We have shown by detailed simulations using ABEL that 
pairs, especially their azimuthal angular distributions, carry very
important information for the measurement of nanometer beam sizes. At
first sight, the results are surprising, since it has been expected to
be impossible to preserve such information under a large disruption of
beams at IP. The reason for the preservation is the large
deflection angles of low-energy pairs. Especially the same-charge
particles in the pairs are deflected strongly due to the repulsive
force of the oncoming beam. Escaping from the beam immediately after
their creation, they continue to feel an electromagnetic field just
during a collision where the beam is not disrupted very much.
The simulations have taken place under realistic experimental
conditions for the JLC-I(
=250GeV), such as a horizontal
beam crossing(
=8mrad) and a solenoidal magnet of 2
Tesla. Employing particles deflected with maximum angles, we have
explicitly demonstrated the possibility of precise measurements of the
horizontal beam size(
), the aspect ratio(R), the vertical
displacement(
) and the transverse rotation(
).
Actually, from measurements of and R, a vertical beam
size of nanometers can be obtained. Since the statistical
accuracies of the measurements are sufficient at least with a single
pulse-train crossing, i.e. at 150Hz, this method will be
very useful for a real-time feedback operation to realize stable
collisions between nanometer beams at linear colliders. Although
the simulations have been executed for the JLC-I as a typical future
linear collider, the method can be applied directly for other linear
colliders.