Brookhaven physicists produce "doubly strange nuclei"

August 20, 2001

First large-scale production of nuclei containing two strange quarks

UPTON, NY -- Strange science has taken a great leap forward at the U.S. Department of Energy's Brookhaven National Laboratory. There, physicists have produced a significant number of "doubly strange nuclei," or nuclei containing two strange quarks. Studies of these nuclei will help scientists explore the forces between nuclear particles, particularly within so-called strange matter, and may contribute to a better understanding of neutron stars, the superdense remains of burnt-out stars, which are thought to contain large quantities of strange quarks.

The 50 physicists collaborating on the experiment, who represent 15 institutions in six countries, describe their findings in an upcoming isssue of Physical Review Letters.

"This is the first experiment to produce large numbers of these doubly strange nuclei," said Brookhaven physicist Adam Rusek, a co-spokesperson for the collaboration. Four previous experiments conducted over the past 40 years in the U.S., Europe, and Japan have produced one such nucleus each, with varying degrees of certainty. In the current publication, which is based on data taken in 1998, the Brookhaven collaboration describes 30 to 40 events out of several hundred produced. "That's enough events to begin a study using statistical techniques," Rusek said.

To create the nuclei, the scientists aim the world's most intense proton beam -- produced at one of Brookhaven's particle accelerators, the Alternating Gradient Synchrotron -- at a tungsten target. From the particles produced in those collisions, the scientists separate out an extremely intense beam of negatively charged kaons, which are each composed of one "strange" quark and one "up" antiquark. When these negative kaons then strike a beryllium target and interact with its protons, some of the energy is converted into new strange quarks and strange antiquarks.

These quarks then regroup to form a variety of particles, some of which continue to interact. Occasionally, a structure containing a proton, a neutron, and two lambda particles (each composed of one up, one down, and one strange quark) is formed. This double-lambda structure, with its two strange quarks, is the observed doubly strange nucleus.

Detecting the formation of this strange species is no easy task. It's more like finding a subatomic needle in a particle-soup haystack. For one thing, many other species are produced in the collisions. Plus, the scientists can't "see" the double lambda structure directly. Instead, they look for pions, a subatomic product the lambdas emit as they decay in less than one billionth of a second. Furthermore, in order to infer that the pions came from a nucleus containing two lambdas, there must be two pion decay signals at very specific energies.

Sophisticated computers and careful analyses helped narrow the search from 100 million potentially interesting events, to 100,000 where two strange quarks were produced, to the 30 to 40 where those two strange quarks existed for a fleeting instant inside the same nucleus. "The most important part is eliminating all the other possible explanations for these events," said Sidney Kahana, a theoretical physicist at Brookhaven. "We're left with this double lambda species as the only explanation," he said.

Now that they believe they have a reliable method for producing the double lambda species, the scientists would like to produce more so they can get better measurements of the binding energy, or force of interaction, between the two lambda particles. "We can use this nucleus as a laboratory in which the two lambdas can be held together long enough to study," Kahana said.

Based on the current data, the interaction between lambdas appears to be rather weak -- possibly too weak for the two particles to merge to produce a postulated, six-quark structure called an H particle. But further experiments are necessary, the scientists say.

The interaction between lambdas may also offer insight into the properties of neutron stars, which are thought to contain vast numbers of strange particles, including lambdas. Neutron stars are the only place in the universe scientists believe such strange matter exists in a stable form.

With the ability to produce appreciable numbers of doubly strange nuclei, "Brookhaven is now the best place in the world to study strange matter," said Morgan May, who leads the strangeness nuclear physics program at Brookhaven.
-end-
This work was funded by the U.S. Department of Energy, which supports basic research in a variety of scientific fields.

The U.S. Department of Energy's Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies. Brookhaven also builds and operates major facilities available to university, industrial, and government scientists. The Laboratory is managed by Brookhaven Science Associates, a limited liability company founded by Stony Brook University and Battelle, a nonprofit applied science and technology organization.

BACKGROUNDER

Additional Information on "Doubly Strange Nuclei"

Participating institutions:

Brookhaven National Laboratory (BNL); Carnegie Mellon University; University of Freiburg, Germany; Hampton University; High Energy Accelerator Research Organization (KEK), Japan; Institute of Nuclear Research (INR), Russia; Kyoto University, Japan; University of Manitoba, Canada; University of New Mexico; Osaka University, Japan; Temple University; University of Tokyo, Japan; Pusan National University, Korea; TRIUMF, Canada; Osaka Electro-Communication University, Japan.

Collaboration spokespersons:

Tomokazu Fukuda, physicist
Osaka Electro-Communication University
phone: 011-81-72-820-4552
e-mail: fukuda@nexus.kek.jp

Robert Chrien, physicist, BNL
phone: 631-344-3903
e-mail: chrien1@bnl.gov

Adam Rusek, physicist, BNL
phone 631-344-5830
e-mail: rusek@bnl.gov

Other scientists who can be contacted for comment:

Robert L. Jaffe, physics professor
Massachusetts Institute of Technology
phone: 617-253-4858
e-mail: jaffe@mit.edu

Benjamin Gibson, theoretiacal physicist
Los Alamos National Laboratory
phone: 505-667-5059
e-mail: bfgibson@lanl.gov

Madappa Prakash, physics professor
Stony Brook University
phone: 631-632-8126
e-mail: prakash@nuclear.physics.sunysb.edu

For information about fundamental particles and interactions, go to: http://particleadventure.org/, and specifically: http://particleadventure.org/frameless/chart.html

For a link to a manuscript version of the Physical Review Letters paper, go to: http://www.bnl.gov/bnlweb/PDF/krev9-1.pdf

DOE/Brookhaven National Laboratory

Related Quarks Articles from Brightsurf:

Observation of four-charm-quark structure
Hadrons are composed of quarks, a type of fundamental particle, bound by the strong interaction.

New research deepens mystery of particle generation in proton collisions
Researchers have shown that in polarized proton-proton collisions, the neutral pions in the very forward area of collisions -- where direct interactions involving quarks and gluons are not applicable -- still have a large degree of left-right asymmetry.

Scientists shed light on mystery of dark matter
Nuclear physicists at the University of York are putting forward a new candidate for dark matter -- a particle they recently discovered called the d-star hexaquark.

Exploring strangeness and the primordial Universe
Within quark-gluon plasma, strange quarks are readily produced through collisions between gluons.

Deuteron-like heavy dibaryons -- a step towards finding exotic nuclei
Using supercomputer, TIFR's physicists have predicted the existence of deuteron-like exotic nuclei for the first time as well as provided their masses precisely.

FSU physics researchers break new ground, explore unknown energy regions
Florida State University physicists are using photon-proton collisions to capture particles in an unexplored energy region, yielding new insights into the matter that binds parts of the nucleus together.

A novel tool to probe fundamental matter
The origin of matter remains a complex and open question.

CEBAF turns on the charm
The world's most advanced particle accelerator for investigating the quark structure of the atom's nucleus has just charmed physicists with a new capability.

Physicists reveal why matter dominates universe
Physicists in the College of Arts and Sciences at Syracuse University have confirmed that matter and antimatter decay differently for elementary particles containing charmed quarks.

Physicists solve 35-year-old mystery about quarks
Physicists from Tel Aviv University, the Massachusetts Institute of Technology and the Thomas Jefferson National Accelerator Facility now know why quarks, the building blocks of the universe, move more slowly inside atomic nuclei, solving a 35-year-old-mystery.

Read More: Quarks News and Quarks Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.