Thursday, 7 July 2016

SUSY 2016: Day Four Session One

I didn't try to liveblog the first few days of SUSY, which was a mistake.  It turns out that doing this really does help me focus and pay attention.  So I'm starting with Thursday, which happens to be the flavour session.

9:00 am: Quark Flavour Physics, Concezio Bozzi

Flavour physics in the SM is highly predictive (in the quark sector).  Equivalently, this means that it is a good avenue for searching for new physics.  A brief overview of the current experimental facilities: LHCb, Belle and even the general detectors.

Recent progress in measuring the unitarity triangle angle γ; uncertainty at LHCb down to 8%, about half of previous efforts.

Long-standing tension in measurements of Vub between inclusive and exclusive measurements.  Probing at LHCb measuring the ratio Vub/Vcb, which is non-trivial at a hadron machine as we can't use the beam energy as a constraint.  Exploit rare decays of Λb baryons, suppressing backgrounds with isolation criteria and (measurable) flight direction as kinematic constraint.  Different measurement to previous exclusive observables based on B decays; agrees with exclusive result over inclusive measurement.  Excludes possible right-handed currents as explanation for discrepancy.

New measurements of mass difference on D-sector (D versus D*) that indirectly constrains Vtd.

CP violation in B mixing another prior tension with SM.  LHCb does not agree with this tension, but there is still an order of magnitude to go in improving the experimental error before it can compare to the theory uncertainty.

Probing the second (squashed) unitarity triangle.  Interesting measurement in that it looks at interference effects in various b to c decays.

This talk is running into the standard experimental plenary talk problem: lots of results, little context.

Jumping ahead to the discrepancy in the B to K*μμ differential distributions, LHCb has performed a full angular analysis with 8 differential observables.  3σ discrepancy seen, also in a related point in Belle.  Some efforts to explain using effective operators; when all observables are included, it is not clear how significant this result is.  Claim from Ciuchini et al that can be explained by long-distance charm loops.  More data needed to help resolve this question.

Deviation in lepton universality in B decays is still there.  LHCb can exploit presence of second (hadronic) B and large b quark boost to perform superior measurements.  Combined measurement deviates by 4σ.  Many related observables to be probed in the near future that will help understand this case.

Dominant uncertainties in B to K*μμ decays? Plots shown were for asymmetries, so robust against small systematics.
Question on role of right-handed currents in Vub measurements, but I missed it.
Questions from the chair of the session where I literally could not make out the question.

9:30 am: Flavour Physics Theory, Xiao-Gang He

Worth remembering: we now know there are only three generations.  Additional heavy generations getting their masses from the Higgs can be excluded already from measurements of the Higgs couplings to diphotons/digluons.  Light states including extra light neutrinos are excluded from measurements of the Z decay; cosmology gives the same bound on the number of neutrino species.  Which is a very powerful & interesing recent result, when you think about about it.

Three generations of particles in general must mix.  But the fundamental flavour question is why the mixing has the pattern that it does: hierarchical in the quark sector and democratic in the lepton sector.  A related "problem" is that so far, the SM explains everything: there is no need for NP, which means we have no hard guidance in how to answer these questions.

First choice for an anomaly to discuss: small deviation in branching ratio for Bd to μμ.  Which is what, 2σ?  But "it works with SUSY".  Whatever.  Other anomalies involving B decays, some of which were covered in the previous talk.  It's hard to follow this talk, partly because how fast the speaker is talking, and partly because his slides are absolutely crammed with text, formulae and tables with no clear structure.

Three whole slides on MFV.  Looking ahead, I'm not quite sure why.

OK, he is actually using this in his discussion of flavour-violating Higgs decays.  I just couldn't recognise it among all the clutter.  Conclusion is ... CP violating Higgs decays might exist?

Jumping through things too fast for me to understand what points, if any, are being made.

But we come to SO(10) flavour.  Then a discussion of relating the 750 GeV diphoton excess to a flavour-related field.  Or, as far as I can tell, taking the usual model of extra scalar and asserting it is related to flavour.  Unrelated to a GUT, why are they in the same section?  Another random thing shoved into the same section: the recent Be anomaly and possible 17 MeV boson.

You know what this reminds me of?  The comment I made in the previous talk.  Lots of basically unrelated things given one or two slides at most.  In an experimental talk it's somewhat understandable (though why I tend to dislike experimental plenaries).  In a theory talk, I think it shows you need to learn to edit.

10:00 am: Latest Results from Neutrino Oscillation Experiments, Anelmo Cervera Villanueva

A general talk from a T2K speaker.  A straightforward review of neutrino sources and mixing.  Then oscillations, the fundamental tool for measuring neutrino flavour parameters.

Experimental strategies.  θ13 with reactor measurements, νe disappearance at short-baseline experiments.  Long-baseline searches for νe appearance gives sensitivity to δCP as well.  Daya Bay is the most notable one at the moment, since it made the discovery.  Note that its source is the fourth largest nuclear reactor in the world, which helps give it such good statistics.  Double-Chooz has not updated since Moriond while Reno is mentioned.

T2K is an off-axis accelerator experiment with a 300km baseline.  Current goal is to search for anti-νe appearance.  This will directly probe CP violation.  Source is a 30 GeV proton beam at J-PARC.  Detector off-axis because this leads to a quite peaked spectrum, and further choose the angle so that the peak is where the oscillation probability is maximised.  Some evidence for anti-νe appearance, but short of 5σ; results to be updated at ICHEP.  Joint analysis gives 90% exclusion of δCP equal to 0.

NOνA in US another long-baseline accelerator experiment.  Better sensitivity to hierarchy than T2K.  Results give (modest) exclusion of maximal 2-3 mixing.

"The combination of all current experiments will probably result in a measurement of the mass hierarchy and an indication of non-zero δCP (2-3 sigma)."  An actual measurement of δCP requires the next generation of experiments.  Quick review of those experiments: T2K phase II, Hyper-K and DUNE.

Current significance on δCP? No combined result yet, probably close (slightly above) to 2 sigma.
What of JUNO in China?  Will measure solar parameters and hierarchy.  Solar parameters not so important at the moment.
What upgrades planned for T2K II?  Increased beam power, upgrades to near detectors and 30 times the exposure.

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