“Impossible” particles add a piece to the puzzle of strong force

This spring, in Syracuse University Quark Physics Group Meeting, Ivan Polyakov He announced that he had revealed the fingerprints of a semi-legendary particle.

We said: It is impossible. What’s wrong with you? ” sheldon stonegroup leader.

Polyakov went away and reviewed his analysis of data from the Beauty Large Hadron Collider (LHCb) experiment of which the Syracuse group is a part. Evidence held. He showed that a certain group of four fundamental particles called quarks can form a tight clique, contrary to what most theorists believe. The LHCb collaboration reported the discovery of the complex particle, nicknamed the double-enchanted tetraquark, at a conference in July and in two Leaves published earlier this month and is now subject to peer review.

The unexpected discovery of a double-enchanted tetraquark highlights an uncomfortable truth. While physicists know the exact equation that defines the strong force — the fundamental force that holds quarks together to make protons and neutrons in the cores of atoms, as well as other composite particles like tetraquarks — they can rarely solve this strange, endless iterative equation, so they struggle to predict the effects of the force. powerful.

The quaternary quark now offers theorists a solid target to test their mathematical mechanism for approximating the strong force. Refining their estimates is the main hope for physicists to understand how quarks behave inside and outside atoms — and to keep traces of quarks away from the subtle signs of the new fundamental particles that physicists seek to follow.

cartoon quark

The strange thing about quarks is that physicists can approach them on two levels of complexity. In the 1960s, in conflict with a zoo of newly discovered composite particles, they developed the cartoon “quark model,” which simply says that the cartoon quarks come together in complementary groups of three to form the proton, neutron, and other baryons, while pairs of quarks form species different from meson particles.

Gradually, a deeper theory known as quantum chromodynamics (QCD) emerged. Draw the proton in the form of Boil a block of quarks They are held together by tangled strands of “gluon” particles, carrying the intense force. Experiments have confirmed many aspects of QCD, but there are no known mathematical techniques that can systematically Uncover the central equation of the theory.

In a way, the quark model can represent the most complex reality, at least when it comes to the set of baryons and mesons discovered in the 20th century. But the model failed to predict Transient tetraquarks and pentaquarks that began to appear in the 2000s. These strange particles certainly stem from QCD, but for nearly 20 years, theorists have been puzzled over how this might happen.

“We don’t know the pattern yet, which is embarrassing,” he said Eric Brattain, a particle theorist at The Ohio State University.

The latest tetraquark sharpens the mystery.

Featured in the debris of nearly 200 collisions in the LHCb experiment, protons smashed into each other 40 million times every second, giving quarks endless opportunities to hollow out in all the ways that nature allows. Quarks come in six “flavors” of mass, with heavier quarks rarely appearing. Each of these 200 collisions produced enough energy to make two flavor quarks, which weigh more than the lightweight quarks that make up protons but less than the giant “beauty” quarks that make up the main quarry of the Large Hadron Collider. The average weight charm quarks are also close enough to attract each other and the ropes into two lighter weight quarks. Polyakov’s analysis suggested that the four quarks held together for 12 millionths of a second before the energy fluctuation caused the formation of two additional quarks and the group disintegrated into three mesons.

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