). The search for unspecified neutral particles was also previously performed by the TA (Abbasi et al. 2015). The limit on the point-source flux of neutral particles obtained in that work is close to the present photon point-source flux limits. 

   more » « less
2. Testing the Compatibility of the Depth of the Shower Maximum Measurements performed at Telescope Array and the Pierre Auger Observatory: Auger-TA Mass Composition Working Group Report

   https://doi.org/10.1051/epjconf/202328302008  

   Bergman, Douglas ; Bellido, Jose ; de Souza, Vitor ; Engel, Ralph ; Gerber, Zane ; Kim, JiHyun ; Mayotte, Eric ; Tkachenko, Olena ; Unger, Michael ; Yushkov, Alexey ( January 2023 , EPJ Web of Conferences)

   De Mitri, I. ; Barbato, F.C.T. ; Boncioli, D. ; Evoli, C. ; Pagliaroli, G. ; Salamida, F. (Ed.)

   The Telescope Array and the Pierre Auger Observatory estimate the composition of ultra-high-energy cosmic rays by observing the distribution of depths of air-shower maxima, X max . Both experiments directly observe the longitudinal development of air showers using fluorescence telescopes with surface particle detectors used in conjunction to provide precision in determining air-shower geometry. The two experiments differ in the details of the analysis of events, so a direct comparison of X max distributions is not possible. The Auger – Telescope Array Composition Working Group presents their results from a technique to compare X max measurements from Auger with those of Telescope Array. In particular, the compatibility of the first two moments of the X max distributions of Auger with the data from the Black Rock Mesa and Long Ridge detectors of the Telescope Array is tested for energies above 10 18.2 eV. Quantitative comparisons are obtained using air-shower simulations of four representative species made using the Sibyll 2.3d high-energy interaction model. These are weighted to fit the fractional composition seen in Auger data and reconstructed using the Telescope Array detector response and analysis methods. 

   more » « less
3. Direct measurement of the muonic content of extensive air showers between $$\mathbf { 2\times 10^{17}}$$ and $$\mathbf {2\times 10^{18}}~$$eV at the Pierre Auger Observatory

   https://doi.org/10.1140/epjc/s10052-020-8055-y  

   Aab, A. ; Abreu, P. ; Aglietta, M. ; Albury, J. M. ; Allekotte, I. ; Almela, A. ; Alvarez Castillo, J. ; Alvarez-Muñiz, J. ; Anastasi, G. A. ; Anchordoqui, L. ; et al ( August 2020 , The European Physical Journal C)

   null (Ed.)

   Abstract The hybrid design of the Pierre Auger Observatory allows for the measurement of the properties of extensive air showers initiated by ultra-high energy cosmic rays with unprecedented precision. By using an array of prototype underground muon detectors, we have performed the first direct measurement, by the Auger Collaboration, of the muon content of air showers between $$2\times 10^{17}$$ 2 × 10 17 and $$2\times 10^{18}$$ 2 × 10 18 eV. We have studied the energy evolution of the attenuation-corrected muon density, and compared it to predictions from air shower simulations. The observed densities are found to be larger than those predicted by models. We quantify this discrepancy by combining the measurements from the muon detector with those from the Auger fluorescence detector at $$10^{{17.5}}\, {\mathrm{eV}} $$ 10 17.5 eV and $$10^{{18}}\, {\mathrm{eV}} $$ 10 18 eV . We find that, for the models to explain the data, an increase in the muon density of $$38\%$$ 38 % $$\pm 4\% (12\%)$$ ± 4 % ( 12 % ) $$\pm {}^{21\%}_{18\%}$$ ± 18 % 21 % for EPOS-LHC , and of $$50\% (53\%)$$ 50 % ( 53 % ) $$\pm 4\% (13\%)$$ ± 4 % ( 13 % ) $$\pm {}^{23\%}_{20\%}$$ ± 20 % 23 % for QGSJetII-04 , is respectively needed. 

   more » « less
4. The Beamforming Elevated Array for COsmic Neutrinos (BEACON): A Radio Detector for Earth-Skimming Tau Neutrinos

   Zeolla, A for ( June 2022 , 9th International Workshop on Acoustic and Radio EeV Neutrino Detection Activities - ARENA2022)

   When ultrahigh energy tau neutrinos skim the Earth, they can generate tau leptons that then decay in the atmosphere, forming upgoing extensive air showers. The Beamforming Elevated Array for COsmic Neutrinos (BEACON) is a novel detector concept that utilizes a mountaintop radio interferometer to search for the radio emission due to these extensive air showers. The prototype, located at the White Mountain Research Station in California, consists of 4 custom crossed-dipole antennas operating in the 30-80 MHz range and uses a directional interferometric trigger to achieve reduced thresholds and background rejection. The prototype will first be used to detect extensive air showers from down-going cosmic rays to validate the detector model. In this talk, we give an overview of the BEACON concept and the status of its prototype. We also discuss the ongoing cosmic ray search which utilizes both data analysis and simulation. 

   more » « less
5. Modeling and Validating RF-Only Interferometric Triggering with Cosmic Rays for BEACON

   https://doi.org/10.22323/1.395.1072  

   Zeolla, Andrew ; Wissel, S. A. ; Alvarez-Muñiz, J. ; Carvalho Jr., W. ; Cummings, A. C. ; Curtis-Ginsberg, Z. ; Deaconu, C. ; Hughes, K. ; Ludwig, A. ; Mulrey, K. ; et al ( March 2022 , 37th International Cosmic Ray Conference (ICRC2021))

   When Earth-skimming tau neutrinos interact within the Earth, they generate upgoing tau leptons that can decay in the atmosphere, forming extensive air showers. The Beamforming Elevated Array for COsmic Neutrinos (BEACON) is a novel detector concept that utilizes a radio interferometer atop a mountain to search for the radio emission due to these extensive air showers. The prototype, located at the White Mountain Research Station in California, consists of 4 crossed-dipole antennas operating in the 30-80 MHz range and uses a directional interferometric trigger for reduced thresholds and background rejection. The prototype will first be used to detect down-going cosmic rays to validate the detector model. A Monte-Carlo simulation was developed to predict the acceptance of the prototype to cosmic rays, as well as the expected rate of detection. In this simulation, cosmic ray induced air showers with random properties are generated in an area around the prototype array. It is then determined if a given shower triggers the array using radio emission simulations from ZHAireS and antenna modelling from XFdtd. Here, we present the methodology and results of this simulation. 

   more » « less