[Paper Review] The Andyrchy-BUST experiment: primary spectrum and composition around the knee

V. B. Petkov|arXiv (Cornell University)|Nov 30, 2009

Advanced MRI Techniques and Applications3 citations

TL;DR

This study presents simultaneous measurements of the extensive air shower (EAS) size and high-energy muon (Eμ ≥ 230 GeV) components using the Andyrchy-BUST experiment, combining the Andyrchy EAS array and Baksan Underground Scintillation Telescope (BUST). The key finding is that a modified muon production function (MPF) with adjusted parameters yields better agreement with both muon and EAS size spectra than standard QGSJetII-03 model predictions, indicating a need to revise hadronic interaction models near the knee region (10^14–10^15 eV).

ABSTRACT

The main goal of the Andyrchy-BUST experiment is to study the primary cosmic rays spectrum and composition around the knee. The experimental data on the knee, as observed in the electromagnetic and high energy muon components, are presented. The electromagnetic component in our experiment is measured using the "Andyrchy" EAS array. High energy muon component (with 230 GeV threshold energy of muons) is measured using the Baksan Underground Scintillation Telescope (BUST). The location of the "Andyrchy" right above the BUST gives us a possibility for simultaneous measurements of both EAS components.

Motivation & Objective

• To determine the primary cosmic ray spectrum and composition around the knee (10^14–10^15 eV) using simultaneous measurements of EAS and muon components.
• To test the consistency of current hadronic interaction models (QGSJetII-03, Fluka) with multi-component EAS data.
• To identify discrepancies between simulated and observed EAS size and muon number spectra for different primary compositions.
• To derive a modified muon production function (MPF) that better fits experimental data across multiple observables.
• To constrain the primary composition across the knee by comparing simulated and measured correlations between EAS size and muon content.

Proposed method

• The Andyrchy EAS array (37 scintillation detectors, 5×10^4 m² area) measures EAS size in relativistic particle (r.p.) units via energy deposition and lateral distribution function fitting.
• The Baksan Underground Scintillation Telescope (BUST, 3180 detectors) measures high-energy muons (Eμ ≥ 230 GeV) with 0.7 m position and 1.5° direction resolution.
• Simultaneous triggers between Andyrchy and BUST are formed within 51.2 μs, enabling correlated analysis of EAS size and muon content.
• The NKG lateral distribution function is used to reconstruct EAS core position and size (Nr.p.) from measured energy depositions.
• Muon production function (MPF) is modeled as $ \overline{N}_{\mu}/A = b\left[\left(E_0/A\right)^\alpha - c\right]^\beta $, with parameters fitted to CORSIKA simulations.
• A modified MPF with $ b=0.0035 $, $ c=14 $, $ \alpha=0.42 $, $ \beta=1.54 $ is derived to improve agreement with experimental data.

Experimental results

Research questions

• RQ1 Does the standard QGSJetII-03 hadronic interaction model accurately describe the muon and EAS size spectra observed in the knee region?
• RQ2 What primary composition (proton vs. iron-like) best explains the simultaneous measurements of EAS size and high-energy muon content?
• RQ3 Can a modified muon production function (MPF) improve the agreement between simulation and experiment for both muon number and EAS size spectra?
• RQ4 How do the correlations between EAS size and muon content constrain the primary composition across the knee?
• RQ5 To what extent do discrepancies between simulation and data indicate limitations in current hadronic interaction models?

Key findings

• The standard QGSJetII-03-based MPF yields a muon spectrum that underestimates the observed muon number, particularly at higher energies.
• A modified MPF with parameters $ b=0.0035 $, $ c=14 $, $ \alpha=0.42 $, $ \beta=1.54 $ provides significantly better agreement with the measured integral muon number spectrum.
• The modified MPF results in an asymptotic muon energy dependence of $ \overline{N}_{\mu} \sim E_0^{0.647} $, differing from the standard model's $ E_0^{0.720} $.
• Both the proton-like and iron-like primary compositions fail to simultaneously fit the EAS size and muon number spectra when using the standard MPF.
• The modified MPF allows the first primary composition (proton-like) to achieve good agreement with both EAS size and muon data, suggesting a need to revise the MPF for hadronic models.
• The analysis indicates a heavier primary composition across the knee, with the muon content increasing more strongly with EAS size than predicted by standard models.