A new type of pentaquark is shown as a pair of standard hadrons loosely bound in a molecule-like structure. Credit: CERN
Physicists say they’ve found evidence in data from Europe’s Large Hadron Collider for three never-before-seen combinations of quarks, just as the world’s largest particle-smasher is beginning a new round of high-energy experiments.
The three exotic types of particles — which include two four-quark combinations, known as tetraquarks, plus a five-quark unit called a pentaquark — are totally consistent with the Standard Model, the decades-old theory that describes the structure of atoms.
A ring of magnets runs through the Large Hadron Collider’s 17-mile-round tunnel. (CERN Photo / Samuel Joseph Herzog)
Europe’s Large Hadron Collider has started up its proton beams again at unprecedented energy levels after going through a three-year shutdown for maintenance and upgrades.
It only took a couple of days of tweaking for the pilot streams of protons to reach a record energy level of 6.8 tera electronvolts, or TeV. That exceeds the previous record of 6.5 TeV, which was set by the LHC in 2015 at the start of the particle collider’s second run.
The new level comes “very close to the design energy of the LHC, which is 7 TeV,” Jörg Wenninger, head of the LHC beam operation section and LHC machine coordinator at CERN, said today in a video announcing the milestone.
When the collider at the French-Swiss border resumes honest-to-goodness science operations, probably within a few months, the international LHC team plans to address mysteries that could send theories of physics in new directions.
Experiments at Europe’s Large Hadron Collider have produced hard-to-come-by evidence of interactions between the Higgs boson and top quarks. The findings, announced today at a conference in Bologna, Italy, “give a strong indication that the Higgs boson has a key role in the large value of the top quark mass,” Karl Jakobs, spokesperson for the LHC’s ATLAS collaboration, said in a news release.
A computer graphic shows the spray of particles created by a proton collision in the Large Hadron Collider’s CMS detector. The two green lines indicate the emission of two photons. Physicists say that could be part of an intriguing pattern, or merely a coincidence. (Thomas McCauley / CERN / CMS)
The Higgs boson is the biggest find of the century in particle physics, but for the past few weeks, physicists at the Large Hadron Collider have been considering whether there’s a mystery that’s even bigger. Or at least more massive.
The potential mystery has to do with a pattern of particle decay that results in the emission of two photons. The readings collected so far by the teams using the ATLAS and CMS detectors point to a slight “bump” in the expected pattern.
That may hint at the existence of a previously undetected particle with a mass of about 750 billion electron volts – six times heavier than the Higgs, French physicist Adam Falkowski (a.k.a. Jester) writes in his Resonaances blog.
However, the two-photon excess may be merely a coincidence – the sort of pattern that pops up in an early stage of data collection, but fades away when more readings are factored into the findings.
This computer graphic shows one of the first collisions recorded between two lead ions at the Large Hadron Collider’s top energy. The energy in the center-of-mass system is approximately a quadrillion electron-volts. (Credit: CERN / ALICE Collaboration)
Before the LHC’s startup in 2008, the Internet was set abuzz with worries that high-energy collisions could create globe-gobbling black holes or cosmos-wrecking strangelets. Protests were mounted, lawsuits were filed, and physicists at Europe’s CERN particle physics center had to explain in depth why the nightmare scenarios were nothing more than nightmares. Once the collider went into operation, the lawsuits were dismissed and the hand-wringing settled down.
Now the world’s largest collider is operating at near its design limits, and this week, CERN reported that lead-ion collisions in the LHC’s ALICE detectorreached energies beyond a quadrillion electron-volts – a level also known as 1 peta-electron-volt, or 1 PeV.
“This energy is that of a bumblebee hitting us on the cheek on a summer day. But the energy is concentrated in a volume that is approximately 10 -27 (a billion-billion-billion) times smaller,” Jens Jørgen Gaardhøje, professor at the Niels Bohr Institute at the University of Copenhagen and head of the Danish research group within the ALICE experiment, said in a news release.
At first blush, a quadrillion electron-volts sounds like a huge ramp-up from 13 trillion to 14 trillion electron-volts, or 13 to 14 TeV, the traditionally quoted figures for the high end of the LHC’s collision energy. That’s what set off the doomsayers. In the weeks leading up to the ALICE collisions, there was a drumbeat of postings claiming that “CERN LIED” and warning that 1-PeV smashups would have catastrophic consequences.
