Of Particular Significance

A Few Items of Interest

POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON 05/17/2013

I was sent or came across a few interesting links that relate to things covered on this blog and/or of general scientific interest.

It was announced yesterday that the European Physical Society 2013 High Energy Physics Prize was awarded to the collaboration of experimental physicists that operate the ATLAS and CMS experiments that discovered a type of Higgs particle, with special mention to Michel Della Negra, Peter Jenni, and Tejinder Virdee, for their pioneering role in the development of ATLAS and CMS.  Jenni and Virdee are both at the LHCP conference in Barcelona, which I’m also attending, and it has been a great pleasure for all of us here to be able to congratulate them in person .

One thing that came up a couple of times regarding weather forecasting (for instance, in forecasting the path of Hurricane Sandy) is that the European weather forecasters are doing a much better job of predicting storms a week in advance than U.S. forecasters are.  And I was surprised to learn that one of the the main reasons is simple: U.S. forecasters have less computing power than their European counterparts, which sounds (and is) ridiculous.  The new director of the U.S. National Weather Service, Louis Uccellini, has been successful in his goal of improving this situation, as reported here[Thanks to two readers for pointing me to this article.]

One of the possible interpretations of the new class of high-energy neutrinos reported by IceCube (see yesterday’s post) is that they come from the slow decay of a small fraction of the universe’s dark matter particles, assuming those particles have a mass of a couple of million GeV/c². [That’s much heavier than the types of dark matter particles that most people are currently looking for, in searches that I discussed in a recent article.]  I didn’t immediately mention this possibility (which is rather obvious to an expert) because I wanted a couple of days to think about it before generating a stampede or press articles.  But, not surprisingly, people who were paying more attention to what IceCube has been up to had recently written a paper on this subject[Here’s an older, related paper, but at much lower energy; maybe there are other similar papers that I don’t know about?]  At the time these authors wrote this paper, only the two highest energy neutrinos — which have energies that, within the uncertainties of the measurements, might be equal (see Figure 2 of yesterday’s post) — were publicly known.  In their paper, they predicted that (just as any expert would guess) in addition to a spike of neutrinos, all at about 1.1 million GeV, one would also find a population of lower-energy neutrinos, similar to those new neutrinos that IceCube has just announced. So yes, among many possibilities, it appears that it is possible that the new neutrinos are from decaying dark matter.  If more data reveals that there really is a spike of neutrinos with energy around 1.1 million GeV, and the currently-observed gap between the million-GeV neutrinos and the lower-energy ones barely fills in at all, then this will be extremely strong evidence in favor of this idea… though it will be another few years before the evidence could become convincing.  Conversely, if IceCube observes any neutrinos near but significantly above 1.1 million GeV, that would show there isn’t really a spike, disfavoring this particular version of the idea.

Regarding yesterday’s post, it was pointed out to me that when I wrote “The only previous example of neutrinos being used in astrophysics occurred with the discovery of neutrinos from the relatively nearby supernova, visible with the naked eye, that occurred in 1987,” I should also have noted that neutrinos were and are used to understand the interior of the sun (and vice versa).  And you could even perhaps say that atmospheric neutrinos have been used to understand cosmic rays (and vice versa.)

In sad news, in the “all-good-things-must-come-to-an-end” category, the Kepler spacecraft, which has brought us an unprecedented slew of discoveries of planets orbiting other stars, may have reached the end of the line (see for example here), at least as far as its main goals.  It’s been known for some time that its ability to orient itself precisely was in increasing peril, and it appears that it has now been lost.  Though this has occurred earlier than hoped, Kepler survived longer than its core mission was scheduled to do, and its pioneering achievements, in convincing scientists that small rocky planets not unlike our own are very common, will remain in the history books forever.  Simultaneous congratulations and condolences to the Kepler team, and good luck in getting as much as possible out of a more limited Kepler.

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19 Responses

  1. It is good news that the weather service is improving its modeling capacity.
    It is great news that the focus is not just on the computer hardware, but equally on the physics of weather. The European models perform better not just because they have more computing power, but also because they have a more correct model of how weather behaves. That modeling gap is apparently now getting attention, fortunately.

  2. Dear Professor Strassler,

    I wonder if you could direct me to a credible discussion of quantum computation. I know that it is not your specialist field but I imagine the recent news reports could benefit from a similar deflationary approach to that provided by your website in the particle physics arena.

    Regards, Alex

    1. You might try this MIT professor’s blog (recently tenured) http://www.scottaaronson.com/blog/ . It is not so easy to read, but it gives a more cautious view of the recent quantum computer hype. My own impression is that there’s something real happening in this story (which is indeed why Google is willing to shell out some money to explore it) but it’s a much, much smaller and focused step than the media suggests.

    1. I can’t figure out what you have in mind. What is ricocheting, and what is bouncing? To do physics, you have to be a lot more precise… the details matter a lot.

      1. i know, and i’m sorry.

        if i read correctly, it seems they’d like to determine the source of the initial reaction that set the neutrino in motion. who wouldn’t? could the spike of energy they are seeing be not from the initial reaction outward, but from a collision after the original ‘burst.’ would their neutrality allow them to ‘bounce’ off of things in their path rather than be absorbed by nearby gravitational fields?

        think shrapnel pieces bouncing off a truck after the initial explosion. the blast sends them flying in one path, and over time distance, speed, and energy decrease. but if they hit something in that path, the pieces deflect and change course. after the collision, the speed and energy that was declining after the initial blast, spikes for just a moment. it ‘gains’ energy from the collision. like billiard balls after the break that spin and collide making new sources of energy.

        i understand my questions might be frustrating, and I don’t mean to pester you with their elementary nature; but you explain things well, so it is tempting to ask. 🙂

        1. Just to pile on, maybe two black holes orbiting and something falls into one of them, it flashes, and the radiation is deflected in strange ways by hole number two.

        2. Hmm. Even your example contains many physics misconceptions and errors. So I don’t know where to start exactly.
          It’s not that your questions are frustrating, but there are so many things wrong here that it’s not clear which ones to try to fix.

          Shrapnel: speed and energy of shrapnel do not decrease after an explosion, except (a) when the shrapnel hits something, or (b) due to air resistance, i.e. friction due to air molecules that the shrapnel has to push out of the way.
          Shrapnel is heavy and thick; air that it passes through provides gradual friction; if the shrapnel hits something else that is heavy and thick it will bounce, but (unless the thing it hits is itself moving) the collision will decrease the energy of the shrapnel, or leave it the same, but will not increase it. Your shrapnel “story” simply is wrong.

          But moreover, neutrinos interact with matter very differently from the way shrapnel does. Neutrinos are tiny and light-weight; any material that a neutrino passes through involves objects (electrons, neutrons, protons) that are very heavy by comparison. And neutrinos interact so weakly they will rarely hit anything; it’s as though the material is very diffuse. So this is more like tiny, tiny pieces of shrapnel passing through a parking lot that has no air and has a few trucks scattered around in it. Most of the shrapnel will hit nothing. The shrapnel that does hit something will lose energy. In short; neutrinos passing through matter will not generally gain energy — your intuition for how things work was wrong, and this has misled you.

          Even if the trucks in the parking lot are actually driving around, this generally won’t help. Only trucks driving faster than the shrapnel is moving are likely to give the shrapnel any extra energy.

          So except in extraordinary circumstances, collisions with matter are generally going to lead to lower-energy neutrinos, not higher-energy ones. The matter will have to be moving at nearly the speed of light and be very dense for there to be any effect on neutrinos. Instead, it will be much more efficient to create high-energy neutrinos in high-energy collisions of ordinary matter with other ordinary matter (electrons, protons, neutrons), rather than have the neutrinos themselves participate in bounces or ricochets off ordinary matter, which generally will cause them to lose energy.

          In short, interactions of neutrinos with ordinary matter are a very inefficient way to make high-energy neutrinos. It’s much more efficient to create high-energy ordinary matter, and then to create neutrinos in high-energy interactions of matter with matter

  3. Marshall Eubanks mentioned that the Earth is opaque to neutrinos this energetic. Rather than PeV dark matter, wouldn’t the most likely source just be some random astrophysical fireball that just happens to be dense enough that >PeV neutrinos don’t get out?

    1. Well, it’s hard to say what is more or less “likely”; decaying dark matter is more of a long shot in some sense, but we also don’t know of an appropriate astrophysical fireball yet. What you suggest is probably on the list of possibilities too; I don’t know anything wrong with it. Of course that option would not lead to a spike in energy, and one would expect a slow fall-off rather than a sharp one, since each individual fireball will have a different neutrino energy spectrum and a different amount of matter between the production location and earth. (Marshall Eubanks wasn’t quite right; the Earth isn’t quite opaque at these energies, though some reasonable fraction of the neutrinos at these energies won’t get through.) At this point we don’t have nearly enough data to tell the difference… so we’ll have to see how this data evolves. Keep in mind though that it took two years to get the events we have; it may take five to ten years before we really can start to distinguish between the various options.

        1. There’s certainly a chance it will look very weird, but it’s also possible, with such low statistics, that it will look less weird even if the dark-matter idea is right. Even if the spike is there, we might have 6 events in the spike and we might still only have 2, come 2015.

      1. “Of course that option would not lead to a spike in energy, and one would expect a slow fall-off rather than a sharp one, since each individual fireball will have a different neutrino energy spectrum and a different amount of matter between the production location and earth.”

        I thought a bit about this. There are loads of processes that only happen at a fixed pressure, density or energy. The original neutrino energy spectrum may be fairly constant. And for large enough volumes (at roughly constant density?) where this hypothetical process happens, the average “filtering” before a neutrino escapes would make the cutoff pretty sharp, no?

        1. This seems unlikely to me for several reasons. Typically, such a cutoff would have a tail that falls off rather slowly, like 1/Energy^2 or so, just due to the fact that the original neutrino spectrum would have a tail, and the filter would also have a tail. A spike due to slow dark matter decay would have a much more dramatic cutoff; the only tail would come from the dark matter’s motion, but particles with a mass of 1 million GeV/c^2 will be moving well below the speed of light, with a Boltzmann distribution, which falls off exponentially.

          But a lot of data would be needed to tell the difference. We will have to wait a few years.

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