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In this issue:
Groovy Project Solving Cloudy Problem
Science Today: Taking SUSY One Step Further
National Research Council Recommends Moving Ahead with NASA-DOE Project

SLAC Today

Thursday - September 6, 2007

Groovy Project Solving Cloudy Problem

Mauro Pivi holds a section of beam pipe with built-in grooves.
(Image courtesy of Brad Plummer.)

Experiments in the PEP-II accelerator have shown that beam pipes with grooves can snare unwelcome electrons, greatly reducing the formation of electron clouds that can disturb the beam.

While electron clouds presently pose little threat to the PEP-II beam, they are a major concern for the International Linear Collider (ILC) or a future B-factory project. In high-energy storage rings, synchrotron radiation liberates electrons from the beam pipe walls. A positron or proton beam will accelerate the free electrons, and these electrons can then strike the chamber walls, releasing more electrons in a cascade effect until a cloud forms. Ultimately, scientists think the grooved chambers will be a good solution for certain sections of the ILC positron damping ring.

While PEP-II continued to provide beams for the BaBar experiment this summer, the ILC Group monitored the performance of four segments of beam pipe installed in a straight section of the accelerator where there are no magnets. Two sections have smooth interior walls, like normal beam pipes. Two sections have grooves cut into the interior walls that look like metal teeth on a comb. Data show that the beam pipes with grooves had 20 to 30 times less current from electron clouds than the two smooth segments. The grooves, or teeth, act as traps.  Read more...

(Daily Column - Science Today)

Taking SUSY
One Step Further

Supersymmetry (SUSY), the idea that there is a symmetry between bosons and fermions, is perhaps the most popular framework for new physics beyond the Standard Model. SUSY predicts that every Standard Model particle has an as-yet undiscovered "superpartner." Proponents of the theory believe that these particles will appear at the Large Hadron Collider (LHC) at CERN. Determining whether low-energy SUSY exists will be a major goal of the LHC; if discovered, the study of these particles will become a major activity in high-energy physics.

It is not enough, though, simply to discover the SUSY particles (or "sparticles"). SUSY would imply a major extension of the fundamental laws of nature. It would give us new principles with which to understand the other elementary particle interactions, and it might also give us a particle that makes up dark matter. To learn how the new laws of SUSY operate, we need to measure the masses and properties of the sparticles as accurately as possible.

The SUSY model which contains the standard model, but which adds the fewest new particles, is the Minimal Supersymmetric Standard Model (MSSM). This is not a simple model. It contains some 105 new parameters (beyond the 20 free parameters in the Standard Model). These fundamental parameters determine the masses and couplings of the sparticles and also answer questions about the role of SUSY in the weak interactions, the mass generation for the quark and leptons, and the properties of dark matter. Most of these parameters must be very small to avoid unwanted effects in B physics and Charge Parity (CP) violation. This leaves about 20 new parameters that will be important and must be determined.

We expect to learn a great deal about SUSY at the LHC, but it seems unlikely that we will be able to determine this full set of parameters from the LHC data alone. In a recent paper, Nima Arkani-Hamed, Gordon Kane, Jesse Thaler, and Lian-Tao Wang found examples in which totally different sets of MSSM parameters give indistinguishable experimental signatures at the LHC. They called this problem the "LHC Inverse Problem." This problem is not new to people who have been thinking about future electron–positron colliders.

National Research Council Recommends Moving Ahead with NASA–DOE Project

An artist's impression of the SuperNova/Acceleration Probe (SNAP).

A National Research Council report released yesterday recommends that, of five possible Beyond Einstein missions, NASA should proceed immediately with the Joint Dark Energy Mission (JDEM), a partnership between NASA and the Department of Energy.

Late last year, NASA initiated the study of three mission concepts for JDEM: the SuperNova/Acceleration Probe (SNAP), the Advanced Dark Energy Physics Telescope (ADEPT), and the Dark Energy Space Telescope (Destiny). The JDEM mission that actually flies will be determined by a future, open competition.

SLAC is currently working in collaboration with several institutions on SNAP, which is designed to reveal the nature of dark energy by measuring the light from thousands of distant supernovae and observing the subtle effects of weak gravitational lensing. Work at SLAC focuses on the probe's electronics and its fine guidance control system. Kavli Institute for Particle Astrophysics and Cosmology researchers are also studying how the probe's strong lens survey will further examine the Hubble constant, put independent constraints on cosmology and dark matter, and study galaxy evolution.

"SLAC has been working on this project for several years now," said Aaron Roodman, head of the SLAC SNAP group. "SNAP is a strong JDEM contender and we look forward to the NASA–DOE competition for this mission."

The executive summary of the National Research Council Report, NASA's Beyond Einstein Program: An Architecture for Implementation, is available online. In addition to recommending that JDEM proceed immediately, the report recommends that NASA should invest additional Beyond Einstein funds in technology, development and risk reduction for the Laser Interferometer Space Antenna (LISA), and should increase the readiness of the three remaining dark energy mission areas—Black Hole Finder Probe, Constellation-X, and Inflation Probe.

All five of these missions are part of the Beyond Einstein Program, NASA's research roadmap for proposed mission areas to study the most compelling questions arising at the intersection of physics and astronomy.

Read the National Academies press release...

Read the Lawrence Berkeley National Laboratory press release...

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