Introduction to High Energy Physics for Anyone Interested

1. Introduction to High Energy Physics for Anyone Interested Natalia Kuznetsova Fermi National Accelerator Laboratory Outline: • The main questions particle physics attempts to answer: • What are things made out of? • What holds things together? • How do we know what we know about particles? • What are the remaining unanswered questions? • What are the prospects for high energy physics in the U.S.?

2. What is particle physics? • Particle physics addresses some of the most fundamental questions that people have been pondering for centuries: • What are the building blocks of matter? • Why are these blocks what they are? Can we explain their properties, such as mass? • What holds them together? • In a way, particle physics is complementary to cosmology: • cosmology studies the largest possible objects (such as galaxies, with hundreds of billions of stars!), and particle physics studies the smallest possible objects imaginable.

3. What is elementary? • What is the most elementary building block of matter? First, we need to define elementary: • Let us define an elementary particle as something that • has no discernable internal structure; • appears “pointlike”. • First, people thought that the atom was elementary: The atom, as it was envisioned around 1900 -- a ball with electrical charges inside, bouncing around!

4. The atom has a rich structure! • Eventually, it was realized that the atom is not elementary: • it consists of a positively charged nucleusand negatively charged electrons. • The properties of outermost electrons in atoms give rise to chemistry and biochemistry, with all of its complexity! • Theelectron, as far as we know, is elementary! electron nucleus If the nucleus were as big as a baseball, then the entire atom's diameter would be greater than the length of thirty football fields!

5. Is the nucleus elementary, too? • Unlike the electron, the nucleus is not structureless! It consists of protonsandneutrons. • But protons and neutrons are not elementary, either! • They consist of quarks, which to the best of our knowledge are elementary. nucleus neutron proton

6. What exactly are quarks? • Quarks are elementary building blocks of matter that are only found inside other particles, such as protons and neutrons, which most of the matter around us is made out of (including you!). There are 6 quarks, and they come in pairs: up charm top UCSB HEP group logo: down strange beauty

7. Hadrons • Quarks are never found by themselves, but only with other quarks inside hadrons. Baryons: three quarks Mesons: two quarks protons and neutrons are in fact baryons, made out of u and d quarks examples of mesons are pions (p) and kaons (K)

8. Hadrons are everywhere you look! Everything you can look at contains the simplest hadrons: protons and neutrons!

9. What about the electron? • We said earlier that apart from the six quarks, the electron was also elementary. • It turns out that the electron is not alone -- it belongs to a group of six particles called leptons! Just like quarks, leptons come in pairs: Electron neutrino Muon neutrino Tau neutrino nm (massless (?)) nt (massless (?)) ne (massless (?)) m (mass = 205 x mass of e) t (mass = 3503 x mass of e) e electron muon tau

10. What are neutrinos? • W. Pauli postulated their existence in order to save the energy conservation principle in certain types of radioactive decays, known as beta-decays: • E. Fermi called them "neutrinos" -- "little neutrons" in Italian. • Neutrinos hardly interact with anything at all. In fact, the earth receives more than 40 billion neutrinos per second per cm2. Most of them just pass through the earth, as if it's not even there! neutron decays into proton plus electron plus neutrino

11. Antimatter • Strictly speaking, the particle produced in a beta-decay is called an anti-neutrino. • There is an anti-particle for every particle. The only difference between them is that they have opposite charges. • The predominance of matter over antimatter in the Universe is one of the biggest mysteries of modern high energy physics and cosmology! A photon (which leaves no trace) produced an electron and an anti-electron (positron), which curl in opposite directions in a magnetic field. anti-electron (positron) electron

12. The Standard Model • The most compehensive theory developed so far that explains what the matter is made out of and what holds it together is called the Standard Model. • In the Standard Model, the elementary particles are: • Why do quarks and leptons come in sets (which are called generations)? Why are there three of them? We don't know. • Note that the Standard Model is still a model because it's really only a theory with predictions that need to be tested by experiment! • 6 quarks(which come in three sets) • 6 leptons(which also come in three sets)

13. What holds it together? • Things are not falling apart because fundamental particles interact with each other. • An interaction is an exchange of something. • But what is it that particles exchange? There is no choice -- it has to be some other special type of particles! They are called mediating particles. A rough analogy of an interaction: the two tennis players exchange a ball

14. Four fundamental interations • There are four fundamental interactions between particles: Interaction Mediating particle Who feels this force Strong Gluon (g) Quarks and qluons Photon (g) Electromagnetic Everything electrically charged Weak W and Z Quarks, leptons, photons, W, Z Gravity Graviton (?) Everything!

15. The strong interaction • The strong force holds together quarks in neutrons and protons. • It's so strong, it's as if the quarks are super-glued to each other! So the mediating particles are called gluons. • This force is unusual in that it becomes stronger as you try to pull quarks apart. • Eventually, new quark pairs are produced, but no single quarks. That's called quark confinement. QUARK

16. The electromagnetic interaction • The residual electromagnetic interaction is what's holding atoms together in molecules. • The mediating particle of the electromagnetic interaction is the photon. • Visible light, x-rays, radio waves are all examples of photon fields of different energies. opposite charges attract

17. The weak interaction • Weak interactions are indeed weak: • Neutrinos can only interact with matter via weak interactions -- and so they can go through a light year of lead without experiencing one interaction! • Weak interactions are also responsible for the decay of the heavier quarks and leptons. • So the Universe appears to be made out of the lightest quarks (u and d), the least-massive charged lepton (electron), and neutrinos. 1 light year nm n

18. Gravity • The Standard Model does not include gravity because no one knows how to do it. • That's ok because the effects of gravity are tiny comparing to those from strong, electomagnetic, and weak interactions. • People have speculated that the mediating particle of gravitational interactions is the graviton -- but it has not yet been observed.

19. How do we know what we know? • Some of the major High Energy Physics laboratories: • European Organization for Nuclear Research (CERN) • Stanford Linear Accelerator Center (SLAC) • Fermi National Accelerator Laboratory (FNAL) • What's actually hapenning there? • How can we "look inside" tiny particles? • What are accelerators? • What are detectors?

20. CERN: European Organization for Nuclear Research • The laboratory is located on the Swiss-French border, near Geneva (an awesome location!). • It was founded in 1954, one of the first examples of a major international endeavor. Currently, it includes 20 European countries as member states. • CERN is the birth place of WWW! 5.6 miles

21. SLAC: Stanford Linear Accelerator Center • SLAC is located near the beautiful Stanford University campus, at Menlo Park in California (20 min. to the ocean). • The research performed at SLAC has been recognized withthree Nobel Prizes in physics! • http://www.slac.stanford.edu is the first U.S. Web site!

22. FNAL: Fermi National Accelerator Laboratory • Fermilab is located in Batavia, Illinois (about an hour west of Chicago). • Fermilab is home to the Tevatron, the world’s highest-energy particle accelerator. • Fermilab is also a park, with 1,100 acres of prairie-restoration land!

23. How do we study tiny particles? • Recall how we perceive the world: we detect light (photons) bouncing off objects. • But we can’t use light to see atoms (not to mention, what’s in them!). • That’s because visible light waves have too low energy -- or too large a wavelength. wavelength

24. But we can use something other than light! • It’s not just light that has wave properties - all particles do! • The higher the particle’s momentum, the smaller its wavelength. • Therefore, the more sensitive it is to small objects. Slow electron = large wavelength wave Fast electron = small wavelength wave

25. Accelerators • Accelerators are machines used to speed up particles to very high energies. This way, we achieve two things: • We decrease the particle’s wavelength, so we can use it to poke inside atoms. • We increase its energy, and since E = mc2, we can use that energy to create new, massive particles that we can study. PEP-II accelerator at SLAC

26. Collisions are important events! • After particles have been accelerated, they collide either with a target (fixed target experiments) or with each other (colliding beam experiments). • These collisions are called events. • New particles are created in such a collision. Most of them quickly decay, but we can look at their decay products using detectors.

27. Events • Depending on the energy of the colliding particles, the events can be very messy, with lots of stuff flying out, or they can be relatively clean. • The products of collisions are looked at using detectors. An event from the OPAL experiment at CERN An event from the BaBar experiment at SLAC

28. Our detectors are HUGE! ALEPH detector at CERN CDF detector at FNAL A lot of HEP detectors are as big as a house -- several stories high!

29. Collaborations • Because the experiments are so big, it takes a very large group of physicists and engineers to get things working. • Such groups of scientists are called collaborations. The major collaborations around the world include hundreds or thousands of people from tens of countries! ATLAS Collaboration at CERN: nearly 2,000 people!

30. Why are they so big? • The history of high energy physics is one of a relentless climb to higher and higher energies. • Comparing to one of the first discovered elementary particles, the electron, some of the particles we are studying now are about 400,000 times heavier!

31. Anatomy of a detector: silicon vertex detector • Many particles decay very close to where they were produced. • That’s why at the heart of many detectors is a device needed for finding just where this happened. The vertex point The silicon vertex detector used in the BaBar experiment at SLAC

32. Anatomy of a detector: tracking chambers • Charged particles leave tracks by ionizing gas in tracking chambers. • We can learn a lot by studying these tracks -- for example, a particle’s momentum! 3. electron (from muon) 2. muon (from pion) 1. pion Glowing gas along particle tracks in a streamer chamber!

33. Another tracking chamber example • This tracking chamber is filled with helium gas. • Charged particles ionize this gas and leave tracks in the chamber. • Lots of wires are strung the length of the chamber to pick up electrical signals due to the ionization. The tracking chamber used in the BaBar experiment at SLAC

34. Anatomy of a detector: particle identification • When a charged particle travels in some medium (e.g., water) faster than light does, it emits Cherenkov light. • By analyzing this light, physicists can in some cases tell what kind of a charged particle it was. Rings of Cherenkov light from the Super-Kamiokande experiment in Japan.

35. Anatomy of a detector: calorimeters • Calorimeters allow physicists to measure the total energy deposition of some particles. • This, in turn, allows us to tell what kind of particles they are. showers! photon electron positron Study of electromagnetic calorimeter performance for the CMS detector at CERN (not yet built)

36. Anatomy of a detector: bringing it all together • Different sub-detectors in a single particle detector are used for detecting and analyzing different types of particles

37. Other detectors: neutrino detectors Sudbury Neutrino Observatory in Canada Super-Kamiokande experiment in Japan

38. What are the unanswered questions? • Why is there so much matter in the Universe and almost no anti-matter? • What's "dark matter"? • Why are there three generations of quarks and leptons? • Are quarks and leptons really fundamental? • Why are the particle masses what they are? • How can we unify gravity with the other three forces? • ….

39. Matter-antimatter asymmetry • In the Big Bang, we think that matter and antimatter were created in equal amounts. So where did the antimatter go? • There must be some asymmetry in the behavior of particles and antiparticles. • This effect is called "CP asymmetry", and an example has just been observed by the BaBar experiment at SLAC in the decays of particles called B mesons!

40. Grand Unification • One day, there will exist a theory that unifies all three forces: electromagnetic, weak, and strong. • Physicists have speculated that this merging of all the forces may occur at a very high energy. All three forces may merge at an energy of 1019 GeV, which is about 1,000,000,000,000,000,000,000,000,000 times larger than the energies we are used to dealing with in our everyday life!

41. Where does gravity fit in? • Theories attempting to unify gravity with the other three forces are still in their infancy, but one of them, called supersymmetry, looks quite promising. • Supersymmetry, in turn, follows naturally from a really mind-boggling theory called string theory, where all particles are treated as strings, and which requires extra space dimensions! extra spacial dimensions! one string merge into yet another string! …plus another string

42. Practical applications of high energy physics • Basic research always pays off in the long run. • Apart from invaluable scientific advancement, the tools and methods used in fundamental science often find important practical applications, such as: • Medical physics (e.g., cancer treatment, drug improvement). • Environmental applications (e.g., characterizing environmental wastes using synchrotron radiation). • Computing applications. • Remember that WWW is one of the high energy physics spin-offs! • And much much more!

43. Conclusion • High energy physics addresses some of the most fundamental questions about the Universe. • What's more, it's really fun! • The high energy physics community in the U.S. is strong and thriving -- and will welcome you should you decide to become part of this excitement!

44. Prospects for particle physics in the U.S. Start-up date or Decision Point Lab Experiment U.S. Participartion, % in progress in progress 2006 2006 51/55 CDF/D0 MiniBOONe NuMI/MINOS BTeV 100 FNAL 69 74 CERN ATLAS/CMS 2006 20 SLAC BaBar in progress 2003 2010 2020 Next Linear Collider Very Large Hadron Collider Muon Collider ? ?

45. More Tracking Chamber Images One of the first bubble chambers at CERN Tracks in Brookhaven National Laboratory 7-foot bubble chamber

46. Wiring a Drift Chamber Wiring some 25,000 wires in a drift chamber for the ZEUS detector at DESY (Germany)