E : Proton g 2 Structure Function Fundamental spin observable has never been measured at low or moderate Q 2 BC Sum Rule : violation suggested for proton at large Q 2, but found satisfied for the neutron & 3 He. Spin Polarizability : Major failure (>8  of  PT for neutron  LT. Need g 2 isospin separation to solve. Hydrogen HyperFine Splitting : Lack of knowledge of g 2 at low Q 2 is one of the leading uncertainties. Proton Charge Radius : also one of the leading uncertainties in extraction of from  H Lamb shift. A - rating by PAC33 BC Sum Rule Camsonne, Chen, Crabb, Slifer* g 2 data strongly anticipated by theorists Spin Polarizability  LT

3.3 GeV, 12.5 deg 2.2 GeV, 15 deg 3.3 GeV, 6 deg 2.2 GeV, 6 deg 1.6 GeV, 6 deg 1.1 GeV, 6 deg Polarized beam: nA up to 5 uA? for optics, 30 uA ? for Compton Polarized NH 3 target Slow Raster 25 mm diameter G e p configuration is now basically g 2 p at the elastic setting Two configurations: with septa (6 degree) (target at 87 cm upstream) and without septa (12.5 and 15 degrees) (target at original pivot) g 2 p needs target at 90 degrees for all and 0 degree for 3.3 GeV G E p needs target at 80 degree Kinematics and Instrumentation Requirements

REGION 1 REGION 2REGION 3 REG 4 REGION 5 Slow Raster FZ1 FixedStand FZ2 Telescoping Stand DUMP TARGET Polarized Solid NH 3 Target (Hall C/UVa target) Target material irradiation Beamline (Similar to Hall C) Magnetic Chicane/Beamline modifications. Low beam current BCM/BPMs Slow Raster Hall A Engineering/Design Local Beam Dump Hall Infra-structure Scattering Chamber/ Target/magnet mount Septum Magnets Simulations/Optics/Spectrometer/Detectors/QAD… BPMs Use existing equipments Hall C beamline/target Keep change minimum modify the existing PREX septa use simple local beam dump Major equipments for g 2 p /G E p experiments Septa/HRS

Goal is to measure g2p in the low Q2 region with a precision ~ 5% by measuring transversely polarized cross section difference = A x   Measure both asymmetries and cross sections to 3-4% In addition to statistics, we need to control total systematics to 3-4%, i. e., each system to be below that (1-3%). Main systematics for asymmetries: Target polarization (3%?) Beam polarization (2%?) Dilution factor/density/packing factor (some cancellation?) … Main systematics for cross sections Acceptance/optics (2-3?) Dilution factor/density/packing factor (some cancellation?) Beam charge (1-2?) Position and angle determination (0.1 mm?, 0.03 degree?) Detector efficiencies (~< 1%?) Background (including pions and e+e-) (?) Radiative corrections (including radiative tails) (?) … Experimental Goal/Considerations

Timeline Engineering/Design/Manufacture 5/2011 most engineering/design done by 2/2011 Installation5/ /2011 Commissioning11/2011 Data taking11/2011-3/2012 Remove septa and move target location1/2012 Beamline: Tim Michalski (coordinating), Butch Dillon-Townes(engineering Group) Support from various groups and users Target: Chris Keith (Target group) Support from various groups and users Hall infrastructure/Septum/dump: Al Gavalya (Hall A) Support from various groups and users Others (Spectrometer, detector, DAQ, polarimeters…): Hall A/users Timelines, Main Tasks, Peoplepower

Initial Cost Estimation Procurement: ~650 K Engineering manpower: Engineering/Acc Divisions: ~2.9 FTE = $250 K Physics Division: ~1.5 FTE = $130K Installation manpower: Engineering Division:~1.8 FTE = $160K Physics Division: TBD Total cost = $1.02 M + Installation Cost (160K+TBD) + Overhead 60% User pledged contribution to procurement : $ 80K to Engineering/Installation: ? Total: $140K Will need user to honor the pledges. Applied to DOE for addition (end-of-year) funding for the procurement cost $(650-80)K x (1+60%) ~ 900 K Got approved from DOE for FY 10 ~ 650K. Expect to get the rest ($250K) from DOE in FY11. Manpower cost will be supplied from within JLab. Need user manpower Budget and User Contributions

Coordination: Tim Michalski (Engineering Division) Weekly beamline meeting 8:30-9:30 Tuesday at MCC Topical meeting: PSS-MPS, Diagnostic (BPM/BCM) Engineering/design: Butch Dillon-Townes(Engineering) Conceptual design: done Overview layout: 2 nd draft available, complete by 10/12 Cost/Manpower: draft done, 2 nd iteration next week? Schedule: draft next week? Beam Optics/Transport: Yves Roblin (CASA, Acc. Operation) First round of design: completed Chicane: Remove first girder (BPMs/harps/BLM) FZ1/FZ2 magnets exist, need modifications (vacuum chamber) Power Supplies: from Hall C (status), Owner/Control/Software Stands/support to accommodate all energies ( GeV) Need new stripline BPMs at the last leg with harps. Girder before the Chicane: remove girder/quads, put a new one with only correctors and BLM. Beam Line

Beam diagnostics for low current: John Musson (EESIC) New stripline BPM: testing at NL, install/test in Hall A in 1/2011? (superharp to calibrate) BCM: using existing one with new electronics Tungsten Calorimeter: need significant work Slow Raster: Bill Gunning/Chris Cuevas (Fast Electronics) Magnets, power supplies, control, shielding found Need significant rework PSS-MPS: Kelly Mahoney (SSG) FSD: magnets, anything else? interlock magnets with high beam current? ion chamber: ep not needed, available for other use? Others: Vacuum, Software (EPICS), Alignment, Radcon, … Beam Line (cont.)

Septum: use the room-temperature septum magnets (PREX) add high field coils move coils/yoke? Beam dump: tungsten blocks with cooling (air or water)? Scattering chamber: use the SANE one window design Target/magnet mount Beamline downstream of target Infrastructure Cryogenic Support target material irradiation Hall A Engineering/Design (Al Gavalya)

Polarized NH3 Target (Chris Keith) Status of target magnet (Donal Day) Install the Hall C/UVa target in Hall A New rotatable seal between top flange and 1K fridge to allow rotation from 90 degree to 80 degree at each energy Rotate to 0 degree once at 3.3 GeV Overview of work (Chris’s talk at first onsite meeting) A new 1K refrigerator (UVa one as spare) New pump line/manifold (vertical space limitation) New target Insert, upgrade motion mechanism Microwaves/NMR ok Cryogenics: buffer dewar, new cryoline with valve control Weekly meeting 1:30 pm, room A110) after target group less busy with Qweak/DVCS targets

Target Material Irradiation Options: NIST, FEL, ISU? Had some discussions/meetings with FEL people Use the ERL 10 MeV dump line Do-able: replace a section of beam pipe with a liquid Ar dewar no sure-stopper need a new dewar with less material in beam path and thinner target container can raster beam to a few cm by a few cm movable in vertical direction to reduce access time? Estimation: one week setup time, a couple days running and a couple of days dismount = two weeks Al is working with FEL people to get a scope/cost Likely time to do the irradiation is March 2011 Not in initial cost Will compare with other options before choosing a solution

Onsite User/Hall A People Power PhD Students: Pengjia Zhu (USTC, advisor: Yunxiu Ye), 3 rd year, onsite Min Huang (Duke, Haiyan Gao), 3 rd year, onsite Chai Gu (UVa, Nilanga Liyanaga), 2 nd year, onsite from 1/2011 Melissa Cummings (W&M, Todd Averett), 2 nd year, onsite from 5/2011 Name? (New Hampshire, Karl Slifer), 1 st year, onsite from? ? Postdocs: Kalyan Allada (Hall A) Jixie Zhang (Hall A) Sarah Philips (New Hampshire) ? Narbe Kalantarians(UVa) ? Hovhannes Baghdasaryan (UVa) ? Xiaohui Zhan (Argonne)? ? Physicists: Jian-ping Chen (Hall A) Alexandre Camsonne (Hall A) Doug Higinbotham (Hall A) Karl Slifer (New Hampershire) Guy Ron (LBNL)? ?

Questions and Issues Should we do Compton (need high current, 30 uA, straight-through)? How should we do optcis study- should we have high current (1uA) local beam dump for optics? What optics target(s) should we have? Do we need fast raster? Where to put the ep ion chamber? Is the Al window ok? Do we need water cooling? Do we need He bag? Should we do irradiation at FEL? Should we do target cold test at EEL? Should we do a field map at EEL? Should we add some iron plates to study the effect? Should we do a field map in Hall A (combining target/septa)? Should we and how to measure field direction? Should we use 15N or 14N? Should we take N2 data? How to have students help with target work and get trained to become target “experts”? How to avoid installation manpower conflict with 12 GeV work? …?