Among them, one study which broke new ground was a search for the effect of colour coherence - a QCD phenomenon of interference in the colour field radiation off gluons and quarks. QCD was still being modeled quite incorrectly by Monte Carlo simulations, and that study, along with many others which followed it, provided the data on which more precise modeling of final state radiation was based.
For my study of top decays into hadronic jets, the modeling of QCD radiation was very important: in fact, among the few handles which could separate the top signal into six hadronic jets from the huge background of QCD processes one was the pattern of colour radiation. Jets emitted by W boson decays to quarks were expected to be narrower than jets originated from gluons. On that everybody agreed, and yet all suggestions of kinematic variables that could separate gluon from quark jets were highly frowned upon. But on the matter of the flow of radiation in the regions between different jets there was not even a chance to convince anybody that you could construct a discriminating variable.
One person who studied the phenomenon was my colleague (once in CDF, now in CMS) Avi Yagil - he tried to find a signal of hadronic W boson decays by vetoing jets containing hits in the vertex tracking chamber allegedly originated from "soft" radiation from QCD jets (those jets must be colour-connected to the hadron remnants from the collision). At some point he even thought he had seen a signal, and presented it at the "heavy flavour" group of CDF; but he soon thereafter convinced himself that the signal was too big to be true. The study was soon abandoned.
Another guy who started doing similar things was me - I was observing different patterns of radiation in the data and in the simulation, which could somehow be traced to those colour "strings". But I could not use those tools for the hadronic top observation, which we did publish in 1997. By then, I had started to apply the same ideas to the search of Z->bb decays, of which I did obtain a signal one year later (another "first" at a hadron collider).


Below you can see how the data agrees with the colour-singlet hypothesis. The significance of the result is not to show that W bosons are colour singlets, of course -of that there is overwhelming evidence. What the analysis shows is that the variable can be used to study the pattern of colour radiation in the search for new particles.

The comparison of the data to the two different simulations (one based on Pythia6, the other on Herwig) is also interesting as it determines whether the models are capable of capturing these subtle features of final state QCD radiation. For more details, please read the ATLAS preprint.
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