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RWTH Aachen Particle Physics Theory

The Higgs Boson in 2015

October 23rd, 2015 | by

The Higgs boson has been discovered in 2012 at CERN’s Large Hadron Collider (LHC), or more precisely at the LHC experiments ATLAS and CMS. The discovery of the Higgs resonance is definitely a milestone in particle physics and two of the fathers of the Higgs mechanism, Peter Higgs and Francois Englert, were awarded the nobel prize in physics in 2013.

After the discovery three years ago, there was immediately a decisive question to be answered: Has the discovered particle all the properties which are predicted by the Standard Model (SM) of particle physics. Or turning the question around in more scientific terms: Are there any statistically significant deviations from the SM predictions which can be identified with the recorded proton-proton collisions. Any such deviation would of course call for physics beyond the SM. Until the end of LHC run 1 at the beginning auf 2013, there have been great efforts to collect as many Higgs collisions as possible. And similar efforts have been invested in recent years to extract as much information as possible from the recorded data.

Higgs coupling strength measurements

Signal strength measurements for different Higgs-production channels, where a signal strenath of 1 is the SM expectation (taken from ATLAS CONF-2015-044)

Only recently the Higgs legacy of run 1 has been finalized performing the combination of the Atlas and the CMS data. The so-called signal strength for different production channels and the global signal strength is shown in the diagram on the right relative to the SM prediction. So far, the discovered particle does not give any hints for new physics beyond the SM. It simply looks more or less as predicted decades ago.

For these and similar measurements, the interplay between theory predictions and the experimental analysis is most crucial. Mid of October, experimentalists and theorist working on Higgs physics have met at the conference “Higgs Couplings 2015” which was hosted by the IPPP in Durham and took place in the beautiful medieval Lumley Castle close to Durham. The latest run 1 measurements have been presented and discussed. But run 1 is already part of the past. Everybody is looking forward to seeing the measurements from run 2 and gearing up for the upcoming analyses.

Run 2 has already started this year with the record breaking proton-proton energy of 13 TeV (run 1 has provided 7 and 8 TeV collisions). In 2015, a year to learn how to operate at the record-breaking energy and with collisions every 25 nano-secons, there will be not enough data recorded to make a major step forward in the precision of Higgs measurements (this is very different for other new physics searches, e.g. for multi-TeV resonances). However, the coming years of run 2 will be exciting for Higgs physics for sure.

So far, measurements are still statistically limited, i.e. by the relatively small number of recorded Higgs-bosons. However, residual uncertainties within the theoretical predictions will soon enter as a major player in the quest for ultimate measurements of Higgs properties, and therefore also in the quest for physics beyond the SM in the Higgs sector. Hence, improving theory predictions and making them available for the analysis of the data is more important than ever in the field of Higgs physics, and one of the research topics at our institute. Conferences like the “Higgs Couplings 2015” are providing an important forum for discussions on these topics between experimentalists and theorists.

So, let’s see what nature will teach us about the Higgs in the coming years.



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