1. What is the Higgs??? Prof Nick Evans University of Southampton

2. Electrons are responsible for most of the properties of matter Everything is made of…

3. Who ordered that??? The trouble started in 1936 when Andersson and Nedermeyer saw tracks in a bubble chamber due to cosmic rays of an electron but with 200 times more mass… To this day the muon interacts exactly like an electron only differing in its mass…. Why’s that trouble?

4. Relativity E = m c 2 Einstein taught us that mass is a reflection of the energy store din a particle… Energy is all about interactions though… for example a candle emits heat/light as excited electrons move to orbits closer to the nucleus of their atom…

5. We need a new force! So if the muon and electron masses are different there must be a new interaction that distinguishes the two… That force needs to act everywhere in space evenly so that the particles masses are the same throughout space….

6. The Higgs Boson In the “Standard Model” the origin of mass is addressed using a mechanism named after the British physicist Peter Higgs. This predicts a spinless particle: Higgs boson According to Higgs, space is filled with a new type of field analagous to magnetic or electric fields… The electron and muon couple with different strengths and so get different masses

7. The Search for the Higgs To find the higgs we must “excite” the vacuum – produce a higgs particle… we collide electrons, protons etc so there is 100 times nuclear energy density in some region…. The Large Hadron Collider in Switzerland switched on in late 2009…

8. The ring is 27km round and on average 100m underground CERN - Geneva Probing the structure of matter LHC began science in 2009

9. The Large Hadron Collider collides the nuclei of atoms with 10 times higher energy than has previously been achieved (14 TeV) 1232, 35 ton, superconducting dipole magnets accelerate ions and focus them into bunches for collision 36,000 tons of coolant below 2K!

10. Proton-Proton collisions (hydrogen atom nuclei) 100 billion protons per bunch 20 collisions per crossing 1 crossing every 25ns 600 million collisions per second 14 TeV centre of mass energy To store all collision data would involve storing 10 Petabytes of data a year ie a 20km high stack of CDs… more than can be made

11. Detectors at collision sites: Atlas CMS LHC-b Alice Track particles Measure energy Measure momentum

12. Higgs Production H →  H→ bb H→ WW → ll H → ZZ (*) → 4l ……

13. Exclusion mass range: 110- 122.5, 127 – 600 GeV 5.1 s excess at 125 GeV higgs -> gg higgs -> ZZ 5 s excess at 126 GeV Other decay channels are low stats… the tau channel signal is missing…

14. The Higgs Discovered As of 2013 we have a very clear experimental signal for the standard model higgs boson… nothing else has yet shown up at LHC… It is a remarkable vindication of the theoretical ideas that make up the Standard Model… Questions remain though – is it really the standard model higgs or is there a more complex theory of which we’ve found just the first bit? The theory does not explain why the electron and muon couple differently to the higgs… there must be a reason…