arXiv subjects

Taehyun Kwon

Publications and source records attributed to Taehyun Kwon.

4 recordsLinked to original sources

arXiv2024

Dijet invariant mass distribution near threshold

In this paper, using soft-collinear effective theory we study the invariant mass distribution for dijet production in $e^+e^-$-annihilation. Near threshold, where the dijet takes most of the energy, there arise the large threshold logarithms, which are sensitive to soft gluon radiations. To systematically resum the logarithms, we factorize the scattering cross section into the hard, the collinear, and the soft parts. And we additionally factorize the original soft part into the global soft function and the two collinear-soft functions, where the latter can be combined with the collinear parts to form the fragmentation functions to jet (FFJs). The factorization theorem derived here can be easily applicable to other processes near threshold. Using the factorized result, we show the resummed result for the dijet invariant mass to the accuracy of next-to-leading logarithms. We have also obtained the result in the case of the heavy quark dijet and compared it with the case of the light quark.

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arXiv2022

N-jettiness for muon jet pairs in electroweak high-energy processes

We study the $N$-jettiness in the electroweak high-energy process for the final muon jet pairs, $e^- e^+ \rightarrow μ^+ \ \mathrm{jet} + μ^- \mathrm{jet}$. Compared to QCD, the main difference is that there exist additional gauge nonsinglet contributions in the weak interaction, which make the factorization more elaborate. Especially the nonsinglet contributions arise due to the Block-Nordsieck violation in electroweak processes, which yields the Sudakov logarithms and the rapidity divergence. They change the evolution of the factorized parts considerably in the $N$-jettiness. There are two possible channels, initiated from the gauge bosons $W W \rightarrow \ell_μ \overline{\ell}_μ$, and from the electrons $\ell_e \overline{\ell}_e \rightarrow \ell_μ \overline{\ell}_μ$, where $\ell$ denotes the weak doublet. The latter was discussed previously, and we complete the analysis by studying the first. The factorization for $W W \rightarrow \ell_μ \overline{\ell}_μ$ can be proceeded in a similar way as in the factorization for $\ell_e\overline{\ell}_e \rightarrow \ell_μ \overline{\ell}_μ$, and the result exhibits a rich structure. The new ingredients in this study consist of the $W$ beam functions, and the complex color structure of the soft functions and the hard functions. The resummation of the large logarithms is performed by solving the renormalization group equations with respect to the renormalization scale and the rapidity scale. In the numerical analysis, we confine to the SU(2) weak gauge interaction, and the numerical results are presented for both channels at next-to-leading-logarithmic accuracy including the singlet and the nonsinglet contributions. The nonsinglet contributions turn out to be appreciable in the 2-jettiness.

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arXiv2021

N-jettiness in electroweak high-energy processes

We study $N$-jettiness in electroweak processes at extreme high energies. The description of the scattering process such as $e^- e^+ \rightarrow μ^- μ^+ +X$ is similar to QCD. At present, electroweak processes are prevailed by the processes induced by the strong interaction, but they will be relevant at future $e^- e^+$ colliders at high energy. The main difference between QCD and electroweak processes is that the initial- and final-state particles should appear in the form of hadrons, that is, color singlets in QCD, while there can be weak nonsinglets as well in electroweak interactions. We analyze the factorization theorems for the $N$-jettiness in $e^- e^+ \rightarrow μ^- μ^+ +X$, and compute the factorized parts to next-to-leading logarithmic accuracy. To simplify the comparison with QCD, we only consider the $SU(2)_W$ gauge interaction, and the extension to the Standard Model is straightforward. Put it in a different way, it corresponds to an imaginary world in which colored particles can be observed in QCD, and the richer structure of effective theories is probed. Various nonzero nonsinglet matrix elements are interwoven to produce the factorized results, in contrast to QCD in which there are only contributions from the singlets. Another distinct feature is that the rapidity divergence is prevalent in the contributions from weak nonsinglets due to the different group theory factors between the real and virtual corrections. We verify that the rapidity divergence cancels in all the contributions with a different number of nonsinglet channels. We also consider the renormalization group evolution of each factorized part to resum large logarithms, which are distinct from QCD.

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arXiv2021

Factorization of the dijet cross section in hadron-hadron collisions

The factorization theorem for the dijet cross section is presented in hadron-hadron collisions with a cone-type jet algorithm. We also apply the beam veto to the beam jets consisting of the initial radiation. The soft-collinear effective theory is employed to see the factorization structure transparently when there are four distinct lightcone directions involved. There are various types of divergences such as the ultraviolet and infrared divergences. And when the phase space is divided to probe the collinear and the soft parts, there appears an additional divergence called rapidity divergence. These divergences are sorted out and we will show that all the infrared and rapidity divergences cancel, and only the ultraviolet divergence remains. It is a vital step to justify the factorization. Among many partonic processes, we take $q\overline{q} \rightarrow gg$ as a specific example to consider the dijet cross section. The hard and the soft functions have nontrivial color structure, while the jet and the beam functions are diagonal in operator basis. The dependence of the soft anomalous dimension on the jet algorithm and the beam veto is diagonal in operator space, and is cancelled by that of the jet and beam functions. We also compute the anomalous dimensions of the factorized components, and resum the large logarithms to next-to-leading logarithmic accuracy by solving the renormalization group equation.

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