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

Radioactivity Radiactive material is classified according to its activity – the number of decays per second N decays = N present x  x time interval  is the “lifetime” of the material t 1/2 or “half-life” =  ln 2 =  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 seconds (time it takes light to cross a nucleus) 10 9 years (comparable to age of universe)

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 (10 9 years)  Where does the short lived stuff come from?    Continuously replenished by radiation from Outer Space!!

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

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!

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

Special Relativity Consequences Consequences: –Moving objects look shorter L = L o (1-v 2 /c 2 ) 1/2 –Moving clocks appear to run slower t o = t (1-v 2 /c 2 ) 1/2 –Moving objects get more massive m o = m (1-v 2 /c 2 ) 1/2 Mass and energy are interchangeable E = mc 2 = m 0 c 2 / (1-v 2 /c 2 ) 1/2 Velocity of light ( “c” ) –186,000 miles per second –3 x 10 8 meters per second Effects of relativity are not noticeable in daily life

Consequences v v/c (1-v 2 /c 2 ) 1/2 1/(1-v 2 /c 2 ) 1/2 28,000km/h3 x (Shuttle in orbit) 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!

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

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

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

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

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 = mc 2 ), but all these particles decay eventually into lower generations.

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 cm 2 –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

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 * c 2 = ½ MeV GeV Mass*c 2 of nucleons EeV – (10 18 eV) pitched baseball GeV =====> EeV Sun 1 particle/km2/century Origin Unknown - A dozen seen! Extra-galactic Our Galaxy

Cosmic Rays Primary Cosmic Ray – Nucleus ( H ….Fe) strikes Atmospheric Molecule Secondary particles – nucleons (p,n), pions (  +,  -,  0 ), Kaons…… Secondaries interact with atmospheric molecules Charged pions decay  Neutral pions decay  Low energy muons decay  e  Gamma rays initiate Electromagnetic showers  e+e- Shower debris reaches Earth – , e+,e- - very low energy fragments of original shower

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 ~ sec and they all decay before reaching Earth (  Lifetime of muons is ~ sec At close to speed of light would expect decays  e  S = vt = 3 x 10 8 m/s x 2.2 x 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

Shower Animations – 1 Tev Proton Initiated Shower

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.

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

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

 pion  muon e - electron This bubble chamber picture shows the decay chain   e +  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!) Measuring the curvature determines the sign and momentum of the particles. There is no time information. Bubble Chamber 1.Why are the neutrinos invisible? 2.Why is the muon track so short?

Pierre Auger Observatory – Argentina Surface Array 1600 detector stations 1.5 km spacing 3000 km 2 Fluorescence Detectors 4 Telescope enclosures 6 Telescopes per enclosure 24 Telescopes total

Cosmic ray Distant TV station TV signals TV signal reflected by the cosmic ray Induced shower TV antennas (radar) Data acquisition system and cyberinfrastructure GRID data Ground detectors (scintillators) 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

Radar (EM wave) Reflections from an Ionized Plasma 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: = 8.98 (Hz) n e is the ionization density m e is the electron mass e is the electron charge

Cosmic Ray Coverage The primitive Mariachi array we are implementing now on Long Island covers an area of about 6000 km 2 or twice the area of Auger!

Radar Echo Signals

Radar Echoes from Meteors Typical echo from a meteor trail, with a weak echo from a second TV station. 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.

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.

Charged particle Velocity ~ c Time D/c, 1ns/ft Scintillation Counter Doped plastic emits light Light travels to ends by total internal reflection Transit time ~ 2.5ns/ft 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 Raw pulse from PMT Discriminator Provides standard height and width pulse whenever input pulse is over preset threshold Logic pulse Scintillation Counters and Phototubes D

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

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.

Mariachi Wiki See our wiki based web site at Opportunities to participate in this educational research for teachers and students at all levels!

High Energy Protons see Cosmic Microwave Background as High Energy Gamma Rays! GZK Cutoff  -resonance multi-pions WMAP p+  cmb   +  p +  0  n +  + 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 Milky Way Neighboring Galaxies Galaxy Clusters