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Physics Web, UK
June 20 2005
Strange turn for protons
20 June 2005
Nuclear physicists have found further evidence that strange quarks
can contribute to the structure of the proton. The latest data from
the G-Zero experiment at the Thomas Jefferson National Accelerator
Facility (JLAB) in the US lend further support to recent results from
the HAPPEx experiment, also at JLAB, and other experiments in the US
and Germany. The results could shed more light on the strong
interaction that holds quarks together in protons, neutrons and other
particles (Phys. Rev. Lett. to be published).
Quarks come in six different flavours -- up, down, strange, charm,
bottom and top. A proton contains two up quarks and one down quark
that are held together by gluons, but occasionally these gluons can
fluctuate into quark-antiquark pairs. Although these virtual quarks
only exist for very short times, they can affect the properties of
the proton, such as its magnetic moment. Since the strange quark is
the next-lightest quark after the up and down quarks, it is the most
likely to have a measurable effect.
One way to observe the influence of strange quarks on the proton is
to compare measurements that probe the weak interaction with those
that probe the electromagnetic force. In the G-Zero experiment, a
high-energy beam of electrons was fired at a hydrogen target. The
beam was polarised so that the spins of the electrons either pointed
in the same direction as the beam or in the opposite direction. The
team then measured the rate at which these electrons scattered off
protons in the target.
The difference for the two beam polarizations was about 10 parts per
million. This asymmetry occurs because the electromagnetic force
conserves "parity" (that is, it does not change when all three
directions in space are reversed), while the weak force does not.
According to the G-zero team -- which includes physicists from
Armenia, Canada, France and the US -- this difference implies that
strange quarks must be contributing to magnetic moment and charge
distribution of the proton. The results agree with those recently
reported by the HAPPEx experiment, the SAMPLE experiment at the
MIT-Bates Lab in the US and the A4 experiment at Mainz in Germany.
http://physicsweb.org/articles/news/9/6/13/1
From: Emil Lazarian | Ararat NewsPress
June 20 2005
Strange turn for protons
20 June 2005
Nuclear physicists have found further evidence that strange quarks
can contribute to the structure of the proton. The latest data from
the G-Zero experiment at the Thomas Jefferson National Accelerator
Facility (JLAB) in the US lend further support to recent results from
the HAPPEx experiment, also at JLAB, and other experiments in the US
and Germany. The results could shed more light on the strong
interaction that holds quarks together in protons, neutrons and other
particles (Phys. Rev. Lett. to be published).
Quarks come in six different flavours -- up, down, strange, charm,
bottom and top. A proton contains two up quarks and one down quark
that are held together by gluons, but occasionally these gluons can
fluctuate into quark-antiquark pairs. Although these virtual quarks
only exist for very short times, they can affect the properties of
the proton, such as its magnetic moment. Since the strange quark is
the next-lightest quark after the up and down quarks, it is the most
likely to have a measurable effect.
One way to observe the influence of strange quarks on the proton is
to compare measurements that probe the weak interaction with those
that probe the electromagnetic force. In the G-Zero experiment, a
high-energy beam of electrons was fired at a hydrogen target. The
beam was polarised so that the spins of the electrons either pointed
in the same direction as the beam or in the opposite direction. The
team then measured the rate at which these electrons scattered off
protons in the target.
The difference for the two beam polarizations was about 10 parts per
million. This asymmetry occurs because the electromagnetic force
conserves "parity" (that is, it does not change when all three
directions in space are reversed), while the weak force does not.
According to the G-zero team -- which includes physicists from
Armenia, Canada, France and the US -- this difference implies that
strange quarks must be contributing to magnetic moment and charge
distribution of the proton. The results agree with those recently
reported by the HAPPEx experiment, the SAMPLE experiment at the
MIT-Bates Lab in the US and the A4 experiment at Mainz in Germany.
http://physicsweb.org/articles/news/9/6/13/1
From: Emil Lazarian | Ararat NewsPress