Evidence for the Higgs Boson?

Proton-proton collision event in the CMS experiment Copyright: CERN



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In a scientific seminar that has been broadcast worldwide today, the two large-scale particle physics experiments ATLAS and CMS at CERN, the European Organization for Nuclear Research in Geneva, presented the latest results in their search for the Higgs boson. Three RWTH institutes are participating in the experiments.


The experiments investigate the reactions triggered by the collision of high-energy protons in the Large Hadron Collider (LHC). At a mass of approx. 125 GeV/c2 (giga electron volt), both experiments have gathered evidence for a new particle, which might be the long searched-for Higgs boson. By now it can be ruled out that the observed events are due to statistical fluctuations of the background: in both experiments the probability of such an explanation is less than one in a million. Evidence for the new boson is provided through the decay of it into two photons and two Z bosons.

There is some evidence that the observed particle is indeed the Higgs boson. “Only after further investigations we can decide whether this is really the missing piece in the Standard Model of physics or whether we have found something completely unexpected. Either would be a great discovery,” says Professor Achim Stahl, Chair of Experimental Physics IIIB at RWTH Aachen University. In 1990, the Large Hadron Collider project and its experiments were initiated at a widely noticed workshop in Aachen.

Over the last decades, physicists have developed a very powerful model which is excellent at describing the building blocks of matter and their forces: the Standard Model of particle physics. There is, however, one weakness to the model: exchange particles such as the photon, which carry forces between particles, cannot have mass. While this is true of the photon, the force particles in electroweak interaction are heavier than atoms – that is, heavyweights in the realm of particle physics. In order to resolve this contradiction, in 1964, Peter Higgs and others introduced a new concept, and if this concept is correct, there must be a particle – as yet undiscovered – that today is called the “Higgs boson.” Since then, scientists are on a quest for this elusive particle.

Researchers from RWTH Aachen have played a major role in this recent discovery. They contributed to planning the projects and developing the necessary technologies, and they have assembled parts of the high-resolution silicon strip detector and muon chambers here in Aachen. The detector measures the momentum of charged particles, while the muon chambers are used to identify muons in the variety of generated particles. Both components play an integral role in finding evidence for the Higgs boson. Over the last few years, researchers have focused on the analysis of data, which now has led to finding evidence for the new particle. A further key area in Aachen is computing: Aachen is part of the worldwide computing and data grid for the particle physics experiments and manages a grid node.

For many years, the German research groups contributing to the Compact Muon Solenoid (CMS) have been receiving funding from the Federal Ministry of Education and Research through the BMBF Research Program FSP-102 “Elementary Particle Physics with the CMS Experiment.“ Contributing institutions include the RWTH Physics Institutes IB, IIIA, and IIIB, the KIT Institute of Experimental Nuclear Physics (IEKP) in Karlsruhe, the University of Hamburg Institute for Experimental Physics, and DESY, the German Electron Synchrotron. Spokesperson for the Research Focus FSP-102 in Germany is RWTH Aachen Physicist Achim Stahl.