ULTRA-HIGH ENERGY COSMIC RAY COMPOSITION and MUON CONTENT vs. HADRONIC MODELS Esteban Roulet Bariloche, Argentina
Many observables are sensitive to CR composition Shower maximum TA APP 64 (2014) Auger PRD 90 (2014) Muon production depth Muon number Phys Rev L (2016) inclined vertical Phys Rev D (2014) Phys Rev D (2015) but inferred CR masses dependent on hadronic models
HADRONIC SHOWERS Hadronic interactions produce large number of pions (multiplicity n tot) Neutral pions feed EM component, charged pions reinteract multiplying again the number of hadrons. After 5-6 generations pions can decay muons and neutrinos (typically E EM 0.9 E tot while E ν + Eμ 0.1 E tot ) E 0 /ntot X max λ I + X R ln Ec ( ) λ I σ 1 p air Nuclei behave as A nucleons with E n= E 0 / A less penetrating, smaller fluctuations E=30 EeV
Hadronic interactions int : (inel) - 0 + multiple particle production inelasticity, multiplicity, secondary spectrum in -air (baryon-antibaryon, 0 production) leading hadron (elasticity, spectrum,..) Hadronic models Targeted to air showers (Gribov-Regge FT) Targeted to colliders Pythia, Herwig, Sherpa (emphasis in transverse production) Perturbative QCD, resummation, PDF,.. Multiple parton interactions, soft-cutoff mimic g saturation at low x, Fragmentation & hadronization from phenomenological fits (Lund, cluster,...) Sibyll 2.1 QGSJet 01 DPMJET (<2001) QGSJET II-03 QGSJet II-04 Sibyll 2.3 QGSJet III EPOS EPOS-LHC (~2013) EPOS III (> 2015) soft processes via pomeron exchanges differ in leading particles, Lund/string fragmentation, color reconnection, inclusion of hard processes, partonic energy conservation,... Low energies, < 200 GeV, dealt with Gheisha, Fluka,UrQMD
knee E 2.7 2nd knee E 3 E 3.3 ankle E 2.7 GZK? Tevatron just below the knee, LHC just around the second knee
CONSTRAINTS FROM LHC Some results in central region ( ~0) from CMS, Atlas and Alice results in endcap/forward ( ) from Totem, Castor, LHCf, improved hadronic models Charged multiplicity, cross section, neutral particle production,... η ln (tan(θ/2))
Ralf Ulrich
PROTON-AIR CROSS SECTION FROM AIR SHOWERS Xmax distribution sensitive to depth of first interaction to p-air cross-section exp( X max /Λ η ) 18<log(E/eV)<18.5 Would be steeper for larger cross section Inferred p-air cross section looks 'normal' Auger PRL 2012
AUGER ICRC 2015 17.8<log(E/eV)<18 18<log(E/eV)<18.5
Energy range 18 < log (E/eV) < 18.5 guarantees that systematic due to He polution are not too large
TA measurement ArXiv 1505.01860 PRD 18.3 < log(e/ev) < 19.3 From Glauber theory one can obtain pp cross section and compare with accelerators
Average Xmax vs E and model predictions for p/fe Hadronic models before LHC Hadronic models after LHC Pierog 2014 ( Compared to QGSJET CRs are now 'heavier' )
f19: change wrt to proton Sibyll at 10 EeV
COMPOSITION FROM Xmax TA APP 64 (2014) Auger PRD 90 (2014) When compared to the same reference model the results are consistent HiRes & TA: Xmax with detector bias, Auger: cuts to have unbiased Xmax they should not be plotted together
Auger sets cuts so as to have unbiased Xmax TA include detector bias in simulations Simulated events fitting Xmax Auger data analysed alla TA Now they can be plotted together results actually agree! arxiv:1503.07540
Auger fit with 4 mass components: p, He, N and Fe 1 EeV 10 EeV From light to heavy vs. hadronic models >30 EeV PRD 2014
Composition vs. E & hadronic models p suppressed above 5 EeV, no Fe, rigidity dependent cutoff? Auger, PRD 2014
Trying to explain both spectrum and composition: arxiv:1612.07155 note that hard spectra, dn/de ~ E-1, seems to be required in mixed models to avoid too much mixture at given E, i.e. to reduce RMS(Xmax)
IN THE PeV to EeV RANGE Kascade (Ne and Nmu) Inferred composition across the knee depends on hadronic model considered (old models tuned below the knee) Kascade Grande Fe knee and p recovery features model dependent 1.9 2.1
KG with updated models features are consistent (LHC energies ~ 2nd knee) Would be nice to see updated analysis from Kascade
THE MUONIC COMPONENT vertical Ralph Engel
DEPTH OF MUON PRODUCTION from timing in SD 55 < < 65 Xμmax also suggests transition to heavies, and can discriminate hadronic models EPOS LHC produce muons too deep
(hybrid showers 18.8<log(E/eV)<19.2)
using inclined hybrid showers, compare simulations with similar X max with signal measured at ground need to rescale muons by R ~1.3 to 1.6 Use 62o < < 80o E > 4 EeV (reference model: QGSJet II-03 proton 10 EeV)
Sub-showers from 100 highest energy interactions carry most of the energy but contribute little to muons, which result from low energy interactions after >5 generations Ulrich
Electrons and muons at ground vs. model (at X=1000 g/cm2) E em E 0 E had ng 2 E had E 0 ( ) 3 E had N μ Ec Charge ratio: 2/3 1-c
Sibyll 2.3 includes enhanced 0 production observed in NA22 may account for increased N larger than EPOS/QGSJet by ~ 30% (NA61 C)
Muon number is strongly correlated to invisible energy (muons + neutrinos) in EAS
Use simulations to parameterize Einv (Xground-Xmax,Ecal,S(1000)) quite independent from model or composition Auger data (Mariazzi, Kyoto 2016) the missing energy determined is closer to that expected from Fe than that from protons
Energy Calibration Surface detectors calibrated with Fluorescence detector FD (calorimetric) energy largely independent on composition and hadronic models Atmospheric attenuation derived from data (constant intensity) S38=S(1000)/CIC(θ) MC energy too large Rescaled with FD Proton QGSJET II-03 AGASA energy overestimated
Other possible effects: If standard explanations were to fail:
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Measuring muons directly: Auger Prime