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Pacman bunches Bunches that do not experience the same number of long-range beam-beam interactions left and right from the IP.
Parallel separation Dedicated orbit bumps separate the two LHC beams at the IP during injection, ramp and the optics squeeze. The total beam separation at the IP is called the parallel separation. The LHC baseline foresees horizontal parallel separations in IR1 and IR2 and vertical separations in IR5 and IR8.
Parasitic crossing points Positions in the common part of the Ring 1 and Ring 2 where the two beams can experience long range interactions.
Persistent currents Persistent currents are eddy currents with (ideally) infinitely long time constants that flow in the bulk of the superconducting filaments of a strand and tend to shield the interior of the filament from the external magnetic field changes. These screening currents close inside the superconducting filament, with zero resistance
(in steady state). Hence, for practical purposes, they do not decay in time and for this reason they are referred to as ’persistent’.
Physics run Machine operation at top energy with luminosity optics configuration and beam collisions.
Pile-up Event pile-up μ: Number of visible inelastic proton-proton interactions in a given bunch crossing.
Average pile-up: Mean value of the pile-up over a fill (averaged over all bunch crossings).
Peak pile-up: Maximum pile-up in any bunch crossing at any time (usually at the start of the fill).
Peak average pile-up: Mean pile-up at the beginning of the fill. It corresponds to the peak luminosity of the fill. In practice, it is determined as the maximum of the pile-up values obtained by averaging over all bunch crossings within time intervals of typically one minute.
Average pile-up density: Number of inelastic proton-proton interactions in a given bunch-crossing divided by the size of the luminous region in Z.
Pilot bunch Bunch intensity that assures no magnet quench at injection energy for an abrupt loss of a single bunch but is still large enough provide BPM readings. The pilot bunch intensity of the LHC corresponds to 0.5 × 1010 protons in one bunch.
Piwinski parameter Parameterisation of reduced beam overlap due to finite crossing-angle.

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