284
P. Jenni and T. S. Virdee
6.7.1 Event and Physics Objects Reconstruction and Analysis
Techniques
It is convenient to subdivide the analysis of data relating to Higgs bosons according
to the decay channel, using datasets where the data have been selected to contain
a particular set of final state particles. To improve the sensitivity, the events in this
dataset are usually separated into categories that are intended to reflect the expected
signal-to-background ratio. Several multivariate methods are used in the analyses
– to improve event reconstruction, estimates of the energies/momenta of physics
objects (e.g. photons and electrons, etc.),
– to identify physics objects (such as electrons, photons, b-quarks, tau leptons, etc.)
– to categorize events according to particular production (e.g. ggH, VBF, VH, ttH
etc.), decay mode, or expected signal-to-background ratio.
The reader can find the exact description of the multivariate methods used within
the individual papers referenced in the sections below.
Charged leptons and photons originating from the fundamental partonic processes tend to be “isolated” i.e. no other particles surround the one of interest.
A relative isolation condition is applied on such particles. The sum of transverse
momenta of accompanying particles, within an angular radius of approximately 0.3,
around the particle of interest, is divided by the transverse momentum of the particle
of interest. A cut on this ratio is made, the value of which is separately optimized for
electrons, muons or photons. A correction to the accompanying energy is applied
when the instantaneous luminosity is high and undesirable energy from pileup
interactions is accidentally captured in the region.
6.7.2 The Discovery: Results from the 2011 and Partial 2012
Datasets
In the 2011 data-taking run the ATLAS and CMS experiments recorded data at
√
s = 7 TeV corresponding to an integrated luminosity of ~5 fb −1 . In December
2011, the first “tantalizing hints” of a new particle from both the CMS and
ATLAS experiments were shown at CERN. The general conclusion was that both
experiments were seeing an excess of unusual events at roughly the same place in
mass (in the mass range 120–130 GeV) in two different decay channels. That set the
stage for data taking in 2012.
In January 2012 it was decided to slightly increase the energy of the protons
from 3.5 to 4 TeV, giving a centre of mass energy of 8 TeV. By June 2012 the
number of high-energy collisions examined had doubled and both CMS and ATLAS
had greatly improved their analyses so it was decided to look at the area which
had shown the excess of events but only after all the algorithms and selection
procedures had been agreed, in case a bias was inadvertently introduced. These data
P. Jenni and T. S. Virdee
6.7.1 Event and Physics Objects Reconstruction and Analysis
Techniques
It is convenient to subdivide the analysis of data relating to Higgs bosons according
to the decay channel, using datasets where the data have been selected to contain
a particular set of final state particles. To improve the sensitivity, the events in this
dataset are usually separated into categories that are intended to reflect the expected
signal-to-background ratio. Several multivariate methods are used in the analyses
– to improve event reconstruction, estimates of the energies/momenta of physics
objects (e.g. photons and electrons, etc.),
– to identify physics objects (such as electrons, photons, b-quarks, tau leptons, etc.)
– to categorize events according to particular production (e.g. ggH, VBF, VH, ttH
etc.), decay mode, or expected signal-to-background ratio.
The reader can find the exact description of the multivariate methods used within
the individual papers referenced in the sections below.
Charged leptons and photons originating from the fundamental partonic processes tend to be “isolated” i.e. no other particles surround the one of interest.
A relative isolation condition is applied on such particles. The sum of transverse
momenta of accompanying particles, within an angular radius of approximately 0.3,
around the particle of interest, is divided by the transverse momentum of the particle
of interest. A cut on this ratio is made, the value of which is separately optimized for
electrons, muons or photons. A correction to the accompanying energy is applied
when the instantaneous luminosity is high and undesirable energy from pileup
interactions is accidentally captured in the region.
6.7.2 The Discovery: Results from the 2011 and Partial 2012
Datasets
In the 2011 data-taking run the ATLAS and CMS experiments recorded data at
√
s = 7 TeV corresponding to an integrated luminosity of ~5 fb −1 . In December
2011, the first “tantalizing hints” of a new particle from both the CMS and
ATLAS experiments were shown at CERN. The general conclusion was that both
experiments were seeing an excess of unusual events at roughly the same place in
mass (in the mass range 120–130 GeV) in two different decay channels. That set the
stage for data taking in 2012.
In January 2012 it was decided to slightly increase the energy of the protons
from 3.5 to 4 TeV, giving a centre of mass energy of 8 TeV. By June 2012 the
number of high-energy collisions examined had doubled and both CMS and ATLAS
had greatly improved their analyses so it was decided to look at the area which
had shown the excess of events but only after all the algorithms and selection
procedures had been agreed, in case a bias was inadvertently introduced. These data