Thursday, 2 May 2013

Brookhaven Forum 2013 Day 2

So, yesterday was a pretty good day that reminded me just how much I enjoy conferences.  Hopefully today can continue to deliver.  Conference Website

Talk 1: Lisa Whitehead: "Overview of Neutrino Physics"

So we start with some review on neutrino mixing from a theoretical perspective.  This is the standard quantum mixing, modulated by the possibility of observable oscillations over long distances.

  • "Atmospheric" oscillations (mixing of muon-tau flavour): Super-K, K2K, T2K, MINOS
  • Super-K is direct measurement of atmospheric neutrinos, other experiments check this with reactor/beams.
  • "Solar" oscillations (electron-muon): SNO, KamLAND
  • The Solar neutrino problem was, of course, a long-standing problem that needed reactor beams to confirm as being due to neutrino oscillations, not solar physics.
  • θ13 from last year, of course, giving us the last mixing angle from reactor experiments (alone, but multiple to confirm).
I would expect more details on θ13, since it's the newest thing, making me wonder if this is an old talk.

Big Questions:
  • Mass Scale
  • Hierarchy
  • Dirac vs Majorana
  • CP violation
  • Sterile neutrinos or other extensions of the minimal neutrino sector.
More details on the experimental observations.  Some notable cross checks; muon neutrino disappearance at MINOS or T2K checked by tau neutrino appearance at OPERA (3 events!)

Here's θ13.  Measured both from electron neutrino disappearance at moderate baselines (700km, MINOS) but decisively from electron anti-neutrino disappearance at short baselines (1km, Daya Bay etc).

Interesting results: some (weak) constraints on CP-violating phase, δ.  MINOS using precise reactor measurement of θ13 to get constraints, still not stringent and very dependent on hierarchy.

New experiments:
  • NOvA, first results expected June this year.  Fermilab beam, same path as MINOS.  Looking at electron neutrinos, to pin down δ.  If lucky, can determine (at two sigma) the hierarchy!  
  • LBNE, also using Fermilab beam but with different target (South Dakota), 1300 km baseline.  Approved last December.
  • "Daya Bay II" (not to be at Daya Bay).  60 km baseline in China, looking at small sub-oscillations on top of primary oscillation waveform.
Anomalies, aka things to work on/think about.
  • MiniBooNe/LSND persists.
  • New reactor anomaly.
Neutrinoless double-beta decay: I didn't realise there had been a claim, I should look that up.  Current experiments look to be unable to resolve hierarchy, but next generation should be able to do so unless we are unlucky.  Currently-running EXO-200 running to 2014, needs to be upgraded to nEXO; confirmed yet?

This was very much a summary talk, presenting a lot of results.  Quite a few of these results I'd seen before, so it was less enlightening for me.  There's always a problem with this type of talk, that you just don't have the time to properly go into details on anything, so it all ends up a bit rushed; of course, that's not the fault of the speaker.

Q&A: Best global fit for δ is pi, i.e. no CP violation; though does seem to depend on fit.

Talk 2: 9:40am: Philip Schuster, "Prospects for Low-Energy New Physics Searches"

We know DM exists, but with the LHC putting pressure on naturalness perhaps its not at the weak scale.  Hence low energy searches remain valid.  See also RPV SUSY; many remaining (quasi-)natural models abandon DM to ease constraints.

We always start by explaining the unknown as simply as possible, but that does not always work.  Is this talk going in the direction of complex hidden/dark sectors?

Going at the "portal" couplings to the dark sector, specifically the vector and axion portals.  The latter is strictly non-renormalisable, but allegedly still relevant at low scales.

Reference to check: 1205.2671

I haven't said much on this talk, as again, it's mostly review.

Upcoming experiments that can place constraints:
  • Old experiments in the relevant region beam dumps, or course, limited by rates (small epsilon) or decay to quickly (high epsilon)
  • HPS
  • APEX
  • DarkLight
  • VEPP
  • High-statistics resonance search: high data rate, high mass suppression
  • APEX, Mainz shown to work
  • Displace resonance search: look for vertex signature, HPS
Experiments should finally cover region consistent with g-2 anomaly.  Goal: cover region that would fit DM anomalies, not within range of current experiments but possibly the next generation.

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