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

Abstract

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 <math xmlns="http://www.w3.org/1998/Math/MathML"><msup is="true"><mrow is="true"><mi is="true">J</mi></mrow><mrow is="true"><mi is="true">P</mi></mrow></msup><mo is="true">=</mo><msup is="true"><mrow is="true"><mn is="true">0</mn></mrow><mrow is="true"><mo is="true">+</mo></mrow></msup></math> hypothesis is compared with alternative hypotheses using the Higgs boson decays H→ γγ, <math xmlns="http://www.w3.org/1998/Math/MathML"><mi is="true">H</mi><mo is="true">→</mo><mi is="true">Z</mi><msup is="true"><mrow is="true"><mi is="true">Z</mi></mrow><mrow is="true"><mo is="true">⁎</mo></mrow></msup><mo is="true">→</mo><mn is="true">4</mn><mi is="true">ℓ</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mi is="true">H</mi><mo is="true">→</mo><mi is="true">W</mi><msup is="true"><mrow is="true"><mi is="true">W</mi></mrow><mrow is="true"><mo is="true">⁎</mo></mrow></msup><mo is="true">→</mo><mi is="true">ℓ</mi><mi is="true">ν</mi><mi is="true">ℓ</mi><mi is="true">ν</mi></math>, as well as the combination of these channels. The analysed dataset corresponds to an integrated luminosity of 20.7 fb−1 collected at a centre–of–mass energy of √ s = 8 TeV. For the <math xmlns="http://www.w3.org/1998/Math/MathML"><mi is="true">H</mi><mo is="true">→</mo><mi is="true">Z</mi><msup is="true"><mrow is="true"><mi is="true">Z</mi></mrow><mrow is="true"><mo is="true">⁎</mo></mrow></msup><mo is="true">→</mo><mn is="true">4</mn><mi is="true">ℓ</mi></math> decay mode the dataset corresponding to an integrated luminosity of 4.6 fb−1 collected at √ s = 7 TeV is added. The data are compatible with the Standard Model <math xmlns="http://www.w3.org/1998/Math/MathML"><msup is="true"><mrow is="true"><mi is="true">J</mi></mrow><mrow is="true"><mi is="true">P</mi></mrow></msup><mo is="true">=</mo><msup is="true"><mrow is="true"><mn is="true">0</mn></mrow><mrow is="true"><mo is="true">+</mo></mrow></msup></math> quantum numbers for the Higgs boson, whereas all alternative hypotheses studied in this letter, namely some specific <math xmlns="http://www.w3.org/1998/Math/MathML"><msup is="true"><mrow is="true"><mi is="true">J</mi></mrow><mrow is="true"><mi is="true">P</mi></mrow></msup><mo is="true">=</mo><msup is="true"><mrow is="true"><mn is="true">0</mn></mrow><mrow is="true"><mo is="true">−</mo></mrow></msup><mo is="true">,</mo><msup is="true"><mrow is="true"><mn is="true">1</mn></mrow><mrow is="true"><mo is="true">+</mo></mrow></msup><mo is="true">,</mo><msup is="true"><mrow is="true"><mn is="true">1</mn></mrow><mrow is="true"><mo is="true">−</mo></mrow></msup><mo is="true">,</mo><msup is="true"><mrow is="true"><mn is="true">2</mn></mrow><mrow is="true"><mo is="true">+</mo></mrow></msup></math> models, are excluded at confidence levels above 97.8%. This exclusion holds independently of the assumptions on the coupling strengths to the Standard Model particles and in the case of the <math xmlns="http://www.w3.org/1998/Math/MathML"><msup is="true"><mrow is="true"><mi is="true">J</mi></mrow><mrow is="true"><mi is="true">P</mi></mrow></msup><mo is="true">=</mo><msup is="true"><mrow is="true"><mn is="true">2</mn></mrow><mrow is="true"><mo is="true">+</mo></mrow></msup></math> model, of the relative fractions of gluon–fusion and quark–antiquark production of the spin-2 particle. The data thus provide evidence for the spin-0 nature of the Higgs boson, with positive parity being strongly preferred.