Re: [BLAST_ANAWARE] momentum resolution

From: Adrian T Sindile (asindile@cisunix.unh.edu)
Date: Fri Jun 04 2004 - 19:10:02 EDT


Hi, Genya!
I tried different methods, but the common accepted method seems to be by
comparing the measured electron momentum with the electron momentum
calculated from the electron theta angle.
The formula I derived for that (and which I also found in the common
wc-res.C script, the author should correct me if that formula is
different, please) is:

k' = k / [1 + 2k*sin^2(th/2)/M ], where M is the proton mass, k is initial
electron momentum and th is the scattered electron angle.

You can see from this formula that any uncertainty in electron theta
enters the momentum resolution, like John was saying.
Since our "common" e-p vertex has a width of at least 15 cm (I can send
a plot to show that, if necessary), I think John was saying that affects
our angle resolution, thus our momentum resolution...

Adrian

> I had an impression that we always extract the momentum resolution
> from the sum of electron and
> proton momenta, which is independent of the angle. It does include
> momentum resolution for
> both electron and proton ( or whichever dominates), but that is easy to
> take into account.
> Am I wrong?
> Genya



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