Table of Contents

• Negative weights?
• How to handle it?
• References

Negative weights?

How to handle it?

• Say if there are total of 100 events.. out of them 10 have -ve weights.
• so the 10 events that have -ve weights should be cancelled using 10 +ve weights so in general at the end of day we left we 80 events…
• but we don’t just use the number 80 as it is
• We apply the weight (+1 or -1) to each event as per the weight.
• and we so the scaling like:

  (Cross-sectioon x Lumi) / (Nevents - 2*NNegevents)
  

References

1. https://twiki.cern.ch/twiki/bin/view/CMSPublic/SWGuideMCatNLOInterface
2. TMVA: Negative Weights in Reader; https://sourceforge.net/p/tmva/mailman/tmva-users/?viewmonth=200901
3. Statistical power of negative weights: link
4. https://cds.cern.ch/record/517223/files/cer-002273178.pdf
5. Mulders, M; Direct measurement of the W boson mass in $e^{+}e_{-}$ collisions at LEP; Amsterdam U. Amsterdam 2001. Public copy: https://cds.cern.ch/record/517223/files/cer-002273178.pdf
6. Reason of negative weights; https://arxiv.org/pdf/1908.00167.pdf
7. https://arxiv.org/pdf/hep-ph/0204244.pdf
8. https://indico.cern.ch/event/459797/contributions/1961581/attachments/1181555/1800214/mcaod-Feb15-2016.pdf