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G. Castellini

Publications and source records attributed to G. Castellini.

At least 73 records · Page 4Linked to original sources
arXiv2014

Transverse momentum distribution and nuclear modification factor of forward neutral pion in proton--lead collisions at $\sqrt{s_{NN}} = 5.02$TeV

The transverse momentum ($p_\text{T}$) distribution for inclusive neutral pions in the very forward rapidity region has been measured, with the Large Hadron Collider forward detector (LHCf), in proton--lead collisions at nucleon-nucleon center-of-mass energies of $\sqrt{s_{NN}} = 5.02$TeV at the LHC. The $p_\text{T}$ spectra obtained in the rapidity range $-11.0 < y_\text{lab} < -8.9$ and $0 < p_\text{T} < 0.6$GeV (in the detector reference frame) show a strong suppression of the production of neutral pions after taking into account ultra-peripheral collisions. This leads to a nuclear modification factor value, relative to the interpolated $p_\text{T}$ spectra in proton-proton collisions at $\sqrt{s} = 5.02$TeV, of about 0.1--0.4. This value is compared with the predictions of several hadronic interaction Monte Carlo simulations.

nucl-ex↗
arXiv2013

The performance of the LHCf detector for hadronic showers

The Large Hadron Collider forward (LHCf) experiment has been designed to use the LHC to benchmark the hadronic interaction models used in cosmic-ray physics. The LHCf experiment measures neutral particles emitted in the very forward region of LHC collisions. In this paper, the performances of the LHCf detectors for hadronic showers was studied with MC simulations and beam tests. The detection efficiency for neutrons is from 60% to 70% above 500 GeV. The energy resolutions are about 40% and the position resolution is 0.1 to 1.3mm depend on the incident energy for neutrons. The energy scale determined by the MC simulations and the validity of the MC simulations were examined using 350 GeV proton beams at the CERN-SPS.

physics.ins-det↗
arXiv2013

The cosmic-ray positron energy spectrum measured by PAMELA

Precision measurements of the positron component in the cosmic radiation provide important information about the propagation of cosmic rays and the nature of particle sources in our Galaxy. The satellite-borne experiment PAMELA has been used to make a new measurement of the cosmic-ray positron flux and fraction that extends previously published measurements up to 300 GeV in kinetic energy. The combined measurements of the cosmic-ray positron energy spectrum and fraction provide a unique tool to constrain interpretation models. During the recent solar minimum activity period from July 2006 to December 2009 approximately 24500 positrons were observed. The results cannot be easily reconciled with purely secondary production and additional sources of either astrophysical or exotic origin may be required.

astro-ph.HE↗
arXiv2013

Cosmic-Ray Positron Identification with the PAMELA experiment

The PAMELA satellite borne experiment is designed to study cosmic rays with great accuracy in a wide energy range. One of PAMELA's main goal is the study of the antimatter component of cosmic rays. The experiment, housed on board the Russian satellite Resurs-DK1, was launched on June 15th 2006 and it is still taking data. In this work we present the measurement of galactic positron energy spectrum in the energy range between 500 MeV and few hundred GeV.

astro-ph.HE↗
arXiv2013

An evaluation of the exposure in nadir observation of the JEM-EUSO mission

We evaluate the exposure during nadir observations with JEM-EUSO, the Extreme Universe Space Observatory, on-board the Japanese Experiment Module of the International Space Station. Designed as a mission to explore the extreme energy Universe from space, JEM-EUSO will monitor the Earth's nighttime atmosphere to record the ultraviolet light from tracks generated by extensive air showers initiated by ultra-high energy cosmic rays. In the present work, we discuss the particularities of space-based observation and we compute the annual exposure in nadir observation. The results are based on studies of the expected trigger aperture and observational duty cycle, as well as, on the investigations of the effects of clouds and different types of background light. We show that the annual exposure is about one order of magnitude higher than those of the presently operating ground-based observatories.

astro-ph.HE↗
arXiv2013

Measurement of the isotopic composition of hydrogen and helium nuclei in cosmic rays with the PAMELA experiment

The satellite-borne experiment PAMELA has been used to make new measurements of cosmic ray H and He isotopes. The isotopic composition was measured between 100 and 600 MeV/n for hydrogen and between 100 and 900 MeV/n for helium isotopes over the 23rd solar minimum from July 2006 to December 2007. The energy spectrum of these components carries fundamental information regarding the propagation of cosmic rays in the galaxy which are competitive with those obtained from other secondary to primary measurements such as B/C.

astro-ph.HE↗
arXiv2013

Time dependence of the proton flux measured by PAMELA during the July 2006 - December 2009 solar minimum

The energy spectra of galactic cosmic rays carry fundamental information regarding their origin and propagation. These spectra, when measured near Earth, are significantly affected by the solar magnetic field. A comprehensive description of the cosmic radiation must therefore include the transport and modulation of cosmic rays inside the heliosphere. During the end of the last decade the Sun underwent a peculiarly long quiet phase well suited to study modulation processes. In this paper we present proton spectra measured from July 2006 to December 2009 by PAMELA. The large collected statistics of protons allowed the time variation to be followed on a nearly monthly basis down to 400 MV. Data are compared with a state-of-the-art three-dimensional model of solar modulation.

astro-ph.HE↗
arXiv2012

Measurement of forward neutral pion transverse momentum spectra for $\sqrt{s}$ = 7TeV proton-proton collisions at LHC

The inclusive production rate of neutral pions in the rapidity range greater than $y=8.9$ has been measured by the Large Hadron Collider forward (LHCf) experiment during LHC $\sqrt{s}=7$\,TeV proton-proton collision operation in early 2010. This paper presents the transverse momentum spectra of the neutral pions. The spectra from two independent LHCf detectors are consistent with each other and serve as a cross check of the data. The transverse momentum spectra are also compared with the predictions of several hadronic interaction models that are often used for high energy particle physics and for modeling ultra-high-energy cosmic-ray showers.

hep-ex↗
arXiv2012

Measurement of zero degree inclusive photon energy spectra for $\sqrt{s}=$ 900 GeV proton-proton collisions at LHC

The inclusive photon energy spectra measured by the Large Hadron Collider forward (LHCf) experiment in the very forward region of LHC proton-proton collisions at $\sqrt{s}=$ 900 GeV are reported. The results from the analysis of 0.30 $\mathrm{nb^{-1}}$ of data collected in May 2010 in the two pseudorapidity regions of $η> 10.15$ and $8.77 < η< 9.46$ are compared with the predictions of the hadronic interaction models DPMJET 3.04, EPOS 1.99, PYTHIA 8.145, QGSJET I -.1em I-03 and SIBYLL 2.1, which are widely used in ultra-high-energy cosmic-ray experiments. EPOS 1.99 and SYBILL 2.1 show a reasonable agreement with the spectral shape of the experimental data, whereas they predict lower cross-sections than the data. The other models, DPMJET 3.04, QGSJET I -.1em I-03 and PYTHIA 8.145, are in good agreement with the data below 300 GeV but predict harder energy spectra than the data above 300 GeV. The results of these comparisons exhibited features similar to those for the previously reported data for $\sqrt{s}=$ 7 TeV collisions.

hep-ex↗
arXiv2011

The discovery of geomagnetically trapped cosmic ray antiprotons

The existence of a significant flux of antiprotons confined to Earth's magnetosphere has been considered in several theoretical works. These antiparticles are produced in nuclear interactions of energetic cosmic rays with the terrestrial atmosphere and accumulate in the geomagnetic field at altitudes of several hundred kilometers. A contribution from the decay of albedo antineutrons has been hypothesized in analogy to proton production by neutron decay, which constitutes the main source of trapped protons at energies above some tens of MeV. This Letter reports the discovery of an antiproton radiation belt around the Earth. The trapped antiproton energy spectrum in the South Atlantic Anomaly (SAA) region has been measured by the PAMELA experiment for the kinetic energy range 60--750 MeV. A measurement of the atmospheric sub-cutoff antiproton spectrum outside the radiation belts is also reported. PAMELA data show that the magnetospheric antiproton flux in the SAA exceeds the cosmic-ray antiproton flux by three orders of magnitude at the present solar minimum, and exceeds the sub-cutoff antiproton flux outside radiation belts by four orders of magnitude, constituting the most abundant source of antiprotons near the Earth.

astro-ph.HE↗
arXiv2011

Observations of the December 13 and 14, 2006, Solar Particle Events in the 80 MeV/n - 3 GeV/n range from space with PAMELA detector

We present the space spectrometer PAMELA observations of proton and helium fluxes during the December 13 and 14, 2006 solar particle events. This is the first direct measurement of the solar energetic particles in space with a single instrument in the energy range from $\sim$ 80 MeV/n up to $\sim$ 3 GeV/n. In the event of December 13 measured energy spectra of solar protons and helium were compared with results obtained by neutron monitors and other detectors. Our measurements show a spectral behaviour different from those derived from the neutron monitor network. No satisfactory analytical fitting was found for the energy spectra. During the first hours of the December 13 event solar energetic particles spectra were close to the exponential form demonstrating rather significant temporal evolution. Solar He with energy up to ~1 GeV/n was recorded on December 13. In the event of December 14 energy of solar protons reached ~600 MeV whereas maximum energy of He was below 100 MeV/n. The spectra were slightly bended in the lower energy range and preserved their form during the second event. Difference in the particle flux appearance and temporal evolution in these two events may argue for a special conditions leading to acceleration of solar particles up to relativistic energies.

astro-ph.SR↗
arXiv2011

Measurement of zero degree single photon energy spectra for sqrt(s) = 7TeV proton-proton collisions at LHC

In early 2010, the Large Hadron Collider forward (LHCf) experiment measured very forward neutral particle spectra in LHC proton-proton collisions. From a limited data set taken under the best beam conditions (low beam-gas background and low occurance of pile-up events), the single photon spectra at sqrt(s)=7TeV and pseudo-rapidity (eta) ranges from 8.81 to 8.99 and from 10.94 to infinity were obtained for the first time and are reported in this paper. The spectra from two independent LHCf detectors are consistent with one another and serve as a cross check of the data. The photon spectra are also compared with the predictions of several hadron interaction models that are used extensively for modeling ultra high energy cosmic ray showers. Despite conservative estimates for the systematic errors, none of the models agree perfectly with the measurements. A notable difference is found between the data and the DPMJET 3.04 and PYTHIA 8.145 hadron interaction models above 2TeV where the models predict higher photon yield than the data. The QGSJET II-03 model predicts overall lower photon yield than the data, especially above 2TeV in the rapidity range 8.81<eta<8.99.

hep-ex↗
arXiv2011

PAMELA Measurements of Cosmic-ray Proton and Helium Spectra

Protons and helium nuclei are the most abundant components of the cosmic radiation. Precise measurements of their fluxes are needed to understand the acceleration and subsequent propagation of cosmic rays in the Galaxy. We report precision measurements of the proton and helium spectra in the rigidity range 1 GV-1.2 TV performed by the satellite-borne experiment PAMELA. We find that the spectral shapes of these two species are different and cannot be well described by a single power law. These data challenge the current paradigm of cosmic-ray acceleration in supernova remnants followed by diffusive propagation in the Galaxy. More complex processes of acceleration and propagation of cosmic rays are required to explain the spectral structures observed in our data.

astro-ph.HE↗
arXiv2011

The cosmic-ray electron flux measured by the PAMELA experiment between 1 and 625 GeV

Precision measurements of the electron component in the cosmic radiation provide important information about the origin and propagation of cosmic rays in the Galaxy. Here we present new results regarding negatively charged electrons between 1 and 625 GeV performed by the satellite-borne experiment PAMELA. This is the first time that cosmic-ray electrons have been identified above 50 GeV. The electron spectrum can be described with a single power law energy dependence with spectral index -3.18 +- 0.05 above the energy region influenced by the solar wind (> 30 GeV). No significant spectral features are observed and the data can be interpreted in terms of conventional diffusive propagation models. However, the data are also consistent with models including new cosmic-ray sources that could explain the rise in the positron fraction.

astro-ph.HE↗
arXiv2010

Early results of the LHCf Experiment and their contribution to Ultra-High-Energy Cosmic Ray Physics

LHCf is an experiment dedicated to the measurement of neutral particles emitted in the very forward region of LHC collisions. The physics goal is to provide data for calibrating hadron interaction models that are used in the study of Extremely High-Energy Cosmic-Rays. The LHCf experiment acquired data from April to July 2010 during commissioning time of LHC operations at low luminosity. Production spectra of photons and neutrons emitted in the very forward region ($η>$ 8.4) have been obtained. In this paper preliminary results of the photon spectra taken at $\sqrt{s}$ = 7TeV are reported.

hep-ex↗
arXiv2010

NEUCAL, an innovative neutron detector for e/h discrimination: testbeam results

An excellent hadron to electron discrimination is a crucial aspect of calorimeter-based experiments in astroparticle physics. Standard discrimination techniques require full shower development and fine granularity but in space detectors severe limitations exist due to constraints on dimensions, weight and power consumption. A possible approach is to exploit the different neutron yield of electromagnetic and hadronic showers. NEUCAL is a light and compact innovative neutron detector, to be used as an auxiliary complement of electromagnetic calorimeters. This new approach to neutron counting relies on scintillation detectors which are sensitive to the moderation phase of the neutron component. The NEUCAL prototype has been placed after a conventional calorimeter and tested with high energy beams of pions and positrons. The comparison of experimental data with a detailed Geant4 simulation and the encouraging results obtained are presented.

physics.ins-det↗
arXiv2010

NEUCAL: a prototype detector for electron/hadron discrimination through neutron measurement

NEUCAL is a neutron detector which is currently under study to be used as a sub-detector complementing electromagnetic (e.m.) calorimeters for electron/hadron discrimination in cosmic rays at high energy. Its aim is to reveal the different yield of neutron production in e.m. and hadronic showers, not only by counting signals due to their absorption in some sensible detector after passive moderation, but also looking for signals produced during the moderation phase. The basic idea and a test of a prototype detector are discussed in this paper. A first preliminary comparison of experimental data with simulation is also shown.

physics.ins-det↗