SLAC Today is
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In this issue:
Reference Design Report Released for the ILC
Science Today: BaBar's Astonishing Decays
Scientists + Experiments = Big Fun at Tech Museum
Thursday - February 8, 2007 |
Reference Design Report Released for the ILCThe International Committee for Future Accelerators (ICFA) today announced the release of the Reference Design Report (RDR) for the International Linear Collider (ILC), a proposed future particle accelerator. Hurling some 10 billion electrons and their anti-particles, positrons, toward each other at nearly the speed of light, beams in the ILC will collide 14,000 times every second at extremely high energies500 billion-electronvolts (GeV). These spectacular collisions create an array of new particles that will answer some of the most fundamental questions about the nature of the universe, such as the origin of mass, dark matter, dark energy, extra dimensions and beyond. The current 31-kilometer design allows for an upgrade to a 50-kilometer, 1 trillion-electronvolt (TeV) machine during the second stage of the project. Organized by the Global Design Effort (GDE), a team of more than 60 scientists, the ILC is an international endeavor that brings together more than 1,000 scientists and engineers from more than 100 universities and laboratories in over two dozen countries. Read more... |
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BaBar's Astonishing DecaysIn the year following the discovery at SLAC (and simultaneously at Brookhaven National Lab) of the J/ψ in November 1974, a whole family of particles, whimsically called charmonia, appeared in experiments here and at DESY, in Hamburg, Germany. Heavy members of the family decayed into lighter members of the family, emitting photons or pions, usually. Their predilection to remain within the family was explained by their being composed of a charmed quark and its antiquark. Until the quark and antiquark annihilated, a rare occurrence, they remained charmonia. A charmed quark and its antiquark, given sufficient energy could instead become two charmed particles, but below threshold, where there wasn't sufficient energy to make charmed particles, the quark-antiquark pair persisted a long time: up to 10-20 seconds! The discovery of charmonium states made quarks tangible. No longer could you say quarks were just a mathematical construct. Moreover, you could calculate the properties of charmonium states using techniques developed fifty years earlier to describe simple atoms. There was plenty to measure and theorists had an easy life. These were the halcyon days of particle physics. SLAC's PEP-II asymmetric B factory was built to study the next quark, the b quark and so the energy of the machine is much higher than the energy of SPEAR, where c the quark made its appearance. However, sometimes the colliding electron or positron emits an energetic photon just before colliding with its counterpart coming from the other direction. Indeed sometimes it emits enough energy so that then the electron-positron collision has just about the same energy as there was a SPEAR and it is possible to study the charmonium particles even with PEP-II. Read more... |
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