SLAC Today is available online at:
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In this issue:
Measuring Particle Creation in Style
Colloquium Monday: Dark Energy, or Worse
Image of the Day: The E163 Laser Room

SLAC Today

Friday - November 10, 2006

Measuring Particle Creation in Style

The R-meter will be on display in Neil Calder's office (Building 40, Room G106) for the next three weeks.  (Click on image for larger version, or stop by Neil's office to see it firsthand.)

When you're waiting around for rare particles to present themselves, sometimes it helps to have something nice to look at. That was the rationale behind the ornate and anachronistic rate-meter (or R-meter), which was installed in the SPEAR control room in 1974.

The stylish gauge was recently donated to SLAC by former director Burton Richter, who kept the meter for safekeeping. Richter shares the 1976 Nobel Prize in Physics for the discovery of the J/psi particle, which helped confirm the existence of the charm quark.

The R-meter consists of an old Weston voltmeter that dates from the early 1900s and a digital-to-analog converter. Connected to a fast computer that did the real-time data analysis, it served as an informative faceplate that reflected the rate at which new quarks were created in SPEAR's Mark II detector. The R stands for the "R Ratio," the ratio of the number of hadron events to muon pair events that occur when e+ and e- beams annihilate.  Read more...

Colloquium Monday

Dark Energy, or Worse


Our understanding of the universe is drastically different today than it was just a few decades ago. No longer do we believe that luminous matter alone fills up the vacuum of space. Instead, two mysterious substances—dark matter and dark energy—comprise 96 percent of the universe.

In next week's colloquium, Professor Sean Carroll of CalTech will speak on the mysterious force of dark energy. He will also discuss an alternative theory of why general relativity might be inconsistent with cosmological observations: that Einstein's general relativity breaks down on cosmological scales. Carroll will then go on to explain how this might be possible, invoking models of modified gravity, tests in the solar system and elsewhere, and the consequences for cosmology. The colloquium takes place Monday at 4:15 in Panofsky Auditorium. All are invited to attend.

Image of the Day:
The E163 Laser Room

(Image - Light table)
(Click on image for larger version.)

Inside End Station B's E163 laser room, an array of optics convert an ultrafast infrared (IR) laser pulse into the ultra violet (UV) used to generate photoelectrons for acceleration in the Next Linear Collider Test Accelerator (NLCTA). The laser room also houses additional lasers for use in the upcoming laser acceleration experiments.

The actual laser systems, which are powered off, are in the fore and right side of the image. The optics along the table include the IR to UV conversion (called "the tripler" because it triples the frequency of the light) as well as optics for combining three separate beams: a low-power alignment laser, the UV light, and some of the remaining pulsed IR light.

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