Charles Timmermans

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

A high resolution muon detector

Abstract The design and operation of precision drift chambers with multisampling as well as the concepts and methods for reaching an extraordinary degree of precision in mechanics and calibration are described. Specific instruments were developed for this purpose. The concept of reproducible positioning and the implementation to 30 μm accuracy, showing stability over three years, is given. Calibration and analysis with UV-laser and cosmic test measurements are outlined with the critical results. The experience of calibration and reliability of the large system in an actual L3 running experiment is analyzed. The resolution under “battle conditions” at LEP resulted in Δp p = (2.50±0.04)% at 45.6 GeV and will be presented in detail. The concept is well suited for future TeV energies.

The L3+C detector, a unique tool-set to study cosmic rays

AbstractThe L3 detector at the CERN electron–positron collider, LEP, has been employed for the study of cosmic ray muons.The muon spectrometer of L3 consists of a set of high-precision drift chambers installed inside a magnet with avolume of about 1000 m 3 and a field of 0:5T: Muon momenta are measured with a resolution of a few percentat 50 GeV: The detector is located under 30 m of overburden. A scintillator air shower array of 54 m by 30 mis installed on the roof of the surface hall above L3 in order to estimate the energy and the core position of theshower associated with a sample of detected muons. Thanks to the unique properties of the L3þC detector, muonresearch topics relevant to various current problems in cosmic ray and particle astrophysics can be studied. r 2002Elsevier Science B.V. All rights reserved. PACS: 95.55.Vj; 98.70.Sa; 96.40.Tv; 95.85.RyKeywords: L3+C detector; Cosmic rays; Muon spectrum; Astroparticle physics 1. IntroductionThe L3þ C experiment (Figs. 1 and 2), installedat the Large Electron Positron collider (LEP) atCERN, Geneva, consists of two major parts:firstly, below ground, the L3 muon spectrometer[1], which is comprised of a large 0:5 T magnetwith a volume of 1000 m

measurement of the mass and the width of the W boson at LEP

Abstract.The mass and the total decay width of the W boson are measured with the L3 detector at the LEP e+e– collider using W-boson pairs produced in 0.7 fb–1 of data collected at centre-of-mass energies between 161 and 209 GeV. Combining semi-leptonic and fully-hadronic final states, the mass and the width of the W boson are determined to be

Observation of a Centrality-Dependent Dijet Asymmetry in Lead-Lead Collisions at sqrt[s_{NN}]=2.76 TeV with the ATLAS Detector at the LHC

nbegin{array}{*{20}c}n {m_{{text{W}}} = 80.270}{ pm 0.046}{ pm 0.031;{text{GeV}}}{{text{and}}} n {Gamma _{{text{W}}} = 2.18}{ pm 0.11}{ pm 0.09;{text{GeV}}}{} nn end{array} n

Study of spin and decay-plane correlations of W bosons in the e(+) e(-)-> W+W- process at LEP

where the first uncertainty is statistical and the second systematic.

The Giant Radio Array for Neutrino Detection (GRAND) : Present and Perspectives

The evolution of the electromagnetic coupling, alpha, in the momentum-transfer range 1800GeV^2<-Q^2<21600GeV^2 is studied with about 40000 Bhabha-scattering events collected with the L3 detector at LEP at centre-of-mass energies 189-209GeV. The running of alpha is parametrised as: alpha(Q^2) = alpha_0/(1-C Delta alpha(Q^2)), where alpha_0=alpha(Q^2=0) is the fine-structure constant and C=1 corresponds to the evolution expected in QED. A fit to the differential cross section of the e+e- ->e+e- process for scattering angles in the range |cos theta|<0.9 excludes the hypothesis of a constant value of alpha, C=0, and validates the QED prediction with the result: C = 1.05 +/- 0.07 +/- 0.14, where the first uncertainty is statistical and the second systematic.

The GRANDproto35 experiment

By using the ATLAS detector, observations have been made of a centrality-dependent dijet asymmetry in the collisions of lead ions at the Large Hadron Collider. In a sample of lead-lead events with a per-nucleon center of mass energy of 2.76 TeV, selected with a minimum bias trigger, jets are reconstructed in fine-grained, longitudinally segmented electromagnetic and hadronic calorimeters. The transverse energies of dijets in opposite hemispheres are observed to become systematically more unbalanced with increasing event centrality leading to a large number of events which contain highly asymmetric dijets. This is the first observation of an enhancement of events with such large dijet asymmetries, not observed in proton-proton collisions, which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium.