  We prepare pairs of $^{133}$Cs atoms in a single optical tweezer and perform
Feshbach spectroscopy for collisions of atoms in the states $(f=3, m_f=\pm3)$.
We detect enhancements in pair loss using a detection scheme where the optical
tweezers are repeatedly subdivided. For atoms in the state $(3,-3)$, we
identify resonant features by performing inelastic loss spectroscopy. We carry
out coupled-channel scattering calculations and show that at typical
experimental temperatures the loss features are mostly centred on zeroes in the
scattering length, rather than resonance centres. We measure the number of
atoms remaining after a collision, elucidating how the different loss processes
are influenced by the tweezer depth. These measurements probe the energy
released during an inelastic collision, and thus give information on the states
of the collision products. We also identify resonances with atom pairs prepared
in the absolute ground state $(f=3, m_f=3)$, where two-body radiative loss is
engineered by an excitation laser blue-detuned from the Cs D$_2$ line. These
results demonstrate optical tweezers to be a versatile tool to study two-body
collisions with number-resolved detection sensitivity.
