Studies on UHECR composition and hadronic interactions by the Pierre Auger Observatory

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1 OBSERVATORY Studies on UHECR composition and hadronic interactions by the Pierre Auger Observatory Alexey Yushkov for the Pierre Auger Collaboration 7.html Universität Siegen, Germany Very High Energy Phenomena in the Universe, Quy Nhon, August 7,

2 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

3 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

4 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 E [EeV] LL X max [g/cm ] 6 8 slant depth [g/cm ] Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory /7

5 First two moments of X max distributions ] X max [g/cm EPOS-LHC QGSJetII- Sibyll. proton iron ] ) [g/cm max σ(x Auger preliminary proton iron 8 9 E [ev] 8 9 E [ev] Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory 5/7

6 Elongation rate d X max /d lg E ] X max [g/cm Auger preliminary single line: χ /Ndf = 8./6, P =.5 broken line: χ /Ndf =./, P = 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) = (stat.) Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory 6/7

7 .5.5 ln A X max X p max ln A D / ln(); log (E/eV) log (E/eV).5 SIBYLL..5 EPOS-LHC.5 QGSJet II log (E/eV) log (E/eV) 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

8 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 log (E/eV) log (E/eV) 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

9 Combining σln A and ln A models are consistent with mixed composition within systematic uncertainties ] [g/cm X max ] ) [g/cm max σ(x E [ev] lna σ Sibyll. lna σ EPOS-LHC lna σ QGSJetII line indicates the evolution of mass composition with energy Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory 9/7

10 Combining σln A and ln A models are consistent with mixed composition within systematic uncertainties ] [g/cm X max ] ) [g/cm max σ(x E [ev] lna σ Sibyll. + σ sys lna σ EPOS-LHC + σ sys lna σ QGSJetII- + σ sys line indicates the evolution of mass composition with energy Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory 9/7

11 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 µ X [g/cm ] Alexey Yushkov Composition and hadronic interactions by the Pierre Auger Observatory /7

12 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 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

13 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

14 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 = 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

15 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) 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

16 Mean logarithmic muon scale ln R µ ln Rµ Fe EPOS LHC QGSJet II- QGSJet II- QGSJet N He E = 9 ev, θ = 67 Auger data X max /gcm p Auger data lnr µ ( 9 ev).6 ± (sys.) Fe.8.5 ±.7 EPOS LHC +.5. p (sys.).97 Fe.5.5 ±.7 QGSJet II p (sys.).6 Fe.58.6 ±.7 QGSJet II p (sys.) -.6 Fe.7.6 ±. QGSJet +..5 p (sys.) 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

17 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

18 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