Time distribution of the muons observed with the Muon Detector of the Pierre Auger Observatory

A. ALMELA; A. CANCIO; A. FUSTER; M. R. HAMPEL; M. JOSEBACHUILI; S. MÜLLER; M. RONCORONI; D. SCHMIDT; A. TABOADA; D. RAVIGNANI; B. ANDRADA; A. ETCHEGOYEN; B. GARCÍA; E. HOLT; A. LUCERO; M. PERLIN; F. SÁNCHEZ; M. SCORNAVACCHE; B. WUNDHEILER; J. M. FIGUEIRA; A. M. BOTTI; L. FERREYRO; N. GONZÁLEZ; J. HULSMAN; D. MELO; M. PLATINO; C. SARMIENTO-CANO; G. SILLI

Otro; Notas internas para la Colaboración Pierre Auger; 2019

The Pierre Auger and other contemporary observatories are directing most of their efforts to the quest for the chemical composition of the cosmic rays. It is believed that the best way to make progress in this long standing problem is to observe the same cosmic ray shower simultaneously with different type of detectors. An example of this approach is the Pierre Auger Observatory containing a surface anda fluorescence detector. Following this trend, the Collaboration decided in 2006 to construct a muon detector (MD) and, more recently, the installation of the surface scintillator detectors of AugerPrime.The surface detectors and fluorescence telescopes of Pierre Auger Auger measure signals as function of time. The time is expressed in the common GPS reference frame, so the relative timing among the signals of different detectors can be accounted for. For example, the particle timing allows the reconstruction of the shower geometry with the SD and the selection of the SD detector used in the hybrid reconstruction of the FD. In contrast with the SD and the FD, the MD originally counted muons but did not measure their arrival times as the muon content was the only observable sensitive to the mass composition that was considered during the detector design. However, afterwards time related measurements as the muon production depth were also envisaged as valuable tools to disentangle the chemical composition. In fact, the Collaboration already reported measurements of the muon production depth with the SD using events between 55 ◦ and 65 ◦ of zenith angle, observed by detectors more than 1700 m away from the axis. After applying this stringent distance cut, 481events above 2 × 10 19 eV were selected. The measurement of the muon production depth with the MD requires to measure the arrival timeof muons. In this work we explain how we manage to time the muons without adding a dedicated 1GPS hardware. From the arrival times we measured the time distribution of muons as function of the distance to the shower axis and compared it with the corresponding all-particle distribution measured by the SD. As an application of the muon timing we also reconstructed the geometry of the showers observed by the MD. Along the way we selected the median arrival time as the MD time observable and estimated its uncertainty. We calculated the angular resolution of the MD and measured the angle between the arrival directions reconstructed by the MD and the SD for events observed in coincidence.