This proposal requests continuing support for a program of research for the Wood group at Northeastern University (NEU) in experimental elementary particle physics based primarily on the D0 experiment at the Fermilab Tevatron collider and the CMS experiment at the Large Hadron Collider (LHC) at CERN.
For the past few decades, physicists have been able to describe with increasing detail the fundamental particles that make up the Universe and the interactions between them. Much of this success has been due to the Tevatron program at Fermilab with D0 and CDF making major contributions. This NEU group has made major contributions to the D0 experiment in its construction and in the physics questions proposed as well as in many leadership roles. Wood is presently co-spokesman of D0. The group is pursuing physics topics which are important for understanding the electroweak sector of the Standard Model and physics beyond the Standard Model. These include W/Z + jets production, ZZ production, Higgs searches, and top quark properties. At the same time the LHC and ATLAS will start operation in new regimes of energy and luminosity holding even greater promise for discoveries and measurements leading to revisions of our views on how the world is constructed and the nature of the laws that govern its operation. This group is now transitioning into the CMS program where it will parlay its wealth of experience in muon detection and identification into a leadership role in muon + jets studies - a signature that is sensitive to a variety of new physics processes.
On Broader Impacts, the group will continue its work within the QuarkNet program. With the strong cooperative education program at Northeastern University, the group will continue to routinely involve undergraduates in research with substantial and meaningful six-month projects at CERN. In his role and co-spokesperson of D0, Wood will work actively with the press to share with the public the excitement of the Higgs search and other potential discoveries at the Tevatron. The group plans to host and organize important conferences, and Barberis will continue to communicate the value of high energy research to the US Congress through her work with the Fermilab Users Executive Committee.
This grant supported the work of three professors (Alverson, Barberis, and Wood) plus several postdoctoral scholars, graduate students and undergraduates. This grant period included exciting and productive work at both the DZero experiment at Fermilab and the CMS experiment at CERN. The DZero experiment studies the collisions of protons and antiprotons at the Tevatron collider, with a total collision energy of 2 Teraelectronvolts. At the time the grant began, these were the highest energy collions in the world. DZero was at its peak of producing mature results during this grant period. The CMS experiment was designed to study much higher energy collisions of protons with protons at the Large Hadron Collider. After years of preparation, CMS got its first beam exposure during this grant period and went on to record many collisions at a world-record energy of 7 Teraelectronvolts. These experiments require huge international efforts and require substantial leadership. The DZero experiment, for example, comprised about 500 physicists from 80 institutions in 18 counties. Wood served as co-leader ("spokesperson") of the DZero experiment starting a few months before the start of this grant period and ending in August 2009. This was a very exciting and productive period for DZero, with nearly one hundred publications establishing significant advances in our knowledge of how particles and fields interact at the shortest distances and fasted time scales that we can measure. Many of the results were focused on the elusive Higgs boson, the particle that, if it exists, could be responsible for giving mass to other particles. For the first time since the closing of the LEP collider at CERN in 2000, we were able to directly eliminate possible mass values for the Higgs boson, and thus substantially narrow the range where it could be hiding. This group from Northeastern particularly focused on the searching for the Higgs boson when it is produced with a Z boson that entirely escapes detection by decaying into neutrinos. This would give rise to events such as the one shown in the figure. Analysis continues, and we may soon be able to say if such an event can come from a Higgs or is merely one of the more common processes with a Z bosons and jets of other particles. Another highlight of the work of the Northeastern group on DZero in this period was the measurement of the production of pairs of Z bosons. This process was predicted to exist by the theory of electroweak interactions, but had not ever been observed at a hadron collider before. This was not only an important test of the theory, but is also paves the way for several studies of the Higgs boson that involved pairs of bosons (particles with integer spin). The results and knowledge from DZero were very important for understanding the collisions at the LHC. In particular, the process of a Z boson produced with jets of strongly-interacting particles (hadrons) allowed more precise theoretical prediction for what such events should look like at the LHC. At CMS, it was very satisfying to see the detector perform so well, particularly the cathode strip chambers (CSCs) in the end cap muon system where we had contributed to installation, commissioning, calibration, visualization, and operations. We also took on new responsibilities in the upgrade of the CSC electronics to improve performance and allow efficient operation at future higher luminosities. We were able to get out an early interesting result and capitalize on our muon detection expertise in the search in the CMS data for a particle called a "leptoquark". Leptoquarks, if they exist, would explain why the generations of quarks (up, down, strange, charm, bottom, top) have the same number and a similar structure as the leptons (electrons, muons, taus and the three types of neutrinos). The result, published in Physical Review Letters, extended the sensitivity to much higher leptoquark masses than the previous results from the Tevatron. We also reached out to local high school students and teachers through the QuarkNet program. High school classes came to Northeastern to participate in "Master Classes", where they used video links to Fermilab and other Master Class institutions to study events from particle collisions. Alverson developed special software to allow students to examine these events in three dimensions. Another important part of our mission was the training of the next generation of physicists. We had one students complete a Ph.D. in this period and go on to a research position at CERN. Several undergraduates worked with us through the co-op program and went on to graduate school. Five of our postdoctoral fellows went on to research and teaching positions around the world.
