An Introduction to Cosmic Rays, Relativity, and MARIACHI

1. An Introduction to Cosmic Rays, Relativity, and MARIACHI M. Marx November 16, 2006

2. Radioactivity • Radiactive material is classified according to its activity – the number of decays per second Ndecays = Npresent x t x time interval t is the “lifetime” of the material t1/2 or “half-life” = t ln 2 = 0.6931471806t • Half-life is the time required for half of the radioactive material to decay • We have identified particles and isotopes with half-lives ranging from 10-23 seconds (time it takes light to cross a nucleus) 109 years (comparable to age of universe)

3. Puzzles • Puzzle 1 • There are lots of short lived radioactive isotopes that can be found naturally on the surface of the earth • Deep underground (i.e. in mines) one only finds isotopes whose half lives are comparable to the age of the Earth (109 years) • Where does the short lived stuff come from? •   Continuously replenished by radiation from Outer Space!!

4. Puzzles • Puzzle 2 • Early researchers on radioactivity had great difficulty in shielding their equipment from ubiquitous radiation • Where does it come from? •   Outer Space!!

5. Discovery of cosmic radiation Victor Hess in 1914 • Electroscopes always discharge • Radiation increases with altitude (balloon!) • Varies with location and direction – Earth’s magnetic field! • Led to discoveries of new particles • Positron, muon, pion, strange particles…. • Good example of relativity in action!

6. Special Relativity (1905) • Einstein’s postulates • Nothing can move faster than light in vacuum • Speed of light looks the same to all independent of observer velocity

7. Special Relativity Consequences • Consequences: • Moving objects look shorter L = Lo (1-v2/c2)1/2 • Moving clocks appear to run slower to = t(1-v2/c2)1/2 • Moving objects get more massive mo = m(1-v2/c2)1/2 • Mass and energy are interchangeable E = mc2 = m0c2/ (1-v2/c2)1/2 • Velocity of light ( “c” ) • 186,000 miles per second • 3 x 108 meters per second • Effects of relativity are not noticeable in daily life

8. Consequences vv/c (1-v2/c2)1/2 1/(1-v2/c2)1/2 28,000km/h 3 x 10-5 1 1 (Shuttle in orbit) 0.1 .99 1.005 0.25 .96 1.03 .99 .14 7.07 .9999 .014 70.7 A particle traveling at 99% of speed of light has 7 times more mass, is 1/7 of its length, and lives 7 times as long!

9. Why Study Cosmic Rays? • Cosmic rays are a tool to study phenomena at the extreme ends of sizes • Very small ==> fundamental particles (building blocks of all matter) • Very large ==> window on energetic processes in the universe (supernovae, black holes, colliding galaxies, and the unknown!) • Early discoveries of fundamental particles before the era of accelerators (atom-smashers) • Studies of ultra-high energy particles beyond the reach of man-made accelerators

10. Why Study Cosmic Rays? • Cosmic rays are the prime source of natural background radiation • Short lifetime isotopes continuously replenished • Cosmic radiation increases with altitude – the atmosphere shields us from most of it • Radiation dose doubles every 5000ft! • Deep rocks contain only long-lived isotopes • Cosmic ray interactions with DNA of living cells may be prime (continuing) agent in evolution

11. Fundamental Particles- The Elements The periodicity strongly suggests an underlying structure, i.e. all are composed of common building blocks Now we know that these blocks are proton, neutron, and electron

12. Fundamental Particles – The Atom All atoms are composed of nuclei surrounded by a cloud of electrons The nuclei are composed of protons and neutrons We know now that the protons and neutrons are themselves composed of quarks and gluons

13. Fundamental Particles Generation 1 Generation 2 Generation 3 ALL ordinary matter is composed solely of first generation particles – atoms have nuclei composed of protons (uud) and neutrons (udd) surrounded by clouds of electrons to make the atom electrically neutral. Second and third generation particles can be produced if there is sufficient energy available in a collision ( E = mc2), but all these particles decay eventually into lower generations.

14. Introduction to Cosmic Rays • What are cosmic rays? • Nuclei with composition similar to the solar system + gammas, neutrinos • Interaction and decay products reach the ground • Rates at ground level are 1 per second per cm2 • Huge range of energies Mev – EeV ====> • Different energies come from various sources • Low energies from sun (10 => 100 MeV typical) • Galactic sources – supernovae • Highest energies ( above 10 EeV) are a mystery

15. Cosmic Ray Energy Spectrum Units 1 electron-Volt = 1 eV Energy gain of a charged Particle ( q = 1e) accelerated thru 1V 2 – 4 eV visible light Kev Xrays Mev Binding of nucleons Mass electron * c2 = ½ MeV GeV Mass*c2 of nucleons EeV – (1018 eV) pitched baseball Sun Our Galaxy 1 particle/km2/century Origin Unknown - A dozen seen! Extra-galactic GeV =====> EeV

16. Cosmic Rays Primary Cosmic Ray – Nucleus ( H ….Fe) strikes Atmospheric Molecule Secondary particles – nucleons (p,n), pions (p+, p-, p0), Kaons…… Neutral pions decay p => g g Secondaries interact with atmospheric molecules Charged pions decay p => m n Gamma rays initiate Electromagnetic showers g => e+e- Low energy muons decay m => e n n http://www.auger.org/observatory/image_gallery_index.html Shower debris reaches Earth – m, g, e+,e- - very low energy fragments of original shower

17. Cosmic Rays and Special Relativity • The primary cosmic ray collides with a molecule in the atmosphere transferring much of its energy into a shower of secondary particles • Lifetime of charged pions is ~ 10-8 sec and they all decay before reaching Earth (p => m n) • Lifetime of muons is ~ 10-6 sec • At close to speed of light would expect decays (m => e n n) S = vt = 3 x 108 m/s x 2.2 x 10-6 s = 660m • But most muons reach Earth (10km!!) because their clocks are slowed by relativity! • From the muon’s perspective they see the distance to Earth shrunk to < 660m they could move by their own clocks! • Einstein was amazed by this practical proof of his theory

18. Shower Animations –1 Tev Proton Initiated Shower

19. Detection of Radiation/Particles • We have many ways at our disposal to detect the passage of ionized (i.e. charged) particles – the particles themselves are not visible • Uncharged particles can only be detected indirectly, either by their decay into charged particles, or by their interactions which produce charged particles. • Charged particles disrupt the clouds of electrons surrounding the atoms in their path, exciting the electrons to higher energy states, or by knocking out an electron and ionizing the atom. • The paths are marked by these disturbed electrons which can be collected and measured by several means.

20. Simplest Radiation Detector X-rays are neutral and not detectable – however, they knock out charged electrons ionizing atoms in the film, creating grains that become visible once developed. The picture shows the intensity of X-rays reaching the film (negative!) Film was the medium for Roentgen’s discovery of X-rays and radiation. Film was originally and still is used for studies of cosmic rays through stacks of emulsions. Many of the early discoveries were made with it

21. Nuclear Emulsions (Film) Provides a Complete picture Of an “event” Excellent spatial resolution Excellent energy density gives identification and directions, speed Provides no time information

22. Bubble Chamber m - muon e - electron • This bubble • chamber picture • shows the decay • chain • p => + n • m => e + n + n This decay chain is very common in the debris of a cosmic ray shower From inspection of this picture one can tell the direction of the particles by their ionization (and the magnetic field confirms this!) p - pion Measuring the curvature determines the sign and momentum of the particles. There is no time information. • Why are the neutrinos invisible? • Why is the muon track so short?

23. Pierre Auger Observatory – Argentina Surface Array 1600 detector stations 1.5 km spacing 3000 km2 Fluorescence Detectors 4 Telescope enclosures 6 Telescopes per enclosure 24 Telescopes total http://www.auger.org/observatory/animation.html

24. Cosmic ray TV signals TV signal reflected by the cosmic ray Induced shower Distant TV station Ground detectors (scintillators) TV antennas (radar) Data acquisition system and cyberinfrastructure GRID data data Three Key Pieces of Radar detectors to find reflected TV signals from cosmic rays, meteors, & lightning Scintillator detectors to confirm cosmic ray signals (and do correlations) The “grid” – for data acquisition and analysis

25. Radio (electromagnetic waves) are routinely reflected by metallic objects – “radar” They can also be reflected from areas where the ionization densities are high enough – exceeding the “plasma frequency” given by: Radar (EM wave) Reflections from an Ionized Plasma (Hz) = 8.98 ne is the ionization density meis the electron mass e is the electron charge

26. Cosmic Ray Coverage The primitive Mariachi array we are implementing now on Long Island covers an area of about 6000 km2 or twice the area of Auger! http://www-mariachi.physics.sunysb.edu/wiki/index.php/Ground_Array

27. Radar Echo Signals

28. Radar Echoes from Meteors Meteor data acquired from April 16th to April 26th showing the Lyrids meteor shower that peaked on April 22nd and a secondary minor shower that peaked on April 25th. The diurnal variation is due to the Earth's rotation. Typical echo from a meteor trail, with a weak echo from a second TV station.

29. Why Ground Arrays • Mariachi hopes to exploit the new technique of Radio Cosmic Ray Scatter to detect and then study UHECR (and neutrinos!) • We hope to identify a class of short duration radio echoes that are UHECR candidates • To confirm their identity we need simultaneous detection by proven techniques – we use scintillator ground arrays for their simplicity and reliability. • This also provides the opportunity to include in Mariachi the community of high school teachers and students, to learn about science and cyberinfrastucture, while contributing to the scientific goals of the project.

30. Scintillation Counters and Phototubes Charged particle Velocity ~ c Time D/c, 1ns/ft Raw pulse from PMT Logic pulse D • Photomultiplier Tube • Photon ejects electron by photo-electric effect • Electron guided to dynode ejecting • several electrons • Process repeated many times • Electron cloud arrives at anode – negative pulse • Transit time ~ 100ns Discriminator Provides standard height and width pulse whenever input pulse is over preset threshold • Scintillation Counter • Doped plastic emits • light • Light travels to ends by • total internal reflection • Transit time ~ 2.5ns/ft

31. Scintillator See-through PMT assembly Light-tight student proof lockable case The final design

32. The MARIACHI Grid • The dream: A transparent global network of computing resources available to all users uniformly. Like the World Wide Web via the Internet. • User defines a “job” • An input file. • A program to run (installed or provided). • A place to put the output file. • A set of constraints (CPU speed, memory,etc.). • Users submit job. • ...to chosen Grid sites (OSG) or the entire Grid (LCG) and await results.

33. Mariachi Wiki • See our wiki based web site at http://www-mariachi.physics.sunysb.edu/ • Opportunities to participate in this educational research for teachers and students at all levels!

34. -resonance multi-pions High Energy Protons see Cosmic Microwave Background as High Energy Gamma Rays! WMAP p+cmb +  p + 0  n +  + GZK Cutoff UHECR are too energetic to originate from known sources in our galaxy or nearby galaxies. UHECR are too energetic to propagate through the microwave background from distant sources Neighboring Galaxies Galaxy Clusters Milky Way