Smallest Mass Particle: Electron Neutrino?

[neurocomp2003]

Whats the smallest mass particle? is it the electron? or the electron neutrino?
Or is there something smaller?

 

[dextercioby]

So far,the superior mass limit for the electron neutrino is the smallest.It's ~eV.

Daniel.

 

[neurocomp2003]

and the e-1 neutinro has been observed right? not just theorized.
Any references that i may look up to further some research

 

[SpaceTiger]

and the e-1 neutinro has been observed right? not just theorized.

Yeah, in fact Ray Davis won a Nobel prize for it. Look up the "Homestake solar neutrino experiment".

 

[jtbell]

and the e-1 neutinro has been observed right? not just theorized.

Physicists have been studying neutrinos experimentally for nearly fifty years now, first using neutrinos produced in nuclear reactors (Google on "Reines and Cowan"), then solar neutrinos (Google on "Homestake Davis neutrino"), then neutrinos produced in high-energy collisions at particle-physics labs like Fermilab and CERN (Google on "fermilab neutrino scattering"), and most recently neutrinos produced in collisions between cosmic rays and atomic nuclei in the atmosphere (Google on "Kamiokande atmospheric neutrino")

The hot topic in neutrinos for the past several years has been "neutrino oscillations," in which neutrinos change their "flavor" in flight, from electron neutrino to muon neutrino to tau neutrino.

Any references that i may look up to further some research

Try the Particle Data Group.

 

[Nereid]

Whats the smallest mass particle?

The photon (and the gluon) (Nereid ducks the barrage of rotten fruit thrown by particle physics PF members).

and the e-1 neutinro has been observed right? not just theorized.

Refrain ...
If you find a way to detect the relict neutrinos, a Nobel will surely be yours too!

 

[marlon]

The photon (and the gluon) (Nereid ducks the barrage of rotten fruit thrown by particle physics PF members).
Refrain ...

And do we know why the gluon remains massless, even after symmetry breakdown ?

marlon

 

[arivero]

The photon (and the gluon) (Nereid ducks the barrage of rotten fruit thrown by particle physics PF members).

Bah, the photon and the gluon are forces, no particles.

 

[marlon]

Bah, the photon and the gluon are forces, no particles.

No, they are particles...A 'FORCE' does not exist in QFT

Ahh, those semantics
marlon

 

[Miserable]

And do we know why the gluon remains massless, even after symmetry breakdown ?

marlon

It's because the Higgs is colourless. It doesn't interact with the gluons at tree level, so they don't develope a mass term when it acquires its VeV.

 

[marlon]

It's because the Higgs is colourless. It doesn't interact with the gluons at tree level, so they don't develope a mass term when it acquires its VeV.

Well, yes that must be true, otherwise the Higgs mechanism does not work. But my question really is : why is the Higgs field colourless ?

I'll give away a hint : one can look at the commutation relations of the SU(3)-colour generators , ie : the Gell-Mann-matrices

marlon

 

[neurocomp2003]

ah yes all the astrophysics stuff I learned...and well forgotten...
Its hard for me to keep track of wahts been theorized and proven and what still is just theory.

 

[Miserable]

I don't see that it has anything to do with the colour generators. If the Higgs were coloured, the Yukawa coupling to the quarks wouldn't be gauge invarient under QCD, and the quarks couldn't have mass, which is clearly experimentally wrong. So we choose to have a colourless Higgs, to fit experiment. Just like we choose all the fermion hypercharges so that the photon remains a massless, pure vector interaction. There's nothing magical about it.

 

[ohwilleke]

The photon (and the gluon) (Nereid ducks the barrage of rotten fruit thrown by particle physics PF members).
Refrain ...
If you find a way to detect the relict neutrinos, a Nobel will surely be yours too!

Aren't gluons quite massive?

 

[Nereid]

Aren't gluons quite massive?

"The force between quarks is carried by gluons (from the word ‘glue’), which, like photons, lack mass. Gluons, however, in contrast to photons, also have the property of colour charge, consisting of a colour and an anticolour. This property is what makes the colour force so complex and different from the electromagnetic force." (Source: http://nobelprize.org/physics/laureates/2004/public.html announcement)

"The discovery which is awarded this year's Nobel Prize is of decisive importance for our understanding of how the theory of one of Nature's fundamental forces works, the force that ties together the smallest pieces of matter – the quarks. David Gross, David Politzer and Frank Wilczek have through their theoretical contributions made it possible to complete the Standard Model of Particle Physics, the model that describes the smallest objects in Nature and how they interact. At the same time it constitutes an important step in the endeavour to provide a unified description of all the forces of Nature, regardless of the spatial scale – from the tiniest distances within the atomic nucleus to the vast distances of the universe.")

 

[ohwilleke]

At least I'm not crazy. Here some discussion along the lines I'd been thinking from Wikipedia:Gluon:Discussion:

Question for specialist: are gluons really massless? Following http://hyperphysics.phy-astr.gsu.edu/hbase/particles/expar.html, this is not true. Also, from my (poor) understanding, it is not simply that gluons "bind" the quarks together; they are themselves, sort of, composed of a quarks pair. -- looxix 10:16 Apr 14, 2003 (UTC)

Yes they are massless, and nowhere in the linked page states they aren't. You may be confusing them with the W and Z bosons. Gluons are not composed of a pair of quarks, however they have two color charges, for instance a red-antigreen gluon.
The fact that gluons themselves have color charge causes somewhat erratic behavior(as gluons are creating and annihilating other gluons as well), including the limited range. The W and Z bosons also have limited range, but in their case it is caused by their mass.
63.205.40.10 04:01, 23 Jan 2004 (UTC)
My copy of the 2002 Review of Particle Physics states that a mass of up to a few MeV may not be precluded, so I added that to the article. -- Schnee 23:59, 26 Jul 2004 (UTC)