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	12/9	Proposal for parameters and QUESTIONS.
	11/18	CALENDAR for JANUARY MEETING TIME -check and let me know your preferences!
WHAT'S NEW	11/17	I have started a table of caculated cross sections from each separate analysis	X
	11/16	There will be an informal meeting of the single top group in the CERN cafeteria at 10AM, Monday, 16 November.	X
	11/16	The results of this morning's meeting are described in the minutes section	X

The electroweak interactions of top quarks are expected to be evidenced in their production. Unlike the pair production channels, which are strong interactions, the electroweak interactions will produce single top quarks. The signals will vary depending upon which of several channels are selected. The backgrounds are severe.

2-> 2 process.

The 2-2 channel is one side of a two-sided coin. It is intimately connected with the presumption of a properly characterized b-parton density. This is an approach to sum the collinear logarithms by using a parton density to represent their sum - it's a device. The cross section from this viewpoint is of order alpha_S ln(m_t²/m_b²). From the prespective of theoretical and experimental uncertainties and new physics, this process has different sensitivities from the s-channel process. The sensitivity to V_tb from this process will be dependent on independent knowledge of the gluon and/or b parton densities.

gluon-fusion process

The "viewpoint" represented by gluon-splitting involves a potential double counting problem with the 2-2 process. This diagram represents a NLO correction and when those parts of the diagram are subtracted which are otherwise summed into the pdf, the remaining correction is truely of order alpha_S and negative. In practice, the combination of these two diagrams is problematic.

s-channel process

This channel is perhaps more directly amenable to the extraction of Vtb because of a different sensitivity to pdf's. There is a non-negligible sensitivity to the top quark mass. For LHC, the backgrounds are thought to be difficult, especially that from the gluon-fusion process alone. It is otherwise a relatively clean channel.

Wt process

This process has not been well-studied, perhaps because it is essentially invisible at the tevatron. However, at LHC it has a substantial cross section.

W+jets+bb background

This background is expected to be managable at both the tevatron and LHC, although the reduction required is several orders of magnitude. Efficient tagging will be necessary and perhaps the charm background will affect the search strategy. Stelzer, Sullivan, and Willenbrock [hep-ph/9807340 11 Jul 1998] employ a particular strategy and suggest that 1:1 or 2:1 S:B may be reasonable.

ttbar background

Top backgrounds will be very significant at LHC and the tagging strategy which will be employed will need to distinguish the process ttbar -> W+W+b+bbar, where one of the W's decays hadronically and a jet is missed. A way around this is to require only a single b quark.

 

 

gluon fusion.

From Stelzer, Sullivan, and Willenbrock, hep-ph/9705398 v2 10 Dec 1997. Tait and Yuan also calcuate similar values [hep-ph/9710372] of 2.65 (2.44) pb for the 2-2 (Wg NLO) result at the tevatron for the qtb final state process and 0.84 pb for the s channel process at the tevatron. For LHC, they only give the full NLO result of 239pb for the gluon fusion process and 11 pb for the s channel process. These are for m_t = 175 GeV/c².

 

 

s-channel.

From Smith and Willenbrock, hep-ph/9604223 v2 1 Nov 1996. Here, the uncertainty is an average over pdfs: CTEQ3L,3M, MRSA', and MRSG.

 

 

W-t.

From Heinson, Belyaev and Boos [hep-ph/9612424 19 Dec 1996]. These are for m_t = 180 GeV/c².

 

 

W plus jets background.

From Belyaev, Boos, and Dudko [hep-ph/9806332].

 

 

t-tbar background.

From Laenen, Smith and van Neerven Nucl. Phys B369, 54 (1992); Phys. Lett.B 321, 254 (1994); Berger and Contoponagos Phys Lett B 361, 115 (1995); Phys Rev D54 3085 (1996); Catani, Mangano, Nason, Trentadue, Phys Lett B 378 (1996), Nucl Phys B478, 273 (1996).

last modified: Thursday, December 10, 1998

Maintained by Chip Brock
Raymond Brock, Professor of Physics and Chairperson, Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824,