CREX Magnet Considerations Seamus Riordan University of Massachusetts, Amherst sriordan@physics.umass.edu April 12, 2014 Seamus Riordan CREX Magnet 1/12
Optimize Kinematics Compete against falling rates with higher asymmetry as Q 2 grows Need to optimize to sensitivity of A to marginal changes in radius C-REX: Sensitivity to 1% change in Neutron Radius 9 da/a for a 1% change in Rn 8 da/a (%) 7 6 5 4 3 2 1 C-REX: Absolute Error in Neutron Radius 0.034 dr (fm) 0.032 0.03 0.028 0.026 0.024 0.022 0.02 0.018 2.5 3 3.5 4 4.5 5 5.5 6 6.5 θ (scattering angle) For 2.2 GeV standard-energy beam, θ 4 0.016 2.5 3 3.5 4 5.5 6 4.5 5 θ (scattering angle) δr n 0.02 fm with 35 days beamtime and anticipated systematics Seamus Riordan CREX Magnet 2/12
Septum Magnet Septum Magnet Requirements HRS only go to 12.5, require septum to reach 4 4.3 Sufficient hardware resolution must be maintained, need pure dipole Need to reach 1350 A/cm 2 with 2-coil configuration (factor 2.2 Bdl from PREX) Require new power supply, LCW pumps Target must be moved back 30 cm for 4 acceptance Seamus Riordan CREX Magnet 3/12
Septum Magnet - g p 2 Seamus Riordan CREX Magnet 4/12
HRS and Quartz Detectors HRS has hardware resolution 10 3, use to separate inelastic states 0.2 Y (m) 0.15 0.1 0.05 X-Y of Tracks in HRS Focal Plane Cut defining "in the detector" First excited state 3.84 MeV Elastic events 0-0.05-0.1-0.15-0.2-0.3-0.25-0.2-0.15-0.1-0.05 0 0.05 0.1 X (m) dispersive direction Place quartz Cerenkov detectors to minimize inelastics Several states, but kept to < 0.5%. Asymmetries calculable to some level and are expected to be benign Seamus Riordan CREX Magnet 5/12
CREX Configuration Need 30 cm back for 4.3 (45 cm for 4 ) Scattering chamber radius is 50 cm Rolling pin target 90 cm Seamus Riordan CREX Magnet 6/12
HRSMC HRSMC developed by Jixie for g p 2, G p E Has LeRose transport functions built in as well as support for septum See earlier talk by Jixie Seamus Riordan CREX Magnet 7/12
HRSMC - Optics Magnetic transport through the septum can be used to Look at entrance/exit window event energy degredation Determine quality of optics transport Seamus Riordan CREX Magnet 8/12
HRSMC - Assuming LeRose transport Using only standard LeRose transport, background constributions look good Seamus Riordan CREX Magnet 9/12
HRSMC - Using Geant4+LeRose From Bob and Jixie: Final optics in HRSMC don t seem to show dispersion we would expect Need to look very closely at transport through septum Seamus Riordan CREX Magnet 10/12
APEX Magnet From Bogdan: APEX magnet could provide alternative option to PREX magnet They need 2.2 GeV at 5 Already funded by APEX collaboration/hall A? Need to weigh experimental advantages against practical Seamus Riordan CREX Magnet 11/12
Work To Do Projects: Settle on simulation framework to evaluate optics - HRSMC is likely choice If we need a new tune, we should add collaborators who are experts or grow in-house Finalize expectations for acceptance and resolution at ideal (maybe not optmized ) kinematics Look at field maps for both existing magnet and APEX option - needs to be higher priority as this determines scheduling Seamus Riordan CREX Magnet 12/12
BACKUP Seamus Riordan CREX Magnet 12/12
Beam Request and Proposed Data Energy 2.2 GeV Current 150 µa Polarization Full, 85% Production Commissioning Pol, calib., A T 150 µa available with 50 µa for remaining halls 35 days 5 days 5 days Require full longitudinal and (vertically) transverse beam Measured Asymmetry (p e A) 2 ppm Scattering Angle 4 Detected Rate (each HRS) 140 MHz Statistical Uncertainty of A PV 2.1% Systematic Uncertainty of A PV 1.2% Statistical Uncertainty of A T 0.4 ppm Seamus Riordan CREX Magnet 12/12
Systematic Uncertainties Charge Normalization 0.1% Beam Asymmetries 0.3% Detector Non-linearity 0.3% Transverse 0.1% Polarization 0.8% Inelastic Contribution 0.2% Effective Q 2 0.8% Total 1.2% Statistics dominate total uncertainty CREX more sensitive to Q 2 uncertainty than PREX, angular resolution demonstrated using elastic ep Seamus Riordan CREX Magnet 12/12