Friday, 3 May 2013

Brookhaven Forum 2013 Day 2, Live Blog IV

Final session of the day, the "New Ideas/BSM" session.  Conference Website.

Talk 9: 4:10pm: David Curtin, "Utilizing Colour Flow for Discovery at the LHC"

Global issues in jet substructure; like b-tagging for heavy flavour objects.
  • Hard substructure - used so far, e.g. top tagging
  • Soft substructure - not in the perturbative sense but e.g. quarks vs gluons - developed recently.
  • Not yet verified.
Test case: RPV gluino.

Boosted RPV searches reduce combinatorics.  Used previously for Tevatron.  Can we use it to improve current 650 GeV limit.

Colour flow: radiation sensitive to colour structure of underlying resonance.

Theorist-level analysis already matching full experimental conclusions.

Variables are hard; can we justify them to the experimentalists?  Consider Higgs decay to two gluons.  Impossible at LHC normally.  While preliminary, looks very hard even with colour flow help.

Talk 10: 4:30pm: Deejoon Kim, "A Simple, Yet Subtle 'Invariance' of Two-body Decay Kinematics"

A mass measurement technique.

  • Resonances if all final states visible and clean
  • Unclean final state, e.g. hadronic top
  • Endpoints; edges can be lots be resolution effects.
  • Jacobian peaks; restricted to single production
  • MT2, needs precise measurement of MET.
Rest frame of parent particle is very simple; it would be nice to work in that frame.  In lab frame, energy is not fixed but is instead a distribution; but it peaks at the rest frame energy.

I think I remember this paper, it was interesting.

Key result: peak of E dist. in lab frame is E in parent rest frame.

Direct application to top decay.  Not competitive with traditional methods, but simpler.

Talk 11: 4:50pm: Chris Carone, "A Model of Lepton-Flavour-nonuniversal Dark Gauge Bosons"

Can be thought of as a generalisation of the traditional dark vector.

Coupling goes through a leptonic mass mixing.  SM couples to dark SU(2) primarily through this mixing.

Offers a possible explanation for g-2 that avoid the coming kinetic mixing constraints.

Talk 12: 5:10pm: Bryan Kaufmann, "Mirage Models Confront the LHC: Kahler-Stabilized Heterotic String Theory"

Low energy EFT from heterotic string theory.

Ends up a simple extension of usual MSSM, thanks to hidden sector gauge group; group is asymptotically free.  Additional parameter is integer, constrained by high scale GUT group.

Offers a simple parameter scan on this top-down model.

Looks like this model is in trouble, but not quite possible to rule it out... close though.  NO! Xenon DD experiments can rule it out!

Talk 13: 5:30pm: H-S Lee, "Dark Z (in Comparison to Dark Photon)"

Like a dark photon, but with mass mixing with the Z.

Sorry, I'm finding it hard to write while also paying attention for these shorter talks.  Plus I've read the relevant papers here.

Talk 14: 5:50pm: P-J Tien, "Sniffing out New Physics from WW Cross Section"

Using precise LHC SM measurements to precisely constrain NP.

Small deviation from SM expectations in measurement of WW cross section; less than two sigma.  Theory under-predicts observation.  Combined result actually Three Sigma.

Excess could be due to NP production of real WW; or it could be due to a NP signal faking this.  In particular, we are looking at light sleptons, a popular game right now!  Signal: OS dilepton plus MET plus jet veto.

Turns out that data prefers NP model by small amount, at least from a frequentist perspective.  100 GeV slepton, 80 GeV neutralino.

Bino-like LSP, satisfies relic density with slepton coannihilation.  Potentially observable at XENON 1T.  Can also meet g-2, all in same region of parameter space.

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