Discovery of the Higgs Boson

1. Discovery of the Higgs Boson Gavin Lawes Department of Physics and Astronomy

2. Acknowledgements Includes slides and images from: Robert Harr, Paul Karchin, and Sean Gavin (Wayne State University) LHC (CMS Collaboration) Note: There is a lot more information about the LHC and the Higgs Boson at home.web.cern.ch

3. What do we know about matter?

4. What properties define matter particles? Mass. Spin. (Zero spin particles are bosons, spin ½ particles are fermions) Electric charge. Color charge. (Other)

5. Particles in the Standard model

6. Particle crib sheet Photon g (massless, no charge) Electron e (massive, charged) Muon m (massive, charged) Proton p (massive, charged) Gluon g (massless, “color charge”) Higgs H (massive, ?????)

7. What are gauge bosons? Particles exert forces on one another. These forces are transmitted by gauge bosons. Electromagnetic force (carried by photons [1]) Strong nuclear force (carried by gluons [8]) Weak nuclear force (carried by W and Z particles [3]) e- e- g

8. Where do gauge bosons come from? Gauge bosons reflect underlying symmetries of the universe. The number of gauge bosons for each force is the number of generators for each symmetry group (e.g. the symmetry group for the strong nuclear force has 8 generators, hence 8 gluons). These gauge bosons should be massless. However, the W+, W-, and Z bosons (which mediate the weak nuclear force) are massive.

9. Classical mass

10. Mass in Relativity (special and general)

11. Binding Energy Proton mass, mP=1.6726x10-27 kg Neutron mass, mN=1.6749x10-27 kg 4He mass=6.6446x10-27 kg Less than 2mP+2mN

12. Proton mass Quarks The mass of a proton is much larger than the mass of the quarks that make up the proton. Dynamics 98%

13. Quantum fluctuations The Heisenberg Uncertainty Principle states: DEDt≥h/2p with the Planck constant h=6.636x10-34 m2 kg/s This means that particles are popping in and out of existence continuously (so the vacuum is actually fluctuating). The probability distribution of particles everywhere in space is called a field.

14. Higgs Mechanism In 1964, 6 authors in 3 different papers (Brout and Englert, Higgs, and Guralnik, Hagen, and Kibble) proposed a mechanism for making the weak force carriers massive. Depended on having these gauge bosons couple to something called the Higgs field, which has a fourfold symmetry. When the vacuum fluctuations of the Higgs field become non-zero, the symmetry is broken, which makes the W+, W-, and Z bosons massive and leaves a single massive particle called the Higgs boson. Other particles (electrons, quarks, etc) can also acquire mass by coupling to the Higgs field.

15. How can we find the Higgs boson? Build a giant particle collider. Fortunately, there was already a giant tunnel at CERN. 27 km ring filled with superconducting magnets cooled to just above absolute zero. Large Hadron Collider (LHC) costs about $10B over 20 years. Note: Hadrons are particles containing quarks. ATLAS and CMS projects involve over 3,000 physicists

23. Movie of a collision

24. H gg

25. Same event, different angle

26. H ZZ  mmmm

27. H ZZ  eeee

28. Hgg ATLAS CMS

29. Higgs boson summary Two different experiments (ATLAS and CMS) find a new particle with a mass of 125.6 GeV/c2. This is a spin 0 boson, with properties consistent with the Standard Model Higgs boson. The existence of this particle confirms the point of view that mass is an acquired property (through coupling to the Higgs field) and not an intrinsic property of particles.

30. What next? Want to investigate the properties of the Higgs boson in more detail (e.g. decay paths, coupling to other particles, etc). Are there other Higgs-like particles? The Standard Model assumes a Higgs field with fourfold symmetry, but there are other models that include more Higgs terms. Also, other interesting physics problems to study at the LHC.

31. Quark-gluon plasma Higgs search concentrated on p-p collisions (total of 6 quarks). When colliding nuclei (each with hundreds of quarks) together, one can produce a “quark-gluon” plasma, consisting of quarks and gluons mixed together but not bound into hadrons. Understanding this special state of matter can provide insight into the evolution of the universe, which is believed to have passed through a similar high density/high temperature state nanoseconds after the Big Bang.

33. The phase diagram of QCD Early universe quark-gluon plasma critical point ? Tc Temperature color superconductor hadron gas nucleon gas nuclei CFL r0 baryon density Neutron stars vacuum

34. Note: 1 TeV=1,000 GeV

36. Nuclear Collisions Note: Spherical nuclei look like pancakes because of relativistic length contraction.

37. Hydrodynamics of quark-gluon plasma

38. Quark-gluon plasma acts like a perfect liquid

39. Viscosity of quark-gluon plasma

40. Other new physics The LHC provides a tool for measuring the properties of fundamental particles at high energies and high densities. Because of (possible) phase transitions (e.g. weak symmetry breaking, quark-gluon plasma, etc) the properties of particles under these extreme conditions (high density and high energy) may be very different than their properties under ambient conditions (low density and low energy). This can potentially change our understanding of the fundamental symmetries that govern physical law.

41. The end