Results on high-energy cosmic rays by EAS-TOP at Gran Sasso

Very High-Energy cosmic rays have to be studied through the ground-based detectors of the Extensive Air Showers (EAS) that they produce in the atmosphere. The main measurements to be performed are of: primary energy spectra, composition, anisotropies, «neutral primary» astronomy, and interaction properties. This requires complete detectors of all the EAS components, and for this purpose the EAS-TOP array has been constructed at Campo Imperatore (2000 m a.s.l.) on top of the Gran Sasso underground laboratories. The array has been progressively going into operation since 1988. In this paper we present the status and performances of the different detectors, and the results obtained up to now on the different items under discussion

Muon `Depth -- Intensity' Relation Measured by LVD Underground Experiment and Cosmic-Ray Muon Spectrum at Sea Level

We present the analysis of the muon events with all muon multiplicities collected during 21804 hours of operation of the first LVD tower. The measured angular distribution of muon intensity has been converted to the `depth -- vertical intensity' relation in the depth range from 3 to 12 km w.e.. The analysis of this relation allowed to derive the power index, $\gamma$, of the primary all-nucleon spectrum: $\gamma=2.78 \pm 0.05$. The `depth -- vertical intensity' relation has been converted to standard rock and the comparison with the data of other experiments has been done. We present also the derived vertical muon spectrum at sea level.Comment: 7 pages, 3 figures, to be published on Phys. Rev.

Upper Limit on the Prompt Muon Flux Derived from the LVD Underground Experiment

We present the analysis of the muon events with all muon multiplicities collected during 21804 hours of operation of the first LVD tower. The measured depth-angular distribution of muon intensities has been used to obtain the normalization factor, A, the power index, gamma, of the primary all-nucleon spectrum and the ratio, R_c, of prompt muon flux to that of pi-mesons - the main parameters which determine the spectrum of cosmic ray muons at the sea level. The value of gamma = 2.77 +/- 0.05 (68% C.L.) and R_c < 2.0 x 10^-3 (95% C.L.) have been obtained. The upper limit to the prompt muon flux favours the models of charm production based on QGSM and the dual parton model.Comment: 10 pages, 4 figures, RevTex. To appear in Phys. Rev.

A measurement of the solar and sidereal cosmic-ray anisotropy at E(0)similar to 10(14)eV

The results of the measurement of the cosmic-ray solar and sidereal anisotropies at primary energy E(0) approximate to 10(14) eV performed by the EAS-TOP Extensive Air Shower array (Campo Imperatore, National Gran Sasso Laboratories, 2005 m above sea level, latitude 42 degrees.5 N are presented. The measurement includes 4 years of data taking (1990, 1992, 1993, 1994) for a total of 1.3 x 10(9) events and is performed at two different mean primary energies: (E) over bar(0)(v) approximate to 1.5 x 10(14) eV and (E) over bar(0)(i) approximate to 2.5 x 10(14) eV. The two results are compatible (within 2 sigma) and can therefore be combined. The obtained amplitude and phase of the first harmonic in sidereal time are (in the equatorial plane) A(sid,delta=0c)((E) over bar(0) approximate to 2 x 10(14) eV) = (3.73 +/- 0.57) x 10(-4) and phi(sid) = 1.82 +/- 0.49 hr local sidereal time, with significance 6.5 sigma. The amplitude of the anisotropy exhibits the expected cos delta dependence. A first harmonic in solar time compatible with the expected Compton-Getting effect due to the motion of revolution of the Earth around the Sun is observed with significance 7.3 sigma. The corresponding measured amplitude and phase (also in the equatorial plane) are A(sol,delta=0o)=(4.06 +/- 0.55) x 10(-4) and phi(sol) = 4.92 +/- 0.53 hr, the expected values being 4.7 x 10(-4) and 6.0 hr. Different checks of stability of the detectors and consistency of the data are presented

Search For Gamma-ray Bursts of Energy E-gamma-greater-than-or-equal-to-10-gev and E-gamma-greater-than-or-equal-to-100-tev In Correlation With Batse Events

We present the results of a search for Gamma Ray Bursts at energies E(gamma) greater than or equal to 10 GeV and E(gamma) greater than or equal to 100 TeV made by the EAS-TOP Air Shower Array in correlation with similar to 50 events detected by BATSE in the last 3 years. This analysis gives an indication of the sensitivity of air shower arrays in the detection of GRBs at energies beyond the range seen by satellite experiments

Search for chaotic features in the arrival times of air showers

We study sequences of times between successive arrivals of air showers detected in the EAS-TOP experiment (primary energy between 70 and 1000 TeV) in order to establish their nature, whether stochastic or chaotic

Multicomponent extensive air shower observations at EAS-TOP

The study of cosmic rays at primary energies E-0 > 10(14) eV requires the detection of the different components of Extensive Air Showers through ground based stations. EAS-TOP is such an array (located at Campo Imperatore, 2000 m a.s.l., National Gran Sasso Laboratories), including detectors of the electromagnetic, muon (E-mu approximate to GeV at the surface, and E-mu approximate to TeV in coincidence with the detectors operating in the underground Gran Sasso Laboratories), hadron and atmospheric Cerenkov light components. The combined operation of the detectors is discussed from the point of view of the capability of measuring the cosmic ray primary spectrum and composition. The main lines for checking the significant features of the high energy hadron interaction model used for the interpretation of the data are outlined

Search for gamma-ray bursts at photon energies E>=10 GeV and E>=80 TeV

The EAS-TOP extensive air shower array has been operating since 1992 in the search for gamma-ray bursts at primary energies E(1) greater than or equal to 10 GeV and E(2) greater than or equal to 80 TeV. The study is performed by searching for short transients in the cosmic-ray intensity in the single particle (E(1)) and extensive air shower (E(2)) counting rates at mountain altitude (2005 m above sea level). We discuss the method and the results obtained both in sky survey and in correlation with BATSE events. In both energy ranges, the observed fluctuations in the event rate obtained in the sky survey during similar to 800 days of live time are compatible with the statistical fluctuations of the cosmic-ray background. A single candidate of time duration Delta t similar to 2 s and energy fluence F(10 < E < 100 GeV) = 1.7 x 10(-4)/(cos theta)(10.5) ergs cm(-2) (where theta is the unknown zenith angle) has been observed on 1992 July 15 at 13:22:26 UT in the energy range E(1) greater than or equal to 10 GeV with significance 10.6 and 20.1 sigma in two measurement channels. In the analysis made in correlation with similar to 50 events detected by BATSE, no burst candidate was found in time coincidence or in the 2 hr interval, around the BATSE detection time. The following ranges of upper limits F-max to the energy fluence in the time interval Delta t(90) in which BATSE detected 90% of the counts are obtained: F-max = 2.3 x 10(-5)-7.4 x 10(-3) ergs cm(-2) (10 < E < 100 GeV) F-max = 1.6 x 10(-6)-3.3 x 10(-5) ergs cm(-2) (100 < E < 1000 TeV).4691130531

The limit to the UHE extraterrestrial neutrino flux from the observations of horizontal air showers at EAS-TOP

Extensive Air Showers at large zenith angles theta > 70-degrees (Horizontal Air Showers, HAS) are observed at the EAS-TOP array at Campo Imperatore (Gran Sasso Laboratories). The rate of these events exceeds the one due to primary cosmic rays (at this angles) and therefore these showers have to be generated by penetrating particles. Assuming that they are produced by atmospheric muons we derived the muon flux as F(mu)(> 30 TeV) = 1.1 x 10(-11) cm-2 s-1 sr-1, in good agreement with the underground measurements. The upper limits for diffuse neutrino radiation from these measurements is I(nu)(> 10(5) GeV) < 1.5 x 10(-8) CM-2 S-1 sr-1 for ''all-flavour'' neutrinos and dI(nueBAR)(E0)/dE(nueBAR) < 7.6 x 10(-18) CM-2 s-1 sr-1 GeV-1, for the resonant (E0 = m(W)2/2m(e) = 6.4 x 10(6) GeV) neutrinos

Experimental Eas Data Relevant To Underground Physics - the Eas Size Spectrum and the Rate of Has As A Limit To the Astrophysical Nu-flux

The recent data on the EAS size spectrum, and on the rate of 'Horizontal Air Showers' (HAS), as detected by the EAS-TOP experiment at Campo Imperatore (LNGS), are presented. Their implications for the interpretation of underground muon data, and for UHE neutrino astronomy are discussed