Measuring the CP state of tau lepton pairs from Higgs decay at the ILC

Article, Preprint English OPEN
Jeans, D. ; Wilson, G. W. (2018)
  • Publisher: APS
  • Journal: Physical Review D (issn: 2470-0029)
  • Related identifiers: doi: 10.1103/PhysRevD.98.013007
  • Subject: High Energy Physics - Phenomenology | High Energy Physics - Experiment
    arxiv: Computer Science::Digital Libraries | High Energy Physics::Experiment

In the Standard Model, the Higgs boson is a <math><mrow><mi>C</mi><mi>P</mi></mrow></math>-even state with <math><mrow><mi>C</mi><mi>P</mi></mrow></math>-conserving couplings; any deviations from this would be a sign of new physics. These <math><mrow><mi>C</mi><mi>P</mi></mrow></math> properties can be probed by measuring Higgs decays to <math><mi>τ</mi></math> lepton pairs, in which the transverse correlation between the <math><mi>τ</mi></math> spins depends on <math><mrow><mi>C</mi><mi>P</mi></mrow></math>. This paper develops such an analysis, using full simulation of signal and background events in the International Large Detector concept for the International Linear Collider. We consider Higgs-strahlung events (<math><mrow><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>→</mo><mi>HZ</mi></mrow></math>) in which the <math><mrow><mi>Z</mi></mrow></math> boson decays to electrons, muons, or hadrons, and the Higgs boson decays to <math><mi>τ</mi></math> leptons, which then decay either to <math><mrow><msup><mrow><mi>τ</mi></mrow><mrow><mo>±</mo></mrow></msup><mo>→</mo><msup><mrow><mi>π</mi></mrow><mrow><mo>±</mo></mrow></msup><mi>ν</mi></mrow></math> or <math><mrow><msup><mrow><mi>τ</mi></mrow><mrow><mo>±</mo></mrow></msup><mo>→</mo><msup><mrow><mi>π</mi></mrow><mrow><mo>±</mo></mrow></msup><msup><mrow><mi>π</mi></mrow><mrow><mn>0</mn></mrow></msup><mi>ν</mi></mrow></math>. Assuming <math><mrow><mn>2</mn><mtext> </mtext><mtext> </mtext><msup><mrow><mi>ab</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></math> of integrated luminosity at a center-of-mass energy of 250 GeV, the mixing angle between even and odd <math><mrow><mi>C</mi><mi>P</mi></mrow></math> components of the <math><mi>τ</mi></math> pair from Higgs boson decays can be measured to a precision of 75 mrad (4.3°).
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