What are the heaviest and lightest particles?

[Mk]

Are they the electron neutrino and the Z˚?

[anti_crank]

The top quark is heavier than the Z. There are also massless particles like the photon and gluons.

[Mk]

Ahh, yes I forgot the massless particles... :biggrin:
Ok, excluding those, what are they? Thanks, it was the top quark.

[anti_crank]

The electron neutrino is your best bet; AFAIK the mass differences measured recently from oscillations do not allow to distinguish which of the flavours is lighter. It is probably more correct to say that the lightest neutrino mass state is the lightest particle, since weak force states like electron/muon/tau neutrinos do not have well defined masses in view of oscillations.

There are hypothetical ultra-light particles like axions, and there are hypothetical particles at the grand unification scale of masses around 10^15 GeV. It's also possible that the Higgs boson, if it exists, is heavier than the top quark.

[Lo4eath]

Hija guys... I've got a question, it's for my Physisc teacher.

She asked us to do a project of negligible particles on this world.
I think that the almost massless particle is ELECTRON and PHOTON (i dont know any further). Am I right? I wanna get 10, so I'm asking professionals. :] If you would answer me, may You answer in language known-for-everybody? :] Think you know what I mean. Thx for answers.

[DaleSpam]

What does she mean by "negligible particles"?

[Lo4eath]

negligible means that the particles have almost no mass

[rohanprabhu]

negligible means that the particles have almost no mass

'almost' isn't exactly the kind of term used in particle physics.

[Lo4eath]

'almost' isn't exactly the kind of term used in particle physics.

well then how do you call it? With minimum mass? Could be, couldn't be?

[rohanprabhu]

well then how do you call it? With minimum mass? Could be, couldn't be?

either it has mass [like an electron] or it doesn't at all [like a photon]. There is no particle having a 'negligible mass'. 'Negligible' is a term which depends upon the experiment we conduct. 'Negligible' in a general sense doesn't really mean anything.

[Lo4eath]

Don't blame me, that was her idea to put such a word in there :]

and i've got a note:

if photon carries an energy, then it's obvious that it HAS mass, isn't it?

[_Mayday_]

either it has mass [like an electron] or it doesn't at all [like a photon]. There is no particle having a 'negligible mass'. 'Negligible' is a term which depends upon the experiment we conduct. 'Negligible' in a general sense doesn't really mean anything.

Neglible in terms of a car might be 10 grams, but in particle physics many times smaller than that. Are you saying that the word "negligible" can have an infinite amount of values, another example would be big?

[_Mayday_]

Don't blame me, that was her idea to put such a word in there :]

and i've got a note:

if photon carries an energy, then it's obvious that it HAS mass, isn't it?

It's so obvious, yet you are unsure? :tongue:

Have a look in the FAQ of this forum, it will answer your question. :smile:

[Lo4eath]

so, ELECTRON is the lightest one, if photon doesn't have mass?

[Tachyonie]

so, ELECTRON is the lightest one, if photon doesn't have mass?

Look, if you cannot do quick research using google or wikipedia that's fine with me, but atleast read the whole thread.
As stated above, the lightest particle would probably be neutrino.

[ZapperZ]

I think it's time to bringing in a proper reference here. The Particle Adventure (http://www.particleadventure.org/) webpage is very well-designed for non-physicists to get some idea of the zoo of elementary particles within the Standard Model. This link (http://www.cpepweb.org/cpep_sm_large.html) gives you the most up-to-date info on such particles. One can easily compare the masses and figure out which one is the "heaviest" and which one is the "lightest" and which ones have no mass within our current understanding.

If you want a more technical catalog of these and other "fundamental" particles in high energy physics, then the Particle Data Group (http://pdg.lbl.gov/) would be the place to go.

Hopefully, all of these sites will equipt you on "how to fish", so that you will know where to look next time you have similar questions.

Zz.

[_Mayday_]

Look, if you cannot do quick research using google or wikipedia that's fine with me, but atleast read the whole thread.
As stated above, the lightest particle would probably be neutrino.

I did some quick research on both google and wikipedia and did not find the answer to the question...:confused: Why do you assume he hasn't read the whole thread? He/she is obviously unsure and probably just wants to make sure, I see no harm in that.


Lo4eath, I had a look around and found some information, it is put very simply but should get the message across :smile:

Small Introduction
"Neutrinos are elementary particles that travel close to the speed of light and have a negligible rest mass. Although there are vast numbers of neutrinos arriving at earth from beta decays all over the universe, they lack an electrical charge and are therefore able to pass through ordinary matter almost undisturbed and with very few interactions they are thus extremely difficult to detect."

Answer to your question
"Until recently, it was believed that they had no mass but a few years ago it was found that they have a very small mass, much lighter than electrons."

I think that neutrinos would be along the right lines. Hope this helped. :smile:

EDIT: Thanks for the links ZapperZ, I'll have a look!

[Lo4eath]

yeah, that's right (i have no clue what neutrino is, but.. :] ), but as i have posted it, i want to know which one is lighter in between ELECTRON and PHOTON. So, i think that the answer is: PHOTON is the lighest one, in the case that we are comparing those two, but if photon DOES have a mass... am i right?

[_Mayday_]

yeah, that's right (i have no clue what neutrino is, but.. :] ), but as i have posted it, i want to know which one is lighter in between ELECTRON and PHOTON. So, i think that the answer is: PHOTON is the lighest one, in the case that we are comparing those two, but if photon DOES have a mass... am i right?

A photon has no mass.

[Tachyonie]

I did some quick research on both google and wikipedia and did not find the answer to the question...:confused: Why do you assume he hasn't read the whole thread? He/she is obviously unsure and probably just wants to make sure, I see no harm in that.


Lo4eath, I had a look around and found some information, it is put very simply but should get the message across :smile:

Small Introduction
"Neutrinos are elementary particles that travel close to the speed of light and have a negligible rest mass. Although there are vast numbers of neutrinos arriving at earth from beta decays all over the universe, they lack an electrical charge and are therefore able to pass through ordinary matter almost undisturbed and with very few interactions they are thus extremely difficult to detect."

Answer to your question
"Until recently, it was believed that they had no mass but a few years ago it was found that they have a very small mass, much lighter than electrons."

I think that neutrinos would be along the right lines. Hope this helped. :smile:

EDIT: Thanks for the links ZapperZ, I'll have a look!

I am sorry if I have been too harsh. However there are information about each particle and its weight, if he is really interested, a small research wouldnt hurt.

yeah, that's right (i have no clue what neutrino is, but.. :] ), but as i have posted it, i want to know which one is lighter in between ELECTRON and PHOTON. So, i think that the answer is: PHOTON is the lighest one, in the case that we are comparing those two, but if photon DOES have a mass... am i right?

Photon does not have a mass. Atleast not rest mass.
Therefor, answer to your question, which particle has the least rest-mass is either:
Photons and all the other massles particles.
or - if you want the least amount of mass, but still mass > 0:
Probably neutrinos which are lighter than electrons.

[Lo4eath]

Yes, but we're not rorgeting that, that was my Project Work, and my teacher says it has to be on level of 13 - 14 - 15 years old pupil, so, if i'm gonna say that the photon is the lightest one (how come it doesn't have mass if it DOES carry the energy?) is photon, would it be okay?

EDIT: Okay guys, anyway, thank you a lot anyway, i think this is gonna be good enough for her (well, let's hope :P ). Thank you a lot again.
p.s.: i'm sorry about my english...

[Tachyonie]

Yes, but we're not rorgeting that, that was my Project Work, and my teacher says it has to be on level of 13 - 14 - 15 years old pupil, so, if i'm gonna say that the photon is the lightest one (how come it doesn't have mass if it DOES carry the energy?) is photon, would it be okay?

Well you can prepare two answers and ask the teacher if the criteria include also particles with 0 mass. If she says yes, use photons. If the teacher wants the particle to have certian rest mass then say neutrino.

And to be precise - photon has zero REST MASS or the invariant mass. There is certian difference, even though I wont tell you all the details since I am in the same year group as you are. :)

[Lo4eath]

well, you were already, weren't you

[ZapperZ]

(how come it doesn't have mass if it DOES carry the energy?)

I believe somewhere in this thread, someone has pointed out to you to read the FAQ in the General Physics forum. I'm sure you can guess that this question has been brought up several times already.

Zz.

[Lo4eath]

yeah yeah, right.... coud you be that kind and send that link here?

[_Mayday_]

http://www.physicsforums.com/showthread.php?t=104715

I am afraid you will have to scroll down to find it....near the bottom.

[Tachyonie]

yeah yeah, right.... coud you be that kind and send that link here?

http://www.physicsforums.com/showthread.php?t=104715
And try to find things by yourself, you cant always rely on others.

Tachyon.