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Smin: Measuring the Mass Scale of New Physics in MET Events

This article discusses the concept of Smin, a global and inclusive variable for measuring the mass scale of new physics in MET events. It compares and discusses other variables such as Meff, Mest, Heff, and HT. The article explains the advantages of using Smin and its applications in measuring SUSY masses.

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Smin: Measuring the Mass Scale of New Physics in MET Events

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  1. Smin: a global inclusive variable for measuring the mass scale of new physics in MET events (teaser transparencies) Konstantin Matchev In collaboration with: P. Konar, K. Kong arXiv:0812.1042 [hep-ph] SUSY leptonic mini-team meeting December 16 2008

  2. Outline • Historical interlude: comparative discussion of • Meff • Mest • Heff • HT • What is the problem with measuring the mass scale and how one should deal with it. • What is Smin? • What is Smin good for? • Outlook • Ronny’s plots

  3. Meff • Defined by Frank E. Paige at 1996 Snowmass (hep-ph/9609373). • What is it? It’s neither a mass, nor very effective. 

  4. Mest • Proposed by Dan Tovey in hep-ph/0006276 • You measure Mest and interpret it as Meff(Msusy,Mchi) • The relation is very model-dependent:

  5. Adding to the confusion F. Paige hep-ph/0211017 • Later people started calling Mest by the name Meff as well

  6. Heff and HT Look here! • Conclusion: Meff, Mest,, Heff, HT are all essentially the same! • We use calorimeter HT:

  7. Difference in Philosophy • What is the problem with measuring the mass scale? • Anything you try to measure will depend on both the mass of the parent particles (Msusy) as well as the LSP mass Mchi • How should one deal with it? 2 approaches: • Define an experimental observable which does not depend on the unknown LSP mass Mchi and then interpret it in terms of some function of both Msusy and Mchi. • Example: Mest=Meff(Msusy,Mchi) • Define an experimental observable which does depend on the unknown LSP mass Mchi and then interpret it in terms of Msusy. • Cambridge variable: MT2max(Mchi)=Msusy, • Gator variable: Smin(Mchi)=(2Msusy)2 • The second option is clearly better!

  8. What is Smin? • The minimum value of the Mandelstam variable consistent with the measured values of the total energy E and total visible momentum (Px,Py,Pz) • Advantages: • Uses all available information (not just transverse quantities) • Model-independent: no need for any event reconstruction • Inclusive • Global • Clear physical meaning

  9. What is Smin good for? • As an approximation to the true value of S:

  10. What is Smin good for? • One can measure SUSY masses in terms of the LSP mass:

  11. What is Smin good for? • One can measure SUSY masses in terms of the LSP mass: Gluino-LSP assoc. production Gluino pair production

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