CDF Projected Top Mass Uncertainty
The Top Mass Working Group
download this plot:
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
Since projections are hard, we try to bracket what we might reasonably
expect to achieve by the two curves that are shown.
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
We DON'T want to claim that we think we'll follow the
We DO want to say that we're reasonably confident that
we'll land somewhere in between these two curves.
- 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
- 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
- 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.
( Top Mass Working Group
| CDF Top Physics Group
| CDF Homepage
Last updated: March 09, 2006,