1. Higgs decays to fermions in CMS (H  , Hbb, a)
Rainer Mankel
Deutsches Elektronen Synchrotron (DESY)
for the CMS Collaboration
Standard LHC Conference 2012
Niels Bohr International Academy and Discovery Center, Copenhagen
12 April 2012

2. R. Mankel; Higgs decays to fermions in CMS
Introduction
Standard model (SM) has been extremely successful in describing wide range of phenomena in particle physics
only remaining undiscovered SM particle: Higgs boson
comprehensive approach covering many different production mechanisms & decay channels
Di-fermion final states:
below the thresholds for di-boson (W, Z) production,  lepton and b quark offer relatively large masses for the Higgs to couple to
play important rôle in low-mass region
Beyond a discovery, an essential goal is to investigate the detailed structure of the Higgs sector
di-fermion decays are an important probe distinguishing different structural options
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

3. SM Higgs Production & Decays
gg fusion
VBF
W/Z associated
For a Standard Model Higgs, di-fermion decay modes dominate for mH<130 GeV
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

4. Higgs Sector: Structure?
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

5. Structure of the Higgs Sector
Standard Model
one physical Higgs state (H)
quadratically divergent self-energy corrections at high energies
H bb,  _
MSSM (=minimal supersymmetric extension)
two complex Higgs doublets
physical states: h, H, A, H  (mA, tan )
avoids quadratic divergences
new mass scale parameter  “ term problem”
 
“”
NMSSM (=next to minimal supersymmetric extension)
avoids “ term problem”
two complex Higgs doublets + additional singlet field
physical states are mixtures: h1, h2, h3, a1, a2, H
a 
CP-even
CP-odd
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

6. R. Mankel; Higgs decays to fermions in CMS
H  bb Searches _
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

7. R. Mankel; Higgs decays to fermions in CMS
VHV(bb) _
For a light standard model Higgs, Hbb would be the predominant decay channel
observation of Hbb decay is essential to determine nature of Higgs
For ggH (~17pb for mH=120 GeV), QCD background is overwhelming
relation improves in association with W or Z boson  boosted analysis.
Five final states considered:
W(e)H, W()H
Z(ee)H, Z()H, Z()H
Main backgrounds:
Z/W + jets, t+X, tt, VV, QCD multi-jet
background contributions normalized in control regions
mass-based and boosted decision tree-based (BDT) analyses _ -
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

8. VH(bb) Analysis (cont’d)
(arXiv: , submitted to P.L. B)
Mass-based cut & count analysis
pT(W)>160 GeV
pT(Zll)>100 GeV
ETmiss>160 GeV for Z( )H
ETmiss>35 GeV for W(e)H
Combined Secondary Vertex (CSV) algorithm used for b tagging
combines impact parameter and secondary vertex information in a discriminant
No signal observed
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

9. BDT Output (Selected Channels)
Boosted decision tree technique used to improve separation of signal & background
Variables for selection & training:
For various variables relaxed selection cuts
BDT increases sensitivity by ~10% in each channel
Variable
W(l)H
Z(ll)H
Z()H
pT(j1)
>30 GeV
>20 GeV
>80 GeV
pT(j2)
pT(jj)
>150 GeV
>100 GeV
>160 GeV
pT(V) -
ETmiss
>35 GeV [W(e)H]
(V, H)
CSVmax
>0.40
>0.244
>0.50
CSVmin
Nal =0
Naj
(ETmiss,jet)
>0.5 rad
for mH=115 GeV
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

10. R. Mankel; Higgs decays to fermions in CMS
VHV(bb): Results
No significant signal observed in any of the channels
Total expected limit ~ 3x SM expectation (mH=115 GeV)
Observed limit from combination consistent with expectation
BDT analysis (lower plot) performs 2-20% better than the mass-spectrum- based analysis (upper)
BDT analysis
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

11. R. Mankel; Higgs decays to fermions in CMS
H   Searches
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

12. H    At lowest masses 2nd strongest decay mode after Hbb_
At lowest masses 2nd strongest decay mode after Hbb
Final states:
Standard Model search: event categories by production mechanisms:
(arXiv: , submitted to P.L. B)
 had
New!
e had
e 
 
CMS PAS HIG
e e
had had
Inclusive
Vector Boson Fusion
Boosted
Little sensitivity due to background
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

13. R. Mankel; Higgs decays to fermions in CMS
H    (cont’d)
m() estimated by kinematic maximum likelihood fit
effective resolution ~21%
Irreducible background from Z 
addressed with “embedding method”
in Z events from real data, the ’s are replaced by simulated ’s
New: H
very challenging channel
irreducible background from Z 
addressed by evaluating the distance of closest approach between ’s
signal enhancement with likelihood method
H
VBF category
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

14. R. Mankel; Higgs decays to fermions in CMS
H    (cont’d)
H   
No significant excess over the expected standard model background contributions is observed
Combination e , e had,  had :
expected & observed 95% CL limit ~ 3x SM expectation (mH=115 GeV)
observed limit consistent
Addition of H  channel improves on combined limit from the other three decay
combination result in preparation
[e , e had,  had]
H   
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

15. R. Mankel; Higgs decays to fermions in CMS
 MSSM Search
Non b-Tag:
b-Tag:
Mainly two processes contribute to pp+X
Subsample with one btagged jet has increased sensitivity for MSSM Higgs boson search
smaller relative contribution from inclusive Z production b
Non b-Tag:
b-Tag:  
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

16. R. Mankel; Higgs decays to fermions in CMS
 MSSM Search
Excludes previously unexplored territory
95% CL exclusion range for tan  extends down to 7.1 at mA~160 GeV
narrowed parameter space at low mA
  channel alone fairly competitive with other measurements
H   
[He , e had,  had]
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

17. R. Mankel; Higgs decays to fermions in CMS
a   Search
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

18. R. Mankel; Higgs decays to fermions in CMS
Search for a
CMS PAS HIG
In the NMSSM, one of the two CP-odd scalars could be very light
superposition of CP-odd doublet scalar and the additional singlet scalar  mixing angle A
even m(a)<2 mB thinkable
sensitive to Cabb coupling
Consider here: <ma< 8.8 GeV, <ma< 14 GeV
up to now, strongest constraints come from BaBar through (3S)a
Cross section could be large
(HIGLU)
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

19. R. Mankel; Higgs decays to fermions in CMS
a (cont’d)
Di-muon mass spectrum in  mass region
Main backgrounds:
Upsilon resonances  exclude mass region of 9-11 GeV
QCD continuum
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

20. R. Mankel; Higgs decays to fermions in CMS
a (cont’d)
Range 1
Range 2
Range 1
Range 2
Mass scan with Gaussian signal PDF
Accounting for radiative tail of (1S) in range 1
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

21. R. Mankel; Higgs decays to fermions in CMS
a (cont’d)
Range 1
Improvements on BaBar limits for NMSSM parameter |cos A| in lower mass range
CDF published limits relative to (1S) cross section (not shown)
No BaBar or CDF limits in upper mass region
Range 2
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

22. Di-Fermion Channels in SM Combination
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

23. SM Higgs Searches: Comparison Di-Fermion with Other Channels
(arXiv: , submitted to P.L. B)
Di-fermion channels show very good consistency with the di-boson channels
At mH=125 GeV, consistently see mild excess at level expected by standard model
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

24. CMS SM Higgs Searches Combined
Showing low-mass region, where di-fermion decays contribute most
HWW dominates in GeV (HZZ beyond)
H dominates below 120 GeV
Excluded mass 95% CL:
expected GeV
observed GeV
More data are required to assess nature of observed excess
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

25. R. Mankel; Higgs decays to fermions in CMS
Summary
Di-fermion channels particularly important at low Higgs masses
also sensitive to detailed structure of Higgs sector
Standard Model Higgs search:
in bb and  channels, 95% CL limits at low mass range near 3x SM
recent improvement due to  channel
MSSM search:
 channel excludes wide area in (mA, tan ) parameter space
NMSSM search:
upper limits for very light pseudoscalar Higgs boson ( channel)
Excellent prospects for 2012 LHC run (just started…) _
More CMS results in fermion channels (not shown in this talk):
Search for doubly charged Higgs boson CMS PAS HIG
Search for WH  e(), () CMS PAS HIG
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

26. R. Mankel; Higgs decays to fermions in CMS
Further information
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

27. R. Mankel; Higgs decays to fermions in CMS
SM Higgs Combination
Observed and expected 95% CL confidence limits on the signal strength parameter = / SM for the SM Higgs boson hypothesis
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

28. R. Mankel; Higgs decays to fermions in CMS
SM Higgs Combination
Observed and expected 95% CL confidence limits on the signal strength parameter =/ SM for the SM Higgs boson hypothesis by decay channel
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

29. R. Mankel; Higgs decays to fermions in CMS
SM Higgs Combination ^
Observed local p-value (p0) and best-fit =/ SM
12 April 2012
R. Mankel; Higgs decays to fermions in CMS

30. VHV(bb): Example Control Regions
Background-enhanced distributions
Wbb enhanced for WH (top)
V+udscg enhanced for Z()H (bottom, left)
tt enhanced for Z()H (bottom, right) _
[unboosted] _
[dilepton mass sideband]
[fake MET]
12 April 2012
R. Mankel; Higgs decays to fermions in CMS