
Higgs Couplings from the LHC
The Higgs boson in the Standard Model is not only the last
particle to be discovered (essentially triggering the construction of
the LHC), it is also unique in many ways. One of its exciting aspects
is that for all Standard Model particles the couplings to the Higgs
boson are fixed  they have to be proportinal to the particle's mass.
Any deviation from this structure points to physics beyond the
Standard Model, including predictions of new and unknown physical
states.
Higgs physics at the LHC offers two unique opportunities to test
the Standard Model. First, the Higgs potential is one of very few
windows to couple new particles to the Standard Model without spoiling
renormalizability. This effect is called the Higgs portal and would
appear as a uniform modification of all Higgs coupling. Second, two of
the Higgs work horses at the LHC, the Higgs couplings to gluons and to
photons, do not exist at tree level. Both operators are induced
through quantum effects. In the Standard Model, they are dominated by
effects from the top quark and the W boson, with some contributions
from the bottom quark and the tau lepton. New particles which either
get their mass through the Higgs mechanism or appear in the scalar
Higgs potential will be observable in these two couplings.
If the 126 GeV anomaly in ATLAS and CMS should turn out to be a signal
for a scalar resonance one of the main tasks for the LHC will be to
study the properties of this particle. A complete analysis of all
couplings is a major part of this effort. SFitter unfolds the many
correlated ways the different Higgs couplings affect the observed
counting rates in the different LHC channels. It includes correlated
statistical, systematic, and theory uncertainties. Its output is a
global loglikelihood map plus a detailed local study of its
maxima. If you are interested in an orthogonal appraoch with a focus
on anomalous couplings please check out this nice analysis by
our friends in Barcelona and Sao Paulo.
This private homepage collects Fitter results on the Higgs sector. As
the two theorists on the SFitter project we (Tilman Plehn and Michael
Rauch) would like to thank our ATLAS collaborators Remi Lafaye and
Dirk Zerwas as well as our CMS collaborator Markus Klute for the great
collaboration. Some of the material shown below is made by theorists
for theorists, i.e. it might include published but preliminary
experimental results. If you use any of the results shown here, please
refer to the paper where the corresponding official result is
published and to this website as the actual source.
If you are interested in talking to us or in collaborating with us,
please drop us an email. The modified HDECAY
version we use for our analyses is available upon request. If you use
it, please refer to our first
data analysis. So here are some of our main results, updates, and
a list of publications.
SFitterHiggs update after Moriond and Aspen 2013 and twoHiggsdoublet model analysis. The result includes the new diphoton rate by CMS. As usual, in additional to the universal coupling modification, the second and third entries show the results for a universal gauge boson and fermion coupling. To the right we show the ratio of couplings extracted from data. The paper also gives a detailed analysis for twoHiggsdoublet models.  
SfitterHiggs extrapolation of Higgs coupling measurements at a highluminosity LHC and a LC Higgs factory. The LHC analysis includes a full extrapolation of all experimental and theoretical uncertainties, including the appropriate likelihood treatment of flat theory uncertainties. We also show the crucial combination of LHC and LC measurements for example for the effective Higgsphoton coupling. Note that the main advantage of a linear collider, the actual measurement of the total Higgs width, does not enter this figure.  
SFitterHiggs update, based on 2011 (7 TeV) and 2012 (8 TeV) data as published after ICHEP 2012. For the first time, it includes all tree level Higgs couplings and an additional variable coupling of the Higgs boson to two photons (light blue). In additional to the universal coupling modification, the second and third entries show the results for a universal gauge boson and fermion coupling.  
Projections included in the same publication, based on 2011 data (7 TeV) as published after Moriond 2012. For all scenarios we show the expected measurements, i.e. assuming measurements of the Standard Model central values but with proper error bars. As a direct measurement of the bottom Yukawa couplings we include the boosted VH analysis as estimated in the ATLAS full simulation alaysis.  
First SFitterHiggs publication, based on 2011 data (7 TeV) as published after Moriond 2012. It includes the different tree level Higgs couplings as well as some ratios. The first entry corresponds to a universal form factor modification of all Higgs couplings. The three sets correspond to expected measurements (red), observed measurements (dark blue), and observed measurements with equal W and Z couplings (light blue). 
SFitterHiggs publications  
2013 update and 2HDM analysis  
combination with linear collider  
2012 update  
2011 data and projections  
2009 projections  
SFitter setup (SUSY)  
Further reading  
Higgs and QCD lecture notes 