SETI bioastro: Fw: Physics News Update 666

Date: Thu Dec 18 2003 - 18:25:05 PST

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    ----- Original Message -----
    Sent: Thursday, December 18, 2003 1:55 PM
    To: ljk4_at_MSN.COM
    Subject: Physics News Update 666

    The American Institute of Physics Bulletin of Physics News
    Number 666 December 18, 2003 by Phillip F. Schewe, Ben Stein, and
    James Riordon
    Jefferson National Accelerator Facility in Virginia, a multinational
    research team has determined how quarks in a proton orient their
    "spins," which, roughly speaking, can be visualized as tiny bar
    magnets that point in a certain direction and have a certain
    strength. Information about a quark's spin can provide new details
    of how the tiny particles arrange themselves inside a nucleon
    (proton or neutron). In high-school physics classes, students are
    taught that a proton or neutron simply consists of three quarks,
    which specialists call "valence quarks." A more complete picture
    includes these three valence quarks, plus a sea of quark-antiquark
    pairs that pop in and out of empty space (the vacuum), as well as
    particles called gluons which hold the quarks together.
    Now, for the first time, researchers have precisely measured the
    distribution of spin for a neutron's valence quarks. Strikingly,
    their results reveal the importance of once-neglected orbital
    motions of quarks around the nucleon. Aiming an electron beam at a
    helium-3 target in JLab's Hall A, researchers (led by Jian-Ping
    Chen, and Zein-Eddine Meziani,
    selected a 5.7 GeV beam energy so that the electrons interacted
    mainly with the neutron's valence quarks and not its sea quarks and
    gluons. Interestingly, the researchers applied their new neutron
    data, along with existing proton data, to find out more about the
    proton. Their conclusions: the spins of the proton's two valence up
    quarks are aligned parallel to the overall proton spin, but the same
    is not true for the proton's valence down quark (see image at
    This result disagrees with predictions from an approximation of
    perturbative quantum chromodynamics (pQCD), a widely accepted theory
    of the strong force (which holds the nucleon together). This
    approximation does not account for the quarks' orbital angular
    momenta, which describes the orbital paths of quarks inside the
    nucleon. However, the results agree well with predictions from
    relativistic valence quark model, which does consider quarks'
    orbital angular momenta as they move inside the nucleon. (Zheng et
    al., Physical Review Letters, upcoming article; for more
    information, contact Xiaochao Zheng, Argonne, 630-252-3431, Once omitted in simpler pictures of the nucleon,
    quark orbital angular momentum is also proving important for
    exploring questions about the shape of the proton (see for example
    New Scientist, May 3, 2003.)

    A TRUE ONE-DIMENSIONAL ATOMIC SYSTEM, consisting of a Bose Einstein
    condensate (BEC) of rubidium atoms pulled out into a thin tubelike
    shape, has been experimentally demonstrated for the first time, in
    the ETH lab in Zurich. The ETH researchers begin by loading their
    condensate into an optical lattice, an artificial configuration in
    which atoms are held and moved about in 3D space by criss-crossing
    beams of laser light. In contrast to previous efforts to make
    one-dimensional BECs, this experiment succeeded in extruding a
    condensate into 1000 small needle-like condensates---one dimensional
    strings of 100 atoms or so and not merely cigar shaped
    lozenges---because they used a far more intense laser trapping field
    and higher quality laser beams (more truly Gaussian in their
    profile), the better to keep atoms from tunneling from one needle
    into a neighboring needle (see figure at ). Once the ETH physicists
    had established their one-dimensional atomic gas what did they do
    with it? They set their lean stack of atoms into motion by slightly
    moving the magnetic center of their apparatus. This caused the
    atoms to move up and down in a "breathing mode"at a characteristic
    frequency. Studying this oscillation was analogous to listening a
    one dimensional bell ringing.
    How unusual is the ETH 1D condensate? Well, even two dimensional
    atomic systems are rare in physics: helium films and hydrogen atoms
    sitting atop helium are the prominent examples. The only other 1D
    gas studied in physics consists of electrons moving in "quantum
    wires." One-dimensional systems are interesting because they are
    more intrinsically dominated by quantum effects than 2- or
    3-dimensional systems. According to Tilman Esslinger
    (, ) 1D ensembles of atoms should
    play an important role wherever precision handling of atoms is
    needed: in atom optics, atom interferometry, or sending signals from
    atom lasers down an atom waveguide. (Moritz et al., Physical Review
    Letters, 19 December 2003)

    PHYSICS NEWS UPDATE is a digest of physics news items arising
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