Hi, I'm Daniel and I'm studying the Higgs
boson when it is produced together with a pair of top quarks.
In the ttH production mode the Higgs boson and the top quarks can decay in a number of ways, leading to a whole variety of different final states.
At CMS we grouped these into a few different channels based on the decay products and each of these has its own dedicated search.
In my case I'm looking for the fully hadronic final state where the top quarks each decay to a b-quark and a pair of light flavor quarks
and the Higgs boson decays to a pair of b-quarks.
Quarks undergo a process called hadronization in which they form jets of particles traveling in the same direction which can be detected by the CMS detector.
b-quarks typically have a longer lifetime and can travel some distance up to about two centimeters before they form jets.
We can use this offset to identify jets that are more likely to originate from b-quarks, which we call b-jets.
In my case I'm looking for eight final state jets, four of which are identified as b-jets.
In most ttH searches, the background is much larger than the signal and because of the many final state particles
identifying the correct decay products of the Higgs boson is very difficult.
Making matters worse, the ttH production process is very rare and so there are very few events that we can even look for.
In fact the signal is hiding so well that we had to combine several different final state searches
and use all the data that we've collected in the first
six years just to be sure that we've seen it.
ttH production is the only way that we can get a direct measurement of how strongly the Higgs boson interacts with the top quark called the top-Higgs coupling.
Because the top quark is very heavy, and because the Higgs boson likes mass,
the top quark enters into many loop processes that allow the Higgs to interact indirectly with massless particles
such as in gluon - gluon fusion production and decays to photons.
These processes can give us very accurate measurements of the top Higgs coupling provided that we know exactly what is in the loop.
However unknown particles can enter into these loops, so if the top-Higgs coupling that we infer from these indirect measurements is different
to what we measure from the
TTH production mode, this could indicate the presence of new physics
