The Physics of Particles and Forces David Wilson Particle Physics Masterclass 21st March 2018
Overview David Wilson (TCD) Particles & Forces 2/30 Overview of Hadron Spectrum Collaboration (HadSpec) scattering calculations: Image credit: NASA
Forces David Wilson (TCD) Particles & Forces 3/30 As far as we know, there are four forces in the universe Gravity Electromagnetism Weak force Strong force
Forces David Wilson (TCD) Particles & Forces 4/30 As far as we know, there are four forces in the universe Gravity - a force exerted by objects with mass Electromagnetism - a force between charged particles and photons (light) Weak force - e.g. radioactive decay can turn neutrons into protons Strong force - this holds together the nuclei of atoms and is responsible for most of the mass in the observable universe
Forces David Wilson (TCD) Particles & Forces 5/30 Image credit: google/therugbyblog.com
Forces David Wilson (TCD) Particles & Forces 6/30 electromagnetism electromagnetism gravity gravity electromagnetism electromagnetism electromagnetism electromagnetism
Forces David Wilson (TCD) Particles & Forces 7/30 electromagnetism electromagnetism gravity gravity electromagnetism electromagnetism electromagnetism electromagnetism
Everything is made of atoms David Wilson (TCD) Particles & Forces 8/30 Hydrogen atom 10-10 m 10-15 m nucleus p + electron e - Most of the mass is in here Very dense Made of other (more fundamental) particles Held together by the strong force very light no further substructure (as far as we know)
Everything is made of atoms David Wilson (TCD) Particles & Forces 9/30 Hydrogen atom 10-10 m 10-15 m held together by electromagnetism nucleus p + electron e - Most of the mass is in here Very dense Made of other (more fundamental) particles Held together by the strong force very light no further substructure (as far as we know)
Everything is made of atoms David Wilson (TCD) Particles & Forces 10/30 10-15 m nucleus p + electron e - quarks u + 2 3 d 1 3 gluons u + 2 3 quarks and gluons are strongly interacting particles gluons are the force carrier of the strong force quarks also have an electromagnetic charge their masses are actually very small (not much more than the electron) the strong force binding is so strong it creates much of the mass we see in a proton
Hadrons David Wilson (TCD) Particles & Forces 11/30 There are two common categories of particles produced by the strong force Baryons: three-quarks Mesons: quark-antiquark protons, neutrons, pions, kaons, proton is stable these are all short-lived but are readily produced at machines like the LHC
Confinement David Wilson (TCD) Particles & Forces 12/30 It s hard to get quarks on their own no matter how hard we hit a proton, no one has ever managed to isolate a quark - we say quarks are confined within hadrons Image credit: Jefferson Lab
Anti-particles David Wilson (TCD) Particles & Forces 13/30 The last slide introduced two new concepts: Antiparticles every matter particle we know of has an antimatter particle the antimatter particles have the same mass, but most of their charges or quantum numbers are reversed e.g. the electron and positron particles and anti-particles can be produced as a pairs in high-energy collisions Particle generations there are three copies, or generations, of each type of particle, with increasing mass mass e 0.511 MeV µ 106 MeV 1777 MeV quark charge mass u + 2 3 2 MeV d 1 3 5 MeV c + 2 3 1300 MeV s 1 3 100 MeV t + 2 3 173000 MeV b 1 3 4180 MeV
Anti-particles David Wilson (TCD) Particles & Forces 14/30 Image credit: CERN
Anti-particles David Wilson (TCD) Particles & Forces 15/30 e + e + e e e Image credit: CERN
Anti-particles David Wilson (TCD) Particles & Forces 16/30 e + e + e e e Image credit: CERN
Heavier generations decay weakly David Wilson (TCD) Particles & Forces 17/30 Particle generations mass e 0.511 MeV µ 106 MeV 1777 MeV quark charge mass u + 2 3 2 MeV d 1 3 5 MeV c + 2 3 1300 MeV s 1 3 100 MeV t + 2 3 173000 MeV b 1 3 4180 MeV time
Heavier generations decay weakly David Wilson (TCD) Particles & Forces 18/30 Particle generations mass e 0.511 MeV µ 106 MeV 1777 MeV quark charge mass u + 2 3 2 MeV d 1 3 5 MeV c + 2 3 1300 MeV s 1 3 100 MeV t + 2 3 173000 MeV b 1 3 4180 MeV Neutrinos - light, neutral particles that only interact weakly, hard to detect directly The W-boson is one of the force carriers of the weak force time similar to the photon and gluon it connects different particle generations it connects quarks and leptons
The weak interactions David Wilson (TCD) Particles & Forces 19/30 similarly for nuclear decays -decay As well as decays, in extreme environments, the weak interactions also allow nuclear fusion to take place Image credit: NASA
Summary of the forces David Wilson (TCD) Particles & Forces 20/30 relative strength typical range force carrier typical phenomena Strong 1 10-15 m gluon mesons, baryons Electromagnetic 0.01 photon everything else! Weak 0.000001 10-18 m W, Z bosons nuclear decays Gravity 10-40 planetary orbits, apples falling from trees
David Wilson (TCD) Particles & Forces 21/30
The Higgs particle David Wilson (TCD) Particles & Forces 22/30 Image credit: TCD
The Higgs particle David Wilson (TCD) Particles & Forces 23/30 The Higgs at TCD in 2016 Image credit: TCD
The Higgs particle David Wilson (TCD) Particles & Forces 24/30 responsible for giving mass to the fundamental particles predicted by Higgs, Brout, Englert and others in the 1960s experimentally observed at CERN, announced in 2012
CERN David Wilson (TCD) Particles & Forces 25/30 Image credit: CERN
CERN David Wilson (TCD) Particles & Forces 26/30
The Higgs particle 2e, 2µ candidate event with m4` =124.3 GeV David Wilson (TCD) Particles & Forces 27/30
2e, 2µ candidate event with m 4`=124.3 GeV The Higgs particle David Wilson (TCD) Particles & Forces 28/30 arxiv:1109.5304
Open questions David Wilson (TCD) Particles & Forces 29/30 There are many parameters in the standard model that we have to input - where to do these come from? Does the strong force really only admit quark-antiquark and 3-quark objects? Why not 4, 5-quark objects - some interesting hints in recent years There is much more matter than antimatter in the universe - we don t know why What s beyond the standard model? Dark matter, dark energy
Lattice QCD David Wilson (TCD) Particles & Forces 30/30 η η η K π π π K L 0.7 a 0.6 0.5 0.4 0.3 0.2 0.1 1000 1050 1100 1150 1200 1250 1300 / MeV