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Science

Do Neutrinos Have Mass? 50

Posted by michael from the but-were-afraid-to-ask dept.
amyjigglypuff writes "MINOS, a joint project between Fermi National Accelerator Laboratory and the University of Minnesota, is going to attempt to uncover the mysteries of the neutrino. Scientists plan to study the mass of neutrinos, whether they are stable or oscillate, and their electromagnetic structure. If they are found to have mass, it could prove that neutrinos are responsible for the cosmic "dark matter" that has baffled scientists for decades. Here is a link for scientists and a summary for the general public."
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Do Neutrinos Have Mass? More

Do Neutrinos Have Mass?

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  • yes, they have mass. (Score:3, Funny)

    by Unknown Poltroon ( 31628 ) <unknown_poltroon1sp@myahoo.com> on Friday April 25, 2003 @09:20AM (#5807923)
    but only the really heavy ones.

  • Missing matter (Score:4, Funny)

    by n1ywb ( 555767 ) on Friday April 25, 2003 @09:25AM (#5807957) Homepage Journal
    I thought the missing matter was in all the packing materials for all the equipment the scientists kept buying to try and find the missing matter.
    • Heh, that reminds me of box of computer stuff we got in recently at work. The thing weighed at least 150 pounds, but somehow the UPS shipping reciept had "40 pounds" on it. I think the scientists should definitely look into this.

  • Before someone else says it... (Score:3, Funny)

    by Spamalamadingdong ( 323207 ) on Friday April 25, 2003 @09:31AM (#5808009) Homepage Journal
    Neutrinos have mass? I didn't even know they were Catholic!

  • Wha? (Score:2, Informative)

    by Anonymous Coward
    Yes, Neutrinos have mass [aps.org]. This is old news dude.
    • Okay, so according to that article, one type of neutrino is an electron.

      That doesn't make sense, does it? I thought that the definition of neutrinos were that they had a neutral charge.
    • yes, the european accelerators had already beaten the Fermilab (U.S.A.) folks to the punch on this question, while the U.S.A. was still building this very expensive thing (at two locations in Minnesota and Illinois). But we can't let the U.S. taxpayers feel they've been had, now can we?

      BSD may not really be dying, but Fermilab sure is.

  • WIMPs win (Score:3, Informative)

    by etherlad ( 410990 ) <ianwatson@NosPam.gmail.com> on Friday April 25, 2003 @09:52AM (#5808165) Homepage
    Neutrinos, I believe, count as WIMPs (Weakly Interacting Massive Particles), the current prime candidate for just what makes up dark matter.

    The other theory is that of MACHOs (Massive Compact Halo Objects) - large chunks of presumably baryonic material in a large halo orbiting the Milky Way.

    The two theories are not exclusive, mind.
    • Also, I wonder what nerd came up with "wimps" and "machos" as acronyms. They're probably overjoyed to find out that the wimps are the winners. ;)
    • If neutrinos were the missing mass, wouldn't we be detecting far more of them? Either the mass would be big enough to have shown up earlier, or the sheer number necessary to account for the missing 90% of matter would make them more likely to hit our detectors.

      I thought that the current theories of the big bang set a limit on how many neutrinos would have been produced. If there were lots more neutrinos then the ratio of hydrogen to helium would be different, something like that.

      This is clearly not my

    • I'm doing a study into the intelligence of slashdot readers vs k5 readers for my Phd and I was wondering if you could all have a go at answering this question for me to help with my thesis conclusions

      Imagine you have 2 waves, the sources of which are infinitely far apart. Now the 2 waves are 180o out of phase and so completely destructively interfere. My question is thus. Where does the energy go?

      • If the sources are infinitely far apart, the waves never meet to interfere. Next question?

        And what do you do about doubled /. and K5 readers. :-)
      • They can't be 180 degrees out of phase everywhere and at all times. For example, consider the portions of the wave directly between the two sources. They propagate toward each other and thus you get a standing wave at twice the amplitude of either one (assuming they each have equal amplitudes). In fact, the only place where you could get perfectly destructive interference is directly behind a source, as seen from the point of view of the other source.

    • Re:WIMPs win (Score:5, Informative)

      by Peter T Ermit ( 577444 ) on Friday April 25, 2003 @11:37AM (#5809029)
      Neutrinos are weakly interacting and they've got mass, but they're not a real candidate for exotic dark matter. (There are two types of dark matter: baryonic, which is about 4% of the "stuff" in the universe and exotic, which is about 23% of the stuff. [The remainder is dark energy.])

      Because of oscillation measurements of neutrinos, of CMB fluctuations, and of galaxy clusters, scientists have concluded that neutrinos make up only about 0.5% of the stuff in the universe. This is as much matter as is in the visible stars and galaxies, but it's not enough to account for exotic dark matter.

      (MACHOs are thought to be baryonic dark matter.)

      • Re:WIMPs win (Score:3, Insightful)

        by bcrowell ( 177657 )
        Just to amplify on the parent post, there are a lot of errors in the headline:

        If they are found to have mass
        Neutrinos have already been proved to oscillate between flavors, and that means they have mass. This is no longer an open question. (Technically all it shows is that there's a difference in mass between two flavors, so logically one flavor could still have zero mass.)

        it could prove that neutrinos are responsible for the cosmic "dark matter" that has baffled scientists for decades.
        The parent post

    • Neutrinos, I believe, count as WIMPs (Weakly Interacting Massive Particles), the current prime candidate for just what makes up dark matter.

      Come on, everyone knows that dark matter is the excrement of Nibblonians [fox.com].

  • Some may have mass, and others may not... (Score:5, Informative)

    by kenthorvath ( 225950 ) on Friday April 25, 2003 @09:52AM (#5808171)
    I attended a seminar where one group was attempting to measure neutrino oscillations and found convincing evidence that this happens. In order for neutrinos to oscillate, however, they would have to have some mass. In the model that they proposed, some neutrinos may have mass and some may not. Also, if super symmetry comes into play, you could potentially have some very heavy neutrinos. For some cutting edge theories consult the archives [lanl.gov].

  • Arrrgh! (Score:5, Funny)

    by jwriney ( 16598 ) on Friday April 25, 2003 @10:27AM (#5808469) Homepage
    These Ask Slashdot questions are getting tough. I've got no friggin' idea!

    --riney

  • The LEP results suggested mass (Score:4, Informative)

    by mnmn ( 145599 ) on Friday April 25, 2003 @10:37AM (#5808541) Homepage

    I remember at 117 Gev we had some higgs boson marks, but the results were just beneath the standard deviation. Now we have to wait till 2004 or 2005 till the commecement of the LHC to be sure.

    But the LEP results were close, and many scientists and nonscientists like myself are convinced we have it in that range. At least some neutrinos do have mass.
  • neutrinos have mass

    neutrinos are not dark matter

    scientists remain curious
    • >neutrinos have mass

      >neutrinos are not dark matter

      These 2 statements don't really make sense together... if neutrinos have mass, then they ARE a large component of dark matter. We already know that neutrinos are out there in huge quantities, if they have even a tiny bit of mass it would account for much of the gravity we're seeing from unknown sources (pretty much the definition of dark matter).
      • Not really, the best guess neutrino mass is at least a couple of orders of magnitude smaller than what would be required to explain all the dark matter. So, rather than being a large compinent of dark matter, at best they are a very small component.
  • They've already proven neutrinos have mass [they even had a nightline episode dedicated to it]... and if im not mistaken, scientists have proven it does not make up _all_ of the dark matter.

  • What's really neat about neutrinos (Score:5, Interesting)

    by Mt._Honkey ( 514673 ) on Friday April 25, 2003 @01:22PM (#5810166)
    is that they carry away a significant portion of the energy that stars emit. Something on the order of a few % of the Sun's power is radiated away through neutrinos. Neutron stars cool down because their energy is carried away by neutrinos. It really gets cool in supernovae, because as much as 40% of a supernova's energy is in the form of neutrinos. I believe that this can be detected in theory, but I don't remember if it ever has been.

    Another neat thing is that there may be a 4th neutrino that does not interact via the weak force. Imagine that! It has already been said that a neutino is as close to nothing you can get and still have something, but a neutino that does not weakly interact is virtualy undetectable!

    Cool stuff, if you like physics.


    PIFMA-GASP

    • Re:What's really neat about neutrinos (Score:4, Informative)

      by Christopher Thomas ( 11717 ) on Friday April 25, 2003 @05:33PM (#5812325)
      It really gets cool in supernovae, because as much as 40% of a supernova's energy is in the form of neutrinos. I believe that this can be detected in theory, but I don't remember if it ever has been.

      They have been.

      The neutrino burst from Supernova 1987A was detected and found to coincide with the optical burst to within an hour (an hour before the optical burst, IIRC). This provided a direct demonstration that high-energy neutrinos travel at or extremely close to the speed of light, which in turn placed an upper limit on their mass (a very small value, but neutrino masses measured to date have been very small).

      Another neat thing is that there may be a 4th neutrino that does not interact via the weak force. Imagine that!

      No such neutrino exists, as far as anyone can tell. Neutrinos, leptons, and quarks are grouped into families. The first familiy - the up and down quarks, the electron, and the electron neutrino - are what normal matter is made of (or produces in nuclear reactions, in the case of the neutrino). The other two families contain much more massive particles, and so are only seen in exotic situations (high-energy collisions, and possibly as "strange matter" in neutron stars). The existence of higher-energy quark/lepton families has a measurable effect on lower-energy reactions (as the high energy flavours show up as virtual particles). All measurements to date indicate that there are only three families - the expected effects of higher families have not been seen.

      Perhaps your source was confusing neutrino families with supersymmetric particles, which are strongly hinted to exist and which may qualify as weakly-interacting heavy particle candidates. None that I've heard of would have the properties you describe, however.

      • Re:What's really neat about neutrinos (Score:1, Interesting)

        by Anonymous Coward
        No such neutrino exists, as far as anyone can tell.

        The existence of a sterile neutrino family is strongly suggested by combining the results of the LSND experiment with other [more recent] neutrino data. However it is by no means a certain thing.

        IIRC, one of the goals of (Mini)BooNE is to see if test this specifically.

        I am not a neutrino person myself, but from what I heard at a seminar last week I can tell you that the existence of an additional neutrino family of low mass is still considered quite
      • No such neutrino exists, as far as anyone can tell.

        The theorized neutrino, called the "sterile neutrino" is thought to potentially exist because the way that the mass differences add up for the other 3 neutrinos doesn't work out quite right. In current experiments, we can not detect the masses of neutrinos, only the squares of the differences of the masses between types of neutrinos. IIRC, there is 1 large difference and 2 small differences that can not add up to the first one. For this (and other) re

  • old stuff (Score:3, Informative)

    by g4dget ( 579145 ) on Friday April 25, 2003 @02:17PM (#5810668)
    Check your older Slashdot science stories. Experiments [uci.edu] have already shown that neutrinos oscillate, and that means that they have mass (or we really have to change physics). Also, see here [neutrinooscillation.org].

    However, neutrinos are not sufficient to account for dark matter, and dark matter itself is not sufficient to account for the observed deviations of the shapes of galaxies from what is expected.

  • He mentions a tunnel that the nutrino passes through because it needs a straight-line path. How long is this tunnel? Any idea how much it cost to build?

  • More on neutrino experiments... (Score:5, Informative)

    by apirkle ( 40268 ) on Friday April 25, 2003 @04:31PM (#5811854)
    I've actually been working as an undergrad assistant in a lab at UT Austin that is very active in the MINOS consortium, so it's pretty cool to see the experiment getting some attention.

    There are some neat photos of the detector; the steel scintillator [umn.edu] modules weigh about 5,000 tons (!), and you can see one as it is lifted into place [umn.edu]. The detector uses something like 2000 16 channel photomultiplier tubes [umn.edu] (I don't remember the exact number of tubes) to detect the showers of particles that are created as neutrinos interact with the steel scintillator plates, and the data from those tubes is processed to reconstruct events. Did I mention that the whole thing is in a cavern [umn.edu] about 1/2 mile underground to reduce background noise from cosmic rays?

    The detector is supposed to come online and start collecting real data in 2004.

    Another very interesting neutrino experiment is SNO [queensu.ca], the Sudbury Neutrino Observatory, which is in an underground mine in Canada. SNO resolved the solar neutrino problem; people previously couldn't explain why we weren't seeing the right number of neutrinos coming from the sun - it turns out that they "oscillate" and change into other types of neutrinos, and SNO verified this. The neutrino oscillations also imply that they have a non-zero mass (explanation beyond the scope of this comment ;)

    The point of MINOS is to observe neutrinos from a controlled high-energy accelerator beam, rather than whatever we get from the sun, to very accurately measure the oscillations.
  • "They may have mass, they can hide - but we are gonna smoke them out!", Mr. Bush said during his Fermilab lecture.

    http://www.lns.cornell.edu/~neubert/bush_finds_e rr or.html
  • Newton's third law states, 'If one body exerts a force on another, there is an equal and opposite force, called a reaction, exerted on the first body by the second.

    This is all fine and dandy in a cartesian universe, however in a non cartesian universe this is contradictory. Yeah, YEAH. This can only work in a cartesian universe. In a cartesian universe using euclid the *equal* and *opposite* is in a straight line.

    The logic problem with this is, in the universe we appear to live in, has the *equal* and *op

  • Cosmic Gall
    by John Updike (1963)

    Neutrinos, they are very small.
    They have no charge and have no mass
    And do not interact at all.
    The earth is just a silly ball
    To them, through which they simply pass,
    Like dustmaids down a drafty hall
    Or photons through a sheet of glass.
    They snub the most exquisite gas,
    Ignore the most substantial wall,
    Cold-shoulder steel and sounding brass,
    Insult the stallion in his stall,
    And, scorning barriers of class,
    Infiltrate you and me! Like tall
    And painless guillotines, they fall
    Down thro

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