Wednesday, 11 November 2015

KIAS-CFHEP Workshop Liveblog: Day Three Session One

Our third day, which is a half-day so we can explore Seoul after lunch, is given the vague title "Astro-interplay And other topics".

9:30 am: Recent progress in Neutrino Astroparticle Physics, Carsten Rott

Unfortunately, I've missed the first few minutes of this talk through slightly oversleeping.  Again.  And these slides are not online yet, so I can't check what I missed.  We're currently discussing Cherenkov radiation, the tool used by all modern neutrino telescopes, and the experiments in use.  Includes a discussion of experiments other than IceCube: ANTARES, Lake Baikal and the best-known SuperK.

IceCube is the current cutting edge, so more discussion of data.  100 astrophysical neutrinos a year, against huge backgrounds of astrophysical neutrinos and muons.  Various tools that can be used to distinguish them, in particular direction, time clustering (SN1987A) and energy.  Angular resolution good enough to see deficit of neutrinos in direction of moon (moon discovered with 14 sigma!)

Main science of the talk: the PeV neutrino discovery. Aim was to find GZK neutrinos.  Initial 2 event discovery (already a 2.7 sigma excess over atmospheric expectations) motivated further study of multi-TeV region.  Define veto region and use directional information to cut backgrounds.  Result is now well-known: multiple events, clear excess over atmospheric expectations with steadily growing significance.  More recent data shows softer spectrum; relatively more new TeV events than PeV.  No evidence for correlation in the sky.

Can this observation be independently confirmed?

First attempt is to use other experiments.  ANTARES has done analysis; consistent with IceCube, but also with background.  (Smaller detector, poorer resolution.)  Second attempt is to use other channels at IceCube.  Through-going muons at high energy also show excess over backgrounds.  Unfortunately no directional overlap with neutrino signal, so if are from common source then no evidence against isotropic signal origin.

Attempts to correlate with other cosmic ray signals.  Connection between ANTARES and X-ray signal turned out to the coincidence.  Some very weak evidence of a correlation between IceCube and UHECR from Auger; statistics too weak to say anything useful.

Up-going/down-going ratio? More down-going due to absorption in Earth, but not significant.
Is spectral index sensitive to Glashow resonance? Not sure what the answer was.
Is the gap of no events meaningful? No, more statistics makes it less compelling.

10:10 am: Dark Matter Search at underground, Hyun Su Lee

This is a talk on KIMS.  We had one at CosPA, but not this one.  The most salient feature of KIMS is that it uses NaI, so can directly check DAMA's long-standing claim.  Previous run using CsI crystal detector already sufficient to exclude the DAMA signal in terms of scattering off Iodine in model-independent way.  (Of course, that was the more excluded of the two main DAMA explanations.)

Technical details on the efforts put into making large, pure crystals, efficient shielding and high-sensitivity photomultiplier tubes.  Sounds impressive but I'm not really able to comment.  Main radioactive backgrounds from potassium and lead; matter of purity.  Ongoing efforts.  Also significant background contribution from external sources.  Use liquid scintillator as veto, effective.

Goal is 3 year data run with 200 kg detector.  If no signal, will unambiguously exclude DAMA.  Aim to start taking data in May 2016.

More generally, exclusions from other experiments mean most people outside DAMA don't believe it.  So KIMS also aiming for highest sensitivity at low masses, below 10 GeV.  Main challenge looks to be from SuperCDMS.  Will use different detector, CaMoO4 current frontrunner.  6 to 10 year timeline (for what, exactly?)

Discrimination between nuclear/electron recoils?  Decay time of scintillation light.
Test of DAMA observation?  Annual modulation observation is robust, can you really challenge that?  Or just the WIMP interpretation?  Modulation could be some environmental systematic, that can be tested.

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