1. |
- Abreu, P., et al.
(författare)
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Measurement of the gluon fragmentation function and a comparison of the scaling violation in gluon and quark jets
- 2000
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 13:4, s. 573-589
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Tidskriftsartikel (refereegranskat)abstract
- The fragmentation functions of quarks and gluons are measured in various three-jet topologies in Z decays from the full data set collected with the DELPHI detector at the Z resonance between 1992 and 995. The results at different values of transverse momentum-like scales are compared. A parameterization of the quark and gluon fragmentation functions at a fixed reference scale is given. The quark and gluon fragmentation functions show the predicted pattern of scaling violations. The scaling violation for quark jets as a function of a transverse momentum-like scale is in a good agreement with that observed in lower energy e+e- annihilation experiments. For gluon jets it appears to be significantly stronger. The scale dependences of the gluon and quark fragmentation functions agree with the prediction of the DGLAP evolution equations from which the colour factor ratio CA/CF is measured to be: CA/CF = 2.26 ± 0.09stat. ± 0.06sys. ± 0.12clus.,scale..
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2. |
- Abreu, P., et al.
(författare)
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Study of dimuon production in photon-photon collisions and measurement of QED photon structure functions at LEP
- 2001
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 19:1, s. 15-28
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Tidskriftsartikel (refereegranskat)abstract
- Muon pair production in the process e+e- → e+e- μ+μ- is studied using the data taken at LEP1 (√s ≃ mz) 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 Q2 range accessible at LEP1 (from several GeV2/c4 to several hundred GeV2/c4) 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 Fγ 2. Azimuthal correlations are used to obtain information on additional structure functions, Fγ A and Fγ B, which originate from interference terms of the scattering amplitudes. The measured ratios Fγ A/Fγ 2 and FγB/Fγ 2 are significantly different from zero and consistent with QED predictions.
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3. |
- Aglietta, M, et al.
(författare)
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The cosmic ray primary composition between 10(15) and 10(16) eV from Extensive Air Showers electromagnetic and TeV muon data
- 2004
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Ingår i: Astroparticle physics. - : Elsevier. - 0927-6505 .- 1873-2852. ; 20:6, s. 641-652
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Tidskriftsartikel (refereegranskat)abstract
- The cosmic ray primary composition in the energy range between 10(15) and 10(16) eV, i.e., around the "knee" of the primary spectrum, has been studied through the combined measurements of the EAS-TOP air shower array (2005 m a. s.l., 10(5) m(2) collecting area) and the MACRO underground detector (963 m.a.s.l., 3100 m w.e. of minimum rock overburden, 920 m(2) effective area) at the National Gran Sasso Laboratories. The used observables are the air shower size (N-c) measured by EAS-TOP and the muon number (N-mu) recorded by MACRO. The two detectors are separated on average by 1200 m of rock, and located at a respective zenith angle of about 30degrees. The energy threshold at the surface for muons reaching the MACRO depth is approximately 1.3 TeV. Such muons are produced in the early stages of the shower development and in a kinematic region quite different from the one relevant for the usual N-mu - N-e studies. The measurement leads to a primary composition becoming heavier at the knee of the primary spectrum, the knee itself resulting from the steepening of the spectrum of a primary light component (p, He) of Deltay = 0.7 +/- 0.4 at E-0 similar to 4 x 10(15) eV. The result confirms the ones reported from the observation of the low energy muons at the surface (typically in the GeV energy range), showing that the conclusions do not depend on the production region kinematics. Thus, the hadronic interaction model used (CORSIKA/QGSJET) provides consistent composition results from data related to secondaries produced in a rapidity region exceeding the central one. Such an evolution of the composition in the knee region supports the "standard" galactic acceleration/propagation models that imply rigidity dependent breaks of the different components.. and therefore breaks occurring at lower energies in the spectra of the light nuclei. (C) 2003 Elsevier B.V. All rights reserved.
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4. |
- Aglietta, M, et al.
(författare)
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The cosmic ray proton, helium and CNO fluxes in the 100 TeV energy region from TeV muons and EAS atmospheric Cherenkov light observations of MACRO and EAS-TOP
- 2004
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Ingår i: Astroparticle physics. - : Elsevier. - 0927-6505 .- 1873-2852. ; 21:3, s. 223-240
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Tidskriftsartikel (refereegranskat)abstract
- The primary cosmic ray (CR) proton, helium and CNO fluxes in the energy range 80-300 TeV are studied at the National Gran Sasso Laboratories by means of EAS-TOP (Campo Imperatore, 2005 m a.s.l.) and MACRO (deep underground, 3100 m w.e., the surface energy threshold for a muon reaching the detector being E-mu(th) approximate to 1.3 TeV). The measurement is based on: (a) the selection of primaries based on their energy/nucleon (i.e., with energy/nucleon sufficient to produce a muon with energy larger than 1.3 TeV) and the reconstruction of the shower geometry by means of the muons recorded by MACRO in the deep underground laboratories; (b) the detection of the associated atmospheric Cherenkov light (C.l.) signals by means of the C.l. detector of EAS-TOP. The C.l. density at core distance r > 100 m is directly related to the total primary energy E-0. Proton and helium ("p + He") and proton, helium and CNO ("p + He + CNO") primaries are thus selected at E-0 approximate to 80 TeV, and at E-0 similar or equal to 250 TeV, respectively. Their flux is measured: J(p+He)(80 TeV) = (1.8 +/- 0.4) x 10(-6) m(-1)-s(-1) sr(-1) TeV-1, and J(p+He+CNO)(250 TeV) = (1.1 +/- 0.3) x 10(-7) m(-2)-s(-1) sr(-1) TeV-1, their relative weights being J(p+He)(J(p+He+CNO)) over bar (250 TeV) = 0.78 +/- 0.17. By using the measurements of the proton spectrum obtained from the direct experiments and hadron flux data in the atmosphere, we obtain for the relative weights of the three components at 250 TeV: J(p) : J(He) : J(CNO) = (0.20 +/- 0.08) : (0.58 +/- 0.19) : (0.22 +/- 0.17). This corresponds to the dominance of helium over proton primaries at 100-1000 TeV, and a possible non-negligible contribution from CNO. The lateral distribution of Cherenkov light in Extensive Air Showers (EASs), which is related to the rate of energy deposit of the primary in the atmosphere, is measured for a selected proton and helium primary beam, and good agreement is found when compared with the one calculated with the CORSIKA/QGSJET simulation model. (C) 2004 Elsevier B.V. All rights reserved.
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5. |
- Ambrosio, M, et al.
(författare)
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The MACRO detector at Gran Sasso
- 2002
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier. - 0168-9002 .- 1872-9576. ; 486:3, s. 663-707
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Tidskriftsartikel (refereegranskat)abstract
- MACRO was an experiment that ran in the Laboratori Nazionali del Gran Sasso from 1988 to 2000. Its principal goal was to observe magnetic monopoles or set significantly lower experimental flux limits than had been previously available in the velocity range from about beta = 10(-4) to unity. In addition it made a variety of other observations. Examples are: setting flux limits on other so far unobserved particles such as nuclearites and lightly ionizing particles, searching for WIMP annihilations in the Earth and the Sun and for neutrino bursts from stellar collapses in or near our Galaxy, and making measurements relevant to high energy muon and neutrino astronomy and of the flux of up-going muons as a function of nadir angle showing evidence for neutrino oscillations. The apparatus consisted of three principal types of detectors: liquid scintillator counters, limited streamer tubes, and nuclear track etch detectors. In addition, over part of its area it contained a transition radiation detector. The general design philosophy emphasized redundancy and complementarity. This paper describes the technical aspects of the complete MACRO detector, its operational performance, and the techniques used to calibrate it and verify its proper operation. It supplements a previously published paper which described the first portion of the detector that was built and operated. (C) 2002 Elsevier Science B.V. All rights reserved.
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6. |
- Ambrosio, M, et al.
(författare)
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Muon energy estimate through multiple scattering with the MACRO detector
- 2002
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - 0168-9002 .- 1872-9576. ; 492:3, s. 376-386
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Tidskriftsartikel (refereegranskat)abstract
- Muon energy measurement represents an important issue for any experiment addressing neutrino-induced up-going muon studies. Since the neutrino oscillation probability depends on the neutrino energy, a measurement of the muon energy adds an important piece of information concerning the neutrino system. We show in this paper how the MACRO limited streamer tube system can be operated in drift mode by using the TDCs included in the QTPs, an electronics designed for magnetic monopole search. An improvement of the space resolution is obtained, through an analysis of the multiple scattering of muon tracks as they pass through our detector. This information can be used further to obtain an estimate of the energy of muons crossing the detector. Here we present the results of two dedicated tests, performed at CERN PS-T9 and SPS-X7 beam lines, to provide a full check of the electronics and to exploit the feasibility of such a multiple scattering analysis. We show that by using a neural network approach, we are able to reconstruct the muon energy for E-mu < 40 GeV. The test beam data provide an absolute energy calibration, which allows us to apply this method to MACRO data. (C) 2002 Elsevier Science B.V. All rights reserved.
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7. |
- Ambrosio, M, et al.
(författare)
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Final results of magnetic monopole searches with the MACRO experiment
- 2002
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Ingår i: European Physical Journal C. - : Springer. - 1434-6044 .- 1434-6052. ; 25:4, s. 511-522
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Tidskriftsartikel (refereegranskat)abstract
- We present the final results obtained by the MACRO experiment in the search for GUT magnetic monopoles in the penetrating cosmic radiation, for the range 4 x 10(-5) < 3 < 1. Several searches with all the MACRO sub-detectors (i.e. scintillation counters, limited streamer tubes and nuclear track detectors) were performed, both in stand alone and combined ways. No candidates were detected and a 90% Confidence Level (C.L.) upper limit to the local magnetic monopole flux was set at the level of 1.4 x 10(-16) cm(-2) s(-1) sr(-1). This result is the first experimental limit obtained in direct searches which is well below the Parker bound in the whole 3 range in which GUT magnetic monopoles are,expected.
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8. |
- Ambrosio, M, et al.
(författare)
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Matter effects in upward-going muons and sterile neutrino oscillations
- 2001
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Ingår i: Physics Letters B. - : Elsevier. - 0370-2693 .- 1873-2445. ; 517:1-2, s. 59-66
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Tidskriftsartikel (refereegranskat)abstract
- The angular distribution of upward-going muons produced by atmospheric neutrinos in the rock below the MACRO detector shows anomalies in good agreement with two flavor nu (mu) --> nu (tau) oscillations with maximum mixing and Deltam(2) around 0.0024 eV(2). Exploiting the dependence of magnitude of the matter effect on oscillation channel, and using a set of 809 upward-going muons observed in MACRO, we show that the two flavor nu (mu) --> nu (s) oscillation is disfavored with 99% C.L. with respect to nu (mu) --> nu (tau). (C) 2001 Elsevier Science B.V. All rights reserved.
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9. |
- Ambrosio, M, et al.
(författare)
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Search for cosmic ray sources using muons detected by the MACRO experiment
- 2003
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Ingår i: Astroparticle physics. - : Elsevier. - 0927-6505 .- 1873-2852. ; 18:6, s. 615-627
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Tidskriftsartikel (refereegranskat)abstract
- The MACRO underground detector at Gran Sasso Laboratory recorded 60 million secondary cosmic ray muons from February 1989 until December 2000. Different techniques were used to analyze this sample in search for density excesses from astrophysical point-like sources. No evidence for DC excesses for any source in an all-sky survey is reported. In addition, searches for muon excess correlated with the known binary periods of Cygnus X-3 and Hercules X-1, and searches for statistically significant bursting episodes from known gamma-ray sources are also proved negative. (C) 2002 Elsevier Science B.V. All rights reserved.
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10. |
- Ambrosio, M, et al.
(författare)
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Search for diffuse neutrino flux from astrophysical sources with MACRO
- 2003
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Ingår i: Astroparticle physics. - : Elsevier. - 0927-6505 .- 1873-2852. ; 19:1, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- Many galactic and extragalactic astrophysical sources are currently considered promising candidates as high-energy neutrino emitters. Astrophysical neutrinos can be detected as upward-going muons produced in charged-current interactions with the medium surrounding the detector. The expected neutrino fluxes from various models start to dominate on the atmospheric neutrino background at neutrino energies above some tens of TeV. We present the results of a search for an excess of high-energy upward-going muons among the sample of data collected by MACRO during similar to5.8 years of effective running time. No significant evidence for this signal was found. As a consequence, an upper limit on the flux of upward-going muons from high-energy neutrinos was set at the level of 1.7 x 10(-14) cm(-2) s(-1) sr(-1). The corresponding upper limit for the diffuse neutrino flux was evaluated assuming a neutrino power law spectrum. Our result was compared with theoretical predictions and upper limits from other experiments. (C) 2002 Elsevier Science B.V. All rights reserved.
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