Searching for a twist in neutron spin axis, physicists find nothing—and that's something

March 7, 2013
IU physicists Mike Snow and H. Yan conducted there experiment at the National Institute of Standards and Technology Center for Neutron Research, which ranks among the best research centers of its type in the world. Delivered via beamlines to 29 major analytical instruments—some without parallel in the U.S.—its neutron probes support the research of more than 2,000 scientists and students each year.

( —Besides understanding how much dark matter and dark energy there is—about 95 percent of the universe—scientists also want to know more about what dark matter and dark energy are not, as opposed to what they are. Indiana University's Mike Snow, a nuclear physicist who specializes in precision measurements using low energy neutrons, now has another "what they are not" to add to the list.

In new research published last week in Physical Review Letters, the professor in the IU Bloomington College of Arts and Sciences' Department of Physics reports that the most sensitive test ever—a new upper bound—conducted to identify a new force acting on neutrons as evidenced by a corkscrew motion of the neutron spin axis uncovered no such result. The piece of research also garnered Snow the journal's "Editor's Suggestion" selection, intended to highlight scientific papers which employ ideas from different subfields of physics.

"Despite improving on the sensitivity of previous searches by more than seven orders of magnitude, we saw nothing," Snow said. "That's OK though. Even seeing nothing still helps in eliminating possibilities for new forces. "

Snow and co-author H. Yan, a at IU working with Snow at the Center for the Exploration of Energy and Matter, analyzed data from this IU-led experiment which sent intense beams of low energy, spinning neutrons through one meter of to search for any interaction between the neutron and the helium atoms which could cause a twist of the spin axis. Of the four known forces of nature, three of them—gravity, electromagnetism and the —cannot twist the spin, and the fourth—the —was known to give a small effect in the regime where Snow and Yan were searching.

Snow said more sensitive searches beyond the new upper bound reported in the paper could be performed using neutron spin rotation measurements in heavy nuclei or through analysis of other experiments conducted using delicate measurements with spinning neutrons.

Slow neutron spin rotation is a very sensitive technique used to search for possible exotic long-range neutron interactions which violate parity, or the assumption that nature behaves identically when left and right are reversed. In parity, like interactions whose spatial configurations are switched, as if seen in a mirror, ought to be indistinguishable, but weak interactions allow for parity violations.

The experiment was conducted using the NG-6 beam line in the National Institute of Standards and Technology's Center for Neutron Research in Gaithersburg, Md. Funding for the research that produced the new paper, "New Limit on Possible Long-Range Parity-Odd Interactions of the Neutron from Neutron-Spin Rotation in Liquid 4He," came from the U.S. Department of Energy and the National Science Foundation.

Explore further: Beam line 13 fuels discovery fever for fundamental physicists

Related Stories

Neutrons escaping to a parallel world?

June 15, 2012

In a paper recently published in European Physical Journal C, researchers hypothesised the existence of mirror particles to explain the anomalous loss of neutrons observed experimentally. The existence of such mirror matter ...

New detector can 'see' single neutrons over broad range

March 10, 2008

Researchers at the National Institute of Standards and Technology (NIST) and the University of Maryland have developed a new optical method that can detect individual neutrons and record them over a range of intensities at ...

Recommended for you

Physicists show ion pairs perform enhanced 'spooky action'

March 28, 2017

Adding to strong recent demonstrations that particles of light perform what Einstein called "spooky action at a distance," in which two separated objects can have a connection that exceeds everyday experience, physicists ...

New method heats up ultrasonic approach to treating tumors

March 28, 2017

High-intensity focused ultrasound (HIFU) is a breakthrough therapeutic technique used to treat tumors. The principle of this noninvasive, targeted treatment is much like that of focusing sunlight through a lens, using an ...

Physics can predict wealth inequality

March 28, 2017

The 2016 election year highlighted the growing problem of wealth inequality and finding ways to help the people who are falling behind. This human urge of compassion isn't new, but the big question that remains to be addressed ...


Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (12) Mar 07, 2013
Somebody with the funds model the DM/DE problem as an unknown, massive particle with no charge.

It should be modeled as attracting and being attracted to ordinary matter, but repelling itself. Effectively, it produces "gravity" when interacting with ordinary matter, but produces "anti-gravity" when interacting with other particles of its own kind.

I was thinking it should probably be something like a Neutron or a Neutrino, except for the exotic "psuedo-gravitational" properties.
3.5 / 5 (13) Mar 07, 2013
When I was sitten on the toilet box dis mornin I thougths dat particularoids that makes anti-gravitations is kinda like the ones that makes me poop fast, on account of the gravity bee in reversed to whats makes me get cheesed up, so anti-gravity is like beans and gravity mostly like cheese.

Now I don't know the quantum number for cheese, but lettuce say it's 4, and on account of it being like gravity that makes the quantum number for beans to beez -4, so if you eats equal amounts you should be good to go.

And that goes to show what my paw done said is right causen if he was wrong then something or other about a whoopen upside yer head, and then no quantum of flushen is gonna clear the bowl.

Thank you for your attention.
1 / 5 (13) Mar 07, 2013
…. Of the four known forces of nature, three of them—gravity, electromagnetism and the strong interaction—cannot twist the spin, and the fourth—the weak interaction—was known to give a small effect in the regime where Snow and Yan were searching.

It is interesting to note that even nowadays we have the theories which could make some prediction with all the four forces, but we still could not understand they work! Knowing their physical mechanism (as below) may help to solve the problem.
5 / 5 (6) Mar 07, 2013
@Lurker if it produces anti gravity when clump near itself why does it clump together into clouds? It seems it would dispearse itself if it was anti attractive to itself
3.4 / 5 (5) Mar 07, 2013
Wow, this must be the first time on PhysOrg that all 3 of the first comments show great insight and understanding. :-)

On par with mine. :-) Were they testing for a hypothetical 'extra' force, beyond the standard model?
1 / 5 (6) Mar 07, 2013
@Lurker if it produces anti gravity when clump near itself why does it clump together into clouds? It seems it would dispearse itself if it was anti attractive to itself

In my hypothesis because ordinary matter would be attracted to these particles and vice versa, there would be certain accumulations of the DM stuff in everything, even the matter we think is entirely ordinary might actually be several percent "Dark".

If you imagine a cloud of the stuff, it would all want to push away from itself (attempt to explain Dark Energy,) but because it's all pulling on the ordinary matter, and the ordinary matter pulls back, some of the DM would clump up with ordinary matter in galaxies.

There would be "random" filaments (sheets, halos, and other structures) of these particles, invisible, between all galaxies as the DM particles push away from one another, and these forces would tend to "pile up" the particles in some locations, even though they normally repel themselves...
1 / 5 (6) Mar 07, 2013
If you want to try to understand the mechanics of a stable system involving such particles, you might start with a 3-body that uses 2 of such theoretical particles and one ordinary matter particle. in this case, the stable configuration is for the one ordinary matter particle to be in the center, and the two dark particles will each be on opposite sides, as they repel one another, but they are attracted to the ordinary matter particle.

Thus a hypothetical ordinary matter particle outside that 3-body system would "feel" the "mass" of 3 particles, even though only one of them is ordinary matter.

larger systems are hard to model in your head or on a piece of paper, but it can be done with a bit of a sketch for an aid, and then you can imagine small "galaxy" models and how they interact.

I believe the DM particles, in such a model, should tend to "pile up" a bit in the inter-galactic space, as the concentrations of the same material inside the galaxy pushes these outward to equilibrium.
1 / 5 (6) Mar 07, 2013
The above scenario MAY explain why the proposed "Dark Matter Halo" structure remains stable throughout galactic time scales, instead of collapsing, like it would if DM behaved entirely like ordinary matter...

So in this model, the DM can't undergo a total gravitational collapse, because it's self-repelling, and indeed, the self-repelling aspect actually helps stabilize the galactic halo and the spiral bands, or at least I think it would work.

The size of the attractions and repulsion need not be symmetric, which is another variable that is very hard to model in your head or on paper, but could be fine tuned in a computer model to try to achieve the best results. Remember, asymmetry exists even with ordinary matter.

Modeling this properly on a galactic scale would require immense computing power probably beyond existing super computers.
not rated yet Mar 07, 2013
Very interesting but I don't understand some of it (my ignorance). I assume that helium and neutrons were use because of there degree of inertness but I willing to accept that I'm am being too simplistic. I would like to understand more about the 'twist' on the spin and then maybe I could get to grips with the comments by Lurker2358. As it is I am not sure that the particle repulsion qualifies as 'anitgravity' but then I am thinking in terms of particle charge which might not be appropriate. Can someone offer some help?
1 / 5 (2) Mar 08, 2013
But if helium is a balanced atom, in contrast to atoms such as hydrogen,the spin would be less likely to occur.
Whydening Gyre
1 / 5 (4) Mar 08, 2013
Larry D,
See the article on seeing complex systems.
not rated yet Mar 09, 2013
Whydening Gyre, thanks. Inference diagram C looks very similar to something drawn on the b/board by my tech college teacher way back in the 70's but I haven't got my old notes (flood damage in Thailand). If memory serves it was about the energy difference between ADP & ATP and 'path cycles' in reactions.
Would have to think hard how it relates the this article.
not rated yet Mar 11, 2013
@LarryD: I'm not sure that Lurker is making much sense, full stop, with his 'explanation' here. It also sounds as if he is confusing gravity with magnetism, with the way he seems to be describing his scenario. (@Lurker: Magnetism: like charges repel; opposite charges attract. Gravity, ve is attractive (that is the kind that we know and love); -ve gravity would repel. As such, when two objects are of ve gravity, they attract each other. If they were -ve, they would be doing their darndest to push each other away. -ve gravity may be hypothetical, but is not impossible.) Regards, DH66

PS For those who are unfamiliar with the shorthand notation used here:
-ve = negative, ve = positive
not rated yet Mar 11, 2013
Where 've' is on its own, there is a 'plus' sign missing. The editor kept removing it and wouldn't let me try to put it back in. Next time, I will try putting a number,etc in front and see what happens. Regards, DH66

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.