1. 1 Welcome to the Rice/UH Quarknet Summer workshop! Brought you to by Quarknet The Department of Physics and Astronomy of Rice University The Department of Physics of the University of Houston The National Science Foundation The Department of Energy Please sign in!

2. 2 The nature of science, the definition almost is this: The test of all scientific questions is experiment. Experiment is the sole judge of scientific truth. --Richard Feynman

3. 3 Nature’s Deepest Questions People have wondered about the nature of matter at least since time of the Greeks. Democritis, around 450 BC coined the term atom for what he considered the fundamental particles of nature…the smallest bits of matter that could not be divided further. Atom comes from a Greek word meaning “indivisible”

4. 4 Atoms, the building blocks of matter The Greeks had the idea that there were only a few different types of atoms, and all matter was made up of different combinations of them.

5. 5 Mendeleev and the periodic table Fast forward to the 1800s. As more and more different kinds of atoms were discovered, Mendeleev noticed a pattern that led him to arrange the different kinds of atoms into a table that we now call the periodic chart of the elements

6. 6 Periodic chart of the elements But there are over 100 elements! Seems like too many…

7. 7 The 20th century revolutions There were many revolutions in physics during the 20th century, but one of the most important was the realization that atoms were not indivisible… JJ Thompson discovered the electron in 1897

8. 8 The constituents of the atom In 1912 Rutherford discovered the atomic nucleus

9. 9 Oh well, I guess we can tolerate three... In 1932, Chadwick discovered the neutron, the neutral partner of the proton. It wasn’t really expected, but didn’t seem to complicate things too much... Atoms were then understood as made from a nucleus of protons and neutrons surrounded by the electrons. The nucleus is 100,000 times smaller than the atom.

10. 10 But once again the simple picture broke down... During the 1930s and 40s, cosmic ray experiments and the first accelerators discovered more particles: In 1937 another particle, which we now call the muon was discovered in cosmic ray experiments. I. I. Rabi—”Who ordered that?” In 1946 the pion was discovered the same way

11. 11 Discovery of the Kaon In 1947 a new type of particle called “strange” particles was discovered in cosmic rays Decay of a neutral kaon Decay of a charged kaon

12. 12 Too many fundamental particles !! By about 1965 there were over 100 fundamental particles…again too many. Here is an example page from the Particle Data Book…this is one of several hundred pages of particle listings.

13. 13 Enter the quark Around 1965 Gell-Mann suggested that protons, neutrons, and most of the other particles were made of constituents which he called quarks. “Three quarks for Muster Mark…” Finnegan’s Wake The proton is made of three quarks, and so is the neutron. But the electron is still fundamental.

14. 14 The fundamental particles circa 1965: Three quarks: u, d, s with charges +2/3 and -1/3 in units of the electron charge. Three leptons: electron (e) and muon (  ) and a mysterious, neutral, very weakly interacting particle called the neutrino,. Six…maybe not too bad

15. 15 The November revolution In November of 1974, the world of physics was stunned by the discovery of a fourth quark, the c or “charm” quark This is a picture of the decay of a particle containing a c quark and anti-quark pair.

16. 16 And then there were five. In 1977 yet another quark was discovered, the b or bottom quark at Fermilab The detectorLeon

17. 17 Now we know there are six quarks

18. 18 Are we done yet? Our current understanding of the fundamental particles: Six quarks and six leptons, arranged in three families or generations. These particles have mass and electric charge but apparently no size!

19. 19 The fundamental interactions So we have the quarks and leptons…how do they interact with each other? Through the exchange of one of the force carriers. The photon ( γ) is the force carrier of the electromagnetic force. The gluon (g) is the force carrier of the strong force. The W and Z are the force carriers of the weak force.

20. 20 The fundamental interactions Feynman diagrams showing weak and electromagnetic interactions Feynman developed a pictorial way of thinking about particle interactions called Feynman diagrams.

21. 21 But wait…where does the proton fit in? The quarks combine in two (and only two) ways to form particles that we observe in the lab. Quark-antiquark pairs from mesons:  + = u anti-d K + =u anti-s Three quarks from baryons: Proton=uud neutron=udd So the proton is not fundamental, but is a composite particle, like a nucleus. More on antimatter later!

22. 22 The Importance of Energy New discoveries often follow the opening of a new energy regime: Discovery of the electron 1 eV Discovery of the nucleus 5 MeV Discovery of pion and muon 100 MeV Discovery of the kaon 500 MeV Discovery of the proton substructure 20 GeV Discovery of the top quark 2 TeV

23. 23 The importance of energy To achieve ever higher and higher energies, larger and larger machines have been built, with Fermilab and CERN currently being the largest.

24. 24 Fundamental question #1 Is there another layer of substructure, or more generations? We don’t know, but there is no sign of further substructure yet.

25. 25 The spectrum of masses Let’s look more closely at the masses of the quarks and leptons: Units are 1 GeV, an energy unit equal to the mass of the proton u,d 0.3 GeV e 0.0005 GeV s 0.5 GeV  0.1 GeV c 1.5 GeV  1.8 GeV b 4.5 GeV ? t ?

26. 26 Let’s look more closely at the masses of the quarks and leptons: Units are 1 GeV, an energy unit equal to the mass of the proton u,d 0.3 GeV e 0.0005 GeV s 0.5 GeV  0.1 GeV c 1.5 GeV  1.8 GeV b 4.5 GeV.000000000003 GeV t 172 GeV The spectrum of masses

27. 27 Fundamental question #2 How can something with no physical size have mass and charge? How do these fundamental particles acquire mass, and what determines the values of the masses?

28. 28 Antimatter I wasn’t complete when I listed all the particles…I should have mentioned that all particles have their antiparticles ! When matter and antimatter meet, they annihilate each other in a burst of energy ! Fire up the antimatter drive, Mr. Scott. Dirac predicted antimatter in 1927

29. 29 Antimatter We create antimatter all the time at places like Fermilab, and we can store it for days. But we always make it as matter-antimatter pairs. Antiproton accumulator at Fermilab

30. 30 Fundamental question #3 If we always produce matter and antimatter together, in equal amounts…why is the universe today dominated by matter? The answer is closely linked to symmetries of nature. Electron-positron production from a photon e-e- e+e+ photon

31. 31 Symmetries of nature You may not think about it, but you make assumptions every day about symmetries. If I do an experiment, then pick up my apparatus and move it over 1 m, you do not expect the results to change. The laws of physics are invariant under translations in space. If you do an experiment and then rotate your apparatus 90 degrees, you do not expect the results to change. The laws of physics are invariant to rotations in space. If you do an experiment, wait an hour, and do it again, you do not expect the results to change. The laws of physics are invariant to translations in time.

32. 32 Symmetries and conservation laws There is a one-to-one correspondence between symmetries and conservation laws, discovered in 1915 by mathematician Emmy Noether. Emmy Noether was a German mathematician, described by Einstein and Hilbert as the most important woman in the history of mathematics. After she received her PhD in mathematics, she taught for seven years without pay at he Mathematical Institute of Erlangen. But in 1915 she was invited by Hilbert to join the mathematics faculty at the University of Goettingen, not without controversy. In 1933 she was dismissed from her position because she was Jewish. She accepted a position at Bryn Mawr College and stayed there until her death.

33. 33 Symmetries and Conservation Laws Symmetries of physical systems lead to conservation laws: Symmetry under translations in space → conservation of linear momentum. Symmetry under rotations in space → conservation of angular momentum. Symmetry under translations in time → conservation of energy. These are examples of continuous symmetries.

34. 34 Discrete Symmetries We can also define a discrete symmetry, the most well- known example being parity. The parity operation is the inversion of the coordinate system: x → -x y → -y z → -z This operation is equivalent to reflection in a mirror followed by 180 degree rotation.

35. 35 Reflection about y-axis Rotate 180 degrees about x axis The parity operation is equivalent to reflection in a mirror followed by 180 degree rotation. Initial momentum Final momentum

36. 36 To understand parity, imagine playing a game of pool and playing a bank shot off the wall. If you watched the shot, or watched its mirror reflection, could you tell the difference? Mirror Parity

37. 37 The laws of classical physics are invariant under the parity operation! F=ma Both force and acceleration change sign, so Newton's 2nd -F = -ma law is unchanged. The laws of electromagnetism are also unchanged. Parity

38. 38 In 1956 Lee and Yang, based on puzzles in meson decays, suggested that parity might not be conserved in weak interactions.

39. 39 C. N. Yang and T. D. Lee

40. 40 Within a year, Madam Wu at Columbia demonstrated experimentally that beta decay did not conserve parity—that is, a decay and its mirror image were not identical! Co 60 Nuclear spin electron Nuclear spin electron Mirror Parity Violation

41. 41 In particle physics we have another discrete symmetry that we use often called charge conjugation. This is the symmetry operation of matter ↔ antimatter proton antiproton Do matter and antimatter behave the same way? NO! Within a year it was also shown that the weak interaction distinguishes between matter and antimatter. Another discrete symmetry—charge conjugation

42. 42 Symmetries and the matter-antimatter asymmetry of the universe So why do we care? In 1968 Russian physicist Andrei Sakharov showed that violation of these fundamental symmetries is a necessary condition to generate the matter- antimatter asymmetry of the universe.

43. 43 b b B s 0 meson Anti-B s 0 meson Matter ↔ Antimatter The Standard Model does have a mechanism to cause the violation of these symmetries, but at a level way too small to account for the matter-antimatter asymmetry of the universe.

44. 44 What D0 found... Matter and antimatter can change into each other, that we have known for 50 years. But what we found was that the rate is in B mesons not the same in both directions. And the difference is much larger (40x) than expected in the Standard Model.

45. 45 This result has received a lot of attention because it disagrees with the SM by 3.2 standard deviations, and also because it relates to a 50 year old puzzle that is central to the origin of the universe.

46. 46 Is this result enough to account for the matter-antimatter asymmetry of the universe? We don't know yet. What does it mean? A theorist in Taiwan thinks it is evidence for a 4 th generation, but there are other ideas. There has been lots of press coverage... “A New Clue to Explain Existence” New York Times Joe Lykken, a theorist at Fermilab, said, “So I would not say that this announcement is the equivalent of seeing the face of God, but it might turn out to be the toe of God.” Is it right? Time will tell. http://www- d0.fnal.gov/Run2Physics/top/public/CP_violation_evidence_DZero.html And this discovery was NOT at the energy frontier, but rather at the precision frontier. Implications

47. 47 Summary-what we don’t know (yet) 1. Have we reached the bottom yet? (is there another layer of substructure?) 2. What is the origin of mass, and why do particles have the masses they do? 3. What is the origin of the matter-antimatter asymmetry of the universe?

48. 48 Where do we do these experiments? Aerial view of Fermilab, near Chicago, and Wilson Hall

49. 49 One of the collider detectors And a typical event

50. 50 More views of Fermilab Fermilab is a wildlife refuge as well as a national lab

51. 51