CDF Projected Top Mass Uncertainty

download this plot: (eps) (jpg) (script)

Purpose of the plot

• To make a good faith projection about how precisely CDF can measure the top quark mass as a function of integrated luminosity.

• To advertise that we're doing much better than extrapolations based on Run I experience. In fact, we've already surpassed our goal of measuring Mtop to 3 GeV (that's the star, which is the projection from the CDF Run II TDR).

• To point-out that by the end of Run II the Tevatron (ie. CDF+D0) can reasonably be expected to have measured the top quark mass with a precision <1%.

How the plot was made

The solid curve keeps all the systematic uncertainties fixed at their present values, but scales the statistical and in-situ JES uncertainty (from the W->jj constraint in the l+j channel) with luminosity. The projected CDF-combined top mass uncertainty at a given luminosity is then estimated by repeating the present CDF combination using these projections for the statistical and in-situ JES uncertainties. This curve is then an estimate of the worst we expect to do since it assumes no improvements to the method or in our understanding of the systematics.

The dotted curve scales the total uncertainy with luminosity. It is meant to represent a sort of lower bound on how well we might do. Certainly it would be surprising if the total uncertainty improved faster than that! It is partially motivated by the fact that so far, this is, in fact, how our total uncertainty has been scaling (although we only have 3 points). Clearly the methods we use and our understanding of the systematics will have to improve to follow this curve.

We DON'T want to claim that we think we'll follow the dotted curve.

We DO want to say that we're reasonably confident that we'll land somewhere in between these two curves.

Other Details

• The solid curve is made by repeating the CDF combination as described above assuming luminosities of 1, 2, 4, 6, and 8 fb-1. This accounts for some of the "kinkiness" in the plot. More time/effort could help smooth it. Want to volunteer ?

• The triangles are CDF combined top mass at 110 pb-1 (Run I), 320 pb-1 (first Run II publications), and 680 pb-1 (most recent preliminary results). The Run II combinations include the Run I measurments, although they carry little weight (~1%). See here for more details concerning the CDF combination.

• The results used in the first two triangles have all been published. The third triangle, at 680 pb-1, is dominated by preliminary results.

• The plot is labeled as "l+l and l+j channels combined", but the Run I all-had measurement is included. This measurement carries a small weight in the Run I combination and <1% weight everywhere else. The reason for adding this label is to make it clear that there are obvious ways to improve upon the solid curve - add the all-had channel to Run II measurements, for example.

• The solid curve is labelled as scaling the "stat" with luminosity. As explained above it's stat+in-situ JES, whose sum will scale with 1/root(L) as advertised. In our measurements we actually determine stat+iJES from the likelihood contours. The separation into stat and iJES is a bit articifial and the shorthand "stat" made for an easier reading plot.

• The DM/M<1% is meant to highlight that we should be able to measure the top mass with a precision of 1% or better. When presenting you should be sure to mention that at that level of precision there may be new systematic effects which will become important and we've not yet considered (e.g. color reconnection effects).

• If CDF-alone can reach 1% precision, the combined Tevatron determination will do better still. We're working with D0 to make a Tevatron projection. Hopefully for the summer, when hopefully both experiments will have 1/fb results to combine.

Contacts:

• Doug Glenzinski ,