Michigan Physicists Help Uncover a New Particle Consistent with the Higgs Boson


Jul 27, 2012 Bookmark and Share

Muon detector built by U-M group

This Fourth of July, while the United States celebrated Independence Day, scientists at CERN, near Geneva, Switzerland, including members of the University of Michigan ATLAS group, announced one of the most important discoveries in fundamental physics, the detection of a
new particle with properties consistent with the Higgs boson.

Nearly half a century ago, theoretical physicists Robert Brout, Francois Englert, Peter Higgs, Gerald Guralnik, Carl Hagen, and Tom Kibble developed a scheme called spontaneous symmetry breaking that was able to account for the origin of the masses of fundamental particles. One of the predictions of this very elegant idea was the existence of a new, massive, spinless particle that we now call the Higgs boson.

One of the main goals of the Superconducting Super Collider (SSC), to be built in Texas during the 1990s, was a conclusive search for the Higgs boson. The United States government chose to cancel this project thereby forcing many U.S. physicists to pursue this research overseas at CERN.

In 1998, Professor Homer Neal initiated an effort to assemble a research group at the University of Michigan with the goal of participating in the ATLAS experiment at the Large Hadron Collider (LHC) at CERN. The main goals of this experiment were to make a conclusive search for the Higgs boson and to search for new physics beyond the scope of the existing Standard Model of particle physics.

Professor Neal's effort resulted in one of the largest university groups in the ATLAS collaboration. He has served as the University of Michigan ATLAS Institutional representative since the project’s inception. Prior to data-taking the primary work of the Michigan group, under the leadership of Professors J. Chapman and Bing Zhou, together with Professor Rudolf Thun, was the electronic instrumentation and construction of very large devices for the detection of muons. These proved to be critical in the discovery of the Higgs boson.

Other participants in this nearly decadelong detector construction and software development project included research scientists Edward Diehl, Daniel Levin and Zhengguo Zhao, engineering scientist Tiesheng Dai, engineering technician Curtis Weaverdyck, senior technician Helmut Schick, and several outstanding postdoctoral fellows

Current U-M ATLAS GroupIn parallel with this effort, the Michigan ATLAS group, under the leadership of research scientist Shawn McKee and scientist Robert Ball with support from the University of Michigan, assembled and today continue to operate one of the major ATLAS computing centers. The centers have proven essential for the timely analysis of the enormous data stream generated by ATLAS. After completion of the detector construction phase, the focus of the Michigan ATLAS group shifted to data analysis with emphasis on the search of the Higgs boson. In 1989, the key methods for this search were documented in "The Higgs Hunter's Guide", co-authored by Professor Gordon Kane, a theory colleague in the University of Michigan Physics Department.

Professor Jianming Qian coordinated the effort of over one hundred physicists from all over the world as convener of the ATLAS group searching for the Higgs boson in the W-boson decay channel and is also a major contributor to the statistical analysis of the combination of Higgs searches in different, individual channels. Professors Bing Zhou and Rudolf Thun, and research scientist Haijun Yang have concentrated their analysis on the search in the Z-boson decay channel where a signal was observed at a mass of 126 GeV, thereby determining one of the key parameters of the Higgs boson. These analysis efforts have contributed significantly to the claim of discovery on the Fourth of July. A paper summarizing the discovery will be published in Physics Letters B. Professor Homer Neal has concentrated on developing techniques for studying particle quantum spin and will be applying these to help confirm that the spin and parity of the newly discovered particle is indeed that required of the Higgs by current theory.

Collectively, over 130 Michigan personnel worked on this giant scientific project during the past 14 years. In particular, the Michigan group has provided many opportunities for student participation within the ATLAS collaboration. Over the years, 20 graduate students and 63 undergraduate students have directly contributed to the U-M ATLAS research project. Our group, and department colleague Professor Jean Krisch, have provided the main portal for bright U.S. undergraduates nationwide to spend summers at CERN working on ongoing LHC experiments, including those seeking the Higgs. Over 150 students have been provided this unique opportunity through our program over the past decade.

The University of Michigan ATLAS group looks forward to many years of elucidating the still mysterious Higgs mechanism. The group has recently been joined by a new faculty member, Assistant Professor Junjie Zhu. He is a leading physicist in ATLAS and is studying vector boson scattering and fusion to continue testing the Higgs mechanism and to search for physics beyond the Standard Model.

The CMS and ATLAS Higgs discovery talks can be viewed at:
http://www.youtube.com/watch?v=9iOgAlZOf7k

Additional links of related U-M ATLAS activities and individual perspectives will be added in the near future.