[fegray@berkeley.edu: Re: skimmer question]

[Steven Clayton <smclayto@npl.uiuc.edu>]

Dear Peter,

below is part of an earlier email exchange with Fred.  I remembered
it wrong: Fred removes muSC hits outside of +/- 25us from the
skimmer trigger, not 25us from the endpoints of a wider region.
This means that in the skimmed data a given muSC hit is definitely
25us pileup protected, as promised.  The newer skimmer version Fred
refers to below, which renames muSC hits outside of the 25us gate
to different parameter numbers, would be fine for subsequent capture
searches: an asymmetric -25us/+35us gate (or up to as wide as the
"skim interval") could still be imposed on these skimmed data.
In the old skimmer, as we agreed this evening, the data outside of
+/-25us are suspect and cannot be used for impurity searches, unless
the muPC is very efficient.

There is another problem that just occurred to me: what about the
extra "spark"-triggered skim intervals?  I wonder, if I don't have
the same "spark" vetoes in my part of the analysis, are things screwed?
No, it should be fine as long as any muSC hit that makes it to the
skimmed data is pileup-protected and more than 25us from the skim
interval boundary.  Judging from the MQL code, to the extent that I
can understand it, I think this is the case.

Steven


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From: Frederick Gray <fegray@berkeley.edu>
To: Steven Clayton <smclayto@npl.uiuc.edu>
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On Tue, Jan 31, 2006 at 04:03:22PM -0600, Steven Clayton wrote:
> Hi Fred and Tom,
> 
> I think I understand your (Fred's) point about the edges
> of the skimmed region being problematic for pileup-protection.
> Say the muSC hits are the X's on the following (absolute) timeline:
> 
> <--X-----------X--------X--><--X-----------X----------------X-->
>        |       |       |           |       |       |
>      100us   125us   150us       1000us  1025us  1050us
>

Hi, Steve,

Yes, thanks for making this argument for me.  I was having trouble 
reconstucting it on the phone this morning.  The point is that you don't
know whether or not your first, third, fourth, and fifth hits are
pileup-protected.  Maybe, maybe not; the information you would need to
determine that has been thrown away.

In the main skimmed data production that you are using, I solved this
problem by only keeping muSC hits (parameters 6000-6099) over the 25
microsecond interval, while keeping all other hits for the longer 40
microsecond interval. 

A more recent version of the skimmer (not yet widely used) renames 
parameters 6001-6019 as 6021-6039 when they are outside the 25
microsecond interval.  

The "general skimmer" currently ignores this problem, since I envisoned it as 
primarily useful for making event displays of selected events, where you
would like to see the full context over the interval that you choose to save.

Thanks,

-- Fred

-- Fred Gray / Visiting Postdoctoral Researcher                 --
-- Department of Physics / University of California, Berkeley   --
-- fegray@berkeley.edu / phone 510-642-2438 / fax 510-642-9811  --

----- End forwarded message -----