Recoil Mass of Leptons from Z

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You may find the project at http://code.ihep.ac.cn/liangh/llH_Rec. The website is open to register. When you can access the project, use git clone git@code.ihep.ac.cn:liangh/llh_rec.git to have a local copy of this project.

Introduction

The final states of $llH$ mainly come from the $ZH$ (Higgs-strahlung), where $l$ means charged leptons, as shown in the below

The $Z$ boson can be constructed by the invariant mass of di-lepton, and the Higgs can be constructed by the recoil mass of the $Z$ . This method of construction of Higgs is independent to how Higgs decays, and allows us measure the $ZH$ cross-section model indepently. You can find more details at Cross section and Higgs mass measurement with Higgsstrahlung at the CEPC.

Event Selection

The lepton candidates are selected by the criterion

$E_{l}>25 {\rm GeV}.$

Then di-lepton candidates are selected by the criterion

$|M_{ll} - M_Z | < 10 {\rm GeV}/c^2.$

If there are multiple combinations, the combination with smallest $\vert M_{ll} - M_Z\vert$ is selected. Once the di-lepton is constructed, the recoil mass is calculated by

$M_{\rm recoil} = \sqrt{ (\sqrt{s} - E_{l^-} - E_{l^+})^2 - (p_{l^-} + p_{l^+})^2 }$