
#1
Jan3013, 07:41 PM

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I have not yet studied experimental physics!But I would like to know how can we measure the mass of quark,because we can not to have separate quark for color confinement.In quarkonium,by resonance we know the excited state of quarkonium,but how can we know which state they lie(e.g 2[itex]^{3}[/itex]S).




#2
Jan3013, 08:41 PM

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You have the quarks in different combinations and you can measure the mass of the combinations. We can also measure the energetics of gluons.
It's like those logic puzzles you did as a kid, where you have to figure which bag of coins has the light coin in it. 



#3
Jan3113, 04:10 AM

P: 977

here is one way for measuring top quark mass
http://digitalcommons.unl.edu/cgi/vi...rk%20masses%22 



#4
Jan3113, 05:28 AM

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How can we measure the mass of quarks?
The lifetime of the top quark is extremely short, 5 x 10^{25} sec. Would someone who maintains that virtual particles are not "real" and just a mathematical artifact please tell me  is the top quark real??




#5
Jan3113, 01:33 PM

P: 514

The masses of the quarks can be measured in several ways.
For the up, down, and strange quarks, one can use a quirk of QCD called "chiral symmetry breaking", and measure their masses using the masses of the pions and kaons: m_{pi}^{2} ~ (m_{u} + m_{d})*E_{QCD} m_{K+}^{2} ~ (m_{u} + m_{s})*E_{QCD} m_{K0}^{2} ~ (m_{d} + m_{s})*E_{QCD} One has to do lattice QCD to get the results, and that has the problem that one cannot make the up and down masses too small, or else the pions' Compton wavelengths will cover the entire lattice. So one does the calculations with larger masses, and extrapolates down to observed values. For the charm and bottom quarks, one can get approximate masses from their bound states, like the J/psi, D, upsilon, and B mesons, since those quarks are nonrelativistic in those states. To improve those estimates, one must calculate those states' binding energies with lattice QCD. For the top quark, one must get its mass from the total energy of its decay products, since it decays before it can hadronize. andrien's paper is an example of doing that. 



#6
Jan3113, 05:57 PM

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#7
Feb213, 02:00 PM

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Or would you accept the idea that a bound electron is constantly exchanging particles (photons) with the nucleus? If yes, how many? And how many photons does it exchange with all other particles around it? On the other hand, if you write that in terms of Feynman diagrams, every particle is a virtual particle. Some are just "more virtual" (more offshell, shorter living) than others. 



#8
Feb213, 02:40 PM

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An apparent difference between real and virtual arises because in many cases a virtual particle must be integrated over. At that point we must face the fact that Feynman diagrams represent quantum amplitudes, and consequently one virtual particle contributes to an infinite number of mutually coherent exchange processes. But it's not the particle's fault, or the idea that virtual particles are different somehow, it's just quantum mechanics coming into play. If you Fourier transform a Coulomb field between two charged particles at rest, you find that it is spatially varying but timeindependent, which indicates that their photon carries momentum but zero energy, 



#9
Feb213, 02:52 PM

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