New particles pose puzzle. (Physics).

Physicists have discovered two new members of a family of subatomic particles. The particles' less-than-expected masses are forcing scientists to reconsider how some of nature's most fundamental building blocks, quarks, interact.

Each of the newfound particles, designated respectively as Ds(2317) and Ds (2463), is a so-called Ds meson, which contains a charm quark and an antimatter quark called antistrange. Different members of the Ds family are distinguished by their masses. Three previously discovered members of the family all weighed in at the masses anticipated by theorists, but the newly discovered ones do not.

Racing to explain the mass discrepancies, some theorists have proposed that the newfound Ds particles are not just mesons but elaborate subatomic "molecules" that include other quarks, as well. Other theorists argue that each particle is a never-before-seen partner to one of the previously discovered Ds mesons.

Whatever the explanation, scientists are taking a second look at the theory of quantum chromodynamics, or QCD, which describes the possible interactions of quarks. "This teaches us we didn't know all we thought we knew about QCD," comments Jonathan L. Rosner of the University of Chicago.

Researchers at the Stanford (Calif.) Linear Accelerator Center announced the discovery of Ds(2317) on April 28. Signs of the new particles showed up when the team scanned data on matter-antimatter differences for clues to other phenomena.

Spurred by the Ds (2317) announcement, researchers at Cornell University's CESR particle collider quickly reexamined past experimental data for evidence of the new particle. On May 12, they not only confirmed the Stanford result but also unveiled evidence for the second new underweight meson.--P.W.