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Edges and things, and what experimenters do in HEP.

Discover the different invariant mass distributions in plausible supersymmetric models using the Sequential Branched Damtp Pheno method. Learn how to deduce lower bounds on slepton mass and slepton-neutralino mass differences using mT2.

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Edges and things, and what experimenters do in HEP.

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  1. Edges and things, and what experimenters do in HEP. Christopher Lester

  2. What’s this all about? Damtp Pheno

  3. Decay chains used Sequential Branched Damtp Pheno

  4. Edge positions

  5. Fitted distributions ll llq ll llq S5 lq high lq low lq high lq low O1 llq Xq llq Xq

  6. What the different invariant mass distributions look like for a selection of plausible supersymmetric models. From Miller et. al. hep-ph/0410303

  7. ΔM = MT2(χ) - χ Given: • the lepton momenta • the missing transverse momentum • an estimate “Χ” of the neutralino mass Deduce: • lower bound MT2(Χ) on slepton mass • slepton-neutralino mass difference ΔM Damtp Pheno

  8. How does this mT2 work? • For each event you want a lower bound for mslepton • You get this by trying ALL POSSIBLE neutralino momenta, k, consistent with • observed missing momentum, • identical (unknown) slepton masses, • Hypothesised neutralino mass. • For each of these momenta, k, “that might have been” there is an “mslepton(k) that might have been”. • There is a least such mslepton(k) (call it mT2) which cannot be bigger than the true value of mslepton, because one of the k’s is acutally right! • Hence mT2 is a lower bound for mslepton. Damtp Pheno

  9. So summarising: • In each event: • mT2<=mslepton. • Can show that: • there exist events for which mT2 = mslepton. • So: • the endpoint of the mT2 distribution is mslepton! Damtp Pheno

  10. Example mT2 distributions (This old plot underestimates SM backgrounds) Damtp Pheno

  11. No mqll-thresh, no mlq-low, no mT2 Damtp Pheno

  12. No mlq-low, no mT2 Damtp Pheno

  13. No mT2 Damtp Pheno

  14. Everything! Damtp Pheno

  15. A long cascade decay from pp Damtp Pheno

  16. mothers (0 to 1000 GeV) mneutralino (0 to 600 GeV) Mass Relation Method Results Gluon Squark Neutralino2 Slepton Neutralino1 Damtp Pheno

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