D Zavrtanik

Publications (1065)204.66 Total impact

• Article: Antennas for the Detection of Radio Emission Pulses from Cosmic-Ray induced Air Showers at the Pierre Auger Observatory

  P. Abreu, M. Aglietta, M. Ahlers, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J. Allen, P. Allison, A. Almela, [......], J. Zhou, Y. Zhu, M. Zimbres Silva, M. Ziolkowski, D. Charrier, L. Denis, G. Hilgers, L. Mohrmann, B. Philipps, O. Seeger
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  ABSTRACT: The Pierre Auger Observatory is exploring the potential of the radio detection technique to study extensive air showers induced by ultra-high energy cosmic rays. The Auger Engineering Radio Array (AERA) addresses both technological and scientific aspects of the radio technique. A first phase of AERA has been operating since September 2010 with detector stations observing radio signals at frequencies between 30 and 80 MHz. In this paper we present comparative studies to identify and optimize the antenna design for the final configuration of AERA consisting of 160 individual radio detector stations. The transient nature of the air shower signal requires a detailed description of the antenna sensor. As the ultra-wideband reception of pulses is not widely discussed in antenna literature, we review the relevant antenna characteristics and enhance theoretical considerations towards the impulse response of antennas including polarization effects and multiple signal reflections. On the basis of the vector effective length we study the transient response characteristics of three candidate antennas in the time domain. Observing the variation of the continuous galactic background intensity we rank the antennas with respect to the noise level added to the galactic signal.
  09/2012;
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  Available from: Henry D. Glass

  Article: The Rapid Atmospheric Monitoring System of the Pierre Auger Observatory

  The Pierre Auger Collaboration, P. Abreu, M. Aglietta, M. Ahlers, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J. Allen, P. Allison, [......], B. Zamorano Garcia, E. Zas, D. Zavrtanik, M. Zavrtanik, I. Zaw, A. Zepeda, J. Zhou, Y. Zhu, M. Zimbres Silva, M. Ziolkowski
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  ABSTRACT: The Pierre Auger Observatory is a facility built to detect air showers produced by cosmic rays above 10^17 eV. During clear nights with a low illuminated moon fraction, the UV fluorescence light produced by air showers is recorded by optical telescopes at the Observatory. To correct the observations for variations in atmospheric conditions, atmospheric monitoring is performed at regular intervals ranging from several minutes (for cloud identification) to several hours (for aerosol conditions) to several days (for vertical profiles of temperature, pressure, and humidity). In 2009, the monitoring program was upgraded to allow for additional targeted measurements of atmospheric conditions shortly after the detection of air showers of special interest, e.g., showers produced by very high-energy cosmic rays or showers with atypical longitudinal profiles. The former events are of particular importance for the determination of the energy scale of the Observatory, and the latter are characteristic of unusual air shower physics or exotic primary particle types. The purpose of targeted (or "rapid") monitoring is to improve the resolution of the atmospheric measurements for such events. In this paper, we report on the implementation of the rapid monitoring program and its current status. The rapid monitoring data have been analyzed and applied to the reconstruction of air showers of high interest, and indicate that the air fluorescence measurements affected by clouds and aerosols are effectively corrected using measurements from the regular atmospheric monitoring program. We find that the rapid monitoring program has potential for supporting dedicated physics analyses beyond the standard event reconstruction.
  08/2012;
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  Available from: Jiri Masik

  Article: A study of production in e+e− collisions at –207 GeV

  DELPHI Collaboration, J. Abdallah, P. Abreu, W. Adam, P. Adzic, T. Albrecht, R. Alemany-Fernandez, T. Allmendinger, P. P. Allport, U. Amaldi, [......], M. Winter, M. Witek, O. Yushchenko, A. Zalewska, P. Zalewski, D. Zavrtanik, V. Zhuravlov, N. I. Zimin, A. Zintchenko, M. Zupan
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  ABSTRACT: Measurements are presented of R b, the ratio of the b[`(b)]{\mathrm{b}}\bar{\mathrm{b}} cross-section to the q[`(q)]{\mathrm{q}}\bar{\mathrm{q}} cross-section in e+e− collisions, and the forward-backward asymmetry A FBb at twelve energy points in the range Ös=130\sqrt{s}=130 –207GeV. These results are found to be consistent with the Standard Model expectations. The measurements are used to set limits on new physics scenarios involving contact interactions.
  European Physical Journal C 04/2012; 60(1):1-15. · 3.63 Impact Factor
• Article: Higgs boson searches in CP-conserving and CP-violating MSSM scenarios with the DELPHI detector

  J. Abdallah, P. Abreu, W. Adam, P. Adzic, T. Albrecht, R. Alemany-Fernandez, T. Allmendinger, P.P. Allport, U. Amaldi, N. Amapane, [......], M. Witek, O. Yushchenko, A. Zalewska, P. Zalewski, D. Zavrtanik, V. Zhuravlov, N.I. Zimin, A. Zintchenko, M. Zupan, The NA Collaboration
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  ABSTRACT: This paper presents the final interpretation of the results from DELPHI on the searches for Higgs bosons in the minimal supersymmetric extension of the Standard Model (MSSM). A few representative scenarios are considered, that include CP conservation and explicit CP violation in the Higgs sector. The experimental results encompass the searches for neutral Higgs bosons at LEP1 and LEP2 in final states as expected in the MSSM, as well as LEP2 searches for charged Higgs bosons and for neutral Higgs bosons decaying into hadrons independent of the quark flavour. The data reveal no significant excess with respect to background expectations. The results are translated into excluded regions of the parameter space in the various scenarios. In the CP-conserving case, these lead to limits on the masses of the lightest scalar and pseudoscalar Higgs bosons, h and A, and on tanβ. The dependence of these limits on the top quark mass is discussed. Allowing for CP violation reduces the experimental sensitivity to Higgs bosons. It is shown that this effect depends strongly on the values of the parameters responsible for CP violation in the Higgs sector.
  European Physical Journal C 04/2012; 54(1):1-35. · 3.63 Impact Factor
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  Available from: Pier Giorgio Rancoita

  Article: Search for neutral MSSM Higgs bosons at LEP

  S. Schael, R. Barate, R. Brunelière, I. De Bonis, D. Decamp, C. Goy, S. Jézéquel, J.-P. Lees, F. Martin, E. Merle, [......], G.W. Wilson, J.A. Wilson, T.R. Wyatt, S. Yamashita, D. Zer-Zion, L. Zivkovic, S. Heinemeyer, A. Pilaftsis, G. Weiglein, The LEP Working Group for Higgs Boson Searches
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  ABSTRACT: The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by the Minimal Supersymmetric standard model (MSSM). The data of the four collaborations are statistically combined and examined for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number of “benchmark” models, including CP-conserving and CP-violating scenarios. These interpretations lead in all cases to large exclusions in the MSSM parameter space. Absolute limits are set on the parameter cosβ and, in some scenarios, on the masses of neutral Higgs bosons.
  European Physical Journal C 04/2012; 47(3):547-587. · 3.63 Impact Factor
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  Available from: Jiri Masik

  Article: Search for single top quark production via contact interactions at LEP2

  The DELPHI Collaboration, J. Abdallah, P. Abreu, W. Adam, P. Adzic, T. Albrecht, R. Alemany-Fernandez, T. Allmendinger, P. P. Allport, U. Amaldi, [......], M. Winter, M. Witek, O. Yushchenko, A. Zalewska, P. Zalewski, D. Zavrtanik, V. Zhuravlov, N. I. Zimin, A. Zintchenko, M. Zupan
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  ABSTRACT: Single top quark production via four-fermion contact interactions associated to flavour-changing neutral currents was searched for in data taken by the DELPHI detector at LEP2. The data were accumulated at centre-of-mass energies ranging from 189 to 209 GeV, with an integrated luminosity of 598.1pb−1. No evidence for a signal was found. Limits on the energy scale Λ, were set for scalar-, vector- and tensor-like coupling scenarios.
  European Physical Journal C 04/2012; 71(2):1-13. · 3.63 Impact Factor
• Article: Measurements of CP-conserving trilinear gauge boson couplings WWV (V≡γ,Z) in e+e− collisions at LEP2

  The DELPHI Collaboration, J. Abdallah, P. Abreu, W. Adam, P. Adzic, T. Albrecht, R. Alemany-Fernandez, T. Allmendinger, P. P. Allport, U. Amaldi, [......], M. Winter, M. Witek, O. Yushchenko, A. Zalewska, P. Zalewski, D. Zavrtanik, V. Zhuravlov, N. I. Zimin, A. Zintchenko, M. Zupan
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  ABSTRACT: The data taken by Delphi at centre-of-mass energies between 189and 209GeV are used to place limits on the CP-conserving trilinear gauge boson couplings DgZ1\Delta g^{Z}_{1}, λ γ and Δκ γ associated to W + W − and single W production at Lep2. Using data from the jj ℓ ν, jjjj, jjX and ℓ X final states, where j, ℓ and X represent a jet, a lepton and missing four-momentum, respectively, the following limits are set on the couplings when one parameter is allowed to vary and the others are set to their Standard Model values of zero: ${l}\Delta g^Z_1=-0.025^{+0.033}_{-0.030},\\\noalign{\vskip6pt}\lambda_\gamma =0.002^{+0.035}_{-0.035}\qquad\mbox{and}\\\noalign{\vskip6pt}\Delta\kappa_\gamma =0.024^{+0.077}_{-0.081}.$\begin{array}{l}\Delta g^Z_1=-0.025^{+0.033}_{-0.030},\\\noalign{\vskip6pt}\lambda_\gamma =0.002^{+0.035}_{-0.035}\qquad\mbox{and}\\\noalign{\vskip6pt}\Delta\kappa_\gamma =0.024^{+0.077}_{-0.081}.\end{array} Results are also presented when two or three parameters are allowed to vary. All observations are consistent with the predictions of the Standard Model and supersede the previous results on these gauge coupling parameters published by Delphi.
  European Physical Journal C 04/2012; 66(1):35-56. · 3.63 Impact Factor
• Article: Correlations between polarisation states of W particles in the reaction e−e+→W−W+ at LEP2 energies 189–209 GeV

  The DELPHI Collaboration, J. Abdallah, P. Abreu, W. Adam, P. Adzic, T. Albrecht, R. Alemany-Fernandez, T. Allmendinger, P. P. Allport, U. Amaldi, [......], M. Winter, M. Witek, O. Yushchenko, A. Zalewska, P. Zalewski, D. Zavrtanik, V. Zhuravlov, N. I. Zimin, A. Zintchenko, M. Zupan
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  ABSTRACT: In a study of the reaction e − e +→W − W + with the DELPHI detector, the probabilities of the two W particles occurring in the joint polarisation states transverse–transverse (TT), longitudinal–transverse plus transverse–longitudinal (LT) and longitudinal–longitudinal (LL) have been determined using the final states WW®lnq[`(q)]WW{\rightarrow}l\nu q\bar{q} (l=e,μ). The two-particle joint polarisation probabilities, i.e. the spin density matrix elements ρ TT , ρ LT , ρ LL , are measured as functions of the W − production angle, qW-\theta _{W^{-}}, at an average reaction energy of 198.2GeV. Averaged over all cosqW-\cos\theta_{W^{-}}, the following joint probabilities are obtained: [`(r)]TT=(67±8)%,\bar{\rho}_{TT}=(67\pm8)\%, [`(r)]LT=(30±8)%,\bar{\rho}_{LT}=(30\pm8)\%, [`(r)]LL=(3±7)%.\bar{\rho}_{LL}=(3\pm7)\%. These results are in agreement with the Standard Model predictions of 63.0%, 28.9% and 8.1%, respectively. The related polarisation cross-sections σ TT , σ LT and σ LL are also presented.
  European Physical Journal C 04/2012; 63(4):611-623. · 3.63 Impact Factor
• Article: Investigation of Colour Reconnection in WW events with the DELPHI detector at LEP-2

  J. Abdallah, P. Abreu, W. Adam, P. Adzic, T. Albrecht, R. Alemany-Fernandez, T. Allmendinger, P.P. Allport, U. Amaldi, N. Amapane, [......], M. Witek, O. Yushchenko, A. Zalewska, P. Zalewski, D. Zavrtanik, V. Zhuravlov, N.I. Zimin, A. Zintchenko, M. Zupan, The DELPHI Collaboration
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  ABSTRACT: In the reaction e+e-→WW→(q1q̄2)(q3q̄4) the usual hadronization models treat the colour singlets q1q̄2 and q3q̄4 coming from two W bosons independently. However, since the final state partons may coexist in space and time, cross-talk between the two evolving hadronic systems may be possible during fragmentation through soft gluon exchange. This effect is known as colour reconnection. In this article the results of the investigation of colour reconnection effects in fully hadronic decays of W pairs in DELPHI at LEP are presented. Two complementary analyses were performed, studying the particle flow between jets and W mass estimators, with negligible correlation between them, and the results were combined and compared to models. In the framework of the SK-I model, the value for its κ parameter most compatible with the data was found to be: κSK-I=2.2+2.5 -1.3 corresponding to the probability of reconnection P\textreco\mathcal{P}_{\text{reco}} to be in the range 0.31 < P\textreco < 0.680.31
  European Physical Journal C 04/2012; 51(2):249-269. · 3.63 Impact Factor
• Article: A study of the b-quark fragmentation function with the DELPHI detector at LEP I and an averaged distribution obtained at the Z Pole

  The DELPHI Collaboration, J. Abdallah, P. Abreu, W. Adam, P. Adzic, T. Albrecht, R. Alemany-Fernandez, T. Allmendinger, P. P. Allport, U. Amaldi, [......], M. Winter, M. Witek, O. Yushchenko, A. Zalewska, P. Zalewski, D. Zavrtanik, V. Zhuravlov, N. I. Zimin, A. Zintchenko, M. Zupan
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  ABSTRACT: The nature of b-quark jet hadronisation has been investigated using data taken at the Zpeak by the DELPHI detector at LEP. Two complementary methods are used to reconstruct the energy of weakly decaying b-hadrons, EBweakE_{\mathrm{B}}^{\mathrm{weak}}. The average value of xweakB = EBweak/Ebeamx^{\mathrm{weak}}_{\mathrm{B}} = E_{\mathrm{B}}^{\mathrm{weak}}/E_{\mathrm{beam}} is measured to be 0.699±0.011. The resulting xweakBx^{\mathrm{weak}}_{\mathrm{B}} distribution is then analysed in the framework of two choices for the perturbative contribution (parton shower and Next to Leading Log QCD calculation) in order to extract measurements of the non-perturbative contribution to be used in studies of b-hadron production in other experimental environments than LEP. In the parton shower framework, data favour the Lund model ansatz and corresponding values of its parameters have been determined within PYTHIA6.156 from DELPHI data: a = 1.84+0.23-0.21and b=0.642+0.073-0.063GeV-2,a= 1.84^{+0.23}_{-0.21}\quad\mbox{and}\quad b=0.642^{+0.073}_{-0.063}~\mathrm{GeV}^{-2}, with a correlation factor ρ=92.2%. Combining the data on the b-quark fragmentation distributions with those obtained at the Zpeak by ALEPH, OPAL and SLD, the average value of xweakBx^{\mathrm{weak}}_{\mathrm{B}} is found to be 0.7092±0.0025 and the non-perturbative fragmentation component is extracted. Using the combined distribution, a better determination of the Lund parameters is also obtained: a = 1.48+0.11-0.10and b=0.509+0.024-0.023GeV-2,a= 1.48^{+0.11}_{-0.10}\quad\mbox{and}\quad b=0.509^{+0.024}_{-0.023}~\mathrm{GeV}^{-2}, with a correlation factor ρ=92.6%.
  European Physical Journal C 04/2012; 71(2):1-29. · 3.63 Impact Factor
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  Available from: Jiri Masik

  Article: Study of the dependence of direct soft photon production on the jet characteristics in hadronic Z0 decays

  The DELPHI Collaboration, J. Abdallah, P. Abreu, W. Adam, P. Adzic, T. Albrecht, R. Alemany-Fernandez, T. Allmendinger, P. P. Allport, U. Amaldi, [......], M. Winter, M. Witek, O. Yushchenko, A. Zalewska, P. Zalewski, D. Zavrtanik, V. Zhuravlov, N. I. Zimin, A. Zintchenko, M. Zupan
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  ABSTRACT: An analysis of the direct soft photon production rate as a function of the parent jet characteristics is presented, based on hadronic events collected by the DELPHI experiment at LEP1. The dependences of the photon rates on the jet kinematic characteristics (momentum, mass, etc.) and on the jet charged, neutral and total hadron multiplicities are reported. Up to a scale factor of about four, which characterizes the overall value of the soft photon excess, a similarity of the observed soft photon behavior to that of the inner hadronic bremsstrahlung predictions is found for the momentum, mass, and jet charged multiplicity dependences. However for the dependence of the soft photon rate on the jet neutral and total hadron multiplicities a prominent difference is found for the observed soft photon signal as compared to the expected bremsstrahlung from final state hadrons. The observed linear increase of the soft photon production rate with the jet total hadron multiplicity and its strong dependence on the jet neutral multiplicity suggest that the rate is proportional to the number of quark pairs produced in the fragmentation process, with the neutral pairs being more effectively radiating than the charged ones.
  European Physical Journal C 04/2012; 67(3):343-366. · 3.63 Impact Factor
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  Available from: Jiri Masik

  Article: Measurement of the mass and width of the W boson in e+e- collisions at = 161–209 GeV

  J. Abdallah, P. Abreu, W. Adam, P. Adzic, T. Albrecht, R. Alemany-Fernandez, T. Allmendinger, P.P. Allport, U. Amaldi, N. Amapane, [......], M. Witek, O. Yushchenko, A. Zalewska, P. Zalewski, D. Zavrtanik, V. Zhuravlov, N.I. Zimin, A. Zintchenko, M. Zupan, The DELPHI Collaboration
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  ABSTRACT: A measurement of the W boson mass and width has been performed by the DELPHI collaboration using the data collected during the full LEP2 programme (1996–2000). The data sample has an integrated luminosity of 660pb-1 and was collected over a range of centre-of-mass energies from 161 to 209GeV. Results are obtained by applying the method of direct reconstruction of the mass of the W from its decay products in both the W+W-→ℓν̄ℓqq̄’ and W+W-→qq̄’q̄q’ channels. The W mass result for the combined data set is MW = 80.336 ±0.055 (\textStat.) ±0.028 (\textSyst.) ±0.025 (\textFSI) ±0.009 (\textLEP) \textGeV/c2, M_W = 80.336 \pm0.055 ({\text{Stat.}}) \pm0.028 ({\text{Syst.}}) \pm0.025 ({\text{FSI}}) \pm0.009 ({\text{LEP}}) \text{GeV}/c^2, where FSI represents the uncertainty due to final state interaction effects in the qq̄’q̄q’ channel, and LEP represents that arising from the knowledge of the collision energy of the accelerator. The combined value for the W width is GW = 2.404 ±0.140 (\textStat.) ±0.077 (\textSyst.) ±0.065 (\textFSI) \textGeV/c2. {\Gamma_{W}} = 2.404 \pm0.140 ({\text{Stat.}}) \pm0.077 ({\text{Syst.}}) \pm0.065 ({\text{FSI}}) \text{GeV}/c^2. These results supersede all values previously published by the DELPHI collaboration.
  European Physical Journal C 04/2012; 55(1):1-38. · 3.63 Impact Factor
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  Available from: Olaf Scholten

  Article: A search for ultra-high energy neutrinos in highly inclined events at the Pierre Auger Observatory

  The Pierre Auger Collaboration, P. Abreu, M. Aglietta, M. Ahlers, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J. Allen, P. Allison, [......], A. Yushkov, B. Zamorano, E. Zas, D. Zavrtanik, M. Zavrtanik, I. Zaw, A. Zepeda, Y. Zhu, M. Zimbres Silva, M. Ziolkowski
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  ABSTRACT: The Surface Detector of the Pierre Auger Observatory is sensitive to neutrinos of all flavours above 0.1 EeV. These interact through charged and neutral currents in the atmosphere giving rise to extensive air showers. When interacting deeply in the atmosphere at nearly horizontal incidence, neutrinos can be distinguished from regular hadronic cosmic rays by the broad time structure of their shower signals in the water-Cherenkov detectors. In this paper we present for the first time an analysis based on down-going neutrinos. We describe the search procedure, the possible sources of background, the method to compute the exposure and the associated systematic uncertainties. No candidate neutrinos have been found in data collected from 1 January 2004 to 31 May 2010. Assuming an E^-2 differential energy spectrum the limit on the single flavour neutrino is (E^2 * dN/dE) < 1.74x10^-7 GeV cm^-2 s^-1 sr^-1 at 90% C.L. in the energy range 1x10^17 eV < E < 1x10^20 eV.
  02/2012;
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  Available from: Maria Concetta Maccarone

  Article: Description of Atmospheric Conditions at the Pierre Auger Observatory using the Global Data Assimilation System (GDAS)

  The Pierre Auger Collaboration, P. Abreu, M. Aglietta, M. Ahlers, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J. Allen, P. Allison, [......], A. Yushkov, B. Zamorano, E. Zas, D. Zavrtanik, M. Zavrtanik, I. Zaw, A. Zepeda, Y. Zhu, M. Zimbres Silva, M. Ziolkowski
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  ABSTRACT: Atmospheric conditions at the site of a cosmic ray observatory must be known for reconstructing observed extensive air showers. The Global Data Assimilation System (GDAS) is a global atmospheric model predicated on meteorological measurements and numerical weather predictions. GDAS provides altitude-dependent profiles of the main state variables of the atmosphere like temperature, pressure, and humidity. The original data and their application to the air shower reconstruction of the Pierre Auger Observatory are described. By comparisons with radiosonde and weather station measurements obtained on-site in Malarg\"ue and averaged monthly models, the utility of the GDAS data is shown.
  01/2012;
• Article: Search for Point-like Sources of Ultra-high Energy Neutrinos at the Pierre Auger Observatory and Improved Limit on the Diffuse Flux of Tau Neutrinos

  The Pierre Auger Collaboration, P Abreu, M Aglietta, M Ahlers, E J Ahn, I F M Albuquerque, D Allard, I Allekotte, J Allen, P Allison, [......], Zamorano B Garcia, E Zas, D Zavrtanik, M Zavrtanik, I Zaw, A Zepeda, J Zhou, Y Zhu, Zimbres M Silva, M Ziolkowski
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  ABSTRACT: The surface detector array of the Pierre Auger Observatory can detect neutrinos with energy E ν between 10 17 eV and 10 20 eV from point-like sources across the sky south of +55° and north of –65° declinations. A search has been performed for highly inclined extensive air showers produced by the interaction of neutrinos of all flavors in the atmosphere (downward-going neutrinos), and by the decay of tau leptons originating from tau neutrino interactions in Earth's crust (Earth-skimming neutrinos). No candidate neutrinos have been found in data up to 2010 May 31. This corresponds to an equivalent exposure of ~3.5 years of a full surface detector array for the Earth-skimming channel and ~2 years for the downward-going channel. An improved upper limit on the diffuse flux of tau neutrinos has been derived. Upper limits on the neutrino flux from point-like sources have been derived as a function of the source declination. Assuming a differential neutrino flux k PS · E –2 ν from a point-like source, 90% confidence level upper limits for k PS at the level of ##IMG## [http://ej.iop.org/icons/Entities/ap.gif] ≈ 5 × 10 –7 and 2.5 × 10 –6 GeV cm –2 s –1 have been obtained over a broad range of declinations from the searches for Earth-skimming and downward-going neutrinos, respectively.
  The Astrophysical Journal Letters. 01/2012; 755(1):L4.
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  Available from: Maria Concetta Maccarone

  Article: The effect of the geomagnetic field on cosmic ray energy estimates and large scale anisotropy searches on data from the Pierre Auger Observatory

  P Abreu, M Aglietta, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J Allen, P. Allison, J. Alvarez Castillo, J. Alvarez-Muñiz, [......], G. Yuan, A. Yushkov, B. Zamorano, E. Zas, D Zavrtanik, M. Zavrtanik, I Zaw, A. Zepeda, M. Zimbres-Silva, M Ziolkowski
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  ABSTRACT: We present a comprehensive study of the influence of the geomagnetic field on the energy estimation of extensive air showers with a zenith angle smaller than $60^\circ$, detected at the Pierre Auger Observatory. The geomagnetic field induces an azimuthal modulation of the estimated energy of cosmic rays up to the ~2% level at large zenith angles. We present a method to account for this modulation of the reconstructed energy. We analyse the effect of the modulation on large scale anisotropy searches in the arrival direction distributions of cosmic rays. At a given energy, the geomagnetic effect is shown to induce a pseudo-dipolar pattern at the percent level in the declination distribution that needs to be accounted for.
  11/2011;
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  Available from: Maria Concetta Maccarone

  Article: Trigger and Aperture of the Surface Detector Array of the Pierre Auger Observatory

  J. Abraham, P Abreu, M Aglietta, C Aguirre, E. J. Ahn, D. Allard, I. Allekotte, J Allen, J. Alvarez-Muñiz, M. Ambrosio, [......], T Yamamoto, P. Younk, G. Yuan, A. Yushkov, E. Zas, D Zavrtanik, M. Zavrtanik, I Zaw, A. Zepeda, M Ziolkowski
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  ABSTRACT: The surface detector array of the Pierre Auger Observatory consists of 1600 water-Cherenkov detectors, for the study of extensive air showers (EAS) generated by ultra-high-energy cosmic rays. We describe the trigger hierarchy, from the identification of candidate showers at the level of a single detector, amongst a large background (mainly random single cosmic ray muons), up to the selection of real events and the rejection of random coincidences. Such trigger makes the surface detector array fully efficient for the detection of EAS with energy above $3\times 10^{18}$ eV, for all zenith angles between 0$^\circ$ and 60$^\circ$, independently of the position of the impact point and of the mass of the primary particle. In these range of energies and angles, the exposure of the surface array can be determined purely on the basis of the geometrical acceptance.
  11/2011;
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  Available from: Maria Concetta Maccarone

  Article: The Lateral Trigger Probability function for the Ultra-High Energy Cosmic Ray Showers detected by the Pierre Auger Observatory

  The Pierre Auger Collaboration, P Abreu, M Aglietta, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J Allen, P. Allison, J. Alvarez Castillo, [......], G. Yuan, A. Yushkov, B. Zamorano, E. Zas, D Zavrtanik, M. Zavrtanik, I Zaw, A. Zepeda, M. Zimbres-Silva, M Ziolkowski
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  ABSTRACT: In this paper we introduce the concept of Lateral Trigger Probability (LTP) function, i.e., the probability for an extensive air shower (EAS) to trigger an individual detector of a ground based array as a function of distance to the shower axis, taking into account energy, mass and direction of the primary cosmic ray. We apply this concept to the surface array of the Pierre Auger Observatory consisting of a 1.5 km spaced grid of about 1600 water Cherenkov stations. Using Monte Carlo simulations of ultra-high energy showers the LTP functions are derived for energies in the range between 10^{17} and 10^{19} eV and zenith angles up to 65 degs. A parametrization combining a step function with an exponential is found to reproduce them very well in the considered range of energies and zenith angles. The LTP functions can also be obtained from data using events simultaneously observed by the fluorescence and the surface detector of the Pierre Auger Observatory (hybrid events). We validate the Monte-Carlo results showing how LTP functions from data are in good agreement with simulations.
  11/2011;
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  Available from: Maria Concetta Maccarone

  Article: Search for signatures of magnetically-induced alignment in the arrival directions measured by the Pierre Auger Observatory

  The Pierre Auger Collaboration, P Abreu, M Aglietta, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J Allen, P. Allison, J. Alvarez Castillo, [......], G. Yuan, A. Yushkov, B. Zamorano, E. Zas, D Zavrtanik, M. Zavrtanik, I Zaw, A. Zepeda, M. Zimbres-Silva, M Ziolkowski
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  ABSTRACT: We present the results of an analysis of data recorded at the Pierre Auger Observatory in which we search for groups of directionally-aligned events (or `multiplets') which exhibit a correlation between arrival direction and the inverse of the energy. These signatures are expected from sets of events coming from the same source after having been deflected by intervening coherent magnetic fields. The observation of several events from the same source would open the possibility to accurately reconstruct the position of the source and also measure the integral of the component of the magnetic field orthogonal to the trajectory of the cosmic rays. We describe the largest multiplets found and compute the probability that they appeared by chance from an isotropic distribution. We find no statistically significant evidence for the presence of multiplets arising from magnetic deflections in the present data.
  11/2011;
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  Available from: Maria Concetta Maccarone

  Article: The Pierre Auger Observatory II: Studies of Cosmic Ray Composition and Hadronic Interaction models

  The Pierre Auger Collaboration, P Abreu, M Aglietta, E. J. Ahn, I. F. M. Albuquerque, D. Allard, I. Allekotte, J Allen, P. Allison, J. Alvarez Castillo, [......], G. Yuan, A. Yushkov, B. Zamorano, E. Zas, D Zavrtanik, M. Zavrtnik, I Zaw, A. Zepeda, M. Zimbres-Silva, M Ziolkowski
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  ABSTRACT: Studies of the composition of the highest energy cosmic rays with the Pierre Auger Observatory, including examination of hadronic physics effects on the structure of extensive air showers.
  07/2011;