Friday, 27 November 2015

Friday wrap-up: XMASS again, Fermi...

Feels like a lot of links and not much thinks this week, but we have been madly working to finish a paper before I go home for Christmas in a couple of weeks. I think we'll get there, but in the mean time...

  • XMASS placed on the arXiv the annual modulation analysis we first saw presented at TAUP a couple of months back, showing some preference for negative annual modulation (opposite to the DAMA/LIBRA claim). They write, "The result of a simple modulation analysis, without assuming any specific dark matter model, showed a slight negative amplitude. As the p-values are 6.1 or 17% in our two independent analyses, these results are consistent with fluctuations." However, staring at their Figure 3, I somehow just can't seem to believe it's consistent with fluctuations...


    Sure, the fits in each bin are within 2σ of zero modulation, but there are a very large number of them below 3 keVee going the same way. If indeed the bins are largely independent (larger than resolution) and there is no correlated (annually modulating?) systematic, then at least naively I would expect that to be very improbable. So, an honest question, why is this not reflected in the p-value? An interesting sentence from the paper is, "Note that the energy bin width in Fig. 3 is one fifth of DAMA/LIBRA’s so that our limits would even get stricter with DAMA/LIBRA’s bin width." Is this suggesting that the result becomes more significant when all of those negative bins are collected into a larger bin? Comments are welcome.

    This is yet another annual modulation measurement with an intriguing result to add to the pile, and perhaps we're seeing a conservative downplaying, especially given the history of such measurements.
  • There's a nice article at Scientific American on Fermi's recent contribution to the galactic centre excess saga. The short story is that they confirm the excess above known backgrounds, which when fit with an diffuse NFW source is in broad agreement with previous works, as shown below (one notes the significant uncertainty in the tail as evidenced by the fits assuming different models of the background).


    We're left now with an official analysis which confirms what we have heard for a while now: that there is definitely something unknown there. So, what is it? The leading standard astrophysical explanation is some population of unresolved point sources (such as millisecond pulsars), which Slatyer now claims are favoured by the data. Still, the dark matter hypothesis is alive, albeit grappling with limits from dwarf spheroidals. And perhaps it can be settled soon; one thing I learned from the SA article is that the pulsar hypothesis might be probed in the near future:

    The good news is that if pulsars are behind the excess, more powerful, telescopes in the future should be able to spot the too-faint spinning stars directly. Pulsars would be prime targets for next-generation radio telescopes... “Should we fail to find them in the next five or ten years, a dark matter explanation becomes more likely again,” Weniger says. “This is pretty much a win–win situation. But we have to be patient.”
  • Tommaso Dorigo has found a publisher for his book on the Tevatron (and in particular CDF), "Anomaly! - Scientific Discoveries and the Quest for the Unknown." Should be out end of 2016; very much looking forward to it.
  • Links without thinks...
    • Starts With a Bang: "Strange But True: Dark Matter Grows 'Hair' Around Stars And Planets."
    • SLAC: "Q&A: SLAC Theorist Lance Dixon Explains Quantum Gravity."
    • New Yorker: "The Space Doctor's Big Idea," the Special Theory of Relativity explained in the 1000 most used words in the English language, by xkcd artist Randall Munroe, who also has a related book out. 
    • New Yorker: "The Doomsday Invention," a long read on artificial intelligence; do yourself a favour and get your hands on Nick Bostrom's very interesting book!
    • Nature: "Einstein was no lone genius."
    • Nature: "The quantum source of space-time."
    • Preposterous Universe: "Thanksgiving [for Riemannian Geometry]"
    • Wired: "Physicists Are Desperate to Be Wrong About the Higgs Boson."

Saturday, 14 November 2015

Friday wrap-up: 4/fb, Fermi...

Another two week break, but plenty happened this week!

  • The LHC has finished collecting proton-proton collision data for the year. ATLAS ended up with ~4.0/fb, and CMS with ~3.6/fb.
  • Fermi Collaboration have released their own analysis of the galactic centre excess. I have not had time to read the paper in detail (not that I could comment with much authority even if I had), but it is interesting that they seem to see a residual excess after subtracting known sources, which can be somewhat accounted for by a peaking template (dark matter?). Perhaps we will know more by next week...


    There's a layperson article from The Economist about it which says, "There are still a few die-hards who do not believe in hooperons"! Well, call me a die-hard.
  • The XENON1T direct detection experiment at Gran Sasso was inaugurated on Wednesday. Read the press release here; they write, "Once fully operational, XENON1T will be the most sensitive dark matter experiment in the world. The detector installation has been completed just a few days ago and the first tests of its performance have already been started. The first science results are expected early 2016, as only one week of good data is sufficient to yet again take the lead in the field." And some cool pictures:


  • The $3mil Breakthrough Prize in Fundamental Physics was awarded for the experiments which established neutrino oscillations (the decision was made before the Nobel Prizes were known). The prize was shared equally among the Daya Bay, K2K/T2K, KamLAND, SNO, and Super K collaborations, with two-thirds of each share to the leaders and one-third to the remaining collaboration members: 1370 physicists in all! It is nice to see all of these scientists recognised.

    The Symposium and Panel Discussion are on YouTube. The Fundamental Physics talks are on the future of particle physics and feature Nima Arkani-Hamed, Lawrence Hall, Beate Heinemann, Gabriel Orebi Gann, and Tom Shutt.
  • Worth reading are two articles, one a piece by Ed Witten, "What every physicist should know about string theory," and another an interview with Abhay Ashtekar broken into four parts: 1. Getting started on gravity and cosmology; 2. Learning from Chandra; 3. Challenges in loop quantum gravity; 4. Arrogance in string theory.

    Of course these are bat-signals for Woit and/or Motl, so click their names to read their reactions/reflections too.
  • The people's choice voting is open for photographs from the InterActions Physics Photowalk, featuring shots of CERN, DESY, FermiLab, INFN, KEK, SLAC, SUPL, and TRIUMF.
  • Links without thinks:
    • There's some buzz about a quasipolynomial time algorithm for the graph isomorphism problem. See this blog for a (research-level) detailed description. Else for the layperson see Science, New Scientist, or Motherboard.
    • Nautilus: "Will Quantum Mechanics Swallow Relativity? The contest between gravity and quantum physics takes a new turn."
    • Dan Waddell via Medium: "Saving Tim Hunt," a long read on the Tim Hunt story.
    • Thesis Whisperer: "Academic assholes and the circle of niceness."
    • Nature: "Networking: Hello, stranger," on conference etiquette and career development.
    • Existential Comics: "Trolley Madness."
  • In audio/video media:
    • 2016 Breakthrough Prize Symposium in Fundamental Physics, with: 1. Nima Arkani-Hamed - Motivations for 100km Circular Colliders; 2. Lawrence Hall - New Searches for Dark Matter in Particle Collisions; 3. Beate Heinemann - The LHC and beyond: what can colliders teach us?; 4. Gabriel Orebi Gann - Unravelling the Secrets of the Universe with Neutrinos; 5. Tom Shutt - The Hunt for Dark Matter. [1:36:49]
    • CBS 60 Minutes: "The Collider," on the LHC. [11:54]
    • Catalyst: "Einstein's Extraordinary Universe", featuring visits to LHC, Gran Sasso, and LIGO. [28:17]
    • WHYY RadioTimes: with Lisa Randall on dark matter and the dinosaurs. [48:57]
    • MinutePhysics: "How to go to space," Thing Explainer edition. [2:57]
    • Numberphile: "The Uncracked Problem with 33". [8:28]