Monday, 26 August 2013

SUSY 2013 Live Blog: Day 1

Another conference, and because it went well last time I'm going to continue with live blogging as a proxy for taking notes.  This time it's Supersymmetry 2013, held in Trieste.  Travel here was pretty awful, but I might put my complaints into a different post if I feel like it.  (Protip: don't fly with Alitalia.)

Interestingly, we start with a talk not about LHC results, the Higgs or even SUSY in general.  The first talk after the introduction is Stefano Profumo on Dark Matter.

9:35am: Stefano Profumo: Searching for Dark Matter from the Sky

Specifically, this is a talk on indirect detection.  The defining question of this talk is whether we can do fundamental (particle) physics with ID?  Historically, the answer has been yes; anti-matter, muons, pions and neutrino masses begin examples.

Three candidates for modes statements: the positron excess, gamma ray excess and the 130GeV line.

We start with the positron fraction excess, first really brought to excitement by PAMELA.  It is generic that secondary particles have a declining spectrum as a function of energy, in contrast to the observation.  The first question: is this a real excess?  The observations of other experiments (Fermi, AMS) seem to say yes, very much so.  So the more important question is: what is it?

In general terms, it seems that it has to be an additional source of high energy positrons and electrons.  So the well-known question at this point: DM or Pulsars (or something else)?

The problem with DM, after AMS, is that two-body SM final states are essentially ruled out.  Pulsars seem to work with reasonably choices of parameters.  But can we distinguish the two cases?  What of anisotropy in arrival direction?  This requires a local pulsar, so is not guaranteed.  Alternatively, look for secondary photons (ISR, Inverse Compton).  This is not ruled out yet but is in trouble.  We have no anisotropy but the limits do not yet probe the most likely regions.

Summary: pulsars looking much healthier than DM right now.  ACTs might be able to find an anisotropy and end this debate.

Next we have the galactic centre gamma-ray excess popularised by Dan Hooper among others.  The GC has the best expected signal but worst backgrounds.

If you don't model backgrounds carefully enough, you might generate a "Goodenough Hooperon".  Still, the excess does seem to be real at around 10 GeV of so.

Modelling backgrounds with too much detail can also be a problem.  Too many knobs to tune the backgrounds will absorb almost any possible signal.

In general, all consideration of the GC suffers from the presence of a supermassive black hole,  which easily can generate enough power to explain the possible signal.

Finally we come to the 130 GeV line that has grabbed a lot of attention of late.  It this is a real signal it would have huge implications for e.g. SUSY searches at the LHC, because we would know the LSP mass.  Line seems to exist even after accounting for Fermi bubble backgrounds.  What of systematic effects, especially energy rconstruction?  A new analysis tool, Pass 8, is currently in testing and should help shed light on this point.

Ultimately, we probably have to wait for HESS-2 or CTA, which will say one way or the other.

What of astrophysical origins?  Need a nearly-monochromatic electron beam converting nearly all the electron energy to gamma rays.  Can happen from pulsar winds, but need at least 5 pulsars.  All with the same monochromatic electron energy?  Unlikely.

Final line: calling back to an earlier comment, there is a way to fit all the data with a simple NMSSM model.  Fine-tuned as hell, but this is 2013.

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