Lepton-mass effects in the decays H →Z Z*→ℓ+ℓ-τ+τ- and H →W W*→ℓ ν τ ντ
Abstract
We consider τ -lepton mass effects in the cascade decays H →Z (→ℓ+ℓ-)+Z*(→τ+τ-) and H →W-(→ℓ-ν¯ ℓ)+W+*(→τ+ντ) . Since the scale of the problem is set by the off-shellness q2 of the respective gauge bosons in the limits (mℓ+mℓ')2≤q2≤(mH-mW ,Z)2 and not by mW,Z2, lepton-mass effects are non-negligible for the τ modes in particular close to the threshold of the off-shell decays. Lepton-mass effects show up in the rate and in the three-fold joint angular decay distribution for the decays. Nonzero lepton masses lead to leptonic helicity-flip contributions which in turn can generate novel angular dependencies in the respective three-fold angular decay distributions. Lepton-mass effects are more pronounced in the H →Z (→ℓℓ)Z*(→τ τ ) mode which, in part, is due to the fact that the ratio of lepton helicity-flip/nonflip contributions in the decay Z*→ℓ+ℓ- is fourtimes larger than in the decay W+*→ℓ+ν. Overall the inclusion of τ mass effects leads to a 3.97% reduction in the leptonic H →Z Z*rate. Lepton mass effects are quite pronounced for q2 values from threshold up to ∼200 GeV2 . For example, at q2=50 GeV2 the transverse-longitudinal-scalar helicity composition of the off-shell Z -boson changes from 0.06 :0.94 :0 to 0.04 :0.65 :0.31 for the τ lepton. This has observational consequences for the angular decay distributions of the final-state leptons. We also briefly consider the corresponding off-shell-off-shell decays H →Z*(→ℓ+ℓ-)+Z*(→τ+τ-) and H →W-*(→ℓ-ν¯ℓ)+ W+*(→τ+ντ).
- Publication:
-
Physical Review D
- Pub Date:
- August 2015
- DOI:
- 10.1103/PhysRevD.92.033001
- arXiv:
- arXiv:1505.06568
- Bibcode:
- 2015PhRvD..92c3001B
- Keywords:
-
- 14.80.Bn;
- 14.60.Fg;
- 11.80.Cr;
- Standard-model Higgs bosons;
- Taus;
- Kinematical properties;
- High Energy Physics - Phenomenology;
- High Energy Physics - Experiment
- E-Print:
- 45 pages, 9 figures and 6 tables, published version