Optics, crossing angle and aperture in p-Pb physics conditions in the LHC

The first p-Pb run at the LHC is planned for November 2012. As this is a very new way of operating the machine several uncertainties remain and many aspects have to be studied carefully. This note concentrates on the beam-beam separation and the machine aperture in the interaction regions (IRs). These are two major concerns for determining the bunch spacing and the betatron amplitude function Beta* at the interaction points (IPs). Various schemes of collisions in terms of Beta*-values and crossing angle in the ALICE experiment are considered and compared, in view of the coming choice of these essential parameters for operation and luminosity production.