[Halld-pid-upgrade] Fwd: Re: thoughts after PID session [from Mike]

[Michael Williams]

Sure.  I was just pointing out that we shouldn't just see S/B = 10 and think "no PID required".   This seemed to be the reaction (again, judging from EVO where I couldn't really hear people properly) to some of Paul's slides (not his fault of course).   If S/B = 10 w/o PID and then the PID makes it 20, that factor of 2 is pretty important if f = 0.1 (which I think is probably about what we'd be hoping for).    So S*f goes from 1 to 2 (a nice gain).  

So, I guess I'm just saying that we should be careful when presenting these things publicly to not let "f" get lost in the argument.  I haven't thought about what is the best way to do that.  In my head for the moment I'd probably think f = O(0.1).   If it's much smaller then it'll be very hard to observe convincingly even without background.  If it's much bigger we'll be popping too much Champaign to care about a little bit of bkgd ;-)   

Mike

On Oct 8, 2012, at 6:47 PM, Matthew Shepherd wrote:

> 
> On Oct 8, 2012, at 5:58 PM, Michael Williams wrote:
> 
>> One final question: Do we have any decent predictions for the size of the hybrid rates?  Paul is looking at S/B but we don't really care about S, we care about S*f where f is the fraction of the signal that is from a hybrid.   If the bkgd is of comparable size to the hybrid contribution, then it could be a problem (regardless of how big the non-hybrid signal is).   
> 
> Yes, it can be a problem, but it is more complicated than just a PID problem.
> 
> Definitions:
> 
> S:  number of events with some topology of stable hadrons
> f: fraction of these events that come from exotic resonance decay
> B: number of events that are not of the signal topology
> 
> The PID system is going to help us with S/B.  We hope that nature helps us with f so that S*f is bigger than B.  The idea that S*f is big is one of the arguments for building a photoproduction experiment -- we have to test it.  I don't think we have a good idea of how big f is.
> 
> There are some measurements for S.  See:
> 
> http://argus.phys.uregina.ca/cgi-bin/private/DocDB/ShowDocument?docid=809
> 
> which is an old compilation of cross sections.
> 
> I would tend to focus on S/B in the PID studies, since that is what the PID system will do.  If we want to go a step further we can use PID system to maximize S/B (or some other FOM.. maybe S^2/(S+B)) and then use the size of B to infer some sensitivity limit on f or the hybrid production cross section.  
> 
> It may be more clear in a presentation to say a system gives us sensitivity down to a certain value for S*f, than picking an f, which has a big uncertainty, and quoting S*f/B.  We can ask:  which system gives us the most sensitivity to exotics?  All assumptions that go into such a study would be based on some data or a Pythia model.  
> 
> Matt
> 
> 
> 
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