squark

A squark is a hypothetical particle predicted by supersymmetric extensions of the Standard Model. In supersymmetry, every Standard Model fermion has a bosonic superpartner, and every boson has a fermionic superpartner. Squarks are the scalar (spin-0) partners of quarks, sharing the same color charge and electric charges but differing in spin.

Squarks come in flavors corresponding to quarks: up-tilde (u-tilde), down-tilde (d-tilde), charm-tilde (c-tilde), strange-tilde (s-tilde), top-tilde (t-tilde), and bottom-tilde (b-tilde). Each quark flavor has left-handed and right-handed superpartners, and the physical mass eigenstates are mixtures of these chiral states. In particular, the stop (top-tilde) and sbottom (bottom-tilde) can exhibit significant mixing, which can lead to lighter mass eigenstates.

In many SUSY models with R-parity conservation, the lightest supersymmetric particle (LSP) is stable and a common dark matter candidate. Squarks, when produced in high-energy collisions, typically decay into a quark and the LSP, yielding experimental signatures that include jets and missing transverse energy.

Production and phenomenology: squarks are colored, so they are produced primarily through strong interactions in hadron colliders. Their production rates decrease rapidly with increasing mass, and their experimental signatures depend on the decay chains and the mass spectrum, especially the LSP mass.

Experimental status: as of now, no squark has been observed. Searches at the Large Hadron Collider have set lower mass limits that depend on the assumed SUSY spectrum and decay modes, with stronger constraints for first- and second-generation squarks and substantial but model-dependent limits for stop squarks.