CMS Collaboration / CERN

This proton-proton collision, recorded with the Large Hadron Collider's Compact Muon Solenoid last year, shows the characteristics expected from the decay of the Standard Model Higgs boson to a pair of Z bosons. One of the Z particles subsequently decays to a pair of electrons (green lines and green towers), and the other Z decays to a pair of muons (red lines). The event could also be due to known Standard Model background processes

The subatomic particle discovered last year at Europe's Large Hadron Collider is looking more and more like the fabled Higgs boson, the one fundamental piece that's been missing from the theory that governs particle physics. But at a widely anticipated conference in Italy, physicists said they can't yet confirm 100 percent that this is the particle they're looking for.

Ever since the "Higgs-like particle" was detected, researchers at the LHC have been trying to determine whether this is the one true Higgs boson predicted by the Standard Model, or whether it's just one of several subatomic particles that play a role in imparting mass to other particles. There's even a chance that this particular particle something completely different, possibly linked to the way gravity works, said James Gillies, a spokesman for the CERN particle physics center on the French-Swiss border.

CERN is the international organization in charge of operating the world's biggest and costliest particle accelerator.

The key to confirming the particle's status is to determine a property known as spin, CERN says. If the new particle is spin-zero, then it's a Higgs boson. If it's spin-two, it's something else. The latest results, presented at the annual Moriond conference in La Thuile, Italy, can't yet rule out a spin-two particle, CERN said.

"Until we can confidently tie down the particle's spin, the particle will remain Higgs-like," CERN research director Sergio Bertolucci said in a statement on Wednesday. "Only when we know that is has spin-zero will we be able to call it a Higgs."

Physicists will continue to analyze the data collected at the LHC over the past couple of years, and there's a good chance they'll come up with the confirmation in the months ahead — even though the collider was shut down last month for an upgrade that's expected to require two years of work. That's not guaranteed, however. Raymond Volkas, a physicist from Australia's University of Melbourne, told New Scientist that Higgs-watchers might have to prepare themselves for the possibility that the LHC will never fully confirm the mystery particle to be the Standard Model Higgs.

Last year, scientists were intrigued by an extra "peak" in the data from ATLAS, one of the LHC's main detectors. Some wondered whether that hinted at the existence of two Higgs bosons instead of just one. But now that more readings have been added to the analysis, the anomalous peak is fading.

"When we first saw this excess a year ago, we were excited that it may be real physics and we hoped that by this time we would have a truly significant effect," the ViXra Log's Philip Gibbs writes. "This has not happened."

Gibbs said that yet-to-be-released findings are said to throw even more cold water on the two-boson hypothesis. "This means that expectations of significant BSM [beyond Standard Model] effects from run 1 are now lower," he wrote.

Update for 4 p.m. ET: The consensus appears to be that the results presented at the Moriond conference firm up the Standard Model's view of the subatomic world — which is a bit of a disappointment for those hoping to see clear signs of new physics. "It may well be a 'vanilla Higgs,' though there are still hints of unseen sprinkles," Robert Garisto, editor of the Physical Review Letters, joked in a Twitter update.

"Vanilla" was also the word used by Caltech theoretical physicist Sean Carroll in his Twitter assessment, although Harvard's Lisa Randall replied that there was still a chance of getting "vanilla swirl." On his "Not Even Wrong" blog, Columbia mathematician Peter Woit says it's looking like a "garden-variety [Standard Model] Higgs, which is discouraging for hopes of hints about how to get beyond the Standard Model."

The headline on Wired's report pretty much sums up the mood: "This Just In: Higgs Boson Still Boring."

More about the Higgs boson:

• Physicists to share latest word about Higgs quest
• Higgs-like particle may foretell end of universe
• Special report on the Large Hadron Collider

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.