Working Papers Astronomy and Astrophysics Panel Reports (1991) / Chapter Skim
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Particle Astrophysics
Particle Astrophysics
Pages 153-176
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From page 153... ...
The possible confirmation of the existence of point sources of energetic particles leading to the production of gamma rays, neutrinos and maybe new particles at energies as high as 1014 eV. The understanding of the origin of cosmic rays, including the physical processes responsible for their synthesis and acceleration on a wide variety of scales.
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From page 154... ...
It also appears that quantum fluctuations and topological singularities generated in phase transitions occurring at very high temperature in the early universe could have played a fundamental role in the formation of large scale structure. In addition, it is now well understood how the properties of neutrinos could be responsible for the solar neutrino puzzle, and the powerful acceleration mechanisms evidenced by the highest energy cosmic rays may require new particle physics.
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From page 155... ...
For instance, inflation provides a very attractive explanation for the flatness and old age of the universe and of the primeval density inhomogeneities. In addition, many theories that go beyond the particle physics standard model, such as supersymmetry, predict the existence of stable relic elementary particles that are left over from the early moments after the Big Bang and that may constitute dark matter.
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From page 156... ...
Mass (GeV/c2) Figure 1 Cottstrairlts on the mass arid the cross section of Dark Matter particles, obtained by the LBLUCSB-UCB and the PNL-USC collaborations (as of December 1989~.
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From page 157... ...
Stellar Physics and Particles Neutrinos play an important role in the physics of stars and there again particle physics and astrophysics are intricately intertwined. Neutrinos are elementary particles with very small interaction cross sections which, along with photons and positrons, are emitted in the nuclear processes which power the stars.
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From page 158... ...
. Whatever the solution of the puzzle, an imperfect modeling of the sun or fundamental properties of the neutrinos, it will be important for astrophysics, cosmology and particle physics.
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From page 159... ...
These detectors include solar neutrino detectors, dedicated supernova search detectors, and deep underground scintillation detectors searching for magnetic monopoles and other "cosmic ray" phenomena. Given the importance of this information for refining current understanding of the mechanism of stellar core collapse and of the neutrino sector, all such detectors should be instrumented to maximize supernova detection capability including burst handling and absolute timing.
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From page 160... ...
However, both techniques, the atmospheric Cerenkov technique, and the air shower technique, have a problem with severe backgrounds from ordinary cosmic rays, which arrive isotropically. The ordinary extensive air showers are initiated in the upper atmosphere by protons and heavier nuclei, but the air showers they produce are not easily distinguishable from showers produced by the gamma rays being sought.
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From page 161... ...
There are new technologies using large coverage or tracking detectors whereby the threshold of the air shower technique may be lowered to nearly overlap the atmospheric Cerenkov technique, especially if the detector is located at high altitude. One of these techniques involves the instrumentation of more than 104m2 of a clear lake with photomultipliers so that the observation of an entire air shower by Cerenkov light in the water is possible.
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From page 162... ...
of neutrinos from point sources or results from the Dugway and Los Alamos gamma ray detectors before proceeding with neutrino detectors of larger scale. Cosmic Rays Cosmic rays which can be observed near Earth cover a large range of energies, from the MeV region to 102° eV, and comprise the nuclei of all known elements, as well as electrons, positrons, and antiprotons.
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From page 163... ...
In the search for antiparticles in the cosmic rays, recent balloon measurements have placed stringent limits on possible contributions of annihilations of supersymmetric dark matter particles to cosmic ray antiprotons at low energies. However, in the GeV region, there are indications of fluxes of p's and positrons that are larger than those expected to arise from interstellar nuclear interactions of cosmic rays.
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From page 164... ...
Particle acceleration can be studied in the heliosphere in much more detail than in more remote regions of the galaxy, and will provide invaluable tests for theoretical models that are applicable at larger scales and higher energies. In order to establish the role of low energy cosmic rays in the heating and ionization of the interstellar medium, in situ measurement of these particles will be required in local interstellar space, as pointed out in the 1980 Astronomy and Astrophysics Survey Report (Field Report)
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From page 165... ...
Cosmic rays in the 1015-1019 eV region also present mysteries. They may be galactic in origin but there is no established galactic acceleration mechanisms that can produce protons with energies greater than about 1015
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From page 166... ...
is expected to reach an important milestone in the search for monopoles with a sensitivity below the Parker bound and to improve significantly our searches for high energy neutrinos potentially produced by annihilation of dark matter particles in the sun or the earth. More generally, its large volume and area allows this instrument to detect supernova neutrinos and high energy muons from cosmic rays.
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From page 167... ...
. Cosmic Rays investigations: High priority should be given to carry out expeditiously the space missions recently selected for cosmic ray · The Advanced Composition Explorer (ACE)
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From page 168... ...
New Initiatives in the coming decade The program described above is well balanced with a number of new experiments. However, the scientifically essential supernova watch requires a better coordination, and the proper exploration of the highest energy cosmic rays and the elucidation of the old puzzle of their origin requires a new instrument.
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From page 169... ...
The instrument will be capable of observing cosmic rays down to 1016 eV, and it is likely that at a later date ancillary detectors will be added to enhance the capability of the instrument. For space-borne investigations, the frontiers will remain in the areas of the rare ultraheavy cosmic ray nuclei (up through the actinides)
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From page 170... ...
· The deployment of very large orbiting detectors, 100-1000 m2 ster, with exposure of several years, may allow us to observe directly very high energy primaries (charged and neutral) and allow in particular a direct study of the composition of cosmic rays near the special knee (1016 eV)
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From page 171... ...
New Extensive Air Shower Detectors The lake water Cerenkov detector technology is a radically new technique which exploits the experience gained with water Cerenkov proton decay detectors and potentially offers several advantages with: full calorimetry which may allow excellent hadronic shower rejection, or if necessary the study of the muon anomaly; excellent angular resolution; and low threshold especially at high altitude. This last feature could make this technology competitive with the atmospheric Cerenkov technique, with the additional advantages of an "all" sky sensitivity, continuous operation and the possibility of detecting sources with short duty cycles (if such exist)
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From page 172... ...
As the distinction between particle physics, cosmology or astrophysics becomes increasingly blurred, this Panel feels strongly that too narrow an interpretation of particle physics would be detrimental to scientific productivity; we suggest that the responsibility of DOE in particle astrophysics should be clearly affirmed. Funding decisions of proposals should then be based on their scientific merit, the techniques used and the scientific priorities recommended by the advisory bodies, without attempting to define too rigidly what is particle physics and what is astrophysics.
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From page 173... ...
The problem has been particularly acute for cosmology which appears to have been underfunded in the last decade both for experiments and theory. This suggests that the present funding institutions were unable to adapt to the emergence of a new discipline which cuts across many observational fields (including particle astrophysics)
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From page 174... ...
While helping this new field with their technical expertise, they may benefit from the intellectual stimulation and the diversification provided by a fundamentally multidisciplinary discipline. Ir~terr~atior~al Collaborations The field of particle astrophysics is already strongly benefiting from international collaborations, in part because of the tradition in Particle Physics.
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From page 176... ...
THEORY AND LABORATORY ASTROPHYSICS PANEL DAVID N SCHRAMM, University of Chicago, Chair CHRISTOPHER F
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