Re: Baseline Optimization Memo

From: Josh R Klein <>
Date: Fri May 14 2004 - 14:39:44 CDT

Hi, Jon,
> I'm a little confused by your statments that you'd "rather be statistically
> limited" and "build the biggest experiment you can afford."

        All this means is that the only thing which stops you from gaining
statistics at any baseline is the size of the detector (and how long you're
willing to take). Since the only thing really stopping you from building
it arbitrarily large is money, that sets the scale of the statistics. After
that, choosing a nearer baseline to further increase the statistics at the price of
increased systematics (if that is the case) is a bad exchange---for the same
total uncertainty (statistics+systematics) you're better off being
statistically limited. If your systematic uncertainties are fixed---which is
the usual case for most experiments---then this philosophy doesn't apply, because
the only thing you can do is improve your statistics, and the useful limit is
where you hit the systematics.

> These two points
> of view seem to be inconsistant, so perhaps I did not make myself clear in the
> memo. The statistics limited case is where you can gain in a simple counting
> experiment by increased statistics. If you are in the systematics limited case
> then it does you no good to take more data, at leat in the context of a rate
> only analysis.

        Right---all I am saying is that minimizing the absolute systematic
uncertainty is a bigger win than optimizing for the ratio to the statistics.
As it happens, I think these argue the same way in our case, if you believe
that the rate+shape analysis has inherently smaller systematic uncertainties,
since then you want to be closer anyway. The bottom line is that I think we
should just pick the detector size and fix it, and then re-do your study with
statistics and systematics treated independently.


> Thanks,
> Jon
> Josh R Klein wrote:
> > Hi, Jon,
> > The memo looks very nice. One comment I have is that
> > we probably should not treat systematics and statistics on an
> > equal footing---for the same total uncertainty, I'd rather be
> > statistically limited, since we know how those uncertainties are
> > distributed, and we usually don't know for systematics. In other
> > words, build the biggest experiment you think you can afford, and
> > place it at a baseline which minimizes the absolute systematic
> > uncertainty, not the ratio to statistical uncertainty.
> >
> > In any case, I suppose I would argue for the slightly closer baseline if
> > that allows a better rate+shape analysis. I think that although the sources
> > of uncertainty are larger for such an analysis (relative energy
> > non-linearities and background shapes matter much more), the additional
> > information should provide an overall reduction in the total systematic
> > uncertainty (not to mention, be a more believable measurement in general).
> >
> > Also, Bayes would say that dM2 is likely to go up from where it is,
> > not down, since that is where it came from...though I suppose I wouldn't be
> > willing to bet too much money on it either way.
> >
> > Thanks,
> > Josh
Received on Fri May 14 14:39:51 2004

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