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An upper limit to the photon fraction in cosmic rays above 1019 eV from the Pierre Auger Observatory

Astroparticle Physics 27:2-3 (2007) 155-168

Authors:

J Abraham, M Aglietta, C Aguirre, D Allard, I Allekotte, P Allison, C Alvarez, J Alvarez-Muñiz, M Ambrosio, L Anchordoqui, JC Anjos, C Aramo, K Arisaka, E Armengaud, F Arneodo, F Arqueros, T Asch, H Asorey, BS Atulugama, J Aublin, M Ave, G Avila, J Bacelar, T Bäcker, D Badagnani, AF Barbosa, HMJ Barbosa, M Barkhausen, D Barnhill, SLC Barroso, P Bauleo, J Beatty, T Beau, BR Becker, KH Becker, JA Bellido, S BenZvi, C Berat, T Bergmann, P Bernardini, X Bertou, PL Biermann, P Billoir, O Blanch-Bigas, F Blanco, P Blasi, C Bleve, H Blümer, P Boghrat, M Boháčová, C Bonifazi, R Bonino, M Boratav, J Brack, JM Brunet, P Buchholz, NG Busca, KS Caballero-Mora, B Cai, DV Camin, JN Capdevielle, R Caruso, A Castellina, G Cataldi, L Cazón, R Cester, J Chauvin, A Chiavassa, JA Chinellato, A Chou, J Chye, D Claes, PDJ Clark, RW Clay, SB Clay, B Connolly, A Cordier, U Cotti, S Coutu, CE Covault, J Cronin, S Dagoret-Campagne, T Dang Quang, P Darriulat, K Daumiller, BR Dawson, RM de Almeida, LA de Carvalho, C De Donato, SJ de Jong, WJM de Mello, JRT de Mello Neto, I De Mitri, MAL de Oliveira, V de Souza, L del Peral, O Deligny, A Della Selva, C Delle Fratte, H Dembinski

Abstract:

An upper limit of 16% (at 95% c.l.) is derived for the photon fraction in cosmic rays with energies greater than 1019 eV, based on observations of the depth of shower maximum performed with the hybrid detector of the Pierre Auger Observatory. This is the first such limit on photons obtained by observing the fluorescence light profile of air showers. This upper limit confirms and improves on previous results from the Haverah Park and AGASA surface arrays. Additional data recorded with the Auger surface detectors for a subset of the event sample support the conclusion that a photon origin of the observed events is not favored. © 2006 Elsevier B.V. All rights reserved.
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Anisotropy studies around the galactic centre at EeV energies with the Auger Observatory

Astroparticle Physics 27:4 (2007) 244-253

Authors:

J Abraham, M Aglietta, C Aguirre, D Allard, I Allekotte, P Allison, C Alvarez, J Alvarez-Muñiz, M Ambrosio, L Anchordoqui, JC Anjos, C Aramo, K Arisaka, E Armengaud, F Arneodo, F Arqueros, T Asch, H Asorey, BS Atulugama, J Aublin, M Ave, G Avila, J Bacelar, T Bäcker, D Badagnani, AF Barbosa, HMJ Barbosa, M Barkhausen, D Barnhill, SLC Barroso, P Bauleo, J Beatty, T Beau, BR Becker, KH Becker, JA Bellido, S BenZvi, C Berat, T Bergmann, P Bernardini, X Bertou, PL Biermann, P Billoir, O Blanch-Bigas, F Blanco, P Blasi, C Bleve, H Blümer, P Boghrat, M Boháčová, C Bonifazi, R Bonino, M Boratav, J Brack, JM Brunet, P Buchholz, NG Busca, KS Caballero-Mora, B Cai, DV Camin, JN Capdevielle, R Caruso, A Castellina, G Cataldi, L Cazón, R Cester, J Chauvin, A Chiavassa, JA Chinellato, A Chou, J Chye, D Claes, PDJ Clark, RW Clay, SB Clay, B Connolly, A Cordier, U Cotti, S Coutu, CE Covault, J Cronin, S Dagoret-Campagne, TD Quang, P Darriulat, K Daumiller, BR Dawson, RM de Almeida, LA de Carvalho, C De Donato, SJ de Jong, WJM de Mello, JRT de Mello Neto, I De Mitri, MAL de Oliveira, V de Souza, L del Peral, O Deligny, AD Selva, CD Fratte, H Dembinski

Abstract:

Data from the Pierre Auger Observatory are analyzed to search for anisotropies near the direction of the Galactic Centre at EeV energies. The exposure of the surface array in this part of the sky is already significantly larger than that of the fore-runner experiments. Our results do not support previous findings of localized excesses in the AGASA and SUGAR data. We set an upper bound on a point-like flux of cosmic rays arriving from the Galactic Centre which excludes several scenarios predicting sources of EeV neutrons from Sagittarius A. Also the events detected simultaneously by the surface and fluorescence detectors (the 'hybrid' data set), which have better pointing accuracy but are less numerous than those of the surface array alone, do not show any significant localized excess from this direction. © 2006 Elsevier B.V. All rights reserved.
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Power Corrections for Jets at Hadron Colliders

(2007)

Authors:

Lorenzo Magnea, Matteo Cacciari, Mrinal Dasgupta, Gavin Salam
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Strings in SU(N) gauge theories in 2+1 dimensions: beyond the fundamental representation

Proceedings of Science 42 (2007)

Authors:

B Bringoltz, M Teper

Abstract:

We calculate energies and tensions of closed k-strings in (2+1)-dimensional SU(N) gauge theories with N=4,5,6,8. When we study the dependence of the ground state energy on the string length, we find that it is well described by a Nambu-Goto (NG) free bosonic string for large lengths. At shorter lengths we see deviations which we fit, and this allows us to control the systematic error involved in extracting the tension. We compare the resulting string tensions with Casimir scaling, which we find to be lower than our data by 1% − 4%. Extrapolating our results to N = ∞ we see that our data fits more naturally to 1/N rather than 1/N 2 corrections. Finally, we see that the full spectrum of the k-string states falls into sectors that belong to particular irreducible representations of SU (N).

Structure and properties of the vacuum of the Twisted Eguchi-Kawai model

Proceedings of Science 42 (2007)

Authors:

H Vairinhos, M Teper

Abstract:

We investigate numerically the phase structure of the Twisted Eguchi-Kawai (TEK) model in four dimensions. In the numerical simulations of the zero-temperature TEK model (using a symmetric twist) we observe the existence of new phases that break its ZN4 symmetry at intermediate lattice couplings and for large SU(N) gauge groups. This effect can be explained by the contribution of diagonal configurations with collapsed eigenvalues, which are particular cases of “generalised fluxons”. We also investigate finite-temperature versions of the TEK model using anisotropic lattice couplings, where in particular we find van Baal fluxons contributing at large anisotropies.