[Paper Review] Probing SUSY Naturalness at the CEPC

Lei Wu|arXiv (Cornell University)|May 6, 2017

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper proposes testing the higgsino world scenario in natural SUSY by precisely measuring $e^+e^- \to W^+W^-$ at the CEPC Higgs factory. With 0.1% accuracy at 240 GeV, the CEPC can probe higgsino masses with $\mu \lesssim 210$ GeV, offering a viable alternative to LHC mono-jet searches hampered by systematic uncertainties.

ABSTRACT

The discovery of a 125 GeV SM-like Higgs boson, in conjunction with the very recent null results of the LHC Run-2 searches for sparticles, has jeopardized the naturalness of the minimal supersymmetric Standard Model (MSSM) with light stops and gluino. Therefore, it is necessary to explore other possible scenarios in the minimal framework for which the theory maintains naturalness and is consistent with the current data. Among them, the higgsino world is one of the popular natural SUSY scenarios, in which $|\mu| \ll M_{gauginos} \ll M_{scalars}$. As such, searching for light dgenerate higgsinos becomes an essential task of testing naturalness in supersymmetry (SUSY). At the LHC, the direct way to probe for such a higgsino world from mono-jet (-like) events may be challenging because of the potentially large systematical uncertainties. In this work, I propose to test higgsino world through precision measurement of cross section of the process $e^+e^- o W^+W^-$ at future Higgs factories, such as Circular Electron Positron Collider (CEPC) in China. I find that the higgsino mass parameter $\mu \lesssim 210$ GeV favored by naturalness can be covered if the accuracy of the measurement of $W^+W^-$ production can reach 0.1\% at 240 GeV CEPC.

Motivation & Objective

• To address the challenge of testing natural SUSY in light of LHC null results for sparticles.
• To explore viable natural SUSY scenarios beyond the stop-gluino paradigm.
• To propose a precision measurement at future Higgs factories as a complementary probe to direct LHC searches.
• To demonstrate the feasibility of testing the higgsino world scenario through $e^+e^- \to W^+W^-$ cross-section measurements at CEPC.
• To quantify the sensitivity of CEPC to the higgsino mass parameter $\mu$ under realistic experimental accuracy.

Proposed method

• The study focuses on the $e^+e^- \to W^+W^-$ process at the CEPC collider operating at 240 GeV center-of-mass energy.
• It evaluates the sensitivity of the $W^+W^-$ production cross section to the higgsino mass parameter $\mu$ in the context of the MSSM.
• The analysis assumes a theoretical framework where $|\mu| \ll M_{\text{gauginos}} \ll M_{\text{scalars}}$, characteristic of the higgsino world.
• The method relies on precision measurement of the $W^+W^-$ cross section to constrain $\mu$, leveraging the CEPC's high luminosity and low systematic uncertainties.
• It uses theoretical predictions for the $W^+W^-$ cross section in the MSSM with light higgsinos to determine the required measurement accuracy.
• The key equation involves the $W^+W^-$ cross section as a function of $\mu$, with sensitivity derived from expected experimental precision.

Experimental results

Research questions

• RQ1 Can the CEPC achieve sufficient precision to probe the higgsino mass parameter $\mu$ in the natural SUSY scenario?
• RQ2 How does the $W^+W^-$ production cross section at CEPC depend on $\mu$ in the higgsino world?
• RQ3 What level of measurement accuracy is required at CEPC to test $\mu \lesssim 210$ GeV?
• RQ4 Can $e^+e^- \to W^+W^-$ precision measurements serve as a viable alternative to LHC mono-jet searches for light higgsinos?
• RQ5 What is the sensitivity reach of CEPC to natural SUSY in the higgsino-dominated parameter space?

Key findings

• The CEPC can probe higgsino mass parameters with $\mu \lesssim 210$ GeV if the $W^+W^-$ production cross section is measured with 0.1% accuracy.
• A 0.1% measurement accuracy at 240 GeV CEPC is sufficient to cover the naturalness-favored region of the higgsino world.
• The precision measurement of $e^+e^- \to W^+W^-$ offers a complementary and potentially more robust probe than LHC mono-jet searches.
• The method is particularly effective in the higgsino world where $|\mu| \ll M_{\text{gauginos}} \ll M_{\text{scalars}}$, minimizing model dependence.
• The study demonstrates that future Higgs factories like CEPC can test natural SUSY beyond the reach of current LHC searches.
• The results show that CEPC's high-precision capability makes it a powerful tool for probing the naturalness of the MSSM in the higgsino-dominated regime.