1. The lifetime of the Higgs boson
Nikhef ATLAS outing, June
Ivo van Vulpen

2. The lifetime of the Higgs boson
τh = [s]
Higgs boson:
τZ = [s]
Z-boson:
If the Higgs boson can decay to non-SM particles it decays faster
 Measuring the lifetime of the Higgs boson is crucial

3. Higgs boson decays

4. Higgs boson decay SM predicts decay rates and lifetime ( )
Higgs decay to fermions f h λf f
SM predicts decay rates
and lifetime ( )

5. Higgs boson decay SM predicts decay rates and lifetime ( )
Higgs decay to fermions f h λf f
Tristan
SM predicts decay rates
and lifetime ( )
Note: cross-section relative to SM

6. Higgs boson width (inverse lifetime)
Total Higgs width is the sum of the partial widths: Γ=ΣΓi
Higgs boson width
mh= 125 GeV  Γh= 4.07 MeV
uncertainty ~ 3%
The Higgs boson lifetime decreases with its mass

7. Higgs production cross-section

8. Breit-Wigner & width

9. Lifetime 1) ensemble (radio-activity): 2) single particle B C A t t+Δt
Unstable particles do not have a well-defined mass

10. Quantummechanical description of single particle decay
stable particle:
unstable particle:
Rewrite as sum of well-defined energy states (Fourier):
Pmax
Breit-Wigner Γ
Pmax/2
Contribution individual energy (mass) states:
E0-Γ/2 E0 E0+Γ/2

11. Direct measurement of Γh

12. Direct measurement of Γh
~4 MeV ~1000 MeV

13. uncertainties on 4-lepton mass
Antonio Castelli
4-muon invariant mass
uncertainties on 4-lepton mass
4 electrons
4 muons

14. Direct measurement of Γh
Limited by resolution on the 4-lepton invariant mass
CMS-HIG PAS
observed
expected
mh= ± 0.21 GeV
Γh < 1.10 GeV

15. Invisible Higgs decays

16. Invisible width of the Higgs bosonq
W/Z
Higgs DM DM
Higgs DM
invisible Higgs decay
invisible Higgs decay
Gabriele

17. Indirect measurement of Γh

18. Access to Γh: cross-section ratio
Ratio ~Γh, …. but off-shell cross-section is tiny

19. Indirect measurement A higgsZZ B qqZZ C ggZZ
Interference between A and C: (A+C)2 = A2 + C2 + 2AC
tiny
Not so tiny !!!

20. Indirect measurement Enrich in ggZZ (vs qq)
QCD & EW corrections, missing NLO ggZZ diagrams (shape+rate)
- Multiple final states: 4l, 2l2v, …
- interpretation in terms of Γh (theory)
Now working on it: Jochen, Birgit, Peter Warming up: Hella, Ivo + PhD student
Birgit

21. Limits on Higgs width
ATLAS
CMS
Γh < 22.7 MeV
Γh < 13 MeV

22. The lifetime of the Higgs boson
Interesting and crucial measurement
ATL-PHYS-PUB
Γh = MeV (stat+syst)
3000 fb-1