OBSERVATORY Studies on UHECR composition and hadronic interactions by the Pierre Auger Observatory Alexey Yushkov for the Pierre Auger Collaboration http://www.auger.org/archive/authors 7.html Universität Siegen, Germany Very High Energy Phenomena in the Universe, Quy Nhon, August 7,
Outline Depth of shower maximum X max and σ(x max ) Eun-Joo Ahn, talk at the ICRC (arxiv:7.559) interpretation in terms of logarithmic mass JCAP () 6 (arxiv:.667) Muon production depth Phys. Rev. D 9 () (arxiv:7.599) Muons in highly inclined air showers Submitted to Phys. Rev. D Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory /7
The Pierre Auger Observatory Location: Mendoza province, Argentina Fluorescence detector (FD): [longitudinal profile] + fluorescence telescopes at locations duty cycle % Surface detector (SD): [lateral distribution] area of km 66 water Cherenkov detectors at 5 m spacing duty cycle % Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory /7
Update on X max measurements 8 years of data / / energies E > 7.8 ev the highest energy is 79 ± EeV 987 high-quality FD events systematics: below g/cm resolution: 6 g/cm at 7.8 ev 5 g/cm for E > 9. ev event 68 SD CO LA CO LA )] de/dx [PeV/(g/cm χ /Ndf= 7.7/6 8 6 LM LM LL 65 7 75 8 85 9 95 E [EeV] LL 7 75 76 77 78 79 X max [g/cm ] 6 8 slant depth [g/cm ] Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory /7
First two moments of X max distributions ] X max [g/cm 8 8 8 78 76 7 7 7 EPOS-LHC QGSJetII- Sibyll. proton iron ] ) [g/cm max σ(x 9 8 7 6 5 Auger preliminary proton 68 66 iron 8 9 E [ev] 8 9 E [ev] Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory 5/7
Elongation rate d X max /d lg E ] X max [g/cm 8 8 8 78 76 7 7 7 68 66 667 98 5 6 859 65 8 59 6 Auger preliminary 7 9 96 6 8 single line: χ /Ndf = 8./6, P =.5 broken line: χ /Ndf =./, P =.7-9 8 9 E [ev] E < E E > E D = d X max /d lg E [g/cm /decade] Data Models, A = const 8. ± 5.5 (stat.) 9.9 ±.7 (stat.) 5 6 lg(e /ev) = 8. +.6. (stat.) Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory 6/7
.5.5 ln A.5.5.5 X max X p max ln A D / ln(); 7.8 8 8. 8. 8.6 8.8 9 9. 9. 9.6 9.8 log (E/eV).5 7.8 8 8. 8. 8.6 8.8 9 9. 9. 9.6 9.8 log (E/eV).5 SIBYLL..5 EPOS-LHC.5 QGSJet II-.5.5.5.5.5.5.5.5.5 7.8 8 8. 8. 8.6 8.8 9 9. 9. 9.6 9.8 log (E/eV) 7.8 8 8. 8. 8.6 8.8 9 9. 9. 9.6 9.8 log (E/eV) 7.8 8 8. 8. 8.6 8.8 9 9. 9. 9.6 9.8 log (E/eV).5 SIBYLL. transition from lighter to heavier composition above EeV.5.5 Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory 7/7
Variance of masses σ ln A σ (X max ) σsh + σ ln A (D / ln()) σln A from Auger Data using Air Shower Simulations σ sh shower-to-shower X max fluctuations for a fixed mass; σln A : zero for pure compositions; for 5% p 5% Fe lna σ SIBYLL. lna σ EPOS-LHC lna σ QGSJet II- - - - - 7.8 8 8.8.8.6 8.8 9 9.9.9.6 9.8 log (E/eV) - 7.8 8 8.8.8.6 8.8 9 9.9.9.6 9.8 log (E/eV) - 7.8 8 8.8.8.6 8.8 9 9.9.9.6 9.8 log (E/eV) transition: mixed pure? possible problems for QGSJetII? (σln A <, but within σ) negative variance using QGSJETII- (but within systematics) Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory 8/7
Combining σln A and ln A models are consistent with mixed composition within systematic uncertainties ] [g/cm X max 8 8 8 78 76 7 7 7 68 ] ) [g/cm max σ(x 66 8 9 E [ev] lna σ Sibyll. lna σ EPOS-LHC lna σ QGSJetII- - - - - - -.5.5.5.5.5.5.5.5.5.5.5.5 line indicates the evolution of mass composition with energy Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory 9/7
Combining σln A and ln A models are consistent with mixed composition within systematic uncertainties ] [g/cm X max 8 8 8 78 76 7 7 7 68 ] ) [g/cm max σ(x 66 8 9 E [ev] lna σ Sibyll. + σ sys lna σ EPOS-LHC + σ sys lna σ QGSJetII- + σ sys - - - - - -.5.5.5.5.5.5.5.5.5.5.5.5 line indicates the evolution of mass composition with energy Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory 9/7
Muon production depth (MPD) Method: use muon arrival times to get MPD X µ z ( r ) c(t t ε ) c(t t ε ) + z π X µ = ρ(z )dz z t ε mean kinematic delay; z π pion decay length Analysis details data period / /; energies > EeV (more muons/event); zenith angles [55 ; 65 ] (low EM contamination); distances from the core 7 m < r < m; dn µ /dx [a.u.] 5 MPD for an event with E = ( ± ) EeV fit: Gaisser Hillas function 8 events after selection; 5 systematic uncertainty 7 g/cm ; resolution: (8) g/cm at 9. ev for p (Fe) 5 g/cm at. ev 5 6 8 µ X [g/cm ] Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory /7
Mean reconstructed MPD D µ = d Xµ max /d lg E [g/cm /decade] Data 5 ± (stat.) ± (sys.) Models 5.9 ±. (proton) 8. ±. (iron) ] [g/cm µ max X 6 55 proton 5 98 9 7 5 iron Epos-LHC QGSJetII- 9 9 E [ev] EPOS LHC predictions above data Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory /7
Mean logarithmic mass: MPD vs X max Inconsistent ln A from X max and MPD for EPOS LHC 7 6 QGSJetII- µ Xmax X max 7 6 Epos-LHC 5 Fe 5 Fe p p 8 9 E [ev] 8 9 E [ev] EPOS LHC deeper X µ max (larger elasticity) is due to better description of LHC rapidity-gap distributions (see talk of T. Pierog) Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory /7
Muons in highly inclined events Method: measure muon scale factor N 9 wrt muon reference density profiles ρ µ,9 for EeV proton Universal features ρ µ = N 9 ρ µ,9 ( r; θ, Φ) Convert to R µ = Ndata 9 N9 MC ρ µ,9 shape weakly depends on energy and mass; ρ µ,9 is consistent for different models and EAS codes; N 9 is independent of the zenith angle. reference profile ρ µ,9 (hits/station) MC: proton, QGSJet II- E = 9 ev θ = 8 φ = 5 8 9.5 6 5 km km km Analysis details 5 5 data period / /; energies > EeV (% trigger); zenith angles [6 ; 8 ] (low EM contamination); 7 events after selection; R µ systematic uncertainty %. 7 Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory /7
Mean muon scale R µ. Rµ Calibration for hybrid events Fit: Rµ = a(e/ 9 ev) b 7 Auger hybrid events events 5 5 stdev.±. (Rµ Rµ )/ Rµ 9 E/eV Rµ /(E/ 9 ev)...8.6... Auger data EPOS LHC QGSJet II- Fe p 9 E/eV R data µ is larger than MC values for iron, at odds with ln A from X max similar conclusions for vertical showers can be found in G. Farrar and B. Kegl talks at the ICRC systematic uncertainty on R µ is 8% Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory /7
Mean logarithmic muon scale ln R µ ln Rµ..8.6... Fe EPOS LHC QGSJet II- QGSJet II- QGSJet N He E = 9 ev, θ = 67 Auger data 68 7 7 7 76 78 8 8 X max /gcm p Auger data lnr µ ( 9 ev).6 ±.6 +.68. (sys.) Fe.8.5 ±.7 EPOS LHC +.5. p (sys.).97 Fe.5.5 ±.7 QGSJet II- +.6.8 p (sys.).6 Fe.58.6 ±.7 QGSJet II- +..5 p (sys.) -.6 Fe.7.6 ±. QGSJet +..5 p (sys.).9....6.8 muon content in MC for ln A from X max is ( 8)% smaller than measured values; minimal difference on R µ at.σ (sys.) is between data and EPOS LHC Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory 5/7
Summary Mass composition Elongation rates (if hadronic models fairly describe them) X max analysis: light composition below EeV; then increase of the primary mass up to EeV; muon production depth: indications on increase of ln A for E > EeV; muon scale R µ : indications on increase of ln A for E > EeV. Conversion of X max to the logarithmic mass all models are consistent with mixed composition within systematic uncertainties. Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory 6/7
Summary Hadronic models X max moments unphysical variance (σln A < ) for QGSJetII for E EeV, but within σ. Muon production depth X max µ below prediction for Fe for EPOS LHC, inconsistent with ln A from X max ; deeper X max µ of EPOS LHC is due to better fit of LHC rapidity-gap distributions. Number of muons in inclined showers (assuming ln A from X max analysis) muon content in models is ( 8)% smaller than in data, but the difference with EPOS LHC is at.σ (sys.) ; similar conclusions for the vertical events were obtained in (G. Farrar, B. Kegl, ICRC ). acknowledgments: the speaker is grateful to BMBF and HAP for the financial support Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory 7/7