The Ultimate Structure of Matter Chapter 13 Presented 15 October 2015 Prof. Geller Great Idea: All matter is made of quarks and leptons, which are the most fundamental building blocks of the universe that we know.

Chapter Outline Of What is the Universe Made? Discovering Elementary Particles The Elementary Particle Zoo The Four Fundamental Forces

Of What is the Universe Made?

The Library Superficial description Basic Ultimate description Fundamental building blocks Books Rules for organization Basic Words grammar Ultimate description Letters Spelling

Reductionism Reductionism How simplicity gives rise to complexity Ultimate building blocks How simplicity gives rise to complexity True nature Thought, experiment, observation

The Building Blocks of Matter Fundamental building blocks Changed over time Atom Nuclei and electrons Elementary particles

Discovering Elementary Particles

Cosmic Rays Cosmic Rays Used to understand nucleus Particles emitted by stars Used to understand nucleus Found new elementary particles

Particle Accelerators: The Essential Tool Artificial cosmic rays Ernest O. Lawrence cyclotron Synchrotron Linear accelerator

The Elementary Particle Zoo

Leptons, Hadrons, and Antimatter

Quarks and Leptons Quark Leptons Fundamental building blocks of hadrons Fractional electrical charge Only six kinds Leptons Six kinds Outside nucleus

Quark Confinement Individual quarks Elementary particles No experimental isolation of a quark Elementary particles Difficult to isolate

iClicker Question Which of the following are the most fundamental building blocks of matter in the universe: A atoms and molecules B quarks and leptons C planets and stars D energy and waves

iClicker Question The quest for the “ultimate building blocks” of the universe is referred to by philosophers as: A reductionism B science C atomism

iClicker Question Which of the following lists has the items listed correctly from smallest to largest? A atom, quark, nucleus, neutron, molecule B neutron, quark, nucleus, atom, molecule C quark, neutron, nucleus, atom, molecule D nucleus , quark, neutron, atom, molecule E molecule, atom, nucleus, neutron, quark

iClicker Question The main working part of a synchrotron is: A a large ring of magnets B a nuclear fusion generator C a flux capacitor D a diode

iClicker Question True or False: Moving charged particles are not affected by magnetic fields. A True B False

iClicker Question Which type of elementary particle exists inside the nucleus? A Electron B Hadron C Lepton D None of the above exist within the nucleus

iClicker Question True or False: For every particle in the universe, it is possible to produce an antiparticle. A True B False

iClicker Question What does “PET” (as in PET scan) stand for? A patient electrocardio torture B positron emission tomography C patient electro transmission D positive electron topography E positive emitting typography

iClicker Question Which of the following is made from quarks? A hadrons B leptons C electromagnetic waves

Reviewing Subatomics

Reviewing Subatomics

Reviewing Subatomics

Reviewing Subatomics

Reviewing Subatomics Neutrinos are produced in the “Weak Interaction”, for example Neutrinos from the earth natural radioactivity “Man-made” neutrinos accelerators, nuclear power plants. Astrophysical neutrinos Solar neutrinos Atmospheric neutrinos Relic neutrinos left over from the big bang.

Neutrino Factoids The earth receives about 40 billion neutrinos per second per cm2 from the sun. About 100 times that amount are passing through us from the big bang. This works out to about 330 neutrinos in every cm3 of the universe! By comparison there are about 0.0000005 protons per cm3 in the universe. Our body emits about 340 million neutrinos per day from 40K. Neutrinos don’t do much when passing through matter. Remember, it is very difficult to observe neutrinos.

Neutrino Detection ne nm Electron Muon The neutrino is observed by detecting the product of its interaction with matter. ne Electron nm Muon

iClicker Question True or False: Quarks have actually been isolated and observed in the laboratory. A True B False

The Four Fundamental Forces

The Four Fundamental Forces

Force as an Exchange Forces cause matter to accelerate Gauge particle Produce fundamental forces

Unified Field Theories Fundamental forces seen as different aspects of one force Four fundamental forces may be different aspects of a single force Electroweak force Standard model Theories of Everything

iClicker Question How many fundamental forces are there? A 2 B 4 C 6

iClicker Quesiton Which of the four fundamental forces is the strongest? A strong force B weak force C gravity D electromagnetic

iClicker Question Which of the four fundamental forces is the weakest? A strong force B weak force C gravity D electromagnetic

iClicker Question True or False: The search for a “theory of everything” will be accomplished in my lifetime. A True B False

String Theory: the idea All matter consists of small one-dimensional objects (strings). Strings look like particles when not resolved closely enough All particle types are different normal modes of the string.

String Theory: the interactions All interactions consist of the splitting and joining of these elementary strings. This is currently the best description of the scattering of gravitational waves at very high energies! Looks like General Relativity plus other interactions at low energies. No parameters: string length sets units.

Possible Downsides At first sight there appeared to be a number of different kinds of string theories. Open, closed, heterotic, Type I, Type IIA,... Predicts we live in 10 spacetime dimensions! Experimental update: number of (large) dimensions = 4 Very difficult to experimentally test so far. Strings are so short that once the symmetries and spectrum are gotten right, most of the details are usually also right. Calculation gets known masses right, but….. experiment mexp = 0.00…………….…005 theory mth = 0.00000000

D-Branes String theory is bigger than previously thought. Polchinski String theory is bigger than previously thought. Normally, open strings satisfy Neumann boundary conditions, string ends move at light speed. Dirichlet boundary conditions also make sense string ends live on a surface. This surface is interpreted as a large massive object, a D-brane, in spacetime, much like a monopole.

Why Do This? Good Things Happen if the theory has both strings and D-branes: Previously-hidden duality symmetries emerge, with all known string theories dual to one another under these symmetries! Some weakly-interacting string theories are the duals of the strong-coupling limit of others! Led to discoveries of similar symmetries amongst ordinary particle theories. Conjecture: all known string theories are different solutions to a more fundamental (11-dimensional) theory (M Theory).

String Length Arkani-Hamad, Dvali & Dimopoulos If n = 6 then ls = lw requires a = 105 fm, Could strings be as large as the present-day experimental limit ls = lw? Non-gravitational physics is characterized by the weak scale: GF = lw2 = (10-3 fm)2 Why is lw = 10-3 fm so much larger than lp = 10-19 fm? Why is gravity so weak? Why are stars so big? Weak-Scale Strings: can ls = lw? Geff is nonetheless small enough! If n = 2 then ls = lw requires a = 0.1 mm!!

String Length and Gravity Arkani-Hamad, Dvali & Dimopoulos Could strings be as big as they can be: ls = lw? Non-gravitational physics is characterized by the weak scale: GF = lw2 = (10-3 fm)2 If so, strings may be experimentally discovered ‘tomorrow’! If so, does this explain why lw is so much larger than lp = 10-19 fm? ie: Why is gravity so weak? Why are stars so big? Gravity would be weak because the extra dimensions are large: If n = 2 then ls = lw requires a ~ 0.1 mm!! If n = 6 then ls = lw requires a ~ 105 fm,

Intermediate-Scale Strings CB, Ibanez & Quevedo Q: Can ls and a be similar in size? A: Yes. ls / a = 0.01 works if: I: ls = √(lw lp) =10-11 fm. lw = ls2 / lp naturally arises if supersymmetry breaks on another brane, and is transmitted to our brane by gravity. II: n = 6 extra dimensions. No heirarchy need be dialed in. Other nice things also happen if so: String axions can solve strong CP problem, neutrino masses similar to experiments, etc

String Summary String theory is the only known theory where gravity and quantum mechanics co-exist at high energies. Major Lesson of the 20th Century: Relativity and Quantum mechanics are almost inconsistent, and so together impose extremely strong self-consistency conditions. The string length is likely much longer than the Planck length. Size Matters: much better prospects for comparison with experiments. The intermediate scale is well motivated on particle-physics grounds: ls = √(lw lp) =10-11 fm. We may all be Brane bound.

iClicker Question I find the idea that there might be 10 or 11 dimensions: A exciting B interesting C confusing D scary E nonsense