Chromatic effects and their correction in off-momentum operation of the LHC for p-Pb collisions

The first p-Pb run in the LHC is scheduled for January 2013. This note reports on chromatic effects due to the off-momentum operation required to collide two beams of different species. The most important of these is expected to be beta-beating. Its amplitude strongly depends on the optical functions at the interaction points and can reach up to 12%. A module based on analytical calculations of beta-beating, tune and dispersion has been developed to minimise the intrinsic errors to be superimposed on the statistical ones. The correction can maintain the beta-beating at a few percent while the tune shift remains within tolerances and dispersion-beating is very small for all steps of the squeezing procedure. Sextupoles should be slightly rematched to keep constant chromaticity. Off-centred orbits in octupoles could have a non negligible effect on chromaticity.