BaBar Steadies Omega-minus Spin

Nov 06, 2006
BaBar Steadies Omega-minus Spin
The first evidence of the omega-minus particle in a bubble chamber. Image courtesy of Brookhaven National Laboratory

If you snatch a copy of the Particle Data Book from your colleague's back pocket and flip to the entry for the Omega-minus particle, you'll see that the very first line says the spin is "not yet measured." That entry may soon be changed. The BaBar collaboration has established that the spin of the Omega-minus, a particle that was discovered more than 40 years ago, is 3/2.

"The Omega-minus has been around for a long time and it's got a very interesting history," says BaBar collaborator Bill Dunwoodie. "It was a confirmation of Murray Gell-Mann's ideas about broken symmetry that led eventually to the quark model."

The analysis of BaBar data was primarily conducted by Veronique Ziegler, a graduate student from the University of Iowa, with Dunwoodie. The findings are published in the Sept. 15 issue of Physical Review Letters.

Bubble chamber experiments, like the one that found the first Omega-minus particle in 1964, can produce only a small number of the particles, and the collisions that produced them were not well understood. By studying the angular distribution of the particles produced by the Omega-minus when it decayed, physicists obtained information on the Omega-minus's spin, but they were unable to say anything more than that it did not have spin 1/2.

Ziegler studied Omega-minus particles resulting from the decay of charm baryons that were produced in electron-positron collisions in BaBar.

"These particles are extremely rare, but thanks to the enormous amount and quality of data BaBar has produced, we were able to carry out this analysis," Ziegler said.

In 1962, there were nine baryons (particles containing three quarks) believed to have spin 3/2. In a comment made during a conference at CERN, Murray Gell-Mann predicted there was a tenth particle that had yet to be seen. He named it Omega-minus and predicted its mass and decay properties. He even gave a recipe for the production and observation of the Omega-minus, namely by means of high-energy collisions between negative kaons and the protons in a liquid hydrogen bubble chamber.

Two years later, the short 2-centimeter track of an Omega-minus particle was seen in a photograph from the 80" bubble chamber at Brookhaven National Laboratory. The particle had almost exactly the mass that Gell-Mann had predicted. Only one month previously, Gell-Mann had submitted the first paper outlining the quark model.

Ziegler's analysis has been well-received. One reviewer wrote, "This paper is an instant classic. It will be studied by future generations of graduate students."

Source: By Rachel Courtland, Stanford Linear Accelerator Center

Explore further: New pathway to valleytronics

add to favorites email to friend print save as pdf

Related Stories

Your future office desk may remind you, hey, to move it

1 hour ago

Workers in all industries know by now that having a "desk" job might have its perks but frequent exercise is not one of them. Ample warnings from health experts have been headlined in the press reminding ...

Recommended for you

Particle physicists discuss JUNO neutrino experiment

1 hour ago

The construction of the facilities for the JUNO neutrino experiment has been initiated with an official groundbreaking ceremony near the south Chinese city of Jiangmen. Involved in the Jiangmen Underground ...

New pathway to valleytronics

Jan 27, 2015

A potential avenue to quantum computing currently generating quite the buzz in the high-tech industry is "valleytronics," in which information is coded based on the wavelike motion of electrons moving through ...

New portable vacuum standard

Jan 26, 2015

A novel Portable Vacuum Standard (PVS) has been added to the roster of NIST's Standard Reference Instruments (SRI). It is now available for purchase as part of NIST's ongoing commitment to disseminate measurement ...

Prototype for first traceable PET-MR phantom

Jan 26, 2015

As cancer diagnostic tools, a new class of imagers – which combines positron-emission tomography (PET) with magnetic resonance imaging (MR or MRI) – has shown promise in the few years since these hybrid ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.