Masahiro Morii is a tinkerer at heart, looking under the hood of the universe in hopes of finding unseen particles that explain how it all works.

Morii, a particle physicist and professor of physics at Harvard, is engaged in the search for Kaluza-Klein (K-K) gluons, elusive particles that, if found, would provide evidence that the universe contains dimensions beyond the ones we experience everyday.

Morii is hoping the tracks of decaying particles left in the ATLAS detector point the way back to the K-K gluons, confirming the theories of Harvard theoretical physicist Lisa Randall.

ATLAS, which stands for “A Toroidal LHC Apparatus,” is one of the major experiments at the Large Hadron Collider (LHC) at CERN, the European Organization for Nuclear Research, in Switzerland. After a somewhat balky start-up in September, the collider has been powered down for repairs with re-start-up expected sometime in May 2009.

Until then, Morii said, the postdocs and students working with Morii and other ATLAS-affiliated Harvard faculty, including Donner Professor of Science John Huth, Mallinckrodt Professor of Physics Melissa Franklin, Assistant Professor of Physics Joao Guimaraes da Costa, and Physics Department Associate George Brandenburg, are taking advantage of the downtime to upgrade the detector and make repairs.

“We thought that in September ’08 we had to be ready for beam, so we left some things out,” Morii said. “That [LHC being down] means half a year of repair opportunities.”

Every day, Morii said, the student and fellow at CERN don hard hats, put on radiation exposure tags called film badges, submit to an iris scan to confirm their identity, and descend 100 meters below the surface to the tunnel within which the LHC sits. Using climbing gear to get to the inaccessible places in and around ATLAS, they are installing components and making repairs, so that ATLAS is ready when the LHC’s proton beams begin circulating again. Morii said their to-do list has more than a dozen components that need to be replaced, including things such as optical fiber cable — vulnerable to degradation in radiation — with radiation-hardened cable.

Huth said Morii’s expertise was put to immediate use after he joined the ATLAS project. One of the first things he did was map the device’s magnetic field, which highlighted a problem with the placement of the magnets.

“Masahiro joined ATLAS and made an immediate impact in many areas,” Huth said. “One notable area [involved] the problem of mapping the magnetic field of the detector. Masahiro … created a full three-dimensional map of the complicated field. In the process of trying to make sense of the data, he found that there were substantial discrepancies in the data that could only be explained by the magnets being significantly shifted from the positions indicated in the construction drawings. This was quite a shock to everyone and shows what one talented physicist can do, armed with the simple equations that are taught in the freshman physics classes.”

Morii said that everyone involved in ATLAS — an international collaboration involving some 2,000 scientists — is essentially interested in the same thing: They’re interested in seeing what happens when the most powerful particle accelerator ever built is switched on. The energy it will generate is higher than can be predicted by the dominant model of the physical universe, called the Standard Model. The Standard Model holds that the universe is made up of 40 different elementary particles and sets out the rules by which they interact. Physicists like Morii are eager to watch the standard model break down and glean whatever new clues they can use to inform future theories.

Morii’s love affair with science began early on. Growing up in Osaka, Japan, he remembers telling his first-grade teacher he wanted to be a scientist. Years later, as an undergraduate at Kyoto University, Morii said he became enamored with physics during a laboratory course and, though the experiments didn’t always turn out well, he learned a lot from the professor, who spoke of the active experiments he had at Japan’s KEK accelerator.

“That experience confirmed in me that this is cool. I want to do this for a living,” Morii said.

Morii received a bachelor’s degree from Kyoto in 1986, a master’s degree in 1988, and a doctorate in physics from Tokyo University in 1994. In 1996, he began a postdoctoral fellowship at Stanford University, working at the Stanford Linear Accelerator Center before coming to Harvard in 2000 as an assistant professor.

Since then, Morii was named Loeb Associate Professor of the Natural Sciences in 2004 and professor of physics in July 2007.

Morii calls himself a “born tinkerer” and said he often finds himself engrossed in a problem and can’t put it down. As an experimental physicist, his problems are often those of the machines and detectors he is designing to illuminate some unknown or theorized aspect of the universe.

“I think most of the time, day after day, my motivation is ‘OK, I’m going to make this stupid thing work,’” Morii said. “You made the thing, but you can’t make it work the way you want it to. That’s the day-to-day part of it.”

Being a professor, as well as a laboratory scientist, helps add perspective to his work, Morii said. While in the lab, one can get captivated by the particular tasks that must be completed, while in class, one is forced to step back, take a breath, and look at the big picture.

“In the lab, you can spend years and years without thinking, ‘Why are we doing this?’” Morii said. “Being a professor has big advantages, as it forces us to think about what we’re doing, why young people should make this the focus of their life.”

With ATLAS nearly up and running, Morii is considering where to devote his energies next. He has begun discussions with other Harvard faculty about forming a group focused on dark matter — the mysterious, invisible substance that astronomers say makes up a significant portion of the matter in the universe.

Morii said particles of dark matter — called “weakly interacting massive particles,” or WIMPs — might be detected at the LHC. The particles would be similar to neutrinos, but heavier, possibly much heavier.

“Dark matter particles are supposed to be everywhere; they just don’t interact often so we don’t see them,” Morii said. “The existence of dark matter is almost a certainty, we just don’t know what [it is]. It may be possible to build a table-top experiment — probably located deep underground to avoid background noises — that is sensitive enough to detect the dark matter particles as they pass by. Combining such an observation with findings at the LHC would be a powerful probe into what makes up 25 percent of the universe.”