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Multichannel Investigation of Solar Modulation Effects in Galactic Cosmic Rays

Periodic Reporting for period 1 - MAtISSE (Multichannel Investigation of Solar Modulation Effects in Galactic Cosmic Rays)

Reporting period: 2016-05-05 to 2018-05-04

The topic of the MAtISSE project is the multichannel investigation of solar modulation effects in Galactic Cosmic Rays (CRs).
Solar modulation refers to the time variability of the CR flux inside the heliosphere caused by the 11-year variability cycle of the Sun's magnetic activity. This effect arises from the transport of CRs with the turbulent magnetized plasma carried out by the solar wind, and it is expected to be different for positive and negative particles, or for leptons and nuclei, making their individual studies essential.
Understanding solar modulation is very important for characterising the properties of the heliospheric plasma, for unveiling the origin of CRs, for the search of dark matter annihilation singals, as well as for the planning of interplanetary space missions.

For long time, the study of CR solar modulation has been plagued by two important limitations: the scarcity of long-term CR data, and the poor knowledge of the interstellar CR spectra.
With the new generation space experiments such as the Alpha Magnetic Spectrometer (AMS) experiment on the International Space Station (ISS), the PAMELA instrument, or the EPHIN detector aboard SOHO,
and the Voyager-1 spacecraft in the interstellar space, a large wealth of multi-channel and time-resolved CR data has become available. The MAtISSE project has three main physics goals:
(i) to extend solar modulation measurements of CR leptons and nuclei using the AMS data from the ISS;
(ii) to develop numerical data-driven models of CR transport in the heliosphere;
(iii) to explore a wide range of implications for the astrophysics of Galactic CRs.
The action was concluded with the achievements of its main goals, with only minor deviations from the origin plan. Training, research, dissemination, and communication activities have been carried out. The MAtISSE project lasted 24 months and was structured in eight work packages:
(WP1) Start-up and data collection;
(WP2) Development and optimization of the numerical calculation framework;
(WP3) AMS data analysis on CR proton and nuclei fluxes;
(WP4) AMS data analysis on CR electron and positron fluxes;
(WP5) Model parameters determination;
(WP6) Geomagnetic modulation flux modelling;
(WP7) Development of a web repository for data and model results;
(WP8) Implications for CR propagation.
To keep track of the progress and for the prepartation of the publications, periodic meetings were organised at the host institution and at CERN, Geneva. All tasks were accomplished and considerable scientific results were achieved. The results have been disseminated as: realisation of 10 scientific papers, 5 conference proceedings, 7 research notes, 15 contributions to international conferences. Dedicated resources were utilised for public educational events, communication or promotional initiatives. The researcher was involved in: seminars, lectures, newspaper articles, radio and TV interviews, creation of multimedia contents or infographics.
The action provided considerable results with important consequences in related fields of interest. The main results are summarized as follows.

1) New precision measurements of CR fluxes with AMS.
Within the framework of the AMS international collaboration, MAtISSE has contributed to the data analysis of CR energy spectra and their time dependence. This led to the measurement of the monthly fluxes for proton, helium, electron, and positron over 6 years of observation time (May 2011- May 2017), along with the flux measurement of light nuclei Li, Be, B, He, C, O.
2) Origin of the long-term behaviour in the CR p/He ratio.
The measurements obtained with the AMS data (1) show a remarkable long-term behaviour for the ratio p/He between proton and helium fluxes. Using our numerical model of CR modulation, we have explained this feature in terms of diffusive CR transport through the changing magnetic turbulence of the heliosphere. These results contributed to gain understanding on the basic properties of the heliospheric plasma and its evolution over the solar cycle.
3) Observation of a time lag in CR modulation.
Using our stochastic model of CR modulation interfaced with a large variety of data collected in space, we have reported the evidence of a eight-month time lag between changing solar activity and CR fluxes near-Earth. The existence of such a lag enables us to forecast the CR flux in the heliosphere several months in advance. This result addresses a prerequisite for modeling space weather effects, which is an increasing concern for space missions and air travelers.

4) Transport of antiparticles and particles in the heliosphere.
Based on our results (3), we have made predictions for the time evolution of CR antiparticles, such as positrons or antiprotons, to be tested with the data from the AMS experiment. These results contribute toward answering the question of the origin of cosmic antimatter.

5) Astrophysics of Galactic nuclei, antinuclei, and origin of CRs.
Solar modulation is an important source of uncertainty in astrophysical models of CR acceleration and transport, but it lacks of a proper treatment. Using the models developed in the action, and improved constrained based on recent data, we made new estimates of the solar uncertainties in CR propagation and how they affect the interpretation of light-nuclei or anti-nuclei data. The calculations developed in this action enabled us for several related studies, such as, the astrophysical background calculation of antiprotons, antideuteron and antihelium fluxes, as well as new models of CR acceleration and transport. These works are essential for the search of dark matter annihilation signals in the CR energy spectrum.

6) Space weather and space climate.
Interplanetary manned missions toward Mars and beyond will become reality within the XXI century. In this respect, an important reason to care about solar modulation is that related to human exposure to space radiation such as, in particular, chronic exposure to the CR flux in the interplanetary space. In our research, we demonstrated that the CR radiation level and its temporal evolution can be predicted in advance. Within the MAtISSE action, these aspects have attracted significant attention and media coverage, which resulted in a series of interviews of newspaper articles. Beyond MAtISSE, we expect that further developments will transform the science of space weather by extending its scope from the near-Earth environment to the interplanetary space of the the solar system.

Summary and Outlook
Cosmic ray physics, solar physics and space science are growing fields of research in which European scientists take a leading role. With the release of new precision data, this project has opened new directions and opportunities of physics investigation, that are expected to stimulate further work and transformative advances in scientific understanding of key science problems. On the level of fundamental research, the project has strengthen the role of European research in this highly interdisciplinary field of astroparticle physics. Many of the activities have involved international collaboration across leading institutes such as the Italian Space Agency, the Laboratory of Instrumentation and Experimental Particles Physics in Lisbon, and the European Organization for Nuclear Research in Geneva, thereby sustaining the leading role of European research in astroparticle physics and space science.