Average shape of longitudinal shower profiles measured at the Pierre Auger Observatory

The average profiles of cosmic ray shower development as a function of atmospheric depth are measured for the first time with the Fluorescence Detectors at the Pierre Auger Observatory. The profile shapes are well reproduced by the Gaisser-Hillas parametrization at the 1% level in a 500 g/cm2 interval around the shower maximum, for cosmic rays with log(E/eV) > 17.8. The results are quantified with two shape parameters, measured as a function of energy. The average profiles carry information on the primary cosmic ray and its high energy hadronic interactions. The shape parameters predicted by the commonly used models are compatible with the measured ones within experimental uncertainties. Those uncertainties are dominated by systematics which, at present, prevent a detailed composition analysis.Comment: presented at the UHECR 2018 (Paris, October 2018

Particle physics measurements at the highest energies with the Pierre Auger Observatory

The Pierre Auger Observatory measures cosmic rays with energies between 10 17 . 5 eV and 10 20 eV, based on air shower sampling at ground, complemented with shower development measurements with a smaller duty-cycle. The cross-section for the primary interaction of 10 18 eV protons with air has been measured by analysing the maximum of shower development in the atmosphere. This corresponds to a centre-of-mass energy of 57 TeV, and the LHC results show the same evolution of the proton-proton cross-section at intermediate energies. The depth of shower maximum is sensitive to cross-section and primary mass. Its energy evolution indicates a change towards the behavior expected for heavier primaries or larger cross-sections. We will show also the results on other observables related to primary nuclear mass composition.Peer Reviewe

Anti-neutrino measurements in SNO+

SNO+ is a new neutrino physics experiment, that will start collecting data in 2016, reusing the SNO detector with 780 tons of liquid scintillator as active medium. It will perform several low energy measurements, namely the search for neutrinoless double beta decay, for which the scin- tillator will be loaded with tellurium. Anti-neutrino interactions can be identified through a char- acteristic delayed coincidence signature, between a positron annihilation and a neutron capture. SNO+ will measure anti-neutrinos from nuclear reactors, useful for oscillation studies, and geo- neutrinos, useful for Geophysics studies. The reactor and geo-neutrinos have very different energy spectra, which is the main variable to disentangle them. We explore the possibility to use time variations of the expected fluxes and some direction sensitivity to increase the separation between the anti-neutrino sources, for example between geo-neutrinos from crust and mantle. The main advantage of SNO+ for the anti-neutrino analysis is that the flux is dominated by reac- tors in two different directions and two distances of the order of 100 km, which give rise to sharp spectral features in the oscillated energy spectrum and a high sensitivity to the neutrino squared mass difference parameter. On the other hand, the small number of near-by reactors implies also a small background for the geo-neutrino measurement, to be done in a new geological locationPeer Reviewe

The interplay between the electromagnetic and the muonic longitudinal profile at production

The electromagnetic and the muonic longitudinal profile at production enclosure important information about the primary particle and the hadronic interactions that rule the shower development. In fact, these two profiles provide two different insights of the shower: the electromagnetic component gives a measurement of the energy and the strength of the neutral pion channel; while the muonic profile, being intimately related with the charged mesons decays, can be used as a direct probe for the high energy hadronic interactions. In this work we explore the interplay between the electromagnetic and muonic profiles, by analysing their phenomenologic behaviour for different primary masses and energies, zenith angles, and also different high energy hadronic interaction models. We have found that the muonic longitudinal profile at production displays universal features similar to what is known for the electromagnetic one. Moreover, we show that both profiles have new primary mass composition variables which are fairly independent of the high energy hadronic interaction model. Finally we discuss how the information in the electromagnetic and the muonic longitudinal profile can be combined to break the degeneracy between the primary mass composition and the high energy hadronic physics.Comment: 5 pages, to appear in conference proceedings of International Symposium on Very High Energy Cosmic Ray Interactions (ISVHECRI 2012), Berlin, German

The interplay between the electromagnetic and the muonic longitudinal profile at production

The electromagnetic and the muonic longitudinal profile at production enclosure important information about the primary particle and the hadronic interactions that rule the shower development. In fact, these two profiles provide two different insights of the shower: the electromagnetic component gives a measurement of the energy and the strength of the neutral pion channel while the muonic profile, being intimately related with the charged mesons decays, can be used as a direct probe for the high energy hadronic interactions.Peer Reviewe

Testing Hadronic Interactions at Ultrahigh Energies with Air Showers Measured by the Pierre Auger Observatory

Ultrahigh energy cosmic ray air showers probe particle physics at energies beyond the reach of accelerators. Here we introduce a new method to test hadronic interaction models without relying on the absolute energy calibration, and apply it to events with primary energy 6-16 EeV (E_CM = 110-170 TeV), whose longitudinal development and lateral distribution were simultaneously measured by the Pierre Auger Observatory. The average hadronic shower is 1.33 +- 0.16 (1.61 +- 0.21) times larger than predicted using the leading LHC-tuned models EPOS-LHC (QGSJetII-04), with a corresponding excess of muons.Peer Reviewe

Azimuthal Asymmetry in the Risetime of the Surface Detector Signals of the Pierre Auger Observatory

The azimuthal asymmetry in the risetime of signals in Auger surface detector stations is a source of information on shower development. The azimuthal asymmetry is due to a combination of the longitudinal evolution of the shower and geometrical effects related to the angles of incidence of the particles into the detectors. The magnitude of the effect depends upon the zenith angle and state of development of the shower and thus provides a novel observable, (secθ)max, sensitive to the mass composition of cosmic rays above 3×1018  eV. By comparing measurements with predictions from shower simulations, we find for both of our adopted models of hadronic physics (QGSJETII-04 and EPOS-LHC) an indication that the mean cosmic-ray mass increases slowly with energy, as has been inferred from other studies. However, the mass estimates are dependent on the shower model and on the range of distance from the shower core selected. Thus the method has uncovered further deficiencies in our understanding of shower modeling that must be resolved before the mass composition can be inferred from (secθ)max.Peer Reviewe

Evidence for a mixed mass composition at the ‘ankle’ in the cosmic-ray spectrum

We report a first measurement for ultrahigh energy cosmic rays of the correlation between the depth of shower maximum and the signal in the water Cherenkov stations of air-showers registered simultaneously by the fluorescence and the surface detectors of the Pierre Auger Observatory. Such a correlation measurement is a unique feature of a hybrid air-shower observatory with sensitivity to both the electromagnetic and muonic components. It allows an accurate determination of the spread of primary masses in the cosmic-ray flux. Up till now, constraints on the spread of primary masses have been dominated by systematic uncertainties. The present correlation measurement is not affected by systematics in the measurement of the depth of shower maximum or the signal in the water Cherenkov stations. The analysis relies on general characteristics of air showers and is thus robust also with respect to uncertainties in hadronic event generators. The observed correlation in the energy range around the ‘ankle’ at lg⁡(E/eV)=18.5–19.0 differs significantly from expectations for pure primary cosmic-ray compositions. A light composition made up of proton and helium only is equally inconsistent with observations. The data are explained well by a mixed composition including nuclei with mass A>4 . Scenarios such as the proton dip model, with almost pure compositions, are thus disfavored as the sole explanation of the ultrahigh-energy cosmic-ray flux at Earth.Peer Reviewe

Improved limit to the diffuse flux of ultrahigh energy neutrinos from the Pierre Auger Observatory

Neutrinos in the cosmic ray flux with energies near 1 EeV and above are detectable with the Surface Detector array (SD) of the Pierre Auger Observatory. We report here on searches through Auger data from 1 January 2004 until 20 June 2013. No neutrino candidates were found, yielding a limit to the diffuse flux of ultrahigh energy neutrinos that challenges the Waxman-Bahcall bound predictions. Neutrino identification is attempted using the broad time structure of the signals expected in the SD stations, and is efficiently done for neutrinos of all flavors interacting in the atmosphere at large zenith angles, as well as for “Earth-skimming” neutrino interactions in the case of tau neutrinos. In this paper the searches for downward-going neutrinos in the zenith angle bins 60°–75° and 75°–90° as well as for upward-going neutrinos, are combined to give a single limit. The 90% C.L. single-flavor limit to the diffuse flux of ultrahigh energy neutrinos with an E-2 spectrum in the energy range 1.0×1017  eV–2.5×1019  eV is Eν2dNν/dEν<6.4×10−9  GeV cm−2 s−1 sr−1.Peer Reviewe