A search that began almost 50 years ago is finally coming to a close. “But this is just the begin­ning,” said North­eastern physics pro­fessor Emanuela Bar­beris.

She and her North­eastern col­leagues Darien Wood and George Alverson have been among thou­sands of physi­cists in search of the Higgs Boson with the DZero exper­i­ment at Fer­milab in Illi­nois and the CMS exper­i­ment at CERN in Switzer­land. Ear­lier this week, physi­cists at CERN announced the most defin­i­tive evi­dence yet.

The so-​​called “God par­ticle” was first the­o­rized in the 1960s as essen­tial to the Stan­dard Model of par­ticle physics. Without it, our fun­da­mental under­standing of the uni­verse would be incor­rect and some other expla­na­tion would be necessary.

The Stan­dard Model says that fun­da­mental par­ti­cles in our uni­verse attain mass by passing through a “Higgs field,” which is sim­ilar to an elec­tro­mag­netic field but with one key dif­fer­ence. Instead of gen­er­ating elec­tro­mag­netic radi­a­tion, a Higgs field gen­er­ates mass.

When the field is inter­acting with itself, you get the Higgs boson,” said Bar­beris. “If the field is there, you should observe this particle.”

But the Higgs is one of the heav­iest fun­da­mental par­ti­cles around; as such, it is very unstable and readily decays into lighter par­ti­cles, like elec­trons, muons and pho­tons. In explaining why it took so long for physi­cists to finally see evi­dence of the particle’s exis­tence, Bar­beris explained that the prob­a­bility of pro­ducing it is very small.

The researchers’ chal­lenge was aug­mented by the fact that observing the fun­da­mental building blocks of the uni­verse is no easy task. Sci­en­tists col­lide sub­atomic par­ti­cles, like pro­tons, into one another at a rate near the speed of light. The resulting debris con­sists of a mess of ele­men­tary par­ti­cles, each of whose mass is detected and mea­sured against a back­ground of known par­ticle masses. Any unusual sig­nals could be a sign of a pre­vi­ously unob­served par­ticle — like the Higgs.

Because mass can be cor­re­lated to energy, higher energy col­li­sions will gen­erate par­ti­cles of higher mass. Since the 1990s, when the first Higgs search began in earnest, sci­en­tists have cre­ated col­liders of greater and greater energy, ruling out poten­tial Higgs masses and nar­rowing down the window in which it could be found.

Fermilab’s Teva­tron pro­duced col­li­sions with ener­gies up to two ter­a­elec­tron­volts (or two tril­lion elec­tron­volts) while CERN’s Large Hadron Col­lider can cur­rently reach eight teraelectronvolts.

On Monday, Fer­milab sci­en­tists announced that the Higgs boson would have a mass between 115 and 135 giga­elec­tron­volts. Then, on Wednesday, CERN’s team enhanced that pre­dic­tion by pre­senting spec­tac­ular sig­nals of a new par­ticle with a mass around 125 gigalec­tron­volts. The prob­a­bility that the CERN signal is a fluke is one in three mil­lion.  But there’s still a pos­si­bility that it is not the Higgs at all.

Going for­ward, CERN’s Large Hadron Col­lider will con­tinue col­liding pro­tons with one another and sifting through the resulting frag­ments in an effort to better under­stand the Higgs and all the other par­ti­cles we know of — and per­haps some that we don’t.

This is a piv­otal event that will help us shape the future of par­ticle physics research,” said Bar­beris. “Sci­en­tists will now focus on under­standing the prop­er­ties of the observed par­ticle through its inter­ac­tions with other particles.”