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MET in Atlfast dijet samples

MET in Atlfast dijet samples. MET in Atlfast with constant term. MET in Atlfast dijet samples. MET in Atlfast without constant term. MET in Atlfast dijet samples, CKIN(3) impact. Only lower cut on parton pt, ‘CKIN(3)’ = 500 (Run93), 850 (Run92), 1200 (Run91) No upper cut!.

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MET in Atlfast dijet samples

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  1. MET in Atlfast dijet samples • MET in Atlfast with constant term David - CAT SUSY / MET Meeting

  2. MET in Atlfast dijet samples • MET in Atlfast without constant term David - CAT SUSY / MET Meeting

  3. MET in Atlfast dijet samples, CKIN(3) impact • Only lower cut on parton pt, ‘CKIN(3)’ = 500 (Run93), 850 (Run92), 1200 (Run91) • No upper cut! Samples don’t match! For a given SumET, events seem to differ! David - CAT SUSY / MET Meeting

  4. MET in Atlfast dijet samples, ISR impact • Switching off ISR shows this difference in resolution is due to QCD radiation in the event • Atlfast takes true jets, smears their energy according to jet resolution function, and this is then the reconstructed jet • MET resolution is dominated by contribution of 2 leading jets, hence look at their energy… David - CAT SUSY / MET Meeting

  5. Mean energy of 2 leading jets vs SumET • Threshold where 2 leading jets keep practically all energy from the initial hard process clearly visible • Pronounced difference between 2 samples well beyond threshold, disappears only at ~4200 GeV • Surprising why ISR makes such big difference – not clear why • Probably the reason why MET resolution differs up to 4200 GeV Threshold: 2*CKIN(3) David - CAT SUSY / MET Meeting

  6. Mean energy of 2 leading jets vs SumET • Switching off ISR, the samples overlap nicely once above threshold • The effect on the MET resolution of on average larger energy of the 2 leading jets, when comparing the with-ISR to the without-ISR sample, is compensated by the much smaller number of jets wo/ ISR… Threshold: 2*CKIN(3) David - CAT SUSY / MET Meeting

  7. Mean number of jets vs SumEt • Behaviour below threshold not understood! But very few events • Also this turn-on with ISR not completely obvious to me • As expected the mean number of jets increases dramatically with ISR • And this worsens the MET resolution ? David - CAT SUSY / MET Meeting

  8. Mean number of jets vs SumEt • Behaviour below threshold not understood! But very few events • Also this turn-on with ISR not completely obvious to me • As expected the mean number of jets increases dramatically with ISR • And this worsens the MET resolution • The plateau level (mean number of jets at large SumET) seems to depend on the initial CKIN threshold ? David - CAT SUSY / MET Meeting

  9. Next • Combined samples with proper cross section weight • If bumps and weird structures persist (likely), get in touch with Torbjorn and try to sort this out • Not obvious to me that generating dijet samples with cut on initial parton pt yields samples which can be reasonably combined • I’m in contact with the ATLAS MC / jet experts already, no clue either David - CAT SUSY / MET Meeting

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