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Muon measurements at the Pierre Auger Observatory
by Dariusz Góra
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Submission summary
Authors (as Contributors):  Dariusz Gora 
Submission information  

Arxiv Link:  https://arxiv.org/abs/2209.13392v1 (pdf) 
Date submitted:  20220929 12:28 
Submitted by:  Gora, Dariusz 
Submitted to:  SciPost Physics Proceedings 
Proceedings issue:  51st International Symposium on Multiparticle Dynamics (ISMD2022) 
Ontological classification  

Academic field:  Physics 
Specialties: 

Approach:  Experimental 
Abstract
The Pierre Auger Observatory is the world's largest detector for observation of ultrahighenergy cosmic rays (UHECRs) (above the energy of $10^{17}$ eV). It consists of a Fluorescence Detector (FD) and an array of particle detectors known as the Surface Detector (SD). Observations of extensive air showers by the Observatory can be used to probe hadronic interactions at high energy, in a kinematic and energy region inaccessible to experiments at manmade accelerators and to measure the muon component of the shower. Air showers induced by different primaries have different muon contents. With increasing mass of the primary cosmic ray particle, it is expected that the muon content in the corresponding air showers should also increase. Recent results obtained from the Pierre Auger Observatory and other experiments indicate that all the shower simulations underestimate the number of muons in the showers compared to the data. This is the socalled muon deficit. In this paper we briefly review the muon measurements, and present in more detail recent results on fluctuations in the muon number. These results provide new insights into the origin of the muon deficit in air shower simulations and constrain the models of hadronic interactions at ultrahigh energies. With the current design of the surface detectors it is also difficult to reliably separate the contributions of muons to the SD signal from the contributions of photons, electrons, and positrons. Therefore, we also present a new method to extract the muon component of the signal time traces recorded by each SD station using recurrent neural networks. The combination of such algorithms, with the future data collected by the upgraded Pierre Auger Observatory, will be a major step forward, as we are likely to achieve an unprecedented resolution in mass estimation on an eventbyevent basis.
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Submission & Refereeing History
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Reports on this Submission
Anonymous Report 1 on 20221212 (Invited Report)
Strengths
1. Relevant. This paper presents the status update on the issue of "muon deficit" observed in extended air showers.
2. Well written.
Weaknesses
1. Nothing obvious to me. The paper looks good.
Report
This paper is appropriate for publication in this proceedings. I have only one question and a minor suggestion to the text.
Requested changes
1. The definition of R_\mu is not completely clear to me. What's the difference between integrated number of muons and total number of muons? Is the total number independent of energy? I'm not suggesting a change to the text per se. But a clarification.
2. Page 2, 2nd paragraph: "60% larger what" > "60% larger than what"
Author: Dariusz Gora on 20230102 [id 3200]
(in reply to Report 1 on 20221212)
Dear Reviewer,
Thanks very much for your comments, and please find below my answers:

Reviewer: "The definition of R_\mu is not completely clear to me. "
Answer: The R_\mu is the integrated number of muons at ground divided by the total number of muons N^{MC}{\mu} at the ground obtained by integrating the reference 2D model. R\mu= 1 in fact corresponds to N_\mu = 1.455 × 10^7 muons at the ground with energies above 0.3 GeV.
Reviewer:" What's the difference between integrated number of muons and total number of muons?"
Answer: In this context, the integrated number of muons N_{mu} is the value calculated for real event by using a maximumlikelihood method with the 2D reference model included in the fit, see for more details https://arxiv.org/pdf/1407.3214.pdf.
The total number of muons N^MC_\mu= ∫ dy ∫ ρ_{\mu,19} dx is obtained by integrating the reference 2D model, where ρ_{\mu,19} is the parametrized ground muon density i.e. a two dimensional function of position coordinates (x, y), for a proton shower simulated at 10^{19} eV with the hadronic interaction model QGSJetII03. It was shown in detailed studies that the attenuation and shape of ρ_{\mu,19} depend very weakly on the cosmicray energy E and mass A for showers with zenith angle larger than 60 deg.
The number of muons N_\mu that have reached the ground is obtained and normalized to the number of muons N_{\mu,19} in the reference 2D distribution i.e. R_\mu= N_{mu}/N_{\mu,19}
Reviewer: "Is the total number independent of energy?"
Answer: As above, the total number of muons N^MC_{\mu} = ∫ dy ∫ ρ_{\mu,19} dx is obtained by integrating the 2D reference model. The attenuation and shape of muon density ρ_{\mu,19} depend very weakly on the cosmicray energy E and mass A for showers with zenith angle larger than 60 deg.
Reviewer: "I'm not suggesting a change to the text per se. But a clarification. "

Page 2, 2nd paragraph: "60% larger what" > "60% larger than what"
This typo is now corrected in new version, see attached file D_Gora_ISMD2022v2.pdf for this answer.
Best wishes Dariusz Gora
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Anonymous on 20230111 [id 3227]
(in reply to Dariusz Gora on 20230102 [id 3200])Thank you very much for the clarification. I understand now. I'd suggest then something along these lines: R_mu is the ratio between the integrated number of muons in the event and the total expected number of muons.
Anonymous on 20221212 [id 3127]
This paper is an update report of the issue of "muon deficit" for extensive air showers observed with the largest cosmicray detectors. The paper is well written and appropriate for publication in this proceedings. I have only one question and a minor suggestion. My question is about the definition of R_\mu. It's not clear to me the difference between the integrated number of muon and the total number of muons. Is the total number not a function of energy?
The minor suggestion is in page 2, second paragraph: I'd replace "60% larger what" with "60% larger than what".