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.