Particle detector finds hints of dark matter in space | Hacker News Reader

Particle detector finds hints of dark matter in space

newsoffice.mit.edu

84 points2510c39011c515 comments

From the article: "The new AMS results may ultimately help scientists narrow in on the origin and features of dark matter"

So yet another link-bait headline.

Maybe, but I would wait to hear from a physicist. When I was a student, one of the most important papers one year was about a dark matter (WIMP) detector that failed to find anything, thus "trimming the parameter space" for what the particles might look like. If this is a genuine clue, it's probably very exciting.

> Nearly 85 percent of the universe is made of dark matter

It's a bit ambiguous too: 85% is the proportion of the total mass made up of dark matter. Normally we'd say that 26% of the universe is dark matter, 5% is baryonic matter and the rest is dark energy.

This is a surprisingly Vague article for MIT press. I understand its just the press release and not the white paper but could there not be a little more detail? Perhaps Interns are writing it could it not have a bit more content be it data, opinion from scientist, the leading theory in the area.

Its exciting stuff and not a dead end article, so little progress has been made in this field and the unknowns are so fast that eve a glimpse is interesting.

Hmm... whenever I see this [articles about dark matter or dark energy] nowadays I think back to something Dr. Neil deGrasse Tyson said on the subject along the lines of "We're calling it Dark Matter or Dark Energy because can we measure it (or rather the fact that we're missing a huge chunk of it), but that doesn't mean it's 'dark' or even 'matter' or even one single thing."

It's cool to hear about breakthroughs on the subject but as someone else said, at this point this article feels more like link-bait than anything concrete.

Maybe it's just some folks who are incredibly stoked wanting to share before they have their ducks-in-row. So I'm not trying to say it's intentional.

I'm just hungry for new information, and excited about it, so when it's not all there I'm disappointed. Nerd problems, haha.

> but that doesn't mean it's 'dark' or even 'matter' or even one single thing

An important addendum to this is that it really does look an awful lot like matter that happens to be dark...or to be more specific, electromagnetically inert.

That's not to say it has to be, of course we don't know for sure, but I see a lot of people on the internet apparently quite certain it's not matter at all - often for not very good reasons, or via arguments that aren't remotely that strong.

I think as the earlier comment pointed out this really was about the additional data from AMS that helps refine and/or add confidence to the possible theories - some of which are dark matter related and some which are not. Unfortunately, the article title was blatantly incorrect.

CERN press release: http://press.web.cern.ch/press-releases/2014/09/latest-measu...

The PRLs: http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113...

http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113...

Physics News: http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.113....

Very strange to see this article posted now. This news from the AMS is over a year old. And clearly, there is considerable debate whether the positron excess is from dark matter particle annihilation or from nearby pulsars. There are many papers on the subject - here is just one example that explains some of the issues - http://arxiv.org/pdf/1304.1840.pdf (PS - I am an astronomy graduate student).

This article concerns a new data release from AMS -- 70% more statistics and a much wider energy range.

In the past, they've been careful to avoid saying whether or not the positron fraction flattens/rolls over at higher energy. These papers now give support to that conclusion, at moderate confidence levels.

Excellent callout and my mistake missing the point on the wider energy range and the rollover. Thank you! The additional data will help the determination of dark matter vs. pulsars as the positron source.

"To determine if the observed new phenomenon is from dark matter or from astrophysical sources such as pulsars, AMS is now[sic] making measurements to determine the rate of decrease at which the positron fraction falls beyond the turning point (item 5), as well as to determine the antiproton fraction (the ratio of antiprotons to protons plus anti-protons). These will be reported in future publications."

Compatible with a dark matter particle on the order of 1 TeV - now just turn LHC back on, find a matching supersymmetric particle and give a welcome party for the 5th dimension.

What would the 5th dimension be?

I am not a physicist, therefore this may be complete nonsense. Anyway, as far as I understand it, supersymmetry (all models or only some, I have no idea) adds a new dimension (with non-commutative coordinates?) and when a particle moves along this dimension it turns from a fermion into a boson or vice versa. You take a electron and move it a bit along this dimension and it turns into a photon, you move it back and it becomes an electron again. (Electron and photon are not superpartners, the electron would actually become a selectron, the photon a photino with the photino being one of the candidates for dark matter.)

I've taken courses on supersymmetry and string theory and this is mostly incorrect. The details are fairly complicated, but the general idea is that there are a few essentially unique supersymmetric theories in 10 dimensions that can be "compactified" to a vast variety of effective theories in four dimensions. From a purely phenomenological point of view that can be ignored however and people have come up with various supersymmetric extensions of the standard model of particle physics in four dimensions going by names like MSSM (minimal supersymmetric standard model), basically introducing aditional superpartners of known particles by hand (like the selectron and photino you mentioned) and "completing" the model by computing the deficit for it to be supersymmetric. Those completions are not unique and can be distinguished by the energy scales they introduce new particles at. One major motivation is to constrain the running of the Higgs mass, which sets a natural upper bound for the expected masses of supersymmetric particles to be found. Those bounds have already almost been excluded by the current data, which is scary or exiting depending on who you ask.

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