Data from the particle collider at Cern seems to point to a new massive particle not predicted by the standard model of physics. If confirmed, this could be the biggest discovery in physics since 1975 when a new lepton was found.
The first hint came with an excess of photon pairs reported by Atlas and CMS experiments last year, with the latter proving more convincing in recent analysis using wider set of data.
The small excess of photon pairs with a combined energy around 750 GeV is believed to be due to a new boson that spits out two photons and more as it decays.
The data came from Atlas and CMS, the two largest detectors at the 27-kilometre-circumference LHC at CERN, the European particle-physics laboratory near Geneva, Switzerland.
In the latest CMS analysis the data is 22% larger than the one that the experiment reported in December, as it includes collisions from early in the LHC's 2015 run.
The latest analysis rules out statistical fluctuation and shows after cross-checking the data that the bump representing the new particle remains, and is slightly more pronounced.
"We've re-calibrated our data and made several improvements to our analyses," says Livia Soffi, a postdoc at Cornell University. "These are the best, most refined results we have. But we're still working with the same amount of data we collected in 2015. At this point, only more data could make a significant difference in our ongoing research."
In 2015, LHC scientists recorded data from 20 trillion proton-proton collisions. Some collisions simultaneously produced a high-energy and clean pair of photons. Around 1200 of these photon pairs have a combined energy of 125 GeV. Proceeding into higher energies, there are fewer and fewer pairs recorded till at around 750 GeV, scientists observed only a few dozen photon pairs, and a handful more than predicted. This is what is being ascribed to the new boson.
"I saw this fluctuation while doing my PhD thesis with CMS data from Run 1 and didn't think anything of it," Soffi says. "Now CMS and Atlas have both seen it again in the new data. This could easily be a coincidence. But if it keeps showing up, then we might have something."
New particles
Atlas scientists have had mixed results in two independent searches using different methods. One showed a small excess of photon pairs at 750 GEV but the other showed nothing. A further investigation of the 13 TeV data from 2015 shows that the bump, though present, is not significant.
The Higgs boson or 'god particle' with a mass of 125 GeV discovered in 2012 at Cern was predicted by the standard model of physics. It is responsible for all the mass in the universe. Now the search is for other possible Higgs bosons with higher masses. If similar to Higgs boson, the new particle is expected to spit out more than photons.
A "four-flavoured" quark is the newest elementary particle on the scene, detected at Fermilab by physicists of Indiana University. The new tetraquark has been dubbed X(5568) owing to its mass of 5568 Megaelectronvolts. There are around 61 elementary particles in the standard model today.
While the second run of the LHC has seen collisions at 1.6 times more energies than before, time is required to collect data at the high energy range. In the coming three years, the scientists are hoping to have 30 times more data than available today.
The standard model however only describes around 4% of the known universe. The collisions at high energies are expected to throw up answers to dark matter and energy as also anti-matter. Possibly, also unveil a host of new exotic particles.
