W. Fulgione

The EAS size spectrum and the cosmic ray energy spectrum in the region 1015–1016 eV

Abstract The cosmic ray energy spectrum in the range E 0 = 10 15 –10 16 eV (including the region of the steepening, “knee” ) is studied by means of the EAS-TOP array (Campo Imperatore, Gran Sasso Laboratories, atmospheric depth 820 g cm −2 ). Measurements of the electromagnetic size ( N e = total number of charged particles at the observation level) are performed as a function of zenith angle with statistical accuracies of a few percent. The change of slope of the spectrum is observed in each bin of zenith angle at size values decreasing with increasing atmospheric depth. Its attenuation is compatible with the one of shower particles ( Λ e = 219 ± 3 g cm −2 ). This observation provides a consistency check, supporting a normal behaviour of showers at the break, that make plausible astrophysical interpretations based on an effect on primaries occurring at a given primary energy. The break has a “sharp” shape (i.e., within experimental errors is compatible with two intersecting power laws) that represents a constraint with which any interpretation has to match. The change of slope of the power law index reproducing the size spectrum is Δγ = 0.40 ± 0.09. The derived all particle energy spectrum is in good agreement with the extrapolation of the direct measurements at low energies and with other EAS data at and above the knee. Power laws fits to the energy spectrum below and above the knee give (in units of m −2 s −1 sr −1 TeV −1 ) S ( E 0 ) = (3.48 ± 0.06) × 10 −10 ( E 0 /2300) −2.76±0.03 for 900 TeV E 0 S ( E 0 ) = (3.77 ± 0.08) × 10 −11 ( E 0 /5000) −3.19±0.06 for 5000 TeV E 0 4 TeV. The systematic uncertainties connected to the interaction model and the primary composition are discussed.

UHE cosmic ray event reconstruction by the electromagnetic detector of EAS-TOP

Abstract UHE cosmic rays are studied by means of the detectors of the different components of secondaries produced by their interactions in the atmosphere (EAS). We describe and discuss the reconstruction techniques and accuracies of the e.m. detector of EAS-TOP. They allow, besides independent high resolution measurements of UHE γ-ray astronomy, good correlation possibilities with the detectors of the different EAS components.

The EAS-TOP array at E0 = 1014 − 10 16eV: Stability and resolutions

Abstract The characteristics of the EAS-TOP extensive air shower array as a detector of very high energy cosmic rays ( E 0 ≥ 10 14 eV) for astrophysical studies are discussed. The array is located on top of the underground Gran Sasso Laboratory in central Italy; a subarray (11 modules of the em detector) has been operating since the end of 1987. From such data the stability of the detector, the timing resolution, the accuracies in the determination of the arrival directions ( δθ = 1.2° at E 0 ∼ 200 TeV in the present configuration) and in the reconstruction of the lateral electron distribution and of the shower size are derived.

Prompt-muon production in cosmic rays

SummaryWe discuss here the results obtained calculating the contribution of prompt muons in the vertical atmospheric muon flux, computed taking into account the up-to-date data from experiments at accelerators and the most recent theoretical achievements on charm generation in nucleon-air nucleus interactions. Our results are compared with the experimental data obtained with underground detectors.RiassuntoSi discutono in questo lavoro i risultati ottenuti sul contributo di muoni pronti al flusso atmosferico verticale dei muoni, calcolato utilizzando i dati piú recenti di esperimenti degli acceleratori ed i risultati teorici sulla produzione di particelle charmate in interazioni nucleoni-nuclei atmosferici. I risultati ottenuti sono confrontati con i dati sperimentali forniti da esperimenti sotterranei.РезюмеМы обсуждаем результаты вычислений вклада мгновенных мюонов в вертикальный роток атмосферных мюонов. Вычисления учитывают данные из зкспериментов на ускорителях и недавние теоретические предсказания по рождению очарованных частиц при, взаимодействиях нуклонов с ядрами воздуха. Наши результаты сравниваются с зкспериментальными данными, полученными с помощью подземных детекторов.

A limit to the rate of ultra high energy γ-rays in the primary cosmic radiation

Abstract An upper limit to the flux of Ultra High Energy (UHE) γ-rays in the primary cosmic radiation is obtained through the data of the electromagnetic and the muon detectors of the EAS-TOP Extensive Air Shower array (Campo Imperatore, National Gran Sasso Laboratories, atmospheric depth 810g cm−2). The search is performed by selecting Extensive Air Showers (EAS) with low muon content. For EAS electron sizes Ne > 6.3 · 105, no showers are observed with the core located inside a fiducial area and no muons recorded in the 140 m2 muon detector, during a live time of 8440 h. The 90% c.l. upper limit to the relative intensity of γ-ray with respect to cosmic ray (c.r.) primaries is I γ I c.r. −5 , at primary energy E0 ≥ 1015 eV: this limit is lower than reported in previous measurements.

Results on candidate UHE gamma-ray sources by the EAS-TOP array (1989–1993)

Abstract A search for UHE gamma-rays from 13 candidate point sources observable in the northern hemisphere (the Crab Nebula and Pulsar, Cygnus X-3, Hercules X-1, Geminga and others) has been performed by the EAS-TOP array during four years of operation since January 1989 to December 1993, at different energy thresholds ( E 0 = 30–300 TeV). DC, periodic and sporadic emissions have been studied, and no evidence for significant excesses has been found from any of these searches. The derived 90% c.l. upper limits to the d.c. flux, for a source culminating at the zenith such as Cygnus X-3, are Φ ( E > 230 TeV) −14 cm −2 s −1 , Φ ( E > 90 TeV) −14 cm −2 s −1 and Φ ( E > 25 TeV) −13 cm −2 s −1 . The excess from the Crab Nebula of February 23, 1989, as reported by the EAS-TOP, Baksan and KGF arrays, remains the only sporadic excess detected with statistically significant confidence level (probability of background imitation ≈ 10 −5 ).

Neutrino burst identification in underground detectors

Abstract We discuss the problem of neutrino burst identification in underground ν-telescopes. First the usual statistical analysis based on the time structure of the events is reviewed, with special attention to the statistical significance of burst candidates. Next, we propose a second level analysis that can provide independent confirmation of burst detection. This exploits the spatial distribution of the single events of a burst candidate, and uses the formalism of the entropy of information. Examples of both techniques are shown, based on the LVD experiment at Gran Sasso.

Study of the cosmic ray primary spectrum at 1015 < E0 < 1016 eV with the EAS-TOP array

Abstract The break observed in the electron shower size power law spectrum of Extensive Air Showers (EAS) at corresponding primary energy E0 ∼ (3–5)1015 eV (“knee”) is studied different EAS components (electromagnetic and muonic) and at different atmospheric depths. A consistent description is obtained. The interpretation of data in terms of primary composition, and following the most accepted high energy interaction models, leads to an increasing average primary mass in this energy range. The study of such behaviour is expected to provide a crucial information for the understanding of the physical parameters that characterize the break for the different primaries.

Study of horizontal air showers from EAS-TOP: a possible tool for UHE neutrino detection?

Abstract Horizontal Air Showers, i.e. events observed at “quasi” horizontal incidence, are studied from EAS-TOP at Campo Imperatore (National Gran Sasso Laboratories). The “reality” of such events as due to deeply penetrating particles is discussed from the experimental point of view. We deduce: • -the measurement of the HE muon flux at E μ = 20 TeV : F μ (> 20 TeV ) = (1.3 ± 0.4) × 10 −11 cm −2 s −1 sr −1 , • -the upper limit to the extraterrestrial HE neutrino flux: I ν (> 10 5 GeV ) −9 cm −2 s −1 sr −1 . • The possibility to develop the technique for UHE ν detection is discussed.

The properties of the detection system of the LVD/UNO experiment

Abstract Characteristics of the liquid scintillator modules used in the LVD/UNO experiment at the Gran Sasso Laboratory are discussed, with particular attention to the electronics and data readout system for energy and time measurement.