47 research outputs found
Testing diffusion of cosmic rays in the heliosphere with proton and helium data from AMS
After six years of continuous observations in space, the Alpha Magnetic Spectrometer experiment has released new data on the temporal evolution of the proton and helium fluxes in cosmic rays. These data revealed that the ratio between proton and helium fluxes at the same value of rigidity (momentum/charge ratio) is not constant at 3 GV. In particular, the ratio is found to decrease steadily during the descending phase of Solar Cycle 24 toward the next minimum. We show that such a behavior is a remarkable signature of the dependence in the diffusion of cosmic rays in heliosphere, where is their adimensional speed and is their mean free path, a universal function of rigidity for all nuclei. This dependence is responsible for distinctive charge/mass dependent effects in the time-dependent modulation of low-rigidity particles.Peer Reviewe
Search for Charginos with a Small Mass Difference with the Lightest Supersymmetric Particle at \sqrt{s} = 189 GeV
A search for charginos nearly mass-degenerate with the lightest
supersymmetric particle is performed using the 176 pb^-1 of data collected at
189 GeV in 1998 with the L3 detector. Mass differences between the chargino and
the lightest supersymmetric particle below 4 GeV are considered. The presence
of a high transverse momentum photon is required to single out the signal from
the photon-photon interaction background. No evidence for charginos is found
and upper limits on the cross section for chargino pair production are set. For
the first time, in the case of heavy scalar leptons, chargino mass limits are
obtained for any \tilde{\chi}^{+-}_1 - \tilde{\chi}^0_1 mass difference
Search for Low Scale Gravity Effects in e+e- Collisions at LEP
Recent theories propose that quantum gravity effects may be observable at LEP
energies via gravitons that couple to Standard Model particles and propagate
into extra spatial dimensions. The associated production of a graviton and a
photon is searched for as well as the effects of virtual graviton exchange in
the processes: e+e- -> gamma gamma, ZZ, WW, mu mu, tau tau, qq and ee No
evidence for this new interaction is found in the data sample collected by the
L3 detector at LEP at centre-of-mass energies up to 183 GeV. Limits close to 1
TeV on the scale of this new scenario of quantum gravity are set
The large area detector onboard the eXTP mission
The Large Area Detector (LAD) is the high-throughput, spectral-timing instrument onboard the eXTP mission, a flagship
mission of the Chinese Academy of Sciences and the China National Space Administration, with a large European
participation coordinated by Italy and Spain. The eXTP mission is currently performing its phase B study, with a target
launch at the end-2027. The eXTP scientific payload includes four instruments (SFA, PFA, LAD and WFM) offering
unprecedented simultaneous wide-band X-ray timing and polarimetry sensitivity. The LAD instrument is based on the
design originally proposed for the LOFT mission. It envisages a deployed 3.2 m2 effective area in the 2-30 keV energy
range, achieved through the technology of the large-area Silicon Drift Detectors - offering a spectral resolution of up to
200 eV FWHM at 6 keV - and of capillary plate collimators - limiting the field of view to about 1 degree. In this paper
we will provide an overview of the LAD instrument design, its current status of development and anticipated
performance
Production of Single W Bosons at LEP
We report on the observation of single W boson production in a data sample collected by the L3 detector at LEP2. The signal consists of large missing energy final states with a single energetic lepton or two hadronic jets. The cross-section is measured to be at the centre of mass energy \sqrt{s}=172 \GeV{}, consistent with the Standard Model expectation. From this measurement the following limits on the anomalous WW gauge couplings are derived at 95\% CL: and
Measurement of the Average Lifetime of b-Hadrons in Z Decays
We present a measurement of the average b-hadron lifetime at the collider LEP. Using hadronic Z decays collected in the period from 1991 to 1994, two independent analyses have been performed. In the first one, the b-decay position is reconstructed as a secondary vertex of hadronic b-decay particles. The second analysis is an updated measurement of using the impact parameter of leptons with high momentum and high transverse momentum. The combined result is \begin{center} . \end{center} In addition, we measure the average charged b-decay multiplicity and the normalized average b-energy at LEP to be \begin{center} , \end{center} \begin{center} \end{center
Numerical modeling of cosmic-ray transport in the heliosphere and interpretation of the proton-to-helium ratio in Solar Cycle 24
Thanks to space-borne experiments of cosmic-ray (CR) detection, such as the
AMS and PAMELA missions in low-Earth orbit, or the Voyager-1 spacecraft in the
interstellar space, a large collection of multi-channel and time-resolved CR
data has become available. Recently, the AMS experiment has released new
precision data, on the proton and helium fluxes in CRs, measured on monthly
basis during its first six years of mission. The AMS data reveal a remarkable
long-term behavior in the temporal evolution of the proton-to-helium ratio at
rigidity 3 GV. As we have argued in a recent work, such a behavior
may reflect the transport properties of low-rigidity CRs in the inteplanetary
space. In particular, it can be caused by mass/charge dependence of the CR
diffusion coefficient. In this paper, we present our developments in the
numerical modeling of CR transport in the Milky Way and in the heliosphere.
Within our model, and with the help of approximated analytical solutions, we
describe in details the relations between the properties of CR diffusion and
the time-dependent evolution of the proton-to-helium ratio.info:eu-repo/semantics/publishedVersio
UV photo-responsivity of a large-area MWCNT-Si photodetector operated at cryogenic temperature
In the last decades much effort has been addressed to realize novel solid state photo-detectors with a high quantum efficiency in the UV wavelength region to be used in experiments detecting Cherenkov or fluorescence radiation even at cryogenic temperatures. Among the possible devices with these characteristics, the large-area solid detectors made of n-doped silicon substrate coated with Multi-Walled Carbon Nanotubes (MWCNTs) appear to be particularly promising since they combine the great UV radiation absorbance of MWCNTs (at about 200 nm) with their unique characteristics for electrical conductivity and mechanical resistance at low temperatures. In this work we present the cryogenic characteristics of a MWCNT-Si large-area (1 cm2) photo-detector, in which a UV photo-sensitive heterojunction is obtained growing, by Chemical Vapour Deposition (CVD), multi-walled carbon nanotubes on an n-type silicon substrate. Measurements have been made at various temperatures in the range from 5K to 300K by illuminating the photo-detector with a 378 nm UV continuous laser light source. Results demonstrate the capability of such device to be successfully employed in cryogenic experiments as well at room temperature with high stability and high photon detection efficiency in the UV region