Abstract
A new type of fast luminosity separation scans ("Emittance Scans") was introduced at the CERN Large Hadron Collider (LHC) in 2015. The scans were performed systematically in every fill with full-intensity beams in physics production conditions at the Interaction Point (IP) of the Compact Muon Solenoid (CMS) experiment. They provide both emittance and closed orbit measurements at a bunch-by-bunch level. The precise measurement of beam-beam closed orbit differences allowed a direct, quantitative observation of long-range beam-beam PACMAN effects, which agrees well with numerical simulations from an improved version of the TRAIN code.
Highlights
The transverse beam emittance, and the transverse beam size, is a key parameter defining the luminosity in a collider
For high-intensity beams at the highest energies, it is a quantity challenging to measure with beam instrumentation devices in a non destructive way, as the physical beam sizes are very small due to adiabatic shrinking, and the stored beam energy prohibits the use of invasive devices like wire scanners
We present a new approach to luminosity scans, called “emittance scans,” which can be performed in regular physics production conditions within a few minutes
Summary
The transverse beam emittance, and the transverse beam size, is a key parameter defining the luminosity in a collider. Complementary to beam instrumentation, the convoluted beam width at an interaction point, where the two beams collide, can be measured by separating the beams and observing the change in luminosity. This technique was pioneered by Simon van der Meer [1] at the CERN Intersecting Storage Rings, and is commonly used for calibrating the experiments’ luminosity monitors. The measured closed orbit separations at the interaction points are shown in Sec. VIII and compared to simulations; there, we discuss the recent improvements to the TRAIN simulation code to accurately predict bunch-bybunch beam-beam effects at the LHC
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
