Lucian Harland-Lang: Physics from Photons at the LHC

Friday 14 May 2021, 12:30 → 14:00 Europe/London

https://zoom.us/j/304578256

Abstract: The LHC is a collider of protons and heavy ions, both of which are electromagnetically charged objects; hence, as well as being a QCD machine, it can act as a source of photons. This mechanism often plays an important role in the production of particles with electroweak couplings, and a precise account of photon-initiated (PI) production at the LHC is a key ingredient in the LHC precision physics programme.  While one approach to treating this is to introduce a photon PDF, in line with the QCD partons, I will instead discuss the possibility of modelling PI processes directly via the so-called structure function approach. This can provide percent level precision in the corresponding production cross sections, and is therefore well positioned to account for LHC precision requirements. This formalism in addition allows one to make use of another useful feature of photons, namely that they are colour-singlet and can often be emitted elastically (or quasi-elastically) from the proton/ion. This can provide a unique probe of the Standard Model and physics beyond it. Indeed, there is an exciting and ongoing experimental programme of measuring such processes, including the possibility of tagging the intact protons using dedicated detectors at ATLAS and CMS. I will discuss recent work on applications of the structure function approach to precision calculations of PI production in the inclusive mode, and to 'exclusive' processes with rapidity gaps and/or intact hadrons in the final state.

Connections will begin at 12:30 with the seminar beginning at 13:00. Password for Zoom is NielsBohr.