1. The Higgs Boson: without the maths and jargon David Hall Graduate Seminar Series St Catherine’s College MCR 11 th May 2011

2. Questions to be answered… What is the Higgs boson? Why is it so important? Why do we think it exists? How is the LHC going to find it? + any you might have The Higgs Boson – 11/05/11David Hall1

3. Introduction Everything in the universe is made of atoms These are made of 3 things:  protons  neutrons  electrons Particle physics: Electron is fundamental Protons and neutrons aren’t The Higgs Boson – 11/05/11David Hall2

4. The Standard Model Decades of experiments have lead to the Standard Model Protons and neutrons are made of up and down quarks Ordinary matter is made of just 3 particles Other leptons and quarks are harder to find The Higgs Boson – 11/05/11David Hall3

5. The Standard Model Four fundamental forces  Electromagnetism (electricity, magnetism and light)  Strong (holds the nucleus together)  Weak (radioactive decay)  Gravity (motion of planets, galaxies) Each has associated particles The Higgs Boson – 11/05/11David Hall4

6. Symmetries in nature This all seems great, so why do we need a Higgs boson? Fundamental forces come from symmetries of nature Problem: These same symmetries prevent particles from having mass But we know they do The Higgs Boson – 11/05/11David Hall5

7. The Higgs mechanism To give particles mass, we need to break a symmetry In the SM, this is done through the Higgs mechanism Spontaneous symmetry breaking (pencil analogy) The Higgs Boson – 11/05/11David Hall6

8. The Higgs mechanism To give particles mass, we need to break a symmetry In the SM, this is done through the Higgs mechanism Spontaneous symmetry breaking (pencil analogy) The Higgs Boson – 11/05/11David Hall6 “Mexican hat”

9. The Higgs boson The Higgs mechanism requires a “Higgs field” When a particle interacts with this field, it acquires mass (honey demonstration) The Higgs boson is an excitation of this field So if we find the Higgs boson, then the Higgs mechanism is correct The Higgs Boson – 11/05/11David Hall7

10. The Higgs boson The Higgs mechanism requires a “Higgs field” When a particle interacts with this field, it acquires mass (honey demonstration) The Higgs boson is an excitation of this field So if we find the Higgs boson, then the Higgs mechanism is correct The Higgs Boson – 11/05/11David Hall7 Here I am!

11. Peter Higgs The Higgs Boson – 11/05/11David Hall8

12. Is the Higgs mechanism correct? SM describes perfectly everything ever seen Higgs mechanism predicted mass of W and Z particles Experimentally verified in 1983 The Higgs Boson – 11/05/11David Hall9

13. Is the Higgs mechanism correct? SM describes perfectly everything ever seen Higgs mechanism predicted mass of W and Z particles Experimentally verified in 1983 There are alternatives… But we would also find them at the Large Hadron Collider The Higgs Boson – 11/05/11David Hall9

14. Large Hadron Collider Proton-proton accelerator 27km circumference Nearly 200m underground Highest energy ever! The Higgs Boson – 11/05/11David Hall10

15. Large Hadron Collider Proton-proton accelerator 27km circumference Nearly 200m underground Highest energy ever! ATLAS: Detectors surrounding the collision point Measure particles’ energies and tracks The Higgs Boson – 11/05/11David Hall10

16. Large Hadron Collider The Higgs Boson – 11/05/11David Hall11

17. How is the Higgs boson produced? When the protons collide, new particles can be produced Different particles have different probabilities Very rarely, we will produce a Higgs boson The Higgs Boson – 11/05/11David Hall12

18. Finding the Higgs boson So you’ve made your Higgs boson But it decays immediately What to depends on the mass of the Higgs boson This means we exclude a range of masses The Higgs Boson – 11/05/11David Hall13

19. Finding the Higgs boson The Higgs Boson – 11/05/11David Hall14

20. The future We’re closing in on the Higgs boson If it’s there, we’ll find it in the coming years The Higgs Boson – 11/05/11David Hall15