Using the BRAN Luminosity Detectors for Beam Emittance Monitoring During LHC Physics Runs

The BRAN Ionization Chambers installed at the IP1 and IP5 Interaction Points of the LHC provide a relative measurement of the total and bunch-by-bunch luminosities. This information, combined with the logged bunch charges from a fast BCT monitor, offers the possibility of evaluating the Interaction Area in collision for each of the colliding bunch pairs and monitor its time evolution. An application has been implemented for operators to display the interaction area of the proton bunches interacting in IP1 and IP5 during each of the Physics Runs. This provides a tool for measuring the contribution to the luminosity time decay originating from possible emittance blow-up when operating the Accelerator close to the beam-beam limit. Early results confirm the ability to characterize the bunch-by-bunch emittance behavior during the store and study possible differences among bunches in the same fill. We describe the applications of the detector to beam measurements, from the rate of collisions, to the calculation of crossing angles as well as the measurements of transverse emittance of the beams in collision.