Quarknet 2007

1. Quarknet 2007 Daniela Bortoletto

2. Goals • Welcome to Purdue • This year program is focused on cosmic ray physics and cosmic ray detection • The aim is how to use the Quarknet cosmic ray detector to introduce modern physics in the class room D. Bortoletto

3. Program D. Bortoletto

4. Program D. Bortoletto

5. Photo of a-particles emitted by radioactive source and seen in cloud chamber Nobel Prize 1927 "for his method of making the paths of electrically charged particles visible by condensation of vapour" First evidence • C.T.R Wilson discovered in 1900 the atmospheric ionization. It was believed to be due to the natural radiation of the Earth. In other words, from the ground up. • Wilson developed the first cloud chamber and he noticed the reappearance of drops of condensation in expanded dust free gas, the first cloud chamber. • You can buy or build one D. Bortoletto

6. The Wilson Cloud chamber A cylinder with a glass lid and a piston that could be raised or lowered. The cylinder was filled with moist air; if a charged particle went through the chamber, it would leave an ionization trail behind it. If the piston was then lowered to increase the volume of the cylinder, the water vapor would cool and condense around the ionized air molecules, revealing the "track" of the charged particle. D. Bortoletto

7. The Discover of Cosmic rays • Scientists were puzzled: • More radiation in the environment than could be explained by natural background radiation • In 1912 Hess carried three electrometers to an altitude of 5300 meters in a balloon flight: • Ionization rate decreased up to ~700 m • Above 700 m then it increased with altitude. At 5300 m the ionization rate 4 × rate at ground level • "The results of my observation are best explained by the assumption that a radiation of very great penetrating power enters our atmosphere from above." • Confirmation by Werner Kolhörster in 1913-1914 • Hess received the Nobel prize in 1936 D. Bortoletto

8. Where they from the sun? • During subsequent flights Hess determined that the ionizing radiation was not of solar origin since it was similar for day and night. • It was initially believed that the radiation consisted of gamma rays only. • But there was still a dispute as to whether the radiation was coming from above or from below. D. Bortoletto

9. The Caltech Cloud Chamber • Milliken became President of Caltech and was instrumental in the building of a high magnetic field cloud chamber. • In 1925 Robert Millikan of Caltech introduced the term “cosmic rays” • He concluded that the particles came from above not below a cloud chamber. D. Bortoletto

10. Charged or not charged? • Millikan and Compton, debated about the nature of cosmic rays. • Compton won, arguing that they were charged particles. • Millikan believed they were uncharged. • T.H. Johnson in 1938 discovered that the ionization rate increased from east to west viewing angle: • Positively charged particle • The increase occurs because the rays are deflected by the earths magnetic field, which changes in its strength with latitude D. Bortoletto

11. Charged Particles! • In 1929 a Russian scientists, D. Skobelzyn, discovered ghostly tracks made by cosmic rays in a cloud chamber. • Also in 1929 Bothe and Kolhorster verified that the cloud chamber tracks were curved. Thus the cosmic radiation was charged particles. D. Bortoletto

12. Triggering cloud chamber • Anderson and Needemeyer implement the triggering cloud chamber, critical to the understanding of cosmic rays and the development of particle physics • Cosmic ray appearances in a cloud chamber last a second or so.  Timing of the photograph to document these events is critical. • Idea: Activate the cloud chamber and the camera by identifying the cosmic ray with a Geiger Mueller detector. • The GM detectors used with cloud chambers were flat. Their length is chosen to match the diameter of the cloud chamber over which the tube is positioned. • A flat GM detector was built between 1935 and 1940 at Caltech for use by Anderson and Neddermeyer in triggering their 7 inch cloud chamber.  D. Bortoletto

13. C.D. Anderson and the Caltech Chamber With this chamber Anderson discovered the positron (an antimatter electron) and the muon (a major component of cosmic rays)   and he was awarded the Nobel prize in physics. Thin, curved to left, m ≈ me and q = -e (if from above). Thick, curved to right, m ≈ mp and q = +e (if from above). Thin, curved to right, m ≈ me, q = ? What direction??? Millikan − “Cosmic rays only come from above! Your mass measurement must be wrong.” Anderson − “The mass measurement is reliable: m«mp” D. Bortoletto

14. Determining the direction of the cosmic ray Put 0.5 cm lead plate in chamber. Particle loses energy traversing plate, smaller radius of curvature must be outgoing side. Glen Cowan RHUL Physics D. Bortoletto

15. The first positron Carl Anderson won the 1936 Nobel Prize for Physics for this discovery. • The radius of curvature of the track below the plate is smaller than that above. • The particle is traveling more slowly below the plate  traveling downwards. • Direction the path curves  + charge. • Long range of the upper track  positron • a proton would have come to rest in a much shorter distance. C.D. Anderson 2 August, 1932 D. Bortoletto

16. e+ e- Positron and antimatter Photon conversions g®e+ e- in a bubble chamber • Positively charged electrons • Discovery of antimatter • Positrons predicted by Dirac in 1928 from relativistic theory of electrons Non-relativistic kinetic energy: Relativistic kinetic energy (Einstein): “negative” solution is related to the existence of antimatter D. Bortoletto

17. Discovery of muon (m) Neddermeyer, Anderson 1937 • Negatively charged • Curved to a smaller degree than electrons but more sharply than protons, for particles of the same velocity. • He assumed that these particles were of intermediate mass. For this reason, Anderson initially called the new particle a mesotron, adopting the prefix meso- from the Greek word for "intermediate". • Muons were proven not to have any nuclear interactions and to be just heavier versions of electrons • m decays to electron and two invisible neutrinos via weak interactions (b decay): m-®nm e-ne • first encounter of the generation problem • 70 years later we still don’t have a good answer D. Bortoletto

18. Emulsions • In 1932 Occhialini and Blackett devised a method of making cosmic rays take their own photographs. • They observed in 1932 the formation of multiple particles (pair production) and of particle showers using lead and copper plated plates in the cloud chamber. • Experiments also on-going in Italy (Conversi, Pancini, Piccioni) during armistice in 1943 and after the war • After the war Cecil Powell, Otto Frisch, George Rochester, and Berriman and Waller, the chemists from Kodak and Ilford restarted the work on emulsions and cosmic ray. • By mid 1946 Ilford had produced emulsions with four times the normal silver halide/gelatine ratio, which would record tracks of charged particles of ionisation down to about six times the minimum value. D. Bortoletto

19. Leptons: no strong interactions Hadrons: feel strong interactions Discovery of pion meson (p) • Prediction of pion existence Yukawa 1935 • Nucleons (protons and neutrons) are held together by stronger force than electrostatic repulsion of protons • In 1935 Yukawa predicted existence of a mediator of the strong interactions. Estimated its mass to be around 0.1 GeV. • Discovery of pionsCecil Powell 1947 • Detected in cosmic rays captured in photographic emulsion • Unlike muons they do interact with nuclei • Charged pions eventually decay to muons: p-®m-nm D. Bortoletto

20. The discovery of the pion Balloons Pic du Midi Photos pion to muon electron decays D. Bortoletto

21. Discovery of kaon meson (K) • Rochester, Butler 1947 • Cosmic ray particles with masses in between pions and protons which were just like pions except for strangely long lifetime (decay to pions or a muon and neutrino) • Always produced in pairs • Mass ~ 0.5 GeV Now understood as the lightest 2nd generation meson The “particle Zoo” followed….. D. Bortoletto

22. Extensive air showers • Pierre Auger noticed that two detectors located several meters apart detected particles at the same time. • He discovered EAS, showers of secondary nuclei produced by the interaction of the primary particle with air molecules. (1938) D. Bortoletto

23. Extensive air showers • 1946 Groups led by Bruno Rossi in USA and Georgi Zatsepin in Russia started experiments on the structure of Auger showers. These researchers constructed the first arrays of correlated detectors to detect air showers. Grigorij Zatsepin setting up air shower detectors in Russia. D. Bortoletto

24. It is the secondary particles resulting from the interaction of the primary particle that are detected by the detectors used in our detectors and others arrays. D. Bortoletto

25. Cosmic rays enter the earth’s upper atmosphere and interact with nuclei. Secondary particles result that also interact. The shower grows with time. Certain particles never reach the surface. Some particles, such as muons, do reach the surface and can be detected. It is these that we wish to detect. An Extensive Air Shower D. Bortoletto

26. Detection Techniques • The observation of these events require a huge area • Air fluorescence • Air shower arrays http://astro.uchicago.edu/cosmus/projects/aires/ AIRES simulation of a proton with 1Tev of energy hits the atmosphere about 20km above the ground. The shower is in a 20km x 5km x 5km box superimposed on a scale map of Chicago's lakefront. Electrons and positrons are green, muons are red, and gamma rays are cyan. D. Bortoletto

27. The Energy Spectrum 1/sq km/century above 1020 eV • Existing models for the production of cosmic rays only work to 1015 eV. • CR in excess of 1019 eV are believed to come from sources relatively close to our Galaxy, but the sources are unknown. • The highest energies! (from,www.phys.washington.edu) G T P Exa Zetta D. Bortoletto

28. Cosmic Rays Now Last magnet descending to complete the LHC • Over the next 40 + years accelerators dominated the discoveries in particle physics The Auger Detector in Argentina • …but now since the 1990’s cosmic rays have again come to the forefront as a tool for fundamental physics, complementary to accelerators D. Bortoletto

29. Present Cosmic Ray Studies • Cosmic Ray studies continue in spite of the development of high energy particle accelerators. • The energy of the highest energy cosmic rays still cannot be duplicated in accelerators. • The field is still very active as indicated by the presentation of over 300 papers at the most recent international conference on cosmic rays. D. Bortoletto

30. Primaries are particles with energies from 109 eV to 1021 eV. An eV is a unit of energy. A 40 W reading light uses about 1034 eV of energy in one hour. (from James Pinfoli, Pinfold@phys.ualberta.ca) Cosmic rays within the range of 1012 eV to 1015 eV have been determined to be: 50% protons 25% alpha particles 13% C, N, and O nuclei <1% electrons <0.1% gammas What are cosmic rays? D. Bortoletto

31. In 1991 at the Fly’s Eye CR observatory in Utah a primary particle of 3 x 1020 eV was recorded. This is the equivalent of 51 joules At present particle accelerators can reach energies of 1012 eV. The Fly Eye (from www.physics.adelaide.edu) The “Oh My God” Particle D. Bortoletto

32. Where do they come from? • Low energy rays (less than 10 GeV) come from the sun. • Supernovae may be the source of particles up to 1015 eV. • The sources for ultrahigh cosmic rays are probably, active galactic nuclei and gamma ray bursts. (www.phys.washington.edu) D. Bortoletto

33. Supernovas • Nuclei receive energy from the shock wave of the supernova explosion. • The energy spectrum indicates that most of the supernova particles have less than 1015 eV • (image from:www.drjoshuadavidstone.com/ astro/supernova.jpg Explanation put forward by Fermi in 1947 !!!! D. Bortoletto

34. The AGASMA EVENT • In Japan, in 1993, the worlds largest array recorded a large air shower believed to be the result of a primary particle measured at 1021 eV. D. Bortoletto

35. Greisen-Zatsepin-Kuzmin cutoff • Cosmic ray with energies greater than 5x1019 eV will be absorbed by the Cosmic Microwave Background p + N+ D. Bortoletto

36. Recent results • Agasa and HRES do not agree • We waiting for Auger to settle this question D. Bortoletto

37. The Auger Experiment D. Bortoletto

38. How do particles get accelerated to high energies? • Active Galactic Nuclei? • Gamma Ray Bursts? • Is the source something exotic? New physics • Superheavy particles? D. Bortoletto

39. Cosmic ray projects involving high schools • CROP Cosmic Ray Observatory Project: http://physics.unl.edu/~gsnow/crop/crop.html • SALTA Snowmass Areas Large-scale Time-coincindence array http://faculty.washington.edu/~wilkes/salta/ • NALTAhttp://csr.phys.ualberta.ca/nalta/#NALTA • Tennessee Cosmic ray Observatory Project http://www.phys.utk.edu/tecop/ • Common Idea: Place simple particle detectors in numerous locations, for example on the rooftops of high schools to measure cosmic ray • Low energy cosmic rays are plentiful (many thousand per square metre every second). The highest energy cosmic rays are very rare (less than one hits a square kilometer of the Earth's surface each century). D. Bortoletto

40. Cosmic ray projects D. Bortoletto

41. Summary • Cosmic rays have a venerable history • Exiting scientific field that has lead to the development of particle physics. • It might be that the next progress will come again from looking at the sky D. Bortoletto

42. Lower energy, < 1016 eV: Direct observation possible, 85% are protons. Most likely source are supernova shock wave acceleration. These are particles below the knee in the energy spectrum. Ultra High energy, > 1016 eV. Only indirect EAR shower information is available. Source of the particles with > 1016 eV is unknown. A Summary D. Bortoletto

43. Cosmic rays are composed of : • Nuclei, roughly 87% protons, 12% alpha particles (helium nuclei) and most of the rest being made up of heavier atomic nuclei. • Electrons, gamma rays, and very high-energy neutrinos also make up a much smaller fraction of the cosmic radiation. D. Bortoletto

44. Time line • 1912 — Hess discovered cosmic rays • 1927 — Cosmic rays seen in cloud chamber • 1932 — Anderson discovered antimatter Debate over cosmic rays • 1937 — Discovery of muon • 1938 — Auger discovered extensive air showers • 1946 — First air shower experiments • 1949 — Fermi's theory of cosmic rays • 1962 — First 1020 eV cosmic ray detected • 1966 — Proposal of GZK cutoff energy for cosmic rays • 1967 — Haverah Park cosmic ray detector begins operations • 1991 — Fly's Eye detected highest-energy cosmic ray • 1994 — AGASA high-energy event • 1995 — Pierre Auger Project begun D. Bortoletto