What IS Fundamental???

1. What IS Fundamental??? • Many new particles were discovered with the advent of particle accelerators …are they ALL fundamental??? • Baryons: particles with lifetimes ~ 10-10 seconds, ultimately decaying into protons • Λ0, Σ+, Σ-, Σ0, Ξ-, Ξ0 • Mesons: particles with lifetimes ~ 10-8 seconds, typically lighter than the proton and never decaying into protons • Κ-, Κ0, Κ+, π-, π0, π+ • Antimatter: An antiparticle is simply a particle with opposing quantum numbers

2. Too Many Particles Murray Gell-Mann 1969 Nobel Prizein Physics Why should nature be this complicated? To simplify the picture, and still account for this plethora of particles which were observed, Murray Gell-Mann proposed all these particles were composed of just 3 smaller constituents, called quarks.

3. 3 + 3 = 6 Quarks

4. Three Families of Quarks Increasing mass Also, each quark has a corresponding antiquark.The antiquarks have opposite charge to the quarks

5. How the Quark Model Works To make a proton:We bind 2up quarks of Q = +2/3and 1 down quark of Q = -1/3. The total charge is2/3 + 2/3 + (-1/3) = +1 !To make a neutron: We bind 2 down quarks of Q= -1/3with 1 up quark of Q = +2/3 to get: (-1/3) + (-1/3) + (2/3) = 0 !

6. Hadrons The forces which hold the protons and neutrons together in the nucleus are VERYstrong. Protons and neutrons are among a class of particles called “hadrons” (Greek for strong). Hadrons interact very strongly! Baryons are hadronswhich contain 3 quarks(no anti-quarks).Anti-baryons are hadronswhich contain 3 anti-quarks(no quarks). Mesons are also in the hadron family.They are formed when a quark and an anti-quark “bind” together.

7. Next Big Question • If neutrons & protons are not fundamental, what about electrons? • Are they made up of smaller constituents also? As far as we can tell, electrons appear to be indivisible.

8. Leptons Electrons belong to a general class of particles, called “Leptons”. As far as we can tell, the leptons are “fundamental”. Each charged lepton has an uncharged partner called the “neutrino”. The leptons behave quite differently than the quarks - They don’t form hadrons (no binding between leptons)

9. Are there other types of charged leptons (like the electron)? • 1932: Discovery of the positron,the “anti-particle” of the electron. Anti-particles really exist !!!!! • 1937:Muons (μ- and μ+) discovered in cosmic rays. • M(μ) ~ 200*M(e) • The muon behaves very similarly to the electron (i.e., it’sa lepton).

10. p n e Neutrinos 1934: To account for the “unseen” momentum in the reaction (decay): n  p + e-+ X X Fermi proposed that the unseen momentum (X) was carried off by a particle dubbed the neutrino (n). Nobel Laureate: Enrico Fermi (means “little neutral one”)

11. Lepton Picture continues… 1962: An experiment at Brookhaven National Lab showed that there were in fact at least 2 types of neutrinos.

12. Three happy families… • In 1975, researchers at the Stanford Linear Accelerator discovereda third charged lepton, with a mass about 3500 times that of theelectron. It was named the τ-lepton. • In 2000, first evidence of the τ’s partner, the tau-neutrino (ντ)was announced at Fermi National Accelerator Lab. 3 families, just like the quarks… interesting !!!

13. The Standard Model

14. Search for the Higgs!

15. What are Force Carriers? Now the question is, how are these matter particles held together?? -- by the basic forces in nature! There are four basic forces in nature. These are: • Gravitational interaction which makes apples fall on certain peoples heads. It is also this which pulls together the Earth and the Moon.Newton’s Apple story! • Electromagnetic interaction which assures the cohesion of our bodies and governs all chemistry. It is this which pulls together the electron and the atomic nucleus like earth around the sun!

16. Fundamental Interactions • Strong interaction which unites quarks together and thus the nuclei of atoms i.e. world is not broken apart! • Weak interaction which is responsible for beta radioactivity, which gives us the conception of antimatter! We were talking about forces, but why interactions? Before quantum theory, forces were transmitted by virtue of a mysterious force field emitted by particles. According to quantum theory, forces are not exerted between two fermions unless there is an exchange of a mediator particle, called a boson. Now the heavier the boson, the shorter will be the range of the interaction!

17. Exchange Particles/Force Carriers For electromagnetic interaction the exchange particle is γ. For strong interaction the exchange particles are gluons. For weak interaction the exchange particles are and Z0 bosons. Gravitational interaction has the weakest intensity in particle physics scale!

18. Unification? Up to this we have found the 12 (6 quarks + 6 leptons) fundamental particles as well as four basic forces in nature and also the mediator particles of interactions respectively. What will happen if we try to bring it all together ? ----This synthesis of current knowledge, without any doubt is known as ---- “The Standard Model ” A glimpse into the Big Bang! It is clear from the figure that all 4 forces were created from a super force during the Big-Bang! In reverse way, we are trying to unify these forces to reach the super force, aren’t we?

19. Heisenberg’s Folly? In the 1950s, it was rumored that Heisenberg had done it, and just the details remained to be sketched in. But nothing ever emerged from Heisenberg. So Wolfgang Pauli responded with the following: “Below is the proof that I am as great an artist as Rembrandt; the details remain to be sketched in.”

20. Why Do We Need the LHC? The Standard Model and Beyond. What is Mass? The Higg’s boson What are dark matter and dark energy? Supersymmetric particles Why is there more matter then antimatter? Symmetry breaking What was it like just after the Big Bang? Quark-gluon plasma What about Gravity? Extra dimensions, string theory

21. String Theory