Measurement of Higgs Yukawa coupling to probe new era of high energy physics

2019 Fiscal Year Final Research Report

• Project/Area Number: 17KK0084
• Research Category: Fund for the Promotion of Joint International Research (Fostering Joint International Research)
• Allocation Type: Multi-year Fund
• Research Field: Particle/Nuclear/Cosmic ray/Astro physics
• Research Institution: The University of Tokyo
• Principal Investigator: MASUBUCHI Tatsuya 東京大学, 素粒子物理国際研究センター, 助教 (20512148)
• Project Period (FY): 2018 – 2019
• Keywords: ヒッグス粒子 / LHC / 湯川結合 / ボトムクォーク / ガス検出器 / MPGD

Outline of Final Research Achievements

The main achievement of this research is the first observation of the interaction of the Higgs boson with bottom quarks.
We searched for the decay of the Standard Model(SM) Higgs boson into a bbbar pair with the production in association with a W or Z boson at the LHC-ATLAS experiment. The study using the partial data of 13 TeV proton-proton collision at Run 2 is performed. An observed significance is 5.4 standard deviations with a combination with other searches for the H->bb. The VH production, which is the one of main production channels is also observed at the 5.3 standard deviations.
In the full Run 2 dataset, we measured differential cross sections as a function of the gauge boson transverse momentum in 30-80% uncertainties and found those are consistent with the SM expectations. We also constrained several dimension-6 operators in the effective field theory which contains new interactions expected in the beyond SM.

Free Research Field

素粒子実験

Academic Significance and Societal Importance of the Research Achievements

本研究の重要な成果である、ヒッグス粒子がボトムクォークに崩壊するモードの初観測は、標準模型のパラメータの一つであるヒッグス粒子とボトムクォークの結合が、標準模型の予想通り湯川結合で記述されていることを世界で初めて観測した結果である。これによって、すでに観測されていた崩壊モードと合わせて全ての第3世代クォーク・レプトンと標準模型ヒッグス粒子が結合することが明らかになり、素粒子物理の大きな謎の一つである世代の解明への試金石となった。