In supersymmetry – or SUSY as it is known – there are families
of bosons that twin the known quarks and leptons. These
‘superquarks’ are known as squarks; their superlepton
counterparts are known as sleptons. If SUSY were an exact
symmetry, each variety of lepton or quark would have the same
mass as its slepton or squark sibling. The electron and selectron
would have the same mass as one another; similarly, the up quarks
and the ‘sup’ squark would weigh the same, and so on. In reality this
is not how things are. The selectron, if it exists, has mass far greater
than 100 GeV, which implies that it would be hundreds of
thousands of times more massive than the electron. Similar
remarks can be made for all of the sleptons or squarks.
An analogous statement can be made also about the super-partners
of the known bosons. In SUSY there are families of fermions that
twin the known bosons. The naming pattern here is to add the
appendage ‘-ino’ to denote the super-fermion partner of a standard
boson. Thus there should exist the photino, gluino, zino, and wino
(the ‘ino’ pronounced eeno, thus for example it is weeno and not
whine-o). The hypothetical graviton, the carrier of gravity, is
predicted to have a partner, the gravitino. Here again, were
supersymmetry perfect, the photino, gluino, and gravitino would be
massless, like their photon, gluon, and graviton siblings; the wino
and zino having masses of 80 and 90 GeV like the W and Z. But as
was the case above, here again the ‘inos’ have masses far greater
than their conventional counterparts.
The standard, and feeble, joke is that supersymmetry must be
correct: we have found half the particles already. Put another way:
we have not found clear evidence for a single squark or slepton, nor
photino, gluino, wino, or zino. Searching for them is a high priority
at present.
With such a lack of evidence for superparticles, one might wonder
why theorists believe in SUSY at all. It turns out that such a
symmetry is very natural, at least mathematically, given the nature
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Questions for the 21st century