Jefferson Lab Weekly Briefs November 11, 2009
Jefferson Lab Weekly Briefs
November 11, 2009
12 GeV Upgrade
A system requirements review for the toroid magnet for CLAS12 was held at JLab, marking the start of construction of this key superconducting magnet. An initial review for the construction of the Q1 quadrupole magnet for the Super High Momentum Spectrometer (SHMS) was held at the vendor's offices, Scientific Magnetics in Abingdon, Oxfordshire, in the U.K., also in October. The best and final offers for the cryogenic reservoirs for all five superconducting magnets for the SHMS were received and are being evaluated; this procurement also will include the cryogenic reservoir for the solenoid magnet for Hall D. First full-size prototype arrays were received for the silicon photomultiplier option for the optical readout of the Hall D Barrel Calorimeter detector. These were inspected and shown to be fully operational, with good gain and rise time, and are now undergoing detailed test evaluation.
Hall B is running the first physics production run at JLab with a beam energy greater than 6 GeV. The eg6 run group covers two experiments with very different physics goals but using a common pressurized helium gas cell as a spin-0 scattering target and a low-density radial time-projection chamber (RTPC).
Experiment E07-009 searches for hybrid mesons in the quasi-real photoproduction of mesons off helium-4, where the nucleus remains intact and is detected in the RTPC. The quantum numbers of the helium nucleus limit the number of possible spin-parity combinations for excited mesons and enhance production of mesons with "exotic" quantum numbers that cannot occur in ordinary quark-model states.
Experiment E08-024 runs in parallel and probes the quark structure of the helium-4 nucleus in terms of generalized parton distributions using coherent and incoherent production of high-energy photons through the deeply virtual Compton scattering process. If the handbag mechanism works for helium-4 as it does for hydrogen, the nucleus is described by a single leading twist GPD "H" (compared to four GPDs for protons), which makes the interpretation much simpler. Moreover, the comparison of single spin asymmetries from helium-4 and from the proton is sensitive to the role of transverse degrees of freedom in the nuclear structure and their contribution to the EMC Effect.
The accelerator energy was changed from 5.764 GeV to 6.068 GeV. The GUN2 photocathode was heated and re-activated to provide good quantum efficiencies. Radiofrequency cavities were optimized for high-energy and high-current running. Beam delivery was resumed on Wednesday. After the energy change, the Hall A Compton counts are high, and the accelerator experts have been troubleshooting the problem.
FEL staffers were given an unexpected opportunity for operations this week, and they completed a run for the Light Pseudoscalar and Scalar Search collaboration dark matter experiment. The team learned a lot about the machine from the optimization necessary for this successful beam delivery. LIPPS did six complete runs, typically receiving 500 Watts on the target at a 930-nanometer wavelength. Analysis of the data is underway.
JLab's Safety Numbers
119 Days since Last Recordable Accident (JLab record: 331)
JLab Calendar of Events
Nov. 12: Safety Shoe Vendor onsite
Environment, Safety, Health & Quality
Good safety practice calls for anyone at JLab using a golf cart between dusk and dawn to drive with the golf cart's headlights on. Golf carts that don't have headlights may not be used from dusk to dawn. The Feb. 28 Integrated Safety Management poster titled Motorized Cart Safety offers a list of safety rules, including: Carts operated between sunset and sunrise shall have and operate with headlights turned on. The ISM posters are archived in Docushare.
Computing and Networking Infrastructure
JLab Wireless Access Changes
Linux Patches To Be Sent Out Tuesday
Windows Patches To Be Sent Out Tuesday
Hand Sanitizer for Your Workspace
Large Bottles of Hand Sanitizer Now in JLab Public Areas
Interested In Ordering the Liner for Your JLab Jacket?
Food Drive for Foodbank Underway
Quark Cafe Offers Thanksgiving Feast
Holiday Desserts to Tempt Your Taste Buds