Summary 1/23/18

PARTONS AND TIMELIKE COMPTON SCATTERING

• PARTONS is a C++ software framework dedicated to the phenomenology of Generalized Parton Distributions (GPDs). It provides a necessary bridge between models of GPDs and experimental data measured in various exclusive channels, like Deeply Virtual Compton Scattering (DVCS) and Deeply Virtual Meson Production (DVMP).

• Further details and instructions on using the framework can be found here

• For Timelike Compton Scattering (TCS): a code exists at NLO, but has yet to be implemented.

• Next steps:

• Dialogue between experiment and PARTONS regarding implementation of TCS. There is currently no projected timeframe, but it would benefit from experimental efforts
• Dialogue with experiment to develop support for experiment rate projections and impact of measurement on GPD extractions

TIMELIKE COMPTON SCATTERING EXPERIMENT

• Theoretical motivation includes access to the GPD E, in particular the imaginary part that allows for accessing orbital angular momentum

• New development since 2017 collaboration meeting is the addition of the Compact Photon Source - increased figure of merit

• Based on very preliminary studies, the experiment can make an impact on global GPD extractions and is competitive with other envisioned experiments with transverse target

• Next steps:

• Prepare a proposal to the PAC46 (2018)
• Need to make real rate projections
• Refine physics case
• Check impact of radiation due to e-/e+ production when beam interacts with a 1% radiator (target)
• Correlated with the previous point, check if the envisioned X-Y tracker will be operational in the projected radiation environment. During SANE operations, the tracker suffered from secondaries and was not functional as originally intended

PMT AND HV DIVIDER

• PMTs (R4125 Hamamatsu) have borosilicate windows - should be ok even in high radiation environment as tube is attached to crystal and have many photons (G0 detected SPE and had trouble with borosilicate)

• Active HV divider is a good option - regulation on last two dynodes provides stability and linearity at high rates, large dynamic range

• To confirm performance, tests were done over the last year including performance tests with long cables and LED chain tests in Hall D in collaboration with COMCAL/FCAL projects - results confirm performance

• 320 PMTs were procured in 2017. Note that the first ~100 sockets delivered by Hamamatsu were of the wrong size - required removal of a metal ring, this has been done. Subsequent sockets delivered were of the correct size

• PCB assemblies are done through an outside company, casing material (CL2 and fire rating) may not suitable for cable trays, but not an issue here

• Discussion about production status

• HV divider and PCB are in production - COMCAL is in final assembly
• First articles for NPS procured through OU and on the way to JLab. Tests will include cleanliness of the board, assembly, etc. A report will be procided

• Procedures for production tests are being finalized. A special optical darkbox was constructed for tests in Hall D. A similar one could be constructed for NPS. Different options exist for testing all PMT assemblies or selected ones compared to a reference PMT. A set of tests includes:

• HiPot tests planned for all dividers at -1.1 kV (no arcs, trips, supply current < 430uA) - the voltage margin is to be determined
• Characterization of PMTs on a single HV divider against reference (gain, rise time, linearity)
• Comprehensive characterization of all HV dividers individually (QE pulse height, stability)

• Next steps:

• Decide on connectors
• Finalize patch panels
• Production of HV dividers
• Determine voltage margin
• Study temperature stability of the gain
• Find out when Hall D needs the crystals

NPS FRAME