Last winter physicists detected hints of a potential new subatomic particle. It appeared to exceed their wildest dreams. Soon they may learn for sure if it exists at all. “I’m not aware of anybody who’d predicted the existence of such a particle,” says John Ellis. He’s a theoretical physicist in England at King’s College London.
He likens the new data, he says, to “a dish on the table that nobody can remember ordering.” Everyone looks around in confusion asking: What is that and where did it come from?
Hints of the new particle emerged last December at the Large Hadron Collider, or LHC. It’s the largest and most powerful particle accelerator in the world. It’s located near Geneva, Switzerland. There, it revs up protons (a building block of atoms) to almost the speed of light. Then it smashes beams of them into each other.
Rumors of the new particle emerged when a subtle wiggle showed up in data from two experiments at the LHC. These experiments suggested the new particle was breaking down into two particles of light, or photons. But what the new particle might be is unclear. Its properties don’t line up with anything that scientists had expected.
The hubbub could turn out to be a false alarm. But scientists are excited by the possibility that the new particle is real. Theorists have churned out hundreds of papers. More than 300 of these papers take a shot at explaining the potential particle’s origins. Scientists are now beginning to agree on the most likely explanations.
On April 12, Physical Review Letters published four more papers. These were selected to give a sense of the types of theories that could explain the observations — and how or why such a particle might exist.
One leading idea is that the particle is made of smaller ones. “I think that that’s the model that works the best with the data,” says Kathryn Zurek. She’s a theoretical physicist at Lawrence Berkeley National Laboratory in California. If so, those building-block particles might be held together by a new type of force. It could be much like the strong nuclear force that binds together particles called quarks. (Those quarks are building blocks of the protons and neutrons inside the nucleus of atoms.)
The particle also might resemble another particle, the Higgs boson — but with a mass six times the Higgs’ size. The Higgs boson was discovered at the LHC in 2012.
Still other theories propose that the particle could be a graviton. This type of particle, if it exists, is believed to transmit the force of gravity.
One puzzle is why the new particle appears to decay (break down) in only one way — by producing two photons. Most theories that could explain the particle predict its breakdown would lead to other particles as well, says Matthew Buckley. He’s a theoretical physicist at Rutgers University in Piscataway, N.J.
Some physicists are skeptical that the particle really exists. Instead, they think it is more likely to just end up a blip that will disappear with more data.
Updated analyses in March made physicists more optimistic that such additional data will confirm the proposed new particle as real. Maria Spiropulu is an experimental particle physicist. She worked on one of the LHC experiments. The first signs of the long-sought Higgs bosons showed up in a similar fashion — before they were confirmed. So, she says, theoretical physicists have good reason to be excited now.
The LHC experiments have been paused for a few months. (And operations there were briefly shut down again on April 29 when a small, weasel-like animal known as a beech marten apparently chewed through a power cable.)
Now, the LHC again is gearing up to collect more data. More data could provide additional details — or make the hints of a new particle disappear.
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accelerator (in physics) Also known as a particle accelerator, this massive machine revs up the motion of subatomic particles to great speed, and then beams them at targets. Sometimes the beams are used to deliver radiation at a tissue for cancer treatment. Other times, scientists crash the particles into solid targets in hopes of breaking the particles into their building blocks.
atom The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and neutrally charged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.
boson One of a group of particles that often carry forces between other particles.
collider (in physics) Sometimes called an “atom smasher,” it is a type of particle accelerator that speeds up charged particles (ions) through an electric field inside a hollow tube or racetrack-shaped structure. Eventually the device will direct the ions to collide with an unmoving target or another beam of moving particles. The ensuing collisions force some particles to interact — and break apart or briefly bind. Some of smashed particle also may recombine, creating new particles. The biggest of these machines are used to hunt for the basic building blocks of all nature.
decay (in physics) The process whereby a radioactive isotope — which means a physically unstable form of some element — sheds energy and subatomic particles. In time, this shedding will transform the unstable element into a slightly different but stable element. For instance, uranium-238 (which is a radioactive, or unstable, isotope) decays to radium-222 (also a radioactive isotope), which decays to radon-222 (also radioactive), which decays to polonium-210 (also radioactive), which decays to lead-206 — which is stable. No further decay occurs. The rates of decay from one isotope to another can range from timeframes of less than a second to billions of years.
force Some outside influence that can change the motion of a body, hold bodies close to one another, or produce motion or stress in a stationary body.
hadron One of a group of particles that are made up of other, smaller particles — quarks — held together by a particular kind of force. The protons and neutrons found in the nucleus of atoms are hadrons.
mass A number that shows how much an object resists speeding up and slowing down — basically a measure of how much matter that object is made from. On Earth it’s often referred to as something’s weight.
neutron A subatomic particle carrying no electric charge that is one of the basic pieces of matter. Neutrons belong to the family of particles known as hadrons.
nucleus Plural is nuclei. (in physics) The central core of an atom, containing most of its mass.
photon A particle representing the smallest possible amount of light or other electromagnetic radiation.
physics The scientific study of the nature and properties of matter and energy. Classical physics is an explanation of the nature and properties of matter and energy that relies on descriptions such as Newton’s laws of motion. Quantum physics, a field of study which emerged later, is a more accurate way of explaining the motions and behavior of matter. A scientist who works in that field is known as a physicist.
proton A subatomic particle that is one of the basic building blocks of the atoms that make up matter. Protons belong to the family of particles known as hadrons.
quarks A family of subatomic particles that each carries a fractional electric charge. Quarks are building blocks of particles called hadrons. Quarks come in types, or “flavors,” known as: up, down, strange, charm, top and bottom.
strong nuclear force Also called the strong force or strong interaction. One of the four fundamental forces. It’s the force that binds together quarks inside atomic nuclei, to form protons and neutrons (these are known as nucleons). In keeping with its name, it is the strongest known force in nature.
subatomic Anything smaller than an atom, which is the smallest bit of matter that has all the properties of whatever chemical element it is (like hydrogen, iron or calcium).
theoretical physics A branch of physics that uses mathematical models to understand the nature and properties of matter and energy. A scientist who works in that field is known as a theoretical physicist.
theory (in science) A description of some aspect of the natural world based on extensive observations, tests and reason. A theory can also be a way of organizing a broad body of knowledge that applies in a broad range of circumstances to explain what will happen. Unlike the common definition of theory, a theory in science is not just a hunch. Ideas or conclusions that are based on a theory — and not yet on firm data or observations — are referred to as theoretical. Scientists who use mathematics and/or existing data to project what might happen in new situations are known as theorists.
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Original Journal Source: R. Garisto. Editorial: Theorists react to the CERN 750 GeV diphoton data. Physical Review Letters. Vol. 116, April 15, 2016, p. 150001. doi: 10.1103/PhysRevLett.116.150001.
Original Journal Source: M. Delmastro. Diphoton searches in ATLAS, 51st Rencontres de Moriond EW 2016, La Thuile, Italy, March 17, 2016.
Original Journal Source: P. Musella. Diphoton Searches in CMS, 51st Rencontres de Moriond EW 2016, La Thuile, Italy, March 17, 2016.