[Rivet] lifetimes in rivet

[Jonathan Butterworth]

Hi Frank,

Frank Siegert wrote:
> Jonathan Butterworth, Wednesday 07 April 2010:
>> I think a confusion has crept in. We are talking about the lifetime for
>> a species, not how long a particular instance of a particle lasts.
> 
> Ah, thanks for clarifying.
> But now I am confused: How can an experimental analysis do this kind of 
> thing without using a model to unfold the particles which actually 
> happened to decay before the detector? Is this really something that 
> should be encouraged?

All one is really doing here is correcting for a well-known exponential, 
so I think it's pretty sound. One wouldn't do this for anything but 
particles which are metastable, lifetimes > 10ps or so.

> I don't think it will really matter much. But then it also doesn't matter 
> whether we do it with the actual lifetime or the mean lifetime, does it? 
> So it would be possible quite easily and generator-independent.

It's really the mean lifetime we want. Basically a measurement will 
typically be defined as including (e.g.) all K_S as final state 
particles, or none of them, not a mixture depending on when they 
actually decayed particle-by-particle.

So it is generator independent in principle. But the implementation in 
practice would be tricky, as I said in the previous mails, since it 
would involve tracking the decay history at very least.

Cheers,
Jon

> 
> Cheers,
> Frank

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Prof. Jonathan Butterworth,              http://www.hep.ucl.ac.uk/~jmb/
Physics and Astronomy Department                  Tel: +44 20 7679 3444
ATLAS, CERN                                       Tel: +41 22 76  72340
University College London                 Gower St, London WC1E 6BT, UK
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