If the gravitino (G) is very light and all the other supersymmetric particles
are above threshold, supersymmetry may still be found at colliders, by looking
at processes with only gravitinos and ordinary particles in the final state. We
compute here the cross-sections for some distinctive signals at hadron
colliders: photon plus missing energy, induced by (q antiquark -> G G photon),
and jet plus missing energy, induced by (q antiquark -> G G g), (q g -> G G q),
and (g g -> G G g). From the present Tevatron data, we estimate the bound
m_{3/2} > 2.3 10^-5 eV on the gravitino mass, corresponding to the bound
sqrt{F} > 310 GeV on the supersymmetry-breaking scale. We foresee that the
upgraded Tevatron and the LHC will be sensitive to values of m_{3/2} up to 4.0
10^-5 eV and 6.2 10^-4 eV, corresponding to sqrt{F} up to 410 GeV and 1.6 TeV,
respectively.Comment: 19 pages, Latex, epsfig, 13 figures This revised version supersedes
that published in Nucl. Phys. B526 (1998) 136, and contains important
changes. The correction of a sign error modifies the relevant partonic
cross-sections. The sensitivity to the supersymmetry-breaking scale
(gravitino mass) is only slightly weakene