Search for photons with energies above 1018 eV using the hybrid detector of the Pierre Auger Observatory

THE PIERRE AUGER COLLABORATION, INCLUYE S. MOLLERACH

JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS

IOP PUBLISHING LTD

Lugar: Londres; Año: 2017

1475-7516

A search for ultra-high energy photons with energies above 1 EeV isperformed using nine years of data collected by the Pierre AugerObservatory in hybrid operation mode. An unprecedented separation powerbetween photon and hadron primaries is achieved by combiningmeasurements of the longitudinal air-shower development with theparticle content at ground measured by the fluorescence and surfacedetectors, respectively. Only three photon candidates at energies1-2 EeV are found, which is compatible with the expectedhadron-induced background. Upper limits on the integral flux ofultra-high energy photons of 0.027, 0.009, 0.008, 0.008 and 0.007km-2 sr-1 yr-1 arederived at 95% C.L. for energy thresholds of 1, 2, 3, 5 and 10 EeV.These limits bound the fractions of photons in the all-particle integralflux below 0.1%, 0.15%, 0.33%, 0.85% and 2.7%. For the first time thephoton fraction at EeV energies is constrained at the sub-percent level.The improved limits are below the flux of diffuse photons predicted bysome astrophysical scenarios for cosmogenic photon production. The newresults rule-out the early top-down models - in which ultra-highenergy cosmic rays are produced by, e.g., the decay of super-massiveparticles - and challenge the most recent super-heavy dark mattermodels.