Today, at the International Conference for High Energy Physics (ICHEP 2020), the ATLAS Collaboration announced first results using the ATLAS Forward Proton (AFP) spectrometer. With this instrument, physicists directly observed and measured the long sought-after prediction of proton scattering when particles of light turn into matter.

Whether searching for signs of new physics, or making precise measurements of known interactions, it is essential to know the total number of proton-proton collisions that the LHC delivers in ATLAS. This parameter, known as “luminosity”, is a vital part of ATLAS analysis.

On Thursday morning the first fill reached “Stable Beam”.

Tuesday at 23:55 I called the ATLAS shift leader and told them to stop the elastic physics run and ramp down the inner detector as the elastic program was over.

No time to waste after the alignment.

I have the pleasure to work for a very special sub-detector of ATLAS, called “Absolute luminosity For ATLAS” or ALFA in short.

One of the most basic quantities in particle physics, the rate at which protons scatter off of one another (the cross section), cannot be calculated from the theory of strong interactions, quantum chromodynamics. It must instead be measured, and those measurements can then be used to tune the numerical models of LHC proton–proton collisions.

ATLAS is ready for Run 2 of the Large Hadron Collider (LHC) where proton beams will be collided together at a higher centre of mass collision energy of 13 TeV, and reach higher luminosities than ever before.

Data from a special run of the LHC using dedicated beam optics at 7 TeV have been analysed to measure the total cross-section of proton-proton collisions in ATLAS. Using the Absolute Luminosity For ATLAS (ALFA), a Roman Pot sub-detector located 240 metres from the collision point, ATLAS has determined the cross-section with unprecedented precision to be σ_tot (pp → X) = 95.4 ± 1.4 millibarn.