- #1
wlln
- 7
- 0
Could you explain the meanings of EW global fit,pole mass,gluon fusion? Thank you very much!
In summary, EW global fit is a method used in particle physics to compare measured quantities with the predictions of the Standard Model. Pole mass is a way of defining mass in quantum field theory, where it is defined as the value of momentum at which the field propagator diverges. Gluon fusion is a process in which two gluons interact to produce a particle, unlike photons which cannot interact with each other due to their electric neutrality. This process is important in understanding the strong nuclear force in quantum chromodynamics (QCD).
- #2
blechman
Science Advisor
- 779
- 8
EW Global fit: Ignoring neutrino masses for the moment, there are 19 parameters in the Standard Model of particle physics. However, there are dozens of measured quantities. Therefore, the study of particle physics is overconstrained and we can use this over-measuring to see if we can find discrepancies. So we use the first 19 of the measurements to nail down the parameters, and then we can compare the remaining measurements to what the theory predicts.
Pole Mass: Mass is a funny thing in quantum field theory. Technically it's not well defined (it's divergent). One must specify a "renormalization scheme" by which we define the mass. "Pole Mass Scheme" is a particular (but by no means unique!) choice, where we DEFINE the mass as the value of the momentum where the field propagator (2-point Green's function) diverges (has a pole). The full inverse propagator goes like
(p^2 - m0^2 - A(p^2))
and we define the number Mpole^2 to be the value of p^2 that makes this denominator vanish. Here m0 is the "bare mass" - the parameter in the theory before renormalization.
Gluon fusion: This is just the Feynman diagram where two gluons come together and produce something. Gluons (unlike photons) can do this due to the nature of QCD - that is, photons cannot interact with each other (since they're electrically neutral) but gluons carry strong nuclear charge and can therefore interact. In fact, there IS such a thing as photon fusion, but it's VERY suppressed and therefore not worth talking about, unless you're doing quantum optics, which is another forum.
Hope this helps get you started. Also check out the standard sites like wikipedia, or even google.
Pole Mass: Mass is a funny thing in quantum field theory. Technically it's not well defined (it's divergent). One must specify a "renormalization scheme" by which we define the mass. "Pole Mass Scheme" is a particular (but by no means unique!) choice, where we DEFINE the mass as the value of the momentum where the field propagator (2-point Green's function) diverges (has a pole). The full inverse propagator goes like
(p^2 - m0^2 - A(p^2))
and we define the number Mpole^2 to be the value of p^2 that makes this denominator vanish. Here m0 is the "bare mass" - the parameter in the theory before renormalization.
Gluon fusion: This is just the Feynman diagram where two gluons come together and produce something. Gluons (unlike photons) can do this due to the nature of QCD - that is, photons cannot interact with each other (since they're electrically neutral) but gluons carry strong nuclear charge and can therefore interact. In fact, there IS such a thing as photon fusion, but it's VERY suppressed and therefore not worth talking about, unless you're doing quantum optics, which is another forum.
Hope this helps get you started. Also check out the standard sites like wikipedia, or even google.
- #3
wlln
- 7
- 0
thank you very much
1. What is EW global fit and why is it important in particle physics?
EW global fit is a statistical analysis technique used in particle physics to determine the values of the fundamental parameters of the Standard Model, such as the masses of the W and Z bosons. It is important because it allows us to test the consistency of the Standard Model and search for any deviations or new physics that may exist beyond it.
2. What is the pole mass and why is it relevant in the context of particle physics?
The pole mass is the mass of a particle calculated using the pole of the propagator in a Feynman diagram. It is relevant because it is a physical quantity that can be measured experimentally, and it is often used to compare with theoretical predictions in particle physics calculations.
3. How does gluon fusion play a role in the EW global fit?
Gluon fusion is a process where two gluons interact to produce a new particle, such as a Higgs boson. In the EW global fit, gluon fusion contributes to the total cross-section for Higgs boson production, which is an important parameter in the fit.
4. Can you explain the significance of the gluon fusion process in the search for new physics?
Gluon fusion is a key process in the search for new physics, particularly in the context of the Higgs boson. Any new particles that interact with the Higgs boson can affect its production through gluon fusion, providing valuable information about the nature of these new particles.
5. How do the results of the EW global fit and pole mass calculations impact our understanding of the Standard Model?
The results of the EW global fit and pole mass calculations allow us to test the predictions of the Standard Model and validate its consistency with experimental data. Any discrepancies or deviations from the expected values can indicate the presence of new physics beyond the Standard Model.
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