Searching for Z Bosons in Proton-Antiproton Collisions

I have been searching the CDF data for a signal of Z boson decays to b quark pairs. This decay of the Z boson, like all the others, has been studied to the highest detail with the LEP and SLC electron-positron accelerators, but at a hadron collider (proton-antiproton) it has never been seen before. It's not like saying that phisicists don't believe it's there: the importance of finding a signal in proton-antiproton collisions relies on the fact that it is the most similar process to the one everybody is interested in, the decay of the Higgs boson, a particle that high-energy physicists have been looking for since the seventies. The big chances to see it in the data that CDF and D0, the experiments active at the Tevatron collider, will have when they start taking data in the year 2000, make a Z -> bb signal an important sign that the Higgs can be reconstructed too.

The problem with finding Z decays to b quark pairs, a process that has been happening during data taking every minute or so (we have produced with CDF about 120 thousands of them) is that they are indistinguishable from a similar process, the production of b quark pairs by the strong interaction, that has a rate about 10,000 times higher. So the name of the game has been to try and find ways to reduce this enormous background, increasing the relative size of the signal in the selected events.

The search has started from a dataset of about 5.5 million events collected by requiring the presence of a well identified muon candidate: these are mostly produced in b quark decays. I have found a signal in that dataset, about 70+-20 events over a background of 250.

The preliminary results of this analysis were blessed by the CDF Collaboration on June 18th, 1998. Feel free to browse through a copy of a paper submitted to the Los Alamos Preprint Server , which summarizes the results obtained.

If you are a particle physicist and need a more detailed explaination and all the available support plots, then you may consider getting it here.

You might also be interested to know how do we reconstruct the mass of this particle and how do we correct our jet momenta to be able to have the best possible resolution. A copy of the slides I made to present this work can be found here.

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