Correlation between selections


The correlations between the selections run in the DC04v2 stripping (using DaVinci v12r16) are all available. Because of the to loose bandwidth requirements (1/1000 BB events, a factor about 50 to loose) the correlations between preselections are not of great relevance for this task force. More intereseting are the correlations between the offline selections that are closer to what might be the output of a real data stripping. They are selections 63 to 83 in the full correlation table.

Diagonalisation into blocks

It is straight-forward to diagonalise the sub-matrix into blocks of correlated selections. The full result is available below.

Note that this matrix is built from very few events (at most a few hundered, usually less) so 0% (not shown) and a few percent overlap have very similar meanings.

The see the following blocks, from top left to bottom right:

  • Dimuons (B->J/psi{K,Ks,K*} B->llK and B->MuMuK*) that have overlaps ranging from a few percent to 60% (B->MuMuK* does not have overlaps, which reflects the non-standard way this selection is done. This is solved with DC06.)
  • Dielectrons (Bs->J/psiKs and Phi). Funilly they don't have any overlap. They could potentially also have an overlap with B->llK but don't either. These selections are usually related to partner dimuon selections, which could suggest to put them in a same file. But one could also split the B->llK events into B->eeK and B->mumuK candidates.
  • B->hh selections with correlations up to 70%.
  • Bs->DsH selections
  • The correlation of the B->D0X selections is low. We need much more data (or knowledge about these selections) to decide what belongs together.
  • The B->GammaX also do not show any overlap.

Off-block overlaps

Very few events end up in more than one selection, at most 2-3% for a given selection or block. There are a few non-surprising correlations like between unrelated B->4body decays as Bs->DsK, B->D*Pi, B->MuMuK* and B->D0K*. The only clearly random correlations are between 4-body and 2-body selections. They are likely to be due to large events.


One can easily diagonalise the correlation matrix, just applying common sense. The remaining overlaps with other samples should not exceed 1-3%.

-- PatrickKoppenburg - 06 Sep 2006

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Topic revision: r5 - 2007-01-24 - UlrikEgede
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