Evidence for the spin-0 nature of the Higgs boson using ATLAS data

Evidence for the spin-0 nature of the Higgs boson using ATLAS data

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New data obtained by experiment ATLAS enabled detailed investigation of properties of new particle discovered in last year. Studies of the spin and parity quantum numbers of the Higgs boson are presented, based on proton–proton collision data collected by the ATLAS experiment at the LHC. The Standard Model spin–parity JP = 0+ hypothesis is compared with alternative hypotheses using the Higgs boson decays H→γγ, H→ZZ*→4ℓ (image 1) and H→WW*→ℓνℓν, as well as the combination of these channels. The data are compatible with the Standard Model JP = 0+ quantum numbers for the Higgs boson (image 2), whereas all alternative hypotheses studied in this Letter, namely some specific JP = 0,1+,1,2+ models, are excluded at confidence levels above 97.8 %. The results are compatible with spin zero and positive parity and are in agreement with the Standard Model expectations.

Physicists from Institute of Physics ASCR are members of ATLAS collaboration since 1992. They contributed in development and building of tracking and calorimeter detectors. These devices played a crucial role in the discovery of Higgs boson.

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Image 1: Higgs boson production candidate which had decayed into two muons and two antimuons. Parity and spin characteristics of the decaying particle could be obtained from the angular distribution of the decay products.
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Image 2: Measured angular distribution of photons from H→γγ decay (background noise subtracted).