F. Ruggieri

Direct observation of the decay of beauty particles into charm particles

Abstract The associated production of a pair of beauty particles B− and B 0 by a 350 GeV π− interaction has been observed in an emulsion target inserted in an array of silicon microstrip detectors. Both beauty particles decay into charm particles, both of which are also observed to decay in the emulsion. Two negative muons were identified and their momenta measured in a large muon spectrometer. One muon has a pT of 1.9 GeV/c and is associated with a beauty particle decay. The other, with a pT of 0.45 GeV/c is associated with a charm particle decay. The flight times of the two beauty particles are respectively (0.8 ± 0.1) × 10−13 s and (5+2−1) × 10−13 s. Alternative interpretations of this event have negligible probability.

A Comparison of Charged Current Cross Sections and Structure Functions for Neutrino and Antineutrino Beams on Hydrogen and Neon

Abstract Using BEBC equipped with a hydrogen-filled neon-surrounded track-sensitive target, the charged current cross sections and structure functions of hydrogen and neon targets traversed by the same neutrinos and antineutrinos are compared directly. The measured total cross-section ratios between hydrogen and neon allow precise total cross-section values for hydrogen to be inferred. Using this normalization, the ν and ν hydrogen data are combined and the quark distributions in free nucleons, parametrised as functions of ξ, are extracted. This free-nucleon parametrisation is then compared directly with the neon data in order to measure nuclear effects such as those recently reported by the EMC collaboration. Only small effects are seen, in excellent agreement with recent SLAC data in a more similar A and q 2 range.

An investigation of the EMC effect using antineutrino interactions in deuterium and neon

Abstract Antineutrino interactions in BEBC are compared to look for differences between the differential cross sections per nucleon in neon and in deuterium. The identical geometries, beam spectra and muon identification criteria and acceptances allow comparison with very small systematic errors. The results are compared in detail with μ and e scattering data from EMC and SLAC. We find no rise in the ratio d σ/ d x ( ν Ne )/σ/ d x ( ν D 2 ) at low x, independent of Q2 up to Q2 ∼ 14 GeV2.

Performance of a limited streamer tube hadron calorimeter

The energy response and the resolution of a hadron calorimeter test module prepared by the ALEPH collaboration at LEP have been studied between 5 and 50 GeV. The energy resolution for pions follows a 0.78√E law for orthogonally incident particles. Effects of different incident polar angles (θ = 90°, 60°, 50°) are studied. The wire readout and the trigger capability are also discussed.

A-dependence of the charm production cross section in 300 GeV/c proton interactions

Abstract The A-dependence of the charm production cross section is determined by measuring the yield of prompt single muons in a beam-dump experiment, using a 300 GeV/c proton beam on Al, Fe, and U targets. Assuming that the production cross section varies as Aα, we obtain α(μ+) = 0.79±0.12 and α(μ−) = 0.76±0.13 in the kinematical region xF≳0.1 of the charm.

STUDY OF THE DIFFUSE GAMMA-RAY EMISSION FROM THE GALACTIC PLANE WITH ARGO-YBJ

The events recorded by ARGO-YBJ in more than fiveyears of data collection have been analyzed to determine the diffuse gamma-ray emission in the Galactic plane at Galactic longitudes 25° < l < 100° and Galactic latitudes b 5 ∣ ∣< °. The energy range covered by this analysis, from ∼350 GeV to ∼2 TeV, allows the connection of the region explored by Fermi with the multi-TeV measurements carried out by Milagro. Our analysis has been focused on two selected regions of the Galactic plane, i.e., 40° < l < 100° and 65° < l <8 5 °( the Cygnus region), where Milagro observed an excess with respect to the predictions of current models. Great care has been taken in order to mask the most intense gamma-ray sources, including the TeV counterpart of the Cygnus cocoon recently identified by ARGO-YBJ, and to remove residual contributions. The ARGO-YBJ results do not show any excess at sub-TeV energies corresponding to the excess found by Milagro, and are consistent with the predictions of the Fermi model for the diffuse Galactic emission. From the measured energy distribution we derive spectral indices and the differential flux at 1 TeV of the diffuse gamma-ray emission in the sky regions investigated.

THE DOUBLE ASSOCIATED PRODUCTION OF CHARMED PARTICLES BY THE INTERACTION OF 350 GEV/C PI-MESONS WITH EMULSION NUCLEI

Abstract Evidence is reported for the simultaneous production of four charmed particles in interactions induced by 350 GeV/ c π − mesons in stacks of nuclear emulsions. The events were found during a search for beauty particles among a sample of about 200 interactions with candidates for charmed particles. The events selected required the presence of at least one muon with a high component of momentum transverse to the beam direction.

CRAB NEBULA: FIVE-YEAR OBSERVATION WITH ARGO-YBJ

The ARGO-YBJ air shower detector monitored the Crab Nebula g amma ray emission from 2007 November to 2013 February. The integrated signal, consisting of ∼3.3× 105 events, reached the statistical significance of 21.1 standard deviations. The obtained energy spectrum in t he energy range 0.3-20 TeV can be described by a power law function dN/dE = I 0 (E / 2 TeV)−α, with a flux normalization I 0 = (5.2± 0.2)× 10−12 photons cm−2 s−1 TeV−1 andα = 2.63± 0.05, corresponding to an integrated flux above 1 TeV of 1.97 × 10−11 photons cm−2 s−1. The systematic error is estimated to be less that 30% for the flux normalization and 0.06 for the spectral index. Assuming a power law spectrum with an exponential cut off dN/dE = I0 (E / 2 TeV)−α exp (-E / Ecut), the lower limit of the cutoff energy Ecut is 12 TeV, at 90% confidence level. Our extended dataset allow s the study of the TeV emission over long timescales. Over five years, the lig t curve of the Crab Nebula in 200-day bins is compatible with a steady emission with a probability of 7.3 × 10−2. A correlated analysis with Fermi-LAT data over∼4.5 years using the light curves of the two experiments gives a Pearson correlation coefficient r = 0.56± 0.22. Concerning flux variations on timescales of days, a “bl ind” search for flares with a duration of 1-15 days gives no excess with a significance higher than four standard eviations. The average rate measured by ARGOYBJ during the three most powerful flares detected by Fermi-L AT is 205± 91 photons day −1, consistent with the average value of 137 ± 10 day−1.

A Hybrid Experiment to Search for Beauty Particles

We give here a detailed description of experiment WA75, which was performed at CERN to search for beauty particles. Events containing at least one muon with a high momentum transverse to the beam direction were selected; then the primary interactions and decay vertices, located in stacks of nuclear research emulsions, were examined and analysed. The various parts of the apparatus are described and the off-line analysis and search in emulsion are discussed. An estimate is made of the sensitivity of the experiment to beauty- and charmed-particle production.

Experimental study of uranium-scintillator and iron-scintillator calorimetry in the energy range 135–350 GeV☆

Abstract Results are reported of measurements made using a sampling hadronic calorimeter in the energy range 135–350 GeV. The responses to hadronic showers at various energies using iron and uranium of different thicknesses as absorbers have been compared. The results obtained in iron are in substantial agreement with the existing data, while those in uranium show an unexpected overcompensation in the hadronic response. Direct measurement of the e π ratio is in agreement with this statement.