High energy leptonic collisions and electroweak parton distribution functions

Tao Han,Keping Xie,Yang Ma

doi:10.1103/physrevd.103.l031301

Tao Han, Keping Xie + Show 1 more

Open Access

https://doi.org/10.1103/physrevd.103.l031301

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Abstract

In high-energy leptonic collisions well above the electroweak scale, the collinear splitting mechanism of the electroweak gauge bosons becomes the dominant phenomena via the initial state radiation and the final state showering. We point out that at future high-energy lepton colliders, such as a multi-TeV muon collider, the electroweak parton distribution functions (EW PDFs) should be adopted as the proper description for partonic collisions of the initial states. The leptons and electroweak gauge bosons are the EW partons, that evolve according to the unbroken Standard Model (SM) gauge group and that effectively resum potentially large collinear logarithms. We present a formalism for the EW PDFs at the Next-to-Leading-Log (NLL) accuracy. We calculate semi-inclusive cross sections for some important SM processes at a future multi-TeV muon collider. We conclude that it is appropriate to adopt the EW PDF formalism for future high-energy lepton colliders.

Highlights

With the discovery of the Higgs boson at the CERN Large Hadron Collider (LHC), the particle spectrum of the Standard Model (SM) is complete
Contributions from the quark and gluon initial states are sub-leading as seen in the parton luminosities in Fig. 2(b), and we do not include them in the cross section calculations throughout this paper
It is important to note that, there is no logarithmic evolution for the WL parton distribution functions (PDFs), the partonic subprocess cross sections are much enhanced for WLWL; ZLZL → tt; ttH and H; ZH; HH, due to the Goldstone-boson interactions

Summary

INTRODUCTION

With the discovery of the Higgs boson at the CERN Large Hadron Collider (LHC), the particle spectrum of the Standard Model (SM) is complete. As the beam energy increases, the initial state radiation (ISR) becomes substantial. It degrades the colliding energies of the leptons, and generates new reactions of the radiation fields. ; ð1Þ where the splitting functions are Pγ=lðxÞ1⁄4ð1þð1−xÞ2Þ=x for l → γ and Pl=lðxÞ 1⁄4 ð1 þ x2Þ=ð1 − xÞ for l → l, with an energy xE off the charged lepton beam of energy E This is the leading order effective photon approximation (EPA). At s 1⁄4 10 TeV (30 TeV), the cross section for μþμ− → tt production can be enhanced by 40% (60%) due to the ISR effects. Owing to the collinear enhancement, the two-photon (γγ) fusion processes grow

Published by the American Physical Society

DISCUSSIONS AND CONCLUSION