# The International Cosmic Ray Conference 2017

12-20 July 2017
BEXCO
Asia/Seoul timezone
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# Contribution

BEXCO - Room F(201/202/203/204)

# [CRI016] Probing QCD approach to thermal equilibrium with ultrahigh energy cosmic rays

## Speakers

• Jorge FERNANDEZ SORIANO

## Co-authors

• Aric HACKEBILL (Department of Physics, The Graduate Center, City University of New York)
• Luis ANCHORDOQUI (Department of Physics and Astronomy, Lehman College, City University of New York)
• Thomas PAUL (Department of Physics and Astronomy, Lehman College, City University of New York)
• Thomas WEILER (Department of Physics and Astronomy, Vanderbilt University)

## Description

The Pierre Auger Collaboration has reported an excess in the number of muons of a few tens of percent over expectations computed using extrapolation of hadronic interaction models tuned to accommodate LHC data, Very recently, we proposed an explanation for the muon excess assuming the formation of a deconfined quark matter (fireball) state in central collisions of ultrarelativistic cosmic rays with air nuclei. At the first stage of its evolution the fireball contains gluons as well as $u$ and $d$ quarks. The very high baryochemical potential inhibits gluons from fragmenting into $u ar u$ and $d ar d$, and so they fragment predominantly into $s ar s$ pairs. In the hadronization which follows this leads to the strong suppression of pions and hence photons, but allows heavy hadrons to be emitted carrying away strangeness. In this manner, the extreme imbalance of hadron to photon content provides a way to enhance the muon content of the air shower. In this communication we study theoretical systematics from hadronic interaction models used to describe the cascades of secondary particles produced in the fireball explosion. We compare the predictions of the leading LHC-tuned models (EPOS-LHC and QGSJet-II-04) considered in the Auger analysis.