Astroparticle Physics

7.6 Problems 169‘Milky Way’ of galaxies whose center lies in the directionof the Virgo cluster. The local group of galaxies, of whichour Milky Way is a member, has a distance of about 20 Mpcfrom the center of this local supergalaxy and the members ofthis supergalaxy scatter around the supergalactic center onlyby about 20 Mpc.Even though the origin of the highest-energy cosmicrays is still unknown, there are some hints that the sourcesfor these high-energy events really lie in the supergalacticplane. Certainly more events are required to confirm in detailthat such a correlation really exists. The Auger experimentunder construction in Argentina should be able to solve thequestion of the origin of high-energy cosmic rays.Finally, ideas have also been put forward that the extreme-energycosmic rays are not the result of the accelerationof protons or nuclei but rather decay products of unstableprimordial objects. Candidates discussed as possiblesources are decays of massive GUT particles spread throughthe galactic halo, topological defects produced in the earlystages of the universe like domain walls, ‘necklaces’ of magneticmonopoles connected by cosmic strings, closed cosmicloops containing a superconducting circulating current,or cryptons – relic massive metastable particles born duringcosmic inflation.Virgo clusterexotic candidates7.6 Problems1. The pressure at sea level is 1013 hPa. Convert this pressureinto a column density in kg/cm 2 !2. The barometric pressure varies with altitude h in the atmosphere(assumed to be isothermal) likep = p 0 e −h/7.99 km .What is the residual pressure at 20 km altitude and whatcolumn density of residual gas does this correspond to?3. For not too large zenith angles the angular distributionof cosmic-ray muons at sea level can be parameterizedas I(θ) = I(0) cos 2 θ. Motivate the cos 2 θ dependence!4. Figure 7.22 shows the rate of stopping muons underground.Work out the rate of stopping atmosphericmuons (curve labeled 1) as a function of depth undergroundfor shallow depths!