C. Vigorito

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.

Measurement of the cosmic ray hadron spectrum up to 30-TeV at mountain altitude: The Primary proton spectrum

The flux of cosmic ray hadrons at the atmospheric depth of 820 g/cm^2 has been measured by means of the EAS-TOP hadron calorimeter (Campo Imperatore, National Gran Sasso Laboratories, 2005 m a.s.l.). The hadron spectrum is well described by a single power law : S(E_h) = (2.25 +- 0.21 +- 0.34(sys)) 10^(-7)(E_h/1000)^(-2.79 +- 0.05) m^(-2) s^(-1) sr^(-1) GeV^(-1) over the energy range 30 GeV-30 TeV. The procedure and the accuracy of the measurement are discussed. The primary proton spectrum is derived from the data by using the CORSIKA/QGSJET code to compute the local hadron flux as a function of the primary proton spectrum and to calculate and subtract the heavy nuclei contribution (basing on direct measurements). Over a wide energy range E_0 = 0.5-50 TeV its best fit is given by a single power law : S(E_0) = (9.8 +- 1.1 +- 1.6(sys)) 10^(-5) (E_0/1000)^(-2.80 +- 0.06) m^(-2) s^(-1) sr^(-1) GeV^(-1). The validity of the CORSIKA/QGSJET code for such application has been checked using the EAS-TOP and KASCADE experimental data by reproducing the ratio of the measured hadron fluxes at the two experimental depths (820 and 1030 g/cm^2 respectively) at better than 10% in the considered energy range.

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.

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 LVD experiment at Gran Sasso

SummaryThe Large-Volume Detector (LVD) in the Gran Sasso underground Laboratory is a multipurpose detector consisting of a large volume of liquid scintillator (at present 562 tons are in data taking) interleaved with limited-streamer tubes. Several physical problems are investigated with LVD, the major being the search for neutrino bursts from gravitational stellar collapses in our Galaxy. In this paper we discuss some results on cosmic neutrinos and cosmic-ray muons obtained with the first of the five towers of LVD (operational since June 1992) and part of the second tower (operational since June 1994). The results of the search for supernovae neutrinos show that LVD is a neutrino observatory able to detect neutrinos of different flavours from gravitational stellar collapses in all our Galaxy, over a wide range of burst durations. Indeed, the carbon-based liquid-scintillator target gives a unique possibility to directly detect neutral- and charged-currents neutrino interactions with a very good signature. This characteristic of LVD allows us to make an indirect estimate of the neutrino rest mass and of neutrino oscillations from supernovae in our Galaxy. No evidence for burst candidates has been found in the data recorded from June 1992 to March 1995, for a total live time of 682 days and a total exposure of 613 tons per year. We present the results of a time coincidence analysis between low-energy signals, eventually due to neutrinos of different flavours, and γ-ray bursts (GRBs) detected by the BATSE experiment. This search covers the period from June 1993 to March 1995, during which 41 GRBs have been selected from the BATSE data. Since no excess of events in LVD has been found, upper limits on the neutrino fluxes are reported for (νe, p), and for neutral- and charged-currents neutrino interactions of different flavours with the C-nuclei of the scintillator. The muon intensity as a function of slant depth is presented. These measurements, obtained during a live time period of 11.556 hours, cover a slant depths range from about 3000 to about 20 000 hg/cm2 of standard rock and extend over five decades of intensity. An interesting result is that the muon flux is independent of slant depth beyond a depth of about 14 000 hg/cm2 of standard rock, and corresponds to near horizontal muons. This is direct evidence that this flux is due to atmospheric neutrinos interacting in the rock surrounding LVD.

Studies of the knee in the electron and muon components of extensive air showers at EAS-TOP

The region of the “knee” of the cosmic ray primary spectrum (10 15 0 16 eV) is studied in the electromagnetic and muon components of Extensive Air Showers by means of the EAS-TOP array. Independent and correlated analysis of the two measurements are presented as a function of zenith angle (i.e. atmospheric depth).

The proton attenuation length and the p-air inelastic cross section at √s2 TeV from EAS-TOP

The attenuation length of proton primaries and the proton-air inelastic cross section are studied at energies E 0 ≈ 10 15 eV by using the EAS-TOP array data. Proton initiated Extensive Air Showers, in the energy range (2 ÷ 4) 10 15 eV and near maximum development, are selected from their N μ ( E μ > 1 GeV) and N e sizes. The experimental attenuation length A obs is compared with those obtained from simulations, including the full detector response. based on different interaction models (HDPM, VENUS, DPMJET, QGSJET and SIBYLL) in the frame of CORSIKA code. The proton-air inelastic cross section is also inferred by using the factor k = Λ obs sim /λ p —air sim obtained from each interaction model.