LECTURE 7 The Standard Model Instructor: Shih-Chieh Hsu Announcement 2 ¨ ATLAS Virtual Visit (PAB A110) ¤ Sep 7 – Vidyo connection will start from 9:20am ¤ At least one question for CERN host from each group http://atlas-live-virtual-visit.web.cern.ch/atlas-live-virtual-visit/2016/20160907-Seattle.html The CMS Masterclass 3 ¨ LHC – CMS Masterclass (PAB A110) ¤ Sep 8 and Sep 9 ¨ Team-up with your symposium group ¤ At least one laptop per group (two laptops are better) ¤ Make sure your browser can run iSpy and CIMA software https://canvas.uw.edu/courses/1089028/pages/cms-masterclass-2016 ¨ Read introduction and analysis tips before lectures ¤ Let’s re-discovery W, Z and possibly H boson using CMS real data! Lecture 7 4 ¨ The Particle Adventure http://www.particleadventure.org 5 New Quantum Theory (First Quantization) First Quantization 6 ¨ The quantization of equation of motion of electron of atom is induced by the boundary condition of wave function from electric field of positive nucleus ¨ Successfully describe the spectrum of atom. ¨ Electron is moving in the speed v << c. Quantum Mechanics + Newtonian Relativity 2 2 ∂ − ∇ Ψ(r ,t) + U (r )Ψ(r ,t) = i Ψ(r ,t) 2m ∂t Schrödinger equation Dirac Equation 7 ¨ Dirac tries to go beyond: Quantum Mechanics + Special Relativity -> Difficulty of negative energy -> Difficulty of develop motion of equation for photon Dirac equation 2nd Quantization 8 From Particle to Field ¨ Single-particle to Many-particle theory ¨ Particle is an excitation (cluster of energy) of quantum field ¨ Each type of particle has a corresponding Field ¨ This leads to a complete quantum theory of electron and light!!! Timeline I 9 Timeline II 10 H The Modern Atom Model 11 If protons and neutrons a centimeter in diameter electrons and quarks would be less than the diameter of a hair the entire atom's diameter would be greater than the length of thirty football fields! Scale of the atom 12 We don't know exactly how small quarks and electrons are; they are definitely smaller than 10-18 meters, and they might literally be points, but we do not know. It is also possible that quarks and electrons are not fundamental after all! What are we looking for? 13 We have now discovered about two hundred particles (most of which aren't fundamental). They are named with letters from the Greek and Roman alphabets. Enrico Fermi said “Young man, if I could remember the names of these particles, I would have been a botanist!" The Standard Model 14 6 quarks. 6 leptons. The best-known lepton is the electron. We will talk about leptons in just a few pages. Force carrier particles, like the photon. We will talk about these particles later. Quarks and Leptons 15 Everything you saw is made from quarks and leptons. Quarks behave differently than leptons, and for each kind of matter particle there is a corresponding antimatter particle. Matter and Antimatter 16 Antiparticles look and behave just like their corresponding matter particles, except they have opposite charges. What is Antimatter 17 evidence for antimatter in this early bubble chamber photo. The magnetic field in this chamber makes negative particles curl left and positive particles curl right. the "up quark" u has an "up antiquark”, pronounced u-bar. The antielectron is called a positron and is designated e+.) Quarks 18 Quarks have the unusual characteristic of having a fractional electric charge Quarks also carry another type of charge called color charge, Naming of Quarks 19 1964, Murray Gell-Mann and George Zweig suggested that hundreds of the particles known at the time could be explained as combinations of just three fundamental particles. Gell-Mann chose the name "quarks," pronounced "kworks," Gell-Mann George Zweig Quarks Naming 20 There are six flavors of quarks. "Flavors" just means different kinds. The two lightest are called up and down. The third quark is called strange. It was named after the "strangely" long lifetime of the K particle, the first composite particle found to contain this quark. The fourth quark type, the charm quark, was named on a whim. It was discovered in 1974 almost simultaneously at both the Stanford Linear Accelerator Center (SLAC) and at brookhaven National Laboratory. Heavy Quarks 21 The bottom quark was first discovered at Fermi National Lab (Fermilab) in 1977, in a composite particle called Upsilon . The top quark was discovered last, also at Fermilab, in 1995. It is the most massive quark. It had been predicted for a long time but had never been observed successfully until then. Hadrons: Baryons and Mesons 22 Like social elephants, quarks only exist in groups with other quarks and are never found alone. Composite particles made of quarks are called (uud), protons Pion , which is made of an up quark and a down anitiquark. Leptons 23 "Lepton" comes from the Greek for "small mass," However, the tau lepton is more than 3000 times as massive as the electron. Quarks are sociable and only exist in composite particles with other quarks, whereas leptons are solitary particles. Lepton Decays 24 the muon and the tau, are not found in ordinary matter at all. This is because when they are produced they very quickly decay, or transform, into lighter leptons. Physicists have observed that some types of lepton decays are possible and some are not. In order to explain this, three lepton families: the electron and its neutrino, the muon and its neutrino, and the tau and its neutrino. The number of members in each family must remain constant in a decay. Lepton Type Conservation 25 We use the terms "electron number," "muon number," and "tau number" to refer to the lepton family of a particle. Electrons and their neutrinos have electron number +1, positrons and their antineutrinos have electron number -1, Quiz 26 Which lepton decays are possible? Why or why not? Yes! Charge, tau number, electron number, and energy are all conserved. No! Muon number is not conserved. A muon has a muon number of 1, and thus the right side of the decay equation has muon number 1 No! energy is not conserved. A muon has a lot more mass than an electron, Neutrinos 27 it was through a careful study of radioactive decays that physicists hypothesized the neutrino's existence. because neutrinos were produced in great abundance in the early universe and rarely interact with matter, there are a lot of them in the Universe. Their tiny mass but huge numbers may contribute to total mass of the universe and affect its expansion. Quiz 28 What are protons made of? Protons are made of two up quarks and one down quark, expressed as uud. What are electrons made of? As far as we know, electrons aren't composed of smaller particles, they are fundamental! Which of the following are made of quarks? Baryons? Yes, they are made of three quarks put together. Mesons? Yes, they are made of one quark and one antiquark. Barons? Yes, the English nobility are also made of quarks. The Four Interactions 29 What holds things together? What's the difference between a force and an interaction? a force is the effect on a particle due to the presence of other particles. The interactions of a particle include all the forces that affect it, but also include decays and annihilations that the particle might go through. the particles which carry the interactions force carrier particles. Elementary Particles 30 How does matter interact? 31 How do two magnets "feel" each other's presence and attract or repel accordingly? How does the sun attract the earth? We know the answers to these questions are "magnetism" and "gravity," but what are these forces? At a fundamental level, a force isn't just something that happens to particles. It is a thing which is passed between two particles. The Unseen effect 32 You can think about forces as being analogous to the following situation: all interactions which affect matter particles are due to an exchange of force carrier particles Electromagnetism 33 The carrier particle of the electromagnetic force is the photon Photons have zero mass, as far as we know, and always travel at the "speed of light", c, which is about 300,000,000 meters per second, or 186,000 miles per second, in a vacuum. Residual EM force 34 Atoms usually have the same numbers of protons and electrons. They are electrically neutral, Since they are neutral, what causes them to stick together to form stable molecules? the charged parts of one atom can interact with the charged parts of another atom. This allows different atoms to bind together, an effect called the residual electromagnetic force. What about the nucleus? 35 What binds the nucleus together? why doesn't the nucleus blow apart? Since neutrons have no charge and the positively-charged protons repel one another, So how can we account for this dilemma? Strong and Color Charge 36 Quarks have an altogether different kind of charge called color charge The force between color-charged particles is very strong, so this force is "creatively" called “Strong” The force carrier is called “Gluon” composite particles made out of quarks have no net color charge (they are color neutral). Color Charge 37 Gluons carry two colors "Color charge" has nothing to do with the visible colors, it is just a convenient naming convention for a mathematical system physicists developed to explain their observations about quarks in hadrons. Quark Confinrment 38 Color-charged particles cannot be found individually. For this reason, the color-charged quarks are confined in groups (hadrons) with other quarks. These composites are color neutral.