S. J. De Jong

The Fluorescence Detector of the Pierre Auger Observatory

The Pierre Auger Observatory is a hybrid detector for ultra-high energy cosmic rays. It combines a surface array to measure secondary particles at ground level together with a fluorescence detector to measure the development of air showers in the atmosphere above the array. The fluorescence detector comprises 24 large telescopes specialized for measuring the nitrogen fluorescence caused by charged particles of cosmic ray air showers. In this paper we describe the components of the fluorescence detector including its optical system, the design of the camera, the electronics, and the systems for relative and absolute calibration. We also discuss the operation and the monitoring of the detector. Finally, we evaluate the detector performance and precision of shower reconstructions.

The OPAL silicon microvertex detector

A silicon strip microvertex detector has been designed, constructed and commissioned in the OPAL experiment at the LEP electron-positron collider. The microstrip devices incorporate a new FoxFET biassing scheme developed together with Micron Semiconductor Ltd., UK. The devices digitise with a precision close to 5 μm and have an exceptionally high signal-to-noise ratio. The associated microelectronics were all custom made for the OPAL project. The detector began operation in 1991 and has since continued to be part of the OPAL experiment, performing to a very high standard and opening up new areas of physics studies.

Upper Limit on the Diffuse Flux of Ultrahigh Energy Tau Neutrinos from the Pierre Auger Observatory

The surface detector array of the Pierre Auger Observatory i s sensitive to Earthskimming tau-neutrinosντ that interact in the Earth’s crust. Tau leptons from ντ charged-current interactions can emerge and decay in the at mosphere to produce a nearly horizontal shower with a significant electromagneti c component. The data collected between 1 January 2004 and 31 August 2007 are used t o place an upper limit on the diffuse flux ofντ at EeV energies. Assuming an E ν differential energy spectrum the limit set at 90 % C.L. is E ν dNντ /dEν < 1.3 × 10 −7 GeV cm s sr in the energy range 2× 10eV < Eν < 2× 10 eV. The detection of Ultra High Energy (UHE) cosmic neutrinos at EeV (1 EeV≡ 10 eV) energies and above is a long standing experimental chall enge. Many experiments are searching for such neutrinos, and there are se veral ongoing efforts to construct dedicated experiments to detect them [Halzen et a l.(2002), Halzen(2007), Falcke et al.(2004)]. Their discovery would open a new windo w to the universe [Becker(2007)], and provide an unique opportunity to test fundamental parti cle physics at energies well beyond current or planned accelerators. The observati on of UHE Cosmic Rays (UHECRs) requires that there exist UHE cosmic neutrinos, ev en though the nature of the UHECR particles and their production mechanisms are s till uncertain. All models of UHECR origin predict neutrino fluxes from the decay of charged pions which are produced either in interactions of the cosmic rays in their sources, or in their subsequent interactions with background radiation fi elds. For example, UHECR protons interacting with the Cosmic Microwave Background ( CMB) give rise to the so-called ‘cosmogenic’ or GZK neutrinos [Berezinsky et al. (1969)]. The recently reported suppression of the cosmic ray flux above ∼ 4 × 10 eV [Abbasi et al.(2007), Yamamoto(2007), Pierre Auger Collaboration(2007a)] as we ll as the observed correlation of the highest energy cosmic rays with relatively nea rby extragalactic objects [Pierre Auger Collaboration(2007b)] both point to UHECR in teractions on the infrared or microwave backgrounds during extragalactic propagatio n. These interactions must result in UHE neutrinos although their flux is somewhat uncer tain since this depends on the primary UHECR composition and on the nature and cosmolog ical evolution of the sources as well as on their spatial distribution [Engel et al .(2001), Allard et al.(2006)]. Tau neutrinos are suppressed in such production processes r elative toνe or νμ, because they are not an end product of the charged pion decay c hain and far fewer are made through the production and decay of heavy flavours su ch as charm. Nevertheless, because of neutrino flavour mixing, the usual 1:2 ratio of νe to νμ at production is altered to approximately equal fluxes for all flavo urs after travelling cosmological distances [Learned et al.(1995)]. Soon after the discovery of neutrino oscillations [Fukuda et al.(1998)] it was shown that ντ entering the Earth just below the horizon (Earth-skimming) [Fargion(2002), Letessier-Sel von(2001), Feng et al.(2002)] can undergo charged-current interactions and produce τ leptons. Since aτ lepton can travel tens of kilometers in the Earth at EeV energies, it can emerge into the atmosphere and decay in flight producing an nearly horizontal extensive a r shower (EAS) above the detector. In this way the effective target volume for neu trinos can be rather large. The Pierre Auger Observatory [Abraham et al.(2004)] has bee n designed to measure UHECRs with unprecedented precision. Detection of UHE CRs is being achieved

The extended OPAL silicon strip microvertex detector

Abstract The OPAL experiment at the CERN LEP collider recently increased the geometrical acceptance of its silicon microvertex detector. The azimuthal coverage is improved by adding one pair of detector modules to each of the two layers, while the polar angle coverage is extended by adding new detector modules in line with the existing ones. This improves the efficiency for high quality tracking in OPAL and in particular for b quark tagging in Higgs boson searches. A description of the detector is given, with emphasis on new or modified elements with respect to the earlier version. Results on the performance of the new detector are presented.

Constraints on the origin of cosmic rays above 10(18) eV from large-scale anisotropy searches in data of the Pierre Auger Observatory

A thorough search for large-scale anisotropies in the distribution of arrival directions of cosmic rays detected above 10(18) eV at the Pierre Auger Observatory is reported. For the first time, these large-scale anisotropy searches are performed as a function of both the right ascension and the declination and expressed in terms of dipole and quadrupole moments. Within the systematic uncertainties, no significant deviation from isotropy is revealed. Upper limits on dipole and quadrupole amplitudes are derived under the hypothesis that any cosmic ray anisotropy is dominated by such moments in this energy range. These upper limits provide constraints on the production of cosmic rays above 10(18) eV, since they allow us to challenge an origin from stationary galactic sources densely distributed in the galactic disk and emitting predominantly light particles in all directions.A thorough search for large scale anisotropies in the distribution of arrival directions of cosmic rays detected above 1018 eV at the Pierre Auger Observatory is reported. For the first time, these large scale anisotropy searches are performed as a function of both the right ascension and the declination and expressed in terms of dipole and quadrupole moments. Within the systematic uncertainties, no significant deviation from isotropy is revealed. Upper limits on dipole and quadrupole amplitudes are derived under the hypothesis that any cosmic ray anisotropy is dominated by such moments in this energy range. These upper limits provide constraints on the production of cosmic rays above 1018 eV, since they allow us to challenge an origin from stationary galactic sources densely distributed in the galactic disk and emitting predominantly light particles in all directions. Subject headings: astroparticle physics — cosmic rays The large scale distribution of arrival directions of Ultra-High Energy Cosmic Rays (UHECRs) as a function of the energy is a key observable to provide further understanding of their origin. Above ≃ 0.25 EeV, the most stringent bounds ever obtained on the dipole component in the equatorial plane were recently reported, being below 2% at 99% C.L. for EeV energies (Auger Collaboration 2011a). Such a sensitivity provides some constraints upon scenarios in which dipolar anisotropies could be imprinted in the distribution of arrival directions as the result of the escape of UHECRs from the Galaxy up to the ankle energy (Ptuskin et al. 1993; Candia et al. 2003; Giacinti et al. 2012). On the other hand, if UHECRs above 1 EeV have already a predominant extragalactic origin (Hillas 1967; Blumenthal 1970; Berezinsky et al. 2006; Berezinsky et al. 2004), their angular distribution is expected to be isotropic to a high level. Thus, the study of large scale anisotropies at EeV energies would help in establishing whether the origin of UHECRs is galactic or extragalactic in this energy range. The upper limits aforementioned are based on first harmonic analyses of the right ascension distributions in several energy ranges. The analyses benefit from the almost uniform directional exposure in right ascension of any ground based observatory operating with high duty cycle, but are not sensitive to a dipole component along the Earth rotation axis. In contrast, using the large amount of data collected by the surface detector array of the Pierre Auger Observatory, we report in this letter on searches for dipole and quadrupole patterns significantly standing out above the background noise whose components are functions of both the right ascension and the declination (a detailed description of the present analysis can be found in (Auger Collaboration 2012)).

Search for Randall-Sundrum Gravitons in the Dielectron and Diphoton Final States with 5.4 fb(-1) of Data from p(p)over-bar Collisions at root s=1.96 TeV

Using 5.4 fb-1 of integrated luminosity from ppbar collisions at sqrt(s)=1.96 TeV collected by the D0 detector at the Fermilab Tevatron Collider, we search for decays of the lightest Kaluza-Klein mode of the graviton in the Randall-Sundrum model to ee and gammagamma. We set 95% C.L. lower limits on the mass of the lightest graviton between 560 GeV and 1050 GeV for values of the coupling k/Mbar_pl between 0.01 and 0.1.

Interpretation of the depths of maximum of extensive air showers measured by the Pierre Auger Observatory

To interpret the mean depth of cosmic ray air shower maximum and its dispersion, we parametrize those two observables as functions of the first two moments of the

Measurement of the t(t)over-bar production cross section in p(p)over-bar collisions at root s=1.96 TeV

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Measurement of the muon charge asymmetry in pp¯→w+x→μν+x events at s√=1.96 tev

distribution. We examine the goodness of this simple method through simulations of test mass distributions. The application of the parameterization to Pierre Auger Observatory data allows one to study the energy dependence of the mean

Radiation monitoring and beam dump system of the OPAL silicon microvertex detector

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