Particle physics at the Pierre Auger Observatory Jan Ebr* for the - PowerPoint PPT Presentation

Particle physics at the Pierre Auger Observatory Jan Ebr* for the Pierre Auger Collaboration *Institute of Physics, ASCR Prague MESON 2014, Krakow 2. 6. 2014

Jan Ebr for the Pierre Auger Collaboration, 2. 6. 2014, MESON 2014 Krakow 2/20 Overview • Ultra-high energy cosmic rays (UHECR) and Extensive air showers (EAS) • Pierre Auger Observatory • Longitudinal developement - primary beam composition - proton-air cross-section • Muon content at ground level • Comparison with current hadronic interaction models

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Jan Ebr for the Pierre Auger Collaboration, 2. 6. 2014, MESON 2014 Krakow log(size,฀km) 1฀au฀฀฀฀฀฀฀1฀pc฀฀1฀kpc฀฀1฀Mpc −9 −3 3 9 15 3฀฀฀฀฀6฀฀฀฀฀9฀฀฀฀฀12฀฀฀฀15฀฀฀฀฀18฀฀฀฀21 log(Magnetic฀field,฀gauss) Fe฀(100฀EeV) Clusters Protons Ultra-high energy CR • Highest-energy astrophysics • Exotic sources: AGNs, BHs ... • Both acceleration and propagation in magnetic fields → particle identification (“mass composition”) essential for interpretation 4/20 J. Cronin SNR nuclei Zevatrons? (100฀EeV) (1฀ZeV) Neutron star White dwarf Protons GRB halo galaxies Colliding hot−spots jets lobes LHC: Hillas-plot (necessary but not sufficient!) a g c a ILC: t l i a v x e i e s Galactic disk

Schematic Shower Development Jan Ebr for the Pierre Auger Collaboration, 2. 6. 2014, MESON 2014 Krakow 5/20 Below: pion interactions in one simulated 10 19 eV • Muons ( π ± , K ... decay) • Electromagnetic cascade ( π 0 decay) • Secondary hadrons (mostly pions) • For UHECR: billions of particles Extensive Air Showers J. Knapp proton shower → lots of meson physics! energy, particle type, direction ??? ������ �� : near shower axis � : more widely spread µ ����� �� � � � � � �� � : � from � 0 � µ decays � 10 MeV � �� � � � µ : � � from � ± ������� decays � � 1 GeV � � �� � � ��� � � � µ � 10 - 100 varying with �� � � �� �� � � � � � core distance, energy, mass, � , ... �� � � � � � � � � � Details depend on: �� �� � � � hadronic and el.mag. particle production, � � � ��� � cross-sections, decays, transport, .... � �� �� � � � � at energies from � 10 6 ... >10 20 eV � � � � � � � (far above man-made accelerators) � Earth magnetic field, .... � � � � � � the ever-changing atmosphere .... � � Complex interplay with many correlations � � �� � � �� � ��������������� �������� ������ ����������

Jan Ebr for the Pierre Auger Collaboration, 2. 6. 2014, MESON 2014 Krakow • Fluorescence detector: 24+3 - atmospheric monitoring • Auxiliary devices - good energy resolution - 13% duty cycle - UV light from excited N 2 telescopes of 28°×30° FOV - AMIGA: 750 m spacing → E > 10 17.5 eV 6/20 - 1500 m spacing → E > 10 18.5 eV - well-known aperture - 100 % duty cycle - particles arriving at ground level detectors accross 3000 km 2 • Surface detector: 1600 water Cherenkov The Pierre Auger Observatory - detector callibration

Jan Ebr for the Pierre Auger Collaboration, 2. 6. 2014, MESON 2014 Krakow 7/20 Surface detector

Jan Ebr for the Pierre Auger Collaboration, 2. 6. 2014, MESON 2014 Krakow 8/20 Fluorescence detector

Jan Ebr for the Pierre Auger Collaboration, 2. 6. 2014, MESON 2014 Krakow 9/20 Fluorescence detector • Calorimetric energy measurement (minus “invisible energy”) • Calibrate energy estimators of SD • Systematic uncertainty on the energy scale: 14% (before update 22%) • Energy resolution: 7–8 % (FD), 17–12 % (SD) R. Šmída

Jan Ebr for the Pierre Auger Collaboration, 2. 6. 2014, MESON 2014 Krakow - stops with π ± decay to muons 10/20 Air Showers - simplified model! In pratice: Monte Carlo simulations - depends both on composition and interaction - shallower for heavier nuclei ( A lower-energy showers) • X max ~ λ + ln( E 0 ) – ln( N ) – ln( A ) E 0 / A - Superposition model for nuclei: A showers with energy M. Unger - ≈ 1/3 of secondaries π 0 → EM cascades - mean free path of 1st interacion λ • Hadronic cascade more complex (Heitler-Matthews) - X max ≈ X 0 ln( E / E crit ) - when E < E crit ( ≈ 87 MeV) shower stops growing - n lengths → 2 n particles, each carries E = E 0 /2 n - splitting length ≈ radiation length X 0 • Electromagnetic cascade (Heitler model) - multiplicity N of interactions Longitudinal shower developement indirect measurement of E and A 0 E 0 � requires detailed simulation of cascades (CORSIKA, Aires...) X 0 Heitler model electromagnetic cascades: 2X 0 � radiation length X 0 � 2 n particles after n · X 0 3X 0 � shower stops if E i < E γ crit → N max = E 0 / E γ crit , X max = X 0 ln ( E 0 / E γ crit ) 4X 0 hadronic showers: (Matthews 2005) � superposition E 0 → E 0 / A depth � multiplicity f ± N × π ± , ( 1 − f ± ) N × π 0 ( f ± ≈ 2 / 3) � shower stops when π ± decay ( E π crit )

The Mean X max and the FD limited Field of View The FD has a limited field of view in elevation ranging from about 2 ◦ to 30 ◦ , introducing a bias in the distribution of X max from the observed showers. This bias is amplified by demanding that X max be within the observed profile ( X max bracketed). The reason for this bias in the X max distribution is because many showers landing close to the FD will have their X max outside (above) the field of view (see fig 7) and the observed profile will not have a bracketed X max or the shower will simply not be detected. As a result the mean X max will appear to be larger Auger fluorescence detector. Jan Ebr for the Pierre Auger Collaboration, 2. 6. 2014, MESON 2014 Krakow appears to be smaller (shallow). In order to avoid the bias in the estimated mean X max , showers with specific geometries relative to the FD are rejected. To identify the optimum shower geometries to be used for These parameters are the lower and upper limits of the slant depth along the shower axis that is inside the FD field of view. These limits may be defined at where the shower axis intercepts the FD field of view limit or where the shower axis intercepts the maximum distance that a shower with energy E is still detectable (as shown in figure 8). Figure 7: Diagram showing the possible bias in the estimated � X max � due to the limitted field of view of the (deeper). A similar bias happen for high energy showers. High energy showers develop their below the ground (see fig 7), therefore rejected from the analysis. In this case the mean X max 11/20 3 interaction models) around 10 18.5 eV • Suggestive for change of composition (or - heavier nuclei: A showers – less fluctuation • Fluctuations corrected for detector resolution • Unbiased distribution by fiducial volume selection Depths of shower maxima – data slant depth along the shower axis that is inside the FD field of view. X max deeper in the atmosphere, then for some vertical (or near vertical) showers X max will be determining the mean X max ( � X max � ) values, we introduced the parameters X up and X low . Figure 8: Diagram showing the definition of X low and X up . X low and X up are the lower and upper limits of the

Jan Ebr for the Pierre Auger Collaboration, 2. 6. 2014, MESON 2014 Krakow 12/20 Depths of shower maxima – interpretation • Not all combinations of mean depth and fluctuations physically possible - n.b.: within erros still agrees with all models