Are there non-hadronic jets?

Question

Hello I am new into jetphysics and I read here that 'Hadronic jets are amongst the most striking phenomena in high-energy physics'.

My small understanding of jets is that they are defined by the hadrons that are composed from the decay process. (Jets are shapes starting from a collision point up and the energy/radiation shower of hadrons that we can observer in the detector calorimeters).

I want to know if there are non-hadronic jets, and if so how are they defined. Or if something fundamental I miss. Any introducttonary textbook suggestions on the subject is very welcome. Thank you in advance

Answer 1

There exists a notion of jets in QED: one such definition of a jet arises due to the $\sigma_{2\rightarrow2}$ electron to muon scattering. Analysis of Feynman diagrams at the next order suggests the inclusion of the two radiative emission diagrams as well, allowing us to calculate $\sigma_{2\rightarrow2}$ as $\sigma_{\rm total} - \sigma_{2\rightarrow3}$, where $\sigma_{2\rightarrow3}$ is $\sigma(e^+e^-\rightarrow\mu^+\mu^-\gamma)$.

Now, in calculating $\sigma_{2\rightarrow3}$, we usually employ "experimental regularisation"$^\dagger$ to counter the IR divergence from the radiative corrections, and posit that the detectors can only detect photons with energy lower than some $E_\gamma$, and that they can only distinguish between the $\mu$ and $\gamma$ impact at an angle greater than $\theta'$. Thus the final two-body state will also be parameterised by $E_\gamma$ and $\theta'$, forming a Sterman-Weinberg jet.

In general, however, QCD hadronic jets are much easier to detect in practice.

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$^\dagger$ Of course, theoretical particle physicists usually prefer to use a photon mass $m_\gamma$ as a regulator during calculations.