Jefferson Lab Weekly Briefs
March 2, 2011
12 GeV Upgrade
The first wire chamber sector for Region 2 of the Hall B CLAS12 spectrometer has been completed and signals seen with cosmic rays. The next Region 2 sector is now being strung at Old Dominion University. The photomultiplier tube and scintillator material orders for the CLAS12 forward time-of-flight panel “1b” have been placed, and the test and assembly line for FTOF-1b has been started at the University of South Carolina. The mask designs for the silicon-strip sensors for the barrel region of the CLAS12 silicon vertex tracker have arrived from the vendor, and a new cleanroom is being prepared for testing the first sensors, expected in late summer.
After completing the threshold electrodisintegration experiment on the deuteron, E08-008, on schedule, the calibration of the neutron array at high missing momenta was completed Friday. Hall A is presently in the process of taking calibration data for the N→Δ experiment, E08-010.
Hall B successfully completed the TPE (two-photon-exchange) experiment. This experiment is unique as the first measurement using a beam consisting of an equal mixture of electrons and positrons to measure electron-proton and positron-proton scattering simultaneously in the CLAS detector. A small difference of a few percent is expected in the elastic scattering cross section for the two processes. This difference is due to opposite signs of the interference term of one-photon and two-photon exchange contributions for positron and electron scattering, respectively. The experiment is motivated by the very large discrepancy in the ratio of electric to magnetic elastic form factors of the proton observed in experiments using the polarization transfer method and experiments using the traditional Rosenbluth separation method. The TPE experiment is expected to clarify the discrepancy.
Last week, CEBAF Operations delivered beam to all three halls up to 4:20 a.m. on Friday; machine availability was 50.9 percent. A power interruption caused by Dominion Virginia Power maintenance work outside JLab resulted in a down. It took more than 20 hours to recover from the power interruption, at which time CEBAF was reconfigured to deliver 1-pass beam to Hall A for the N→Δ experiment. Hall A was the only hall taking beam after the power interruption. Hall B was down due to installation of a new experiment. Hall C was down due to the Qtor power supply. On Saturday, the Hall A target chamber lost vacuum during movement of the BigBite spectrometer; beam delivery was resumed Sunday. There was a Central Helium Liquefier trip on Monday.
The FEL team made progress last week in getting the Laser Personnel Safety System certified for operation with the new ultraviolet capability. First running of the system took place Saturday. The team also spent time setting up a study of halo in the machine with researchers from the University of Maryland.
Theoretical and Computational Physics
A new formulation of one of the major radiative corrections to the weak charge of the proton, that arising from the axial-vector hadron part of the γZ box diagram, ℜe ? γZA, has been derived <arXiv:1102.5334 [hep-ph]>. The formulation is based on dispersion relations and connects the γZ contributions with inelastic intermediate states to moments of γZ structure functions, which can be measured in parity-violating deep-inelastic scattering at JLab. Using the best data currently available, the total correction to the proton's weak charge is found to be ℜe ? γZA = 0.0055(4) at zero energy and ℜe ? γZA = 0.0045(4) at the kinematics of the Q-weak experiment.
JLab Calendar of Events
March 2-4: Muon Accelerator Program-Winter Meeting
Environment, Safety, Health and Quality
In North America, tens of thousands of people are injured or killed every year from falls on stairs. The American National Council on Compensation Insurance estimated in 2001-2002 that the cost of such fall injuries was second only to those caused by motor vehicles.
Building codes for stairs and ramps are rigorous. Good design can substantially reduce the potential for missteps by providing users with the means to regain balance, but even the best design cannot eliminate falling hazards entirely. Many incidents are caused by inattention and unsafe behavior.
The vast majority of stairway falls result from a loss of balance, and one common contributing factor is the neglect to use the handrail. To keep from becoming a statistic, always use the handrail. It helps focus your attention on the task at hand, especially when descending. Additionally, do not carry objects that block your vision when using stairs.
The shop is in the final stages of the manufacture of a Wien filter for the Injector group. This assembly also includes the in-house manufacture of the associated coils. The shop is able to produce manageable-sized magnet coils that, in the past, have been difficult to find outside vendors capable of manufacture.
The shop has been involved heavily in the manufacture of HDice’s “in-beam cryostat” since January 2010. This includes material purchase; coordinating part process manufacturing consisting of machining, welding, inspection and final machining; coil winding; and other processes necessary for the completion of this project.
The shop has processed 400 work requests since Jan. 3.
2011 Benefits Open Enrollment Ends Friday
Annual Property and Key Validation Begins March 15
This year's property validation period is March 15 - April 30. Each custodian must log in to their Property Validation account and validate each item on their respective inventory list and take the Property Custodian Refresher GEN 150 training (about 5 minutes). Also during the validation period, every person who has been issued one or more JLab keys must validate each key issued to them. Further announcements will be made regarding this process once the validation period begins.
Lost and Found