Hi there,

"Given that I want to study the distribution of these x and y points on each detector in each observation, what would be the best structure for this data?"

I'd suggest XML. You could end up with a structure like this:

<observation id="21">
 <detector id="DET-2"> 
   <hitX>896.657564735788</hitX>
   <hitY>678.83860967799</hitY>
</observation>
<observation id="21">
 <detector id="DET-3"> 
   <hitX>32.0939023018969</hitX>
   <hitY>621.656550474314</hitY>
</observation>
<!-- ... and so on ... -->
[download]

Such a structure can then easily be queried using XPath expressiones.

There are powerful and easy to use Perl modules for such tasks, e.g. XML::Simple.
See also:
Writing SAX Drivers for Non-XML Data
Stepping up from XML::Simple to XML::LibXML
XPath Tutorial

donp