Edges and things, and what experimenters do in HEP.

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Edges and things, and what experimenters do in
HEP.

• Christopher Lester

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Whats this all about?
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Decay chains used
Sequential
Branched
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Edge positions
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Fitted distributions
ll
llq
llq
ll
S5
lq high
lq low
lq low
lq high
O1
llq
Xq
Xq
llq
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What the different invariant mass distributions
look like for a selection of plausible
supersymmetric models. From Miller et.
al. hep-ph/0410303
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?M MT2(?) - ?

• Given
• the lepton momenta
• the missing transverse momentum
• an estimate ? of the neutralino mass
• Deduce
• lower bound MT2(?) on slepton mass
• slepton-neutralino mass difference ?M

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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 ks is acutally
  right!
• Hence mT2 is a lower bound for mslepton.

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So summarising

• In each event
• mT2ltmslepton.
• Can show that
• there exist events for which mT2 mslepton.
• So
• the endpoint of the mT2 distribution is mslepton!

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Example mT2 distributions
(This old plot underestimates SM backgrounds)
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No mqll-thresh, no mlq-low, no mT2
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No mlq-low, no mT2
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No mT2
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Everything!
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A long cascade decay from pp
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Mass Relation Method Results
Gluon Squark Neutralino2 Slepton Neutralino1