Jefferson Lab Weekly Briefs
May 14, 2008
12 GeV Upgrade
For the GlueX detector in Hall D, the dominant contributions to the particle detector rates come from background processes that are not of interest for the physics measurement. A so-called "Level-1 trigger" must be created using the electronics and data acquisition systems to select only particles of interest and reduce the rate of stored information from several millions of particles per second down to less than 200,000 for high luminosity running. A recipe, or trigger algorithm, to accomplish this was recently studied using a full GEANT detector simulation that incorporates realistic detector geometry and responses, and the trigger electronics performance. This is implemented on the electronic signal level using the new VXS-based Flash Analog-to-Digital Converters (ADCs) in conjunction with other special VXS-based modules for the Hall D trigger developed by the JLab fast electronics and data acquisition groups. The overall Level-1 trigger rate thus simulated results in a rate of 150,000 particles of interest per second, while maintaining close to 100 percent efficiency.
Hall A successfully completed experiment E04-007 (Electroproduction of Pi-Zero near Threshold) on May 8. Installation of E08-007 (The Proton Form Factor Ratio at Low Q2) is proceeding, and it is expected that the experiment will begin taking data by May 15.
In Hall-B, g12, the experiment for studying cascade baryons and exotic mesons, continues to run smoothly. A CLAS12 systems review took place May 7-9. It went extremely well. All 12 presentations got excellent responses. The review committee did not have any recommendations or comments for CLAS12.
In Hall C, during production running for E04-108, the measurement of GEp/GMp and high Q2, the vacuum in the target scattering chamber started deteriorating. Before the vacuum reached unacceptable levels, beam delivery was paused, and radiation levels were allowed to decay for two days. The O-rings on the chamber were replaced over the weekend, and a good vacuum was obtained after pumping down the scattering chamber. The liquid hydrogen target was recooled, and production data taking resumed.
During this reporting period, Hall A ended the current portion of their experiment, while Hall C stopped taking beam for a few days to fix various problems. Through May 11, the halls divided 185 hours of beam. The accelerator delivered beam to Hall B for a few days, and then Hall C resumed taking beam towards the end of the period. The only significant accelerator problem occurred when a vacuum gasket failed during machine tuning and was quickly replaced.
Free-Electron Laser (FEL)
Work is proceeding to get components prepared for the ultraviolet FEL system installation this summer. The FEL injector group is in the process of refurbishing the FEL gun so that it can be reassembled in June for testing later this summer. Measurements and preparations are being made for more advanced beam diagnostics on the gun test stand.
The Color Glass Condensate (CGC) model is an effective approach to high-energy quantum chromodynamics, which allows one to calculate distributions of partons in heavy nuclei in the limit of high parton densities. Using the CGC model, a collaboration of theorists from JLab and Germany evaluated nuclear quark and gluon generalized parton distributions and the cross section of deeply virtual Compton scattering off heavy nuclear targets in the small Bjorken-x region, arXiv:0804.4424 [hep-ph]. These predictions are relevant for the physics program of the future Electron-Ion Collider and for ultra-peripheral nucleus-nucleus collisions at the Large Hadron Collider at CERN.
The magnet measurement group has started measurements in the Test Lab on the first eight of a total of 26 QX quadrupoles for the FEL for the ultraviolet upgrade. Each magnet has been measured for field strength and harmonic content. The magnets are being powered by the TrimCardII power supply with a ramping protocol programmed onto a chip on the card and controlled by EPICS.
JLab's Safety Numbers
238 Days since Last Recordable Accident (JLab record: 319)
Environment, Safety, Health & Quality
Hurricane season begins officially on June 1. JLab has already begun its advance preparations to ensure the Lab can quickly elevate its readiness should a storm threaten our region. But employees won’t be on site here when the hurricane arrives. By the time conditions are dangerous, you’re most likely to be home, or at some alternate, safer location. Every expert on hurricane preparedness stresses the importance of planning ahead for evacuation, shelter-in-place and other options you may need to take on short notice. Here is a partial preparedness checklist provided by the National Hurricane Center:
For a full list of preparation tips, visit the National Hurricane Center Website.
Computing and Networking Infrastructure (CNI)
jlab_secure Wireless Users Must Update Their Systems Before May 15
JLab Auger/PBS Fedora 8 Compute Farm Update
Controlled Areas Access Announcement for JLab Radiation-Trained Workers
TIAA-CREF June Retirement Counseling Session
Jefferson Ave. Scavengers Taking Anything They Can Carry
JLab Calendar of Events
May 14: JLab Run-A-Round