Scientists participating in experiments at LHC announce discovery of a new subatomic particle that could be the Higgs boson particle, ending a half-century quest

The Higgs boson particle may have been found

August 1, 2012

By Elton Alisson

Agência FAPESP – One of the greatest challenges in science could be coming to an end. This past July 4, scientists participating in experiments at the Large Hadron Collider (LHC) announced the discovery of a new subatomic particle that could be the Higgs boson particle.

The subject of an almost half-century hunt by physicists, the Higgs boson is the key to understanding why elementary particles have mass and could even lead to a new understanding of the origin of the Universe and life itself. Until the recent discovery, the boson was a hypothetical particle first theorized by British physicist Peter Higgs.

The discovery of the boson would represent complete validation of the Standard Model of Physics, a theory that describes the fundamental strong, weak and electromagnetic forces and fundamental particles that constitute all matter.

The announcement came from scientists participating in the ATLAS (A Toroidal LHC Apparatus) and the CMS (Compact Muon Solenoid) experiments at the LHC of the European Organization for Nuclear Science (CERN) in Switzerland. Researchers from Brazil participated in the two experiments.

“I think we have it,” commented Rolf Heuer, director general of CERN, who called the discovery a “historic milestone.” Particle physicists from both ATLAS and CMS found strong indications of a new particle with a mass of 125 or 126 billion gigaelectronvolts (GeV). Higgs, 83, was at CERN during the announcement.

“We observe in our data clear signs of a new particle, at the level of five sigma, in the mass region around 126 GeV. A little more time is needed to finalize these results, and more data and more study will be needed to determine the new particle’s properties,” commented ATLAS spokesperson, Fabiola Gianotti. At CMS, the particle identified has a mass of approximately 126 GeV.

In particle physics, 5 sigma indicates a 99.99% probability that the result is correct and that there is a one in 1.75 millionth of a chance that it is a statistical deviation.

The indications of a new particle were identified by analysis of trillions of collisions among particles conducted at the LHC in 2011 and 2012. The Standard Model of particle physics stipulates that the Higgs boson would decay into different particles, precisely what the LHC has just discovered.

The discovery was also announced at the International Conference of High Energy Physics (ICHEP 2012) in Melbourne, Australia, where detailed analysis was presented throughout the weeklong meeting. At CERN, scientists from the ATLAS and CMS experiments presented preliminary results to the scientists present and to colleagues at hundreds of institutions the world over via video transmitted over the web.

Brazilian researchers are members of both teams, and at the time of the announcement, two of them were at the conference in Melbourne where they presented their work. The scientists are part of the São Paulo Research and Analysis Center (SPRACE), a research group at Universidade Estadual Paulista (UNESP).

Through SPRACE, the Brazilian researchers operate a data processing network and participate in analysis of the data produced by CMS.

The SPRACE group attending the conference in Australia consisted of Sandra Padula, Thiago Tomei, Flávia Dias and Ângelo Santos, in addition to Sérgio Novaes, the SPRACE coordinator and professor of UNESP’s Theoretical Physics Institute (IFT). The group gave a presentation on the consequences of the possible existence of extra dimensions in the Universe and overviewed the recent results obtained from collisions of heavy ions.

According to Novaes, proving the discovery of the Higgs boson will still take time. “Although recent events suggest that we have found the Higgs boson, the confirmation that it is really the particle predicted by the Standard Model will require comparative measures,” he said.

“The intensity of Higgs coupling with different particles (such as photons) is predicted by mathematical models, and this will be the definitive test. Still, this could take time because it requires that more data be collected,” he said.

SPRACE actively participated in Fermilab’s DZero experiment in the United States, which operated until September 2011 and has been developing joint research in the CMS Collaboration at CERN, from which it has published more than 130 scientific works.

The SPRACE cluster is part of the LHC’s Worldwide Computing Grid (WLCG), and through resources granted by FAPESP, more than 64 processing nodes have just been delivered to increase the storage capacity to 1 petabyte.

“FAPESP’s support under the auspices of our Thematic Project has been decisive for our data analysis activities at LHC,” says Novaes. In Brazil, researchers and journalists have followed the event in real time at the SPRACE computational lab at IFT.

The Higgs boson is an unstable particle that survives for a small fraction of a second before decaying into other particles. Because of this, the particle can only be observed based on a measure of its products.

The Standard Model of particle physics, which is the theory of physics that describes matter with extreme precision, estimates that the Higgs boson decays into different combinations of particles or channels, and its distribution among such channels depends on its mass.

The new particle is indicated by events occurring at a mass of approximately 125 GeV (126 GeV). Lower masses have been excluded by other experiments at CERN with the same level of confidence. The LHC continues to provide new data at a high speed. By the end of 2012, CMS expects to more than triple the quantity of data accumulated to date. “These data will allow CMS to clarify the nature of this newly observed particle,” says Novaes.

Impacts of the discovery

According to Sergio Morais Lietti, a researcher at SPRACE, the discovery of the particle was possible due to accumulation of the data generated and the increase in the LHC’s energy load in the last few years.

From 2010 to 2011, the particle accelerators operated at 7 TeV. In the 2011 to 2012 period, the LHC’s energy was increased to 8 TeV per beam, which allowed scientists to increase their chances of producing the Higgs boson.

“The more energy there is in the center of the mass among protons in the accelerator, the greater the chances of producing the Higgs boson,” commented Lietti in an interview with FAPESP. According to him, the confirmation of a new Higgs boson particle will not represent the end of studies on particle physics, but rather, the beginning of research work in the area.

“If the particle is confirmed to be the Higgs boson particle,” highlights Lietti, “more precise and statistical studies will be required to improve the Standard Model.”