Recent content by jkp

Hi I realize that this thread is very old, but it's new to me! Anyway, it seems to me that there are more questions here than answers (and some answers seemed to be misleading). So please allow me to first summarize the calculation in order to clarify the question, and then make a suggestion...

I think that the measurement of the branching ratio for ##B_s\to\mu^+\mu^-## should be seen as a test of the SM rather than of low-energy SUSY. In this context the SM seems to have once again passed this test, although the uncertainty of the result means that we still need to wait for future...

Thanks again Andrien From the reference you provide I now see that the Narrow Width Approximation isn't just that the propagator becomes, $$ \frac{1}{{(q^2-M_W^2)^2+M_W^2\Gamma_W^2}}\to \frac{2\pi\,\delta(q^2-M_W^2)}{2M_W^2\Gamma_W^2} $$ but also that we must approximate, $$...

It seems to me that I need some identity for the polarization vectors such as the following, $$ \varepsilon_\mu^{\lambda_1 *}\varepsilon_\nu^{\lambda_2} =\delta^{\lambda_1\lambda_2}\frac{1}{3} \left(\sum_\lambda \varepsilon_\mu^{\lambda *}\varepsilon_\nu^{\lambda} \right) $$ that is, the...

Thanks for the reply Andrien but maybe you can provide a little more detail. I don't understand how you get ##\lambda_1## in one bracket and ##\lambda_2## in the other. As far as I see it we have, $$ \left| \sum_\lambda {\mathcal M}_1^\mu \epsilon^{\lambda *}_\mu \epsilon^\lambda_\nu...

Hi I'm trying to understand how the sum over spin polarizations is treated when using the Narrow Width Approximation(NWA) with a spin 1 resonance. For a spin zero resonance there is no such problem and the factorization is quite straightforward. I'll go through some details to explain where...

At the LEP experiment Z bosons were produced through colliding electrons and positrons. This was a very clean experiment, unlike the LHC, allowing the properties of the Z boson to be studied to high precision. The presence of the Z boson shows up as a peak in the total cross-section as a...

Indeed at tree-level the Z-boson couplings to quark-anti-quark are flavour-diagonal even after you rotate the quarks to their mass eigenstate basis. This is because the neutral Z must couple to two down-type quarks or two up-type quarks and the combined unitary rotations cancel. The charged W...

Another package you might like to look at is MadGraph5. This package allows you to generate Feynman diagrams, calculate cross-sections and generate events. The generated parton level events can be analysed with an addon package called "MadAnalysis" or passed to a showering/hadronization program...