Measuring beam size with the LHC Beam Gas Vertex detector

The Beam Gas Vertex detector (BGV) is an innovative beam profile monitor being developed as part of the High Luminosity LHC (HL-LHC) project at CERN. The goal is to continually measure the transverse beam size by reconstructing tracks originating from beam-gas interactions using high precision tracking detectors. To confirm the feasibility of such a device, a demonstrator based on eight modules of scintillating fibre detectors has been constructed, installed in the LHC and operated for the past 3 years. It will be shown that using the BGV the average transverse beam size can be obtained with a statistical accuracy better than 5 μm (assuming a Gaussian beam with a sigma of ~200 μm). This precision is obtained with an integration time of less than one minute. In addition, the BGV measures the size of individual bunches with a statistical accuracy of better than 5 % within 5 minutes. Results obtained from data acquired in 2018 will be presented and compared to measurements from other beam profile monitors.