Large Hadron Collider forms rare quadruplets ‘top quarks’

The Large Hadron Collider (LHC) has now “born” rare quadruplets of particles called “top quarks”.

Sina Technology News Beijing time on June 28, according to foreign media reports, at present, the world’s largest atomic collider, the Large Hadron Collider, “born” rare quadruplets of particles called “top quarks”. “.

The “Standard Model”, the dominant theory of physics that governs subatomic interactions, had predicted the existence of such quadruplets, but new physical theories suggest that they may be formed in more numbers than the Standard Model predicted. Finding the quadruplets is the first step in testing the theory, and the latest findings were presented at the LHCP 2020 conference.

According to a 2019 report in the journal Physical Review D, the top quark is the heaviest known fundamental subatomic particle, with each top quark having a mass roughly equivalent to a tungsten atom. However, each top quark is much smaller than a proton, meaning that not only do top quarks hold the record for the heaviest particles, but they are the densest form of mass known.

While large numbers of top quarks were formed in the earliest stages after the Big Bang, they were very short-lived, disappearing completely in about a trillionth of a second. Today, the only environment in which top quarks can be produced and observed is in large particle accelerators.

In 1995, scientists first discovered the top quark in Fermilab’s megaelectron volt accelerator, which was the most powerful particle accelerator at the time, and is now decommissioned.

In 2011, the Large Hadron Collider assumed that the mantle is the most powerful particle accelerator in the world. The collider is composed of nearly 10,000 powerful magnetic rings arranged in a ring structure with a circumference of 27 kilometers, accelerating two proton beams Running in the opposite direction, they collide at an energy of 13 trillion electron volts, a collision frequency 100 times higher than that of a tera electron volt accelerator.

In 1995, particle beams collided at Fermilab’s megaelectron volt accelerator to form pairs of top and antimatter quarks, but these collisions only occurred every few days. In contrast, in the Curved Large Hadron Collider Instrument (ATLAS) experiment and the Compact Muon Solenoid (CMS) experiment, higher energies and higher collision frequencies form a pair of top quarks about every second.

In recent experiments, researchers are looking for the phenomenon that produces two sets of top quark/antiquark pairs at the same time. The Standard Model predicts that these more complex collisions should be 70,000 times more frequent than those that produce a top quark pair. When looking for new particles, what matters is how likely is the number of observed collisions to happen by chance? This result can be measured in sigma units.

In particle physics, the gold standard for declaring a top quark discovery is above 5 sigma, which means that current observations are caused by random fluctuations with a probability of only 1 in 3.5 million. 3 sigma means that the observed signal has a probability of only 1 in 740 by chance, which according to the Fermilab researchers is the “best evidence” for the observation. At present, the evidence that the top quark produces quadruplets is not enough to declare a new discovery.

From 2015 to 2018, physicists looked for quadruplets top quarks in data collected by the ATLAS and CMS instruments, and the ATLAS experimental team announced that they had seen four top quarks at the 4.3 sigma scale forming. At the same time, the European Journal of Physics C published a paper saying that the top quark of the quadruplets found by the CMS instrument researchers was only 2.6 sigma. Before the experiment, the ATLAS and CMS instruments predicted the top quark of the quadruplets with a confidence level of 2.6 sigma.

It is possible that the significance observed by the ATLAS instrument was merely accidental, or it could just be an indication that the production of quadruplets top quark is more common than predicted by the Standard Model, which could also mean that this measurement is an unexpected physical Learn new clues. Additional data from the next LHC run, along with a further expansion of the analytical techniques used, will improve the precision of this challenging measurement, the researchers said. (Ye Qingcheng)

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