Exclusive WW

Start off discussing a paper on yy->yy scattering
Heavy ion collisions are good for this, since the flux of photons is high due to higher Z. But energy is lower in heavy ion than pp (matters for producing massive final states)

What is the definition of an exclusive event?

Exclusive events include events where 0/1/2 protons in the event dissociate
Large eta separation between the tracks

Simone draws two Feynman diagrams
Color exchange = small eta separation
Color neutral = large eta separation (exclusive)

Figure 2: exclusive Higgs production. Net color-flow has to be 0, so you need an additional gluon exchange compared to ordinary ggF

EPA is like PDF modeling photon radiation off of a whole proton

Q: Is the proton also considered as a whole for exclusive Higgs, where gluons are exchanged? Or do you use PDFs?
A: Treating the proton as a whole is an advantage of this process. Exchange of pomerons = color neutral (2 gluons). This is easier to calculate. Exclusive Higgs has (or historically has had) way lower theoretical uncertainties than ordinary ggF

Important processes:
Exclusive WW, exclusive dilepton (for control regions)

Dissociation of the proton is not well-modeled in signal. There is MC that models single- and double- ee and mumu dissociation, and single-dissociation with tautau. The change is conceptually simple, but not technically simple.

Data-driven background uses ee and mumu

Double-dissociation tautau is neglected. Single-dissociation tautau is modeled with Pythia (not LPAIR)
Q: why is this treated differently than ee/mumu?
A: LPAIR is very limited

Use opposite-flavor final state to reduce background from ee and mumu from Drell-Yan, and also from exclusive production

What enters ET miss? Leptons, jets, photons, a “soft term” for extra activity (pileup/UE)
In these events, there are no jets, no photons, no extra activity (exclusivity cut)
ET miss = pT leptons
There is no missing ET cut in the exclusive WW
There is a cut on mT (which is a function of ET miss) in the exclusive Higgs

There is a cut on pT(ll) at 30 GeV. Mainly designed to cut out exclusive di-tau (Fig 7)
Look a the Drell Yan in Fig 7 -> how much larger would this be if we allowed ee and mumu?