Higgs to WW to lnu lnu

Higgs to WW to lnu lnu used to be a channel in which the group has been strongly involved between 2009 and 2018 contributing to the discovery of the Higgs boson in 2012, its property measurement in the subsequent years, and finally searches for heavy neutral Higgs boson using Run1 and the early Run2 data.

Team:

  • Physicist: Zhiqing Zhang
  • Postdoc/visitor: Bruce Mellado (several months in 2009-2010), Weimin Song (Jan. 2016-June 2017)
  • PhD student: Xifeng Ruan (LAL-IHEP, 2009-2012), Yichen Li (LAL-NanJing Univ., 2012-2015), Yongke Zhao (LAL-Shandong Univ., 2014-2018)

Thesis:

  • Search for Higgs boson in the WW* channel in ATLAS and drift time measurement in the liquid argon calorimeter in ATLAS: thesis
  • Observation of Higgs boson and measurement of its properties in the H to WW* channel with the ATLAS detector at the LHC: thesis
  • Recherche d’une résonance lourde dans le canal X->WW->eνµν avec le détecteur ATLAS au LHC: thesis

Documentation:

  • Review of data-driven methods used to control the normalization of the top quark background contribution in the H → WW(∗) → lνlν analyses at the LHC, Li, Y (LAL, Nanjing University) ; Ruan, X (University of the Witwatersrand) ; Yuan, L (Kobe University) ; Zhang, Z (LAL):  ATL-PHYS-INT-2014-037

Selected publications:

  1. Extraction of top background in the Higgs boson search with the H->WW*->lvlv decay with a full-jet veto at the LHC, Bruce Mellado, Xifeng Ruan, and Zhiqing Zhang, Phys. Rev. D 84 (2011) 096005
  2. Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC, ATLAS Collaboration, Phys. Lett. B 716 (2012) 1
  3. Observation and measurement of Higgs boson decays to WW* with the ATLAS detector, ATLAS Collaboration, Phys. Rev. D 92 (2015) 012006
  4. Constraints on the off-shell Higgs boson signal strength in the high-mass ZZ and WW final states with the ATLAS detector, ATLAS Collaboration, Eur. Phys. J. C 75 (2015) 335
  5. Determination of spin and parity of the Higgs boson in the WW* to eνµν decay channel with the ATLAS detector, ATLAS Collaboration, Eur. Phys. J. C 75 (2015) 231
  6. Search for heavy resonances decaying into WW in the eνµν final state in pp collisions at √s=13 TeV with the ATLAS detector, ATLAS Collaboration, Eur. Phys. J. C 78 (2018) 24

Old text:

Higgs to WW to lnu lnu is one of three decay channels which contributed to the discovery of the Higgs-like boson in 2012, and the latest results can be found in the paper: Observation and measurement of Higgs boson decays to WW* with the ATLAS detector .

fig_35

The main contribution of the ATLAS-LAL group is the proposal of a data-driven method for estimating the top background contribution in the dominant 0-jet channel and its application in the H->WW* analysis as well as other ATLAS analyses.
A review can be found in the LAL report 13-373 (Nov. 2013) and an example of application in the measurement of the WW cross section and limits on anomalous gauge couplings

In the early stage of data-taking with the limited integrated luminosity, we have been also interested in searching for the Higgs boson in a model with a fourth generation heavy quarks such that the search sensitivity is much higher by a factor up to 9 than that of the SM (see this article).

We have also contributed to the measurements of the properties of the Higgs boson in terms of couplings, spin and parity and width by maximizing the analysis sensitivity e.g. by extending the analysis to low lepton transverse momentum and using the multivariate technique.

The new interest of the group is to search for additional heavy neutral Higgs boson, which has been performed with Run-1 data (link) and is being continued with Run-2 data (link).

The group is in collaboration through the FCPPL project with a number of Chinese institutions (IHEP, Nanjing Univ. Shandong Univ. and USTC) for the nominal ggF analysis, IFIC for the VBF analysis, Kobe university for the top reduction/improvement in the 1-jet channel and KTH royal institute of technology for Dell-Yan and W+jets background studies.

Group members : Zhiqing Zhang (staff) and Yongke (PhD student) and Weimin Song (visitor of Shandong Univ). Former members of the group: Bruce Mellado (visitor), Xifeng Ruan (joint PhD student with IHEP) and Yichen Li (joint PhD student with Nanjing Univ.).