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66 Section 2: CDF Physics Analysis intellectually persuasive, and we recognize that a serious unbiased search for supersymmetric particles { in particular the Higgs { is a necessity. We choose therefore to concentrate our attention on two samples which are interesting from the SM point of view and which eventually should be sensitive to a Higgs signal: W +jets two jets + missing transverse energy It is understood that a b-tag could be applied to the jets, although not necessarily as an initial selection criteria. W + Jets We consider the sample in which the W has been tagged by a high-P T lepton (electron or muon). When there are at least two jets, then we can identify at least three interesting contributions: 1. pp ! WW with W ! jets 2. pp ! WZ with Z ! bb 3. pp ! Wh with h ! bb. Although the rst two are expected within the SM, they have never been observed, and a clear signal would be a real analysis success. One might hope to study the hadronic decays of vector bosons in pp collisions and compare to what is known from e + e , experiments, possibly learning something about color ow. These events constitute dicult backgrounds in a higgs search, so measuring their rates would be necessary in order to search for the higgs in this channel. Also important in a higgs search is an understanding of di-jet mass reconstruction: these events would provide a nice benchmark for detector and/or jet clustering calibrations. Two Jets + Missing Transverse Energy Without the several levels of careful clean-up procedure detailed in section 2.3.1, this sample would be dominated by \garbage." An loose selection would yield a sample dominated by QCD processes with mis-measured jets. But a tight selection could yield a sample containing contributions from the following interesting processes:
Section 2: Di-Boson Production 67 1. pp ! WZ with Z ! 2. ~t or ~ b pair production 3. pp ! Zh with h ! bb and Z ! 4. pp ! qq with one hard parton going o into so-called \extra" dimensions In some cases a b-tag is called for { but not in all. A sample of events with two jets and missing energy is clearly related to the sample studied by Spiropulu & Huth in the Run I data, but is not the same and could contain dierence signals for New Physics. Still, the experience and in-depth understanding gained from the Run I analysis will prove invaluable for studies of this sample. In the following two sections we describe our plans for these studies in the context of di-boson production and a study of 6E T + jets. 2.4.2 Di-Boson Production (Prof. Franklin, Prof. Schmitt, Dr. Burkett, Dr. Dorigo, Mr. Hall & Ms. Madrak) WW production. Madrak, Dorigo and Franklin have begun investigating the isolation of a WW signal in Run II, starting, of course, with Run I data. The cross section is about 10 pb. An observation of W + W , pairs was reported by CDF in 1996 [18], using the double leptonic topology (see Fig. 33). Although an event sample with two high P T leptons and large 6E T is very clean, this nal state suers from a small rate due to the square of the branching ratio Br(W ! e; ). The nal state involving one hadronic and one leptonic W decay has never been observed at a hadron collider: the main hindrance is the irreducible background from single W production and two jets from gluon radiation in the initial state. This background is larger by roughly two orders of magnitude. We think it may be possible to extract some evidence for the WW ! `jj signal in Run I data by selecting events with a high P T lepton, 6E T , and two jets. We may study the dijet mass spectrum after the application of kinematical selection requirements aimed at dierentiating the QCD radiation processes from the weak W decay. The tagging of charm jets may also constitute a useful tool to reduce the background. If we nd no signal in Run I we can still look forward to rening and optimizing our analysis strategy, in order to be ready to observe a clear peak with Run II data.
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