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Exotic new particles reported found

Nov. 16, 2006
Courtesy Johns Hopkins University 
and World Science staff

Sci­en­tists have re­ported dis­cov­er­ing two new sub­a­tom­ic par­ti­cles, rare but im­por­tant rel­a­tives of the com­mon­place pro­ton and neu­tron. 

Named “Sigma-sub-b” par­ti­cles, the ex­treme­ly short-lived par­ti­cles are like jew­els mined from moun­tains of da­ta, said team lead­er Pe­tar Mak­si­movic of The Johns Hop­kins Uni­ver­si­ty in Bal­ti­more, Md.

Inside view of the Tevatron. (Courtesy FNAL)


“These par­ti­cles are mem­bers of what we call the ba­ry­on­ic fam­i­ly, so-called for the Greek word ba­rys, which means heavy,” Mak­si­mo­vic said. “Ba­ry­ons are par­t­i­cles that con­tain three quarks, which are the fun­da­men­tal build­ing blocks of mat­ter.”

The sim­p­lest bar­y­ons are pro­tons and neu­trons, which make up the nu­clei of or­di­nary at­oms. “These new­est mem­bers of that fam­i­ly are un­sta­ble and eph­em­er­al, but they help us to un­der­stand the for­c­es that bind quarks to­geth­er in­to mat­ter,” Mak­si­mo­vic said.

Con­tain­ing the sec­ond-heav­i­est quark—called the bot­tom quark—the new par­t­i­cles would be the heav­i­est baryons found yet: heav­i­er even than a com­plete he­li­um at­om, which has two pro­tons, though light­er than a lith­i­um at­om, which has three.

The physicists used the Teva­tron, the world’s most pow­er­ful par­ti­cle ac­cel­er­a­tor, at the U.S. En­er­gy De­part­ment’s Fer­mi Na­tion­al Ac­cel­er­a­tor Lab­o­ra­to­ry, al­so known as Fer­milab, in Ba­ta­via, Ill. The ma­chine crashes par­t­i­cles known as pro­tons and antipro­tons to­geth­er at near­ly light speed. These events that trans­form en­er­gy in­to mass ac­cord­ing to Ein­stein’s fa­mous equa­tion E=m­c2.

The team combed through a hun­d­red tril­lion pro­ton-an­ti­pro­ton col­li­sions to find about 240 Sigma-sub-b can­di­dates, Mak­si­mo­vic said. These de­cay in­to oth­er par­t­i­cles with­in a ti­ny frac­tion of a sec­ond.

“We are com­pil­ing an ever-clearer pic­ture of how quarks build mat­ter and how sub­a­tom­ic forc­es hold quarks to­geth­er and tear them apart,” said Mak­si­mo­vic. He added that the find­ing—con­firm­ing the­o­ries that Sigma-sub-b par­ti­cles ex­ist—helps com­plete the so-called “pe­ri­odic ta­ble of baryons.”

There are six types of quarks: up, down, strange, charm, bot­tom and top. One of the new­found baryons would be made of two up quarks and a bot­tom quark, a com­bi­na­tion de­not­ed u-u-b; the oth­er of two down quarks and a bot­tom, or d-d-b. For com­par­i­son, pro­tons are u-u-d, neu­trons d-d-u. 

The Teva­tron helped the physi­cists re­pro­duce ex­ot­ic mat­ter sci­en­t­ists think abound­ed right af­ter the Big Bang that gave birth to the uni­verse. While the mat­ter around us con­tains up and down quarks on­ly, ex­ot­ic mat­ter con­tains oth­er quarks as well, ac­cord­ing to Mak­si­movic. 

The chances of pro­duc­ing bot­tom quark­s—which in turn trans­form in­to the Sigma-sub-b, ac­cord­ing to the laws of quan­tum physic­s—are mi­nus­cule, sci­en­tists said, but they beat the odds by pro­duc­ing bil­lions of col­li­sions per sec­ond.


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Scientists have reported discovering of two new subatomic particles, rare but important relatives of the commonplace proton and neutron. Named “Sigma-sub-b” particles, the extremely short-lived particles are like jewels mined from mountains of data, said team leader Petar Maksimovic of The Johns Hopkins University in Baltimore, Md. “These particles are members of what we call the ‘baryonic’ family, so-called for the Greek word ‘barys,’ which means heavy,” Maksimovic said. “Baryons are particles that contain three quarks, which are the fundamental building blocks of matter.” The simplest baryons are the proton and neutron, which make up the nuclei of ordinary atoms. “These newest members of that family are unstable and ephemeral, but they help us to understand the forces that bind quarks together into matter,” Maksimovic said. Containing the second-heaviest quark—called the bottom quark—the new particles would be the heaviest baryons found yet: heavier even than a complete helium atom, which has two protons, though lighter than a lithium atom, which has three. How rare is Sigma-sub-b? The team combed through a hundred trillion proton-antiproton collisions at the Tevatron, the world’s most powerful particle accelerator, to find about 240 Sigma-sub-b candidates, Maksimovic said. These decay into other particles within a tiny fraction of a second. “We are compiling an ever-clearer picture of how quarks build matter and how subatomic forces hold quarks together and tear them apart,” said Maksimovic, who added that the finding—confirming theories that Sigma-sub-b particles exist—helps complete the so-called “periodic table of baryons.” There are six types of quarks: up, down, strange, charm, bottom and top. One of the newfound baryons would be made of two up quarks and a bottom quark, a combination denoted u-u-b; the other of two down quarks and a bottom, or d-d-b. For comparison, protons are u-u-d, neutrons d-d-u. The Tevatron helped the physicists reproduce exotic matter scientists think abounded right after the Big Bang that gave birth to the universe. While the matter around us contains up and down quarks only, exotic matter contains other quarks as well, according to Maksimovic. The Tevatron is at the U.S. Department of Energy’s Fermi National Accelerator Laboratory, also known as Fermilab, in Batavia, Ill. The machine crashes protons and antiprotons together at nearly light speed, events that transform energy into mass according to Einstein’s famous equation E=mc^2. The odds of producing bottom quarks—which in turn transform into the Sigma-sub-b, according to the laws of quantum physics—are minuscule. But scientists said they beat them by producing billions of collisions per second.