Hadronic production of a Higgs boson in association with two jets at ...

1.3. Higgs searches at colliders 18ratio of 74%). The branching ratios for the decays to τ + τ − , WW ∗ and gg are around7% with the remaining ≈ 4% decay to cc.The final states which were included in the final combined analyses [51–55] werethe four-jet final state (H → bb)(Z → qq), the missing energy final state (H →bb)(Z → νν), the leptonic final state (H → bb)(Z → l + l − ) l ∈ {e, µ} and the taulepton final states, (H → bb)(Z → τ + τ − ) and (H → τ + τ − )(Z → qq). The resultof the combined direct searches, [51] was a limit on the lightest a SM Higgs bosoncould be. They found a lower bound of 114.4 GeV/c 2 at the 95% confidence level.Fig. 1.3 summarises these results.1.3.2 Higgs searches at the Tevatron and the LHCThe two colliders currently searching for the Higgs boson, Fermilab’s Tevatron andCERN’s LHC are both hadronic colliders (the Tevatron collides protons and antiprotons,the LHC collides protons). As such the main Higgs production mechanismsare completely different from those at LEP and are shown in Figs. 1.4-1.5, the largerenergy associated with these colliders also introduces new Higgs decay modes, whichare shown in Fig. 1.6.The dominant production mechanism at both colliders occurs through the gluonfusion process, which is the main topic of the next section. It is interesting tonote the differences between the subdominant production mechanisms between thecolliders. At the Tevatron the second largest source of Higgs bosons occurs throughW and Z Higgsstrahlung, the quark equivalent of the main process at LEP. However,at the LHC it is Vector-boson fusion (VBF or sometimes referred to as WBF) whichis the sub-dominant process. This is not merely due to the difference in centre ofmass energies between the colliders, but due to the fact that in an anti-proton thereare more valence anti-quarks than in a proton and as result processes in which quarkannihilation occur are favoured at the Tevatron.We note that in Fig. 1.6 there is a clear change in Higgs branching ratio aroundm H ≈ 130 GeV below these values the Higgs decays mostly into bb pairs, whilst