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ATLAS “observed” the Higgs Boson decaying into bottom quark pairs

July 18, 2018      Author:

 On July 9th, 2018, ATLAS collaboration, being one of the main experiments at LHC CERN and consisting of ~3000 scientists all over the world, announced, together with its sister CMS experiment, the first "observation" of the signal of Higgs Boson decaying into bottom quark pairs (H→bb).



The Higgs Boson decaying into bottom quark pairs is the decay channel with highest branching ratio, ~58%. The observation of it is a very important knowledge enhancement of Higgs boson properties, which essentially helps to further understanding of the Higgs mechanism, probing and measuring the Higgs to Fermion Yukawa couplings, test of the Standard Model predictions of Higgs boson as well as search of the corresponding new physics in such decay final states.

The ATLAS China Group member institutes/universities have been strongly involved in this milestone achievement. Out of all, the TDLI and SJTU-SPA-INPAC ATLAS group members Shu Li, Chikuma Kato and Yanfeng Hang have made crucial contributions to the Hàbb discovery, via the Z(àll)H(àbb) channel.

ZH(bb) is a very important analysis topic in ATLAS experiment. It is an associate production mode of Higgs boson (in association with a Z boson), being one of the most sensitive channel in Hàbb decay signal searches. Shu Li, Chikuma Kato and Yanfeng Hang creatively introduced constrained fit of llbb kinematic system in the transverse plane to obtain a very high precision b-jet energy correction so that the Higgs boson decaying into bottom quark pairs can be reconstructed with a much better mass resolution (improved by 40%) and reduce the measured experimental uncertainty. Hàbb measurement is now systematic dominant, so such work is a very critical contribution to the 5-sigma observation.

Dr. Chikuma Kato obtained his PhD degree in 2018 from Univ. of Tokyo and during his PhD, he participated in many important ATLAS high energy frontier research projects and essentially contributed to the 2017 Hàbb first 3-sigma evidence paper. He is now a T.D. Lee postdoctoral research fellow of TDLI and is responsible for Muon Condition Data project of ATLAS in general, on behalf of TDLI and SJTU-SPA-INPAC ATLAS group.

Prof. Shu Li did his undergraduate and graduate study at USTC, PhD degree in 2012, under the supervision of Prof. Zhengguo Zhao, academician of CAS. From 2013 to 2017, he worked as a postdoc at Duke University, deeply involved in the ATLAS experiment. He joined TDLI as the first T.D. Lee Junior Fellow, co-appointed by INPAC, SJTU-SPA in 2017. Shu's remarkable research achievements consist of: precise estimate of the SM background of HiggsàWW greatly helping the Higgs discovery in 2012; 1st observation of triboson Zγγ rare process at LHC and 1st probe of Z/γàZγγ aQGC; 1st ATLAS measurement of electroweak Zγ VBS; search for Zγ resonance which greatly helped to resolve the 750GeV puzzle in 2016; 1st LHC search for Higgs+γ resonance. With the high recognition of his contribution, he has been appointed by the ATLAS collaboration (~3000 members in the world) to several important leadership positions such as: 2015/12-2017/01, the convener of the Monte Carlo Validation Group; 2017/04-2018/03, the convener of the Standard Model Electroweak (SM-EWK) Physics Group; 2018/04-Present, the convener of the Monte Carlo Generator Development and Tuning Group. The SM-EWK group has ~200 participants from ~50 institutions including Havard, UC Berkeley, Oxford, Michigan etc., working on dozens of multiboson measurement and anomalous coupling search topics.




Translated by Li Shu   Reviewed by Wang Bingyu