Helicity violation in strong interaction?

In summary, the conversation discusses a scattering process involving a proton and an antiproton via pion exchange. The matrix element for this process involves a coupling constant and 4-momentum of the pion. The issue at hand is that the currents in the helicity basis only yield non-zero results for a change in helicity, suggesting that helicity is not conserved. However, this is consistent with chiral symmetry being broken in QCD, with pions as the goldstone bosons. The conversation ends with the acknowledgment that the original confusion has been cleared up.
  • #1
metter
3
0
I have a proton and an antiproton scattering, via a pion exchange.

The matrix element has the form:
[tex]M=g*(\bar{u}_{1}\gamma ^{5}u_{2})\frac {1} {q^2-m^2}( \bar{v}_{1}\gamma ^{5}v_2) [/tex]
Wher g is my coupling constant, and q the 4-momentum of the pion.

The problem is that when I compute the currents [tex](\bar{u}_{1}\gamma ^{5}u_2)[/tex] and [tex](\bar{v}_{1}\gamma ^{5}v_2)[/tex] in the helicity basis this terms are non zero only for a change of the helicity( my righthanded proton should change into a lefthanded proton and the same for my antiproton).

This would imply that the matrix element for a helicity 1 state going to a helicity -1 state is not zero, which implies helicity is not conserved.

Where am I getting it wrong?
 
Physics news on Phys.org
  • #2
Why do you think helicity conserved in strong interactions?
 
  • #3
A scalar (or pseudoscalar) interaction is always L-R. This follows from Lorentz invariance, or from a more brute-force point of view, from the Dirac equation. The pion is a pseudoscalar, so you expect a helicity flip!

Chiral symmetry is broken in QCD, with pions being the goldstone bosons of the breaking. So this is totally consistent.

This leads to the infamous question that appears on graduate board exams for particle-physics PhD candidates: if there was no Higgs, what would be the mass of the Z boson? Answer: proton mass!
 
  • #4
Thnak you very much. You are right. I was confusing something, and your answers made me realize that.

Thanks again
 

What is helicity violation in strong interaction?

Helicity violation in strong interaction refers to the phenomenon where the spin of a particle in a strong interaction does not align with its direction of motion. In other words, the particle's spin is not conserved during the interaction.

What causes helicity violation in strong interaction?

Helicity violation in strong interaction is caused by the non-conservation of parity, which is a fundamental symmetry in particle physics. Parity violation occurs when the mirror image of a particle behaves differently than the particle itself.

Why is helicity violation in strong interaction important?

Helicity violation in strong interaction is important because it provides evidence for the violation of fundamental symmetries in particle physics and can help us understand the underlying laws of nature. It also has implications for the behavior of particles in the early universe and can help explain the dominance of matter over antimatter.

How is helicity violation in strong interaction measured?

Helicity violation in strong interaction is measured through experiments that observe the decay products of particles involved in the interaction. By comparing the decay rates of particles with opposite helicities, scientists can determine the degree of helicity violation.

Can helicity violation in strong interaction be observed in everyday life?

No, helicity violation in strong interaction is only observed in the microscopic world of particles. It is not observable in everyday life as the effects are very small and require specialized experiments to detect.

Similar threads

A Helicity and electron/positron annihilation
    • High Energy, Nuclear, Particle Physics
Replies
1
Views
1K
I Fixing CP phases to cancel CKM phases
    • High Energy, Nuclear, Particle Physics
Replies
1
Views
925
A Charge-current interaction: linear terms in a given quark
    • High Energy, Nuclear, Particle Physics
Replies
1
Views
940
I Pion Decay Rate: Verifying Decay Rate Formula
    • High Energy, Nuclear, Particle Physics
Replies
13
Views
3K
A Matching interaction terms and decay processes in standard model
    • High Energy, Nuclear, Particle Physics
Replies
2
Views
1K
I Calculating 2nd Order Scattering Amplitude: Feynman Diagrams
    • High Energy, Nuclear, Particle Physics
Replies
6
Views
2K
A Deducing decay processes and Feynman diagrams using Lagrangian and conservation laws
    • High Energy, Nuclear, Particle Physics
Replies
1
Views
1K
Helicity interactions of the Z0
    • High Energy, Nuclear, Particle Physics
Replies
2
Views
2K
I Scattering of a scalar particle and a Fermion
    • High Energy, Nuclear, Particle Physics
Replies
2
Views
2K
I Are SM B & L conservation violations through sphalerons possible?
    • High Energy, Nuclear, Particle Physics
Replies
1
Views
926

Hot Threads

Recent Insights

Back
Top