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P. Abreu

Publications and source records attributed to P. Abreu.

At least 127 records · Page 7Linked to original sources
arXiv2009

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.

astro-ph.IM↗
arXiv2009

Operations of and Future Plans for the Pierre Auger Observatory

Technical reports on operations and features of the Pierre Auger Observatory, including ongoing and planned enhancements and the status of the future northern hemisphere portion of the Observatory. Contributions to the 31st International Cosmic Ray Conference, Lodz, Poland, July 2009.

astro-ph.IM↗
arXiv2009

Upper limit on the cosmic-ray photon fraction at EeV energies from the Pierre Auger Observatory

From direct observations of the longitudinal development of ultra-high energy air showers performed with the Pierre Auger Observatory, upper limits of 3.8%, 2.4%, 3.5% and 11.7% (at 95% c.l.) are obtained on the fraction of cosmic-ray photons above 2, 3, 5 and 10 EeV (1 EeV = 10^18 eV) respectively. These are the first experimental limits on ultra-high energy photons at energies below 10 EeV. The results complement previous constraints on top-down models from array data and they reduce systematic uncertainties in the interpretation of shower data in terms of primary flux, nuclear composition and proton-air cross-section.

astro-ph.HE↗
arXiv2002

Charged and Identified Particles in the Hadronic Decay of W Bosons and in e+e- -> q qbar from 130 to 200 GeV

Inclusive distributions of charged particles in hadronic W decays are experimentally investigated using the statistics collected by the DELPHI experiment at LEP during 1997, 1998 and 1999, at centre-of-mass energies from 183 to around 200 GeV. The possible effects of interconnection between the hadronic decays of two Ws are not observed. Measurements of the average multiplicity for charged and identified particles in q qbar and WW events at centre-of-mass energies from 130 to 200 GeV and in W decays are presented. The results on the average multiplicity of identified particles and on the position xi^* of the maximum of the xi_p = -log(2p/sqrt(s)) distribution are compared with predictions of JETSET and MLLA calculations.

hep-ex↗
arXiv2001

Colour Reconnection at LEPII

The preliminary results on the search of colour reconnection effects (CR) from the four experiments at LEP, Aleph, Delphi, L3 and Opal, are reviewed. Extreme models are excluded by studies of standard variables, and on going studies of a method first suggested by L3, the particle flow method, are yet inconclusive.

hep-ph↗
arXiv2001

Measurement of the B/s0 Lifetime and Study of B/s0 anti-B/s0 Oscillations using D/s l Events

Lifetime and oscillations of B0s mesons have been studied in events with a large transverse momentum lepton and a Ds of opposite electric charge in the same hemisphere, selected from about 3.6 million hadronic Z0 decays accumulated by DELPHI between 1992 and 1995. The B0s lifetime and the fractional width difference between the two physical B0s states have been found to be: τ_(B0s) = (1.42^{+0.14}_{-0.13}(stat.) +/- 0.03(syst.)) ps ΔΓ(B0s)/Γ(B0s) < 0.46 at the 95% C.L. In the latter result it has been assumed that τ_(B0s)=τ_(B0d). Using the same sample, a limit on the mass difference between the physical B0s states has been set: Delta(m_B0s) > 7.4 ps^{-1} at the 95% C.L. with a corresponding sensitivity equal to 8.1 ps^{-1}.

hep-ex↗
arXiv2001

A Study of the Lorentz Structure in Tau Decays

This paper describes a measurement of the Michel parameters, η, ρ, ξ, ξδ, and the average ν_τ helicity, h_{ν_τ}, in tau lepton decays together with the first measurement of the tensor coupling in the weak charged current. The tau+tau- pairs were produced at the LEP e+e- collider at CERN from 1992 through 1995 in the DELPHI detector. Assuming lepton universality in the decays of the tau the measured values of the parameters were: η= -0.005 +/- 0.036 +/- 0.037, ρ= 0.775 +/- 0.023 +/- 0.020, ξ= 0.929 +/- 0.070 +/- 0.030, ξδ= 0.779 +/- 0.070 +/- 0.028, h_{ν_τ} = -0.997 +/- 0.027 +/- 0.011. The strength of the tensor coupling was measured to be κ^W_τ= -0.029 +/- 0.036 +/- 0.018. The first error is statistical and the second error is systematic in all cases. The results are consistent with the V-A structure of the weak charged current in decays of the tau lepton.

hep-ex↗
arXiv2001

Single Intermediate Vector Boson Production in e+e- collisions at sqrt(s) = 183 and 189 GeV

The cross-sections for the production of single charged and neutral intermediate vector bosons were measured using integrated luminosities of 52 pb^{-1} and 154 pb^{-1} collected by the DELPHI experiment at centre-of-mass energies of 182.6 GeV and 188.6 GeV, respectively. The cross-sections for the reactions were determined in limited kinematic regions. The results found are in agreement with the Standard Model predictions for these channels.

hep-ex↗
arXiv2001

Identified Charged Particles in Quark and Gluon Jets

A sample of 2.2 million hadronic Z decays, selected from the data recorded by the Delphi detector at LEP during 1994-1995 was used for an improved measurement of inclusive distributions of pi+, K+ and p and their antiparticles in gluon and quark jets. The production spectra of the individual identified particles were found to be softer in gluon jets compared to quark jets, with a higher multiplicity in gluon jets as observed for inclusive charged particles. A significant proton enhancement in gluon jets is observed indicating that baryon production proceeds directly from colour objects. The maxima, xi^*, of the xi-distributions for kaons in gluon and quark jets are observed to be different.

hep-ex↗
arXiv2001

Study of Dimuon Production in Photon-Photon Collisions and Measurement of QED Photon Structure Functions at LEP

Muon pair production in the process e+e- -> e+e-mu+mu- is studied using the data taken at LEP1 (sqrt(s) \simeq m_Z) with the DELPHI detector during the years 1992-1995. The corresponding integrated luminosity is 138.5 pb^{-1}. The QED predictions have been tested over the whole Q^2 range accessible at LEP1 (from several GeV^2/c^4 to several hundred GeV^2/c^4) by comparing experimental distributions with distributions resulting from Monte Carlo simulations using various generators. Selected events are used to extract the leptonic photon structure function F_2^γ. Azimuthal correlations are used to obtain information on additional structure functions, F_A^γand F_B^γ, which originate from interference terms of the scattering amplitudes. The measured ratios F_A^γ/F_2^γand F_B^γ/F_2^γare significantly different from zero and consistent with QED predictions.

hep-ex↗
arXiv2001

Study of B0_s anti-B0_s oscillations and B0_s lifetimes using hadronic decays of B0_s mesons

Oscillations of B0s mesons have been studied in samples selected from about 3.5 million hadronic Z decays detected by DELPHI between 1992 and 1995. One analysis uses events in the exclusive decay channels: B0s -> Ds- pi+ or Ds- a1+ and B0s -> anti-D0 K- pi+ or anti-D0 K- a1+, where the D decays are completely reconstructed. In addition, B0s anti-B0s oscillations have been studied in events with an exclusively reconstructed Ds accompanied in the same hemisphere by a high momentum hadron of opposite charge. Combining the two analyses, a limit on the mass difference between the physical B0s states has been obtained: Delta(m_B0s) > 4.0 ps^{-1} at the 95% C.L. with a sensitivity of Delta(m_B0s) = 3.2 ps^{-1}. Using the latter sample of events, the B0s lifetime has been measured and an upper limit on the decay width difference between the two physical B0s states has been obtained: tau(B0s) = 1.53^{+0.16}_{-0.15}(stat.) +/- {0.07}(syst.) ps ΔΓ(B0s)/Γ(B0s) < 0.69 at the 95% C.L. The combination of these results with those obtained using Ds+- lepton-+ sample gives: Delta(m_B0s) > 4.9 ps^{-1} at the 95% C.L. with a sensitivity of Delta(m_B0s) = 8.7 ps^{-1}. tau(B0s) = 1.46 +/- 0.11 ps and ΔΓ(B0s)/Γ(B0s) < 0.45 at the 95% C.L.

hep-ex↗
arXiv2001

Measurement of the semileptonic b branching fractions and average b mixing parameter in Z decays

The semileptonic branching fractions for primary and cascade b decays BR(b -> lepton-), BR(b -> c -> lepton+) and BR(b -> cbar -> lepton-) were measured in hadronic Z decays collected by the DELPHI experiment at LEP. The sample was enriched in b decays using the lifetime information and various techniques were used to separate leptons from direct or cascade b decays. By fitting the momentum spectra of di-leptons in opposite jets, the average b mixing parameter chi-bar was also extracted. The following results have been obtained: BR(b -> lepton-) = (10.70 +/- 0.08 (stat) +/- 0.21 (syst)_{+0.44}^{-0.30}(model))% BR(b -> c -> lepton+) = (7.98 +/- 0.22 (stat) +/- 0.21 (syst)^{+0.14}_{-0.20}(model))% BR(b -> cbar -> lepton-) = (1.61 +/- 0.20 (stat) +/- 0.17 (syst)^{+0.30}_{-0.44}(model))% chi-bar = 0.127 +/- 0.013 (stat) +/- 0.005 (syst) +/- 0.004(model)

hep-ex↗
arXiv2001

A Measurement of the Tau Topological Branching Ratios

Using data collected in the DELPHI detector at LEP-1, measurements of the inclusive tau branching ratios for decay modes containing one, three, or five charged particles have been performed, giving the following results: B_1 = B(τ^- -> (particle)^- \geq 0pi^0 \geq 0K^0 ν_τ(\barν)) = (85.316 +/- 0.093 +/- 0.049)%; B_3 = B(τ^- -> 2h^-h^+ \geq 0pi^0 \geq 0K^0 ν_τ) = (14.569 +/- 0.093 +/- 0.048)%; B_5 = B(τ^- -> 3h^-2h^+ \geq 0pi^0 \geq 0K^0 ν_τ) = (0.115 +/- 0.013 +/- 0.006)%, where h is either a charged pi or K meson. The first quoted uncertainties are statistical and the second systematic.

hep-ex↗
arXiv2001

Measurement of the anti-B ---> D* pi lepton anti-neutrino(lepton) Branching Fraction

A study of b semileptonic decays into D, D pi+- and D* pi+- final states is presented. The D0, D+ and D*+ mesons are exclusively reconstructed in Z decay data recorded from 1992 to 1995 in the DELPHI experiment at LEP. The overall branching fractions are measured to be: BR(b -> D^0 \ell^- \barν_{\ell} X) = (7.04 +/- 0.34 (stat) +/- 0.36 (syst.exp) +/- 0.17 (BR_D))% BR(b -> D^+ \ell^- \barν_{\ell} X) = (2.72 +/- 0.19 (stat) +/- 0.16 (syst.exp) +/- 0.18 (BR_D))% BR(b -> D^{*+} \ell^- \barν_{\ell} X) = (2.75 +/- 0.17 (stat) +/- 0.13 (syst.exp) +/- 0.09 (BR_D))% where the D0 and D+ results include also contributions from D*0 and D*+ decays. A fit to the distribution of the pi+- impact parameter to the primary interaction vertex provides a measurement of the b semileptonic branching fractions into the D0 pi+- X, D+ pi+- X and D*+ pi+- X final states. Assuming that single pion decay modes of B mesons dominate, the partial rates for \bar{B} -> D π\ell^- \bar{ν_{\ell}} and \bar{B} -> D^{*} π\ell^- \bar{ν_{\ell}} have been obtained, corresponding to a total branching fraction: BR(\bar{B} -> D π\ell^- \bar{ν_{\ell}}) + BR(\bar{B} -> D^{*} π\ell^- \bar{ν_{\ell}}) = (3.40 +/- 0.52 (stat) +/- 0.32 (syst))% . This result agrees well with the observed difference between the total B semileptonic branching fraction and the sum of the \bar{B} -> D \ell^- \bar{ν_{\ell}} and D^* \ell^- \bar{ν_{\ell}} branching fractions.

hep-ex↗