25 Days of Particles: Day 22

S-Top

Classification: boson
Fundamental: yes (we think)
Mass: Unknown, but heavy enough we haven't seen it yet
Interactions: same as top quark
Spin: 1
Lifetime: Unknown

There is an art to creating elegant theories in physics, an art I don't really understand very well. But I've been told it is built a lot of symmetries and conversation laws. Conversation laws describe those fundamental quantities that aren't changed by all the monkeying around of particle interactions. Symmetries describe how apparently different things act in the same way. Symmetries can seem pretty basic, such as that the laws of physics should behave the same every where in the universe. But they can also have amazing effects.

We've already met one symmetry, a symmetry of charge. The electron and positron are exactly the same except for their charge, and every particle has an antimatter partner with opposite charge. The idea of symmetries between particles has been used again, and in the 1970s a symmetry between bosons and fermions was proposed.

It seems like a crazy idea, but supersymmetry or SUSY as it was called had a few things to theoretically recommend it. Supersymmetric theories help the Standard Model mathematically behave better by canceling out divergences. SUSY theories can unify the strong force with the electroweak force, which has been a goal of theoretical physicists since they successfully showed the electromagentic and weak forces were really high and low masses parts of the same force. Finally, virtually all SUSY theories predict many neutral stable particles that could be dark matter WIMPS.

Experimentally, SUSY theories predict each fermion should have a bosonic partner, and most of the bosons have fermionic partners as well. The Higgs sector goes a little crazy in SUSY, producing five Higgs particles instead of one, some of them charged. But that doubles the amount of fundamental particles out there to be studied. Hence the s-top, or stop, is here on behalf of the entire SUSY family as the bosonic partner of the top quark.

But, we haven't discovered any of these superpartners, which means they don't have the same masses as the particles we now know about it. So this symmetry, if it exists, is broken. That isn't a huge issue, either; we already know the electroweak symmetry is broken into a high-mass part we normally call weak and a low-mass part we normally call electromagnetic. So we're currently searching for the supersymmetric partners at the colliders capable of producing extremely massive particles.

Besides, the stop just has a fun name and has been used in pranks involving traffic signs and its symbol. Because physicsts are geeky that way.