An “impossible” particle adds a piece to the puzzle with strong force


This spring, c At a meeting of the quark physics group at the University of Syracuse, Ivan Polyakov announced that he had found the fingerprints of a semi-mythical particle.

“We said, ‘It’s impossible. What mistake are you making? Sheldon Stone, the group’s leader, recalls.

Polyakov went and re-checked his analysis of the data from the Large Hadron Collider (LHCb) beauty experiment, of which the Syracuse group is a part. Stored evidence. He showed that a certain set of four fundamental particles, called quarks, could form a tight clique, contrary to the belief of most theorists. The collaboration with LHCb announced the discovery of a composite particle called a double-charm tetraquark at a conference in July and in two reports published earlier this month that are now under peer review.

The unexpected discovery of a tetraquark with double charm underscores the uncomfortable truth. While physicists know the exact equation that determines the strong force — the fundamental force that binds quarks together to create protons and neutrons in the hearts of atoms, as well as other constituent particles such as tetraquarks — they can rarely solve this strange, infinite iterative equation. so they struggle to predict the effects of strong force.

The tetraquark now presents theorists with a solid goal against which to test their mathematical mechanisms for converging force. Observing their approximations is the main hope of physicists to understand how quarks behave inside and outside atoms – and to separate the effects of quarks from the subtle signs of new fundamental particles that physicists pursue.

Quark Cartoon

The strange thing about quarks is that physicists can approach them on two levels of complexity. In the 1960s, battling a zoo of newly discovered composite particles, they developed the animated “quark model,” which simply says that quarks are put together in additional sets of three to make a proton, neutron, and other baryons. while quark pairs form different types of meson particles.

Gradually, a deeper theory known as quantum chromodynamics (QCD) emerged. He painted the proton as a boiling mass of quarks connected together by tangled strings of “gluon” particles, carriers of strong force. Experiments have confirmed many aspects of QCD, but none of the known mathematical techniques can systematically reveal the central equation of the theory.

Somehow the quark model may stand for the far more complex truth, at least as far as the menagerie of baryons and mesons discovered in the 20th century is concerned. But the model failed to predict the fleeting tetraquarks and five-quark pentaquarks that began to appear in the 2000s. These exotic particles certainly originate from QCD, but for almost 20 years theorists have wondered how.

“We just don’t know the model yet, which is inconvenient,” said Eric Braten, a particle theorist at Ohio State University.

The latest tetraquark sharpens the mystery.

It appeared in the wreckage of approximately 200 collisions in the LHCb experiment, where protons collide with each other 40 million times every second, giving quartz countless opportunities to turn in all the ways nature allows. Quarks are available in six “flavors” on tables, with heavier quarks occurring less frequently. Each of these 200 collisions generates enough energy to make two charm-flavored quarks that weigh more than light quarks that contain protons, but less than the giant “beauty” quarks that are LHCb’s main career. The charming medium-weight quarks also came together close enough to attract each other and introduce themselves into two light antiques. Polyakov’s analysis suggests that the four quarks combine for a glorious 12 sextillion fractions of a second before the energy fluctuations cause two additional quarks and the group splits into three mesons.



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