What is Particle Physics?

Grand questions

• What is the fundamental object in Nature?

• What kind of physics law governs them?

You may say that everything is made of atom. However, atom is not the fundamental object since it is made of nucleus and electron. Also, we know that nucleus is composed of protons and neutrons. And again, proton and neutron are made of more fundamental objects called quarks, which are the smallest object we confirm experimentally. How about electron? So far, there is no experimental evidence that electron has substructure. Since the fundamental object cannot be decomposed into something more fundamental by definition, quarks and electron (plus similar particles, muon, tau and neutrinos, see below) are the most elementary particles at this moment.

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A theory of those elementary particles is called Standard Model (SM). Thousands of experimental results we have obtained so far are consistent with this model. It is really truly triumph in our history. In September 2012, Higgs boson-like particle was finally discovered at the Large Hadron Collider (LHC). Amazingly, the discovered particle really resembles the Higgs boson predicted by the SM. However, full knowledge about properties of the particle is still missing. We don't know yet whether all elementary particles get their masses from the Higgs field. We don't know how the Higgs field breaks the electroweak symmetry. Ongoing and upcoming collider experiments may shed light on those problems.

Properties of the elementary particles can be found at Particle Data Group.
 

Why cosmology matters?

Particle physics is physics at short distances. Why does it matter to the Universe? Actually, our Universe was small in the past. So, if you want to know early Universe, particle physics is indispensable.

Open questions

• What is dark matter?

• Why is our Universe matter-dominated?

• What is dark energy?

Unfortunately, the SM cannot answer those questions. Particle physicists including myself have been tirelessly tackling them.

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