Thursday, 2 May 2013

Brookhaven Forum 2013 Live Blog II

New session, new blog.
Talk 3: 11am: Gregorio Bernandi, "Tevatron RESULTS Overview

It's not dead, only resting.

Subtitle offers not only talks, but also prospects.  Of course, we know that experiments like this take a long time to finish their data analysis; I've talked before about a LEP paper that came out a decade after that experiment finished running.

Good starting point: the Tevatron initial state offered the prospect of measuring asymmetries, as in the famous tt forward-backward result.  Also, different qq vs gg initial state ratios helps to break degeneracies from the LHC.

Heavy Flavour
  • Like-sign dimuon asymmetry.  I remember this from my last Brookhaven forum.  Result has persisted, though, at the 3 sigma level.
  • DD mixing observed, agrees in physical region with other experiments.
  • Most cases LHC wins
  • Top-pair resonances at "low" energy have some hope; best limits below 700 GeV.  Relevant for RS models, among others.
  • W mass measurements dominated by Tevatron, and can still be improved.
  • Aim: 10 MeV, vs 15 MeV current world average
  • If no change in central value, would actually disagree with SM at two to three sigma.
  • Give indirect constraints on Higgs (with top mass)
  • Improve top mass uncertainty from 0.9 to 0.7 GeV
  • Interestingly, Higgs to two photons is enhanced here!
  • Higgs searches now complete: analysis done with the full data set.
Top Asymmetries
  • Usual asymmetry there with 3 sigma discrepancy
  • Leptonic asymmetry, only partly correlated, order 2 sigma discrepancy; combination of results and full data sets to come.  Looks like this might get stronger in that case.
Looking at the talk as a whole, there where a lot of results presented including many I didn't comment on.  The most interesting points, to me, are the possible implications of the W mass measurement; the top asymmetry anomaly; and the prospects for combining Tevatron and LHC data on Higgs to bb.

The first of these is unlikely to show anything, but it might and so is worth keeping an eye open for.  The top asymmetry persists, and I should really finish my two projects related to it.  Finally, the combination of LHC and Tevatron data offers the only hope of seeing Higgs to bb before the LHC starts up again in two years.

Talk 4: 11:40 am: Alessadro Strumia, "Naturalness After LHC Run I"

This talk is being delayed while the organisers figure out how to make things work.  Oh no, it's working now.

First consideration of naturalness: Thermal DM.  We know the cross section from the relic density, so for a given spin and EW quantum numbers, we get the mass as a prediction.

Second consideration: the usual Higgs mass question.

Even before the LHC, there was a problem from mtop > mHiggs.  A natural cut-off to the top loop corrections would occur at around 400 GeV, which runs into the usual little hierarchy problem: precision measurements seem to push new physics to the multi-TeV range.

It looks like the focus here will be about SUSY.  That's fine, but then your title is too broad.

  • Fine tuning from LEP already, of course; from Higgs measurement
  • SUSY DM also "dead" outside of some special cases
  • CMSSM was something of a spherical cow, though
24 one-letter extensions of MSSM; only J- and LMSSM not invented yet.

Natural SUSY
  • Looks like we finally have exclusions for stops when they are degenerate/lighter than tops
  • Theorist analysis; I need to look this up
  • Might become relevant for hidden sector model: can probably evade those limits
  • Even with light stops, fine tuning is order 10

So Alessandro is not impressed by all the model-building that's gone on; the things that made SUSY attractive can not be kept in light of data.  I think he's going a bit far, and recall a recent quote by someone I've sadly forgotten; thinking SUSY was reasonably two years ago, and unreasonable now, is surely the least justifiable position.

Still, this does bring us to the question: is the weak scale natural?
  • Brings us to finite naturalness, essentially rejecting the idea of quadratic divergences.
  • I remember this paper from recently, indeed I meant to discuss it here.
  • I'll hold a more detailed discussion for later.  I am looking forward to the Q&A session.
  • Always worth reemphasising: Higgs potential seems to vanish at the Planck scale.  Simple origin?
In summary: we should seriously ask if naturalness is a good approach.  Finite naturalness is an alternative, which is better for the Higgs; doesn't work for the Cosmological Constant; and avoids nasty anthropic/landscape stuff.

I think it would be interesting to put finite naturalness on a firmer context within renormalisation theory.  Can we connect this to conformal theories?

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