New ATLAS precision measurements of the Higgs Boson in the 'golden channel'

May 16, 2017
Figure 1: Distribution of the invariant mass of the four leptons selected in the ATLAS measurement of H→ZZ*→4l using the full 2015+2016 data set. The Higgs boson corresponds to the excess of events with respect to the non resonant ZZ* background observed at 125 GeV. Credit: ATLAS Collaboration/CERN

The discovery of a Higgs boson in 2012 by the ATLAS and CMS experiments marked a milestone in the history of particle physics. It confirmed a long-standing prediction of the Standard Model, the theory that comprises our present understanding of elementary particles and their interactions.

With the huge amount of proton–proton collisions delivered by the LHC in 2015 and 2016 at the increased collision energy of 13 TeV, the ATLAS experiment has entered a new era of Higgs boson property measurements. The new data allowed ATLAS to perform measurements of inclusive and differential cross sections using the "golden" H→ZZ*→4ℓ decay.

The four-lepton channel, albeit rare (0.012% branching fraction into final states with electrons or muons), has the clearest and cleanest signature of all the possible Higgs boson decay modes. This is due to the channel's small background contamination. Figure 1 shows a narrow resonant peak at 125 GeV in the reconstructed invariant mass on top of a locally relatively flat background distribution dominated by (non-resonant) qq→ZZ* production.

The Higgs boson's transverse momentum can be used to probe different Higgs production mechanisms and possible deviations from the Standard Model interactions. Figure 2 shows the measured differential cross section of the four-lepton transverse momentum (pT4l) compared to various Standard Model predictions.

Figure 2: Differential cross section for the transverse momentum (pT4l) of the Higgs boson. The measured cross section is compared to different ggF SM predictions. The error bars on the data points show the total uncertainties, while the systematic uncertainties are indicated by the boxes. Credit: ATLAS Collaboration/CERN

By studying the number of jets produced in these events, as well as the transverse momentum of the leading jet, ATLAS can probe and help improve the theoretical modelling of Higgs boson production via gluon fusion. The measured and predicted differential cross sections as a function of the jet multiplicity are shown in Figure 3.

Several differential cross sections have been measured for observables sensitive to Higgs boson production and decay, including kinematic distributions of the jets produced in association with the Higgs boson. Good agreement is found between the data and Standard Model predictions. The measurements are used to constrain anomalous Higgs boson interactions (see Figure 4).

Figure 3: Distribution of the invariant mass of the four leptons selected in the ATLAS measurement of H→ZZ*→4l using the full 2015+2016 data set. The Higgs boson corresponds to the excess of events with respect to the non resonant ZZ* background observed at 125 GeV. Credit: ATLAS Collaboration/CERN

Figure 4: Limits on modified Higgs-boson decays within the framework of pseudo-observables. The limits are extracted in the plane of εL and εR, which modify the contact terms between the Higgs boson and left- and right-handed leptons, assuming lepton-flavour universality. Credit: ATLAS Collaboration/CERN

Explore further: From supersymmetry to the Standard Model: New results from the ATLAS experiment

More information: Presentation at LHCP conference by Eleni Mountricha: Higgs measurements in high resolution channels with ATLAS:

Related Stories

Improving our understanding of di-photons

April 7, 2017

High-energy photon pairs at the Large Hadron Collider are famous for two things. First, as a clean decay channel of the Higgs boson. Second, for triggering some lively discussions in the scientific community in late 2015, ...

ATLAS and CMS experiments shed light on Higgs properties

September 1, 2015

Three years after the announcement of the discovery of a new particle, the so-called Higgs boson, the ATLAS and CMS Collaborations present for the first time combined measurements of many of its properties, at the third annual ...

ATLAS experiment seeks new insight into the Standard Model

May 10, 2017

Ever since the LHC collided its first protons in 2009, the ATLAS Collaboration has been persistently studying their interactions with increasing precision. To this day, it has always observed them to be as expected by the ...

ATLAS sees Higgs boson decay to fermions

November 28, 2013

The ATLAS experiment at CERN has released preliminary results that show evidence that the Higgs boson decays to two tau particles. Taus belong to a group of subatomic particles called the fermions, which make up matter. ...

LHC experiments join forces to zoom in on the Higgs boson

March 17, 2015

Today during the 50th session of "Rencontres de Moriond" in La Thuile Italy, ATLAS and CMS presented for the first time a combination of their results on the mass of the Higgs boson. The combined mass of the Higgs boson is ...

Recommended for you

Weyl fermions exhibit paradoxical behavior

May 23, 2017

Theoretical physicists have found Weyl fermions to exhibit paradoxical behavior in contradiction to a 30-year-old fundamental theory of electromagnetism. The discovery has possible applications in spintronics. The study ...

Astronomers use bubbles to look for WIMPs

May 23, 2017

Invisible, imperceptible and yet far more common than ordinary matter, dark matter makes up an astounding 85 percent of the universe's mass. Physicists are slowly but steadily tracking down the nature of this unidentified ...

Neptune: Neutralizer-free plasma propulsion

May 23, 2017

Plasma propulsion is an important and efficient technology used to control spacecraft for Earth observation, communications and fundamental exploration of outer space.


Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet May 17, 2017
i am waiting for physicists to think through a way to suppress this field now that we have found it. That will change space flight and if low enough energy would change travel on Earth.
Da Schneib
not rated yet May 17, 2017
@Nose, you are thinking about canceling inertia. This is problematic unless you hypothesize that gravitational and inertial mass can be unlinked.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.