[Moller] Noninvasive LHC transverse beam size measurement using inelastic beam-gas interactions

[Jay Benesch]

https://journals.aps.org/prab/abstract/10.1103/PhysRevAccelBeams.22.042801

Noninvasive LHC transverse beam size measurement using inelastic 
beam-gas interactions
A. Alexopoulos et al. (The BGV Collaboration)
Phys. Rev. Accel. Beams 22, 042801 – Published 11 April 2019

The beam-gas vertex (BGV) detector is an innovative instrument measuring 
noninvasively the transverse beam size in the Large Hadron Collider 
(LHC) using reconstructed tracks from beam-gas interactions. The BGV 
detector was installed in 2016 as part of the R&D for the 
High-Luminosity LHC project. It allows beam size measurements throughout 
the LHC acceleration cycle with high-intensity physics beams. A 
precision better than 2% with an integration time of less than 30 s is 
obtained on the average beam size measured, while the transverse size of 
individual proton bunches is measured with a resolution of 5% within 5 
min. Particles emerging from beam-gas interactions in a specially 
developed gas volume along the beam direction are recorded by two 
tracking stations made of scintillating fibers. A scintillator trigger 
system selects, on-line, events with tracks originating from the 
interaction region. All the detector elements are located outside the 
beam vacuum pipe to simplify the design and minimize interference with 
the accelerated particle beam. The beam size measurement results 
presented here are based on the correlation between tracks originating 
from the same beam-gas interaction vertex.

------------------
Seems like it should be easy (i.e. several dissertations) to extend this 
to measuring electrons at 11 GeV, 249 MHz, helicity correlated, to 10ppm 
desired by MOLLER.  Nice reference list.