1. Opportunities for Precision Measurements, New Physics Searches & Low Energy Fixed Target Expts at a Modified “FEL” Accelerator Complex R. D. Carlini 12/7/2011

2. Precision Measurements, New Physics Searches&low Energy Fixed Target Exptsat a Modified “FEL” Accelerator Complex • The FEL “accelerator complex” has several very unique capabilities. • 10 mA re-circulating beam (makes great FEL), but has seen little fundamental science usage to date. • Could be upgraded/modified to allow the extraction of ~1mA of 100MeV - 300MeV polarized electrons for a fixed target program. • Need new “Hall B size” endstation. • Need extraction line. • Need polarized injector & upgraded beam instrumentation. • SRF cavity upgrades to get significantly above ~150 MeV. • For such a fixed target program the user community would basically be Jlab’s existing users, plus a few “low” energy groups.

3. Examples of Physics that Might be Done at a Modified “FEL” Accelerator Complex • Observation: After the 12 GeV upgrade low energy beams for extended periods will for all practical purposes be unavailable at the 4 primary Halls. • Precision PV measurements: • Qweak proton at ultra low Q2 • Ca48 and Pb radius PV measurements • Others • “Axion” style searches (already in pipeline): • Dark Light Experiment • Others • More traditional low energy fixed target expts, but with high beam currents and polarized beam. • Initially scrounge spectrometers from “old” facilities.

5. Qweak-2: An Ultra Low Q2 Measurement Using ~0.5 mA of 200 MeV Polarized Electrons from a Modified FEL Accelerator Complex • A Qweak-2 goal (which seems possible) would be to run for a “similar” duration to Qweak-1 but perhaps halve the final error bar. • The value of such a measurement really comes from it being part of a global fit. It would be another point, at a lower Q2, but with different systematic and theoretical uncertainties – rather simply smaller ones. This should allow a better global extraction of a final result. • Basically it would have ~100x the rate of Qweak-1 but an average Q2 ~10x lower, so the FOM on the asymmetry is similar. • The advantage in FOM on Qweak-2 comes also from the elimination of the "dilution" terms (magnetic moment, plus any strange quark, etc.) and somewhat smaller corrections (such the g-Z Box term). • On the negative side: The asymmetry is smaller, control of beam properties is a bit harder, the required polarimetry is significantly harder, and more cooling power is required for the target. However, Qtor electric costs are way down!

6. Physics Preliminary & Blinded “25%” Measurement Qweak-2: With JLab FEL Accelerator

7. What Might Such an ExptLook Like? Employ ~0.5 mA of ~200 MeV Polarized e- from FEL Accelerator Existing FEL linac can deliver >1 mA of electrons in single pass! Existing Qweak Apparatus Bend for Energy Measurement New Exp Hall • Replace the present FEL e- gun with 1mA capable polarized injector (Matt Poelker indicated it doable). • Extract beam via a simple transport line with 3 triplets between the existing FEL • and wall, a pair after, a 4 period FODO arc (using the GW dipoles now in FEL lab 1 for LIPSS), • followed by a scaled clone of the transport into Hall C (optics by Dave Douglas). • Build ~100’ diameter end station (similar size to Hall B) – close to main He refrigerator. • Move existing Qweak experiment: Qtor magnet, target (already good up to ~200mA’s), • collimators, detectors, etc. • Make necessary changes to Qweak apparatus to optimize figure-of merit. • Add specialized parity instrumentation, polarimetry & feedback systems. R. Carlini – 12/8/2011

8. A First Look at What Would Happen if the Existing Qweak Apparatus Were Used with a 200 MeV Polarized e- Beam Using the existingQweak GEANT3 simulation, for a "plane" detector at 592 cm. No validation of the standard GEANT3 cross section calculation at these low energies, etc. Assume the same length/density target and collimation system with the same relative positions. Figure shows the weighted x:y distribution at the plane detector. We do get a focus at the detectors! • Toroidal spectrometer will not produce fields strong enough to polarize the target. • Existing target system will work up to ~200 mA. Possibly suppress boiling noise at • higher currents by increasing helicity flip rate to 2 KHz & using rf cavity (BCM) • downstream of the target as luminosity/transmission monitor. • Very preliminary simulation (by Juliette Mammei) of rates and achievable Q2 using • three different global materials filling the region between target and detectors. • Air (like present exp)      He (a sharper focus)      Vacuum (reference only) • Q2 (GeV/c)2      6.99 x 10-4             6.97 x 10-4             6.98 x 10-4 • 8 Detector Rate Sum (GHz/mA)   1.2                           1.5                       1.5 • qLab (degrees)          7.7                              7.7                            7.7 • <E'> (MeV)                   193                               193                          193 R. Carlini – 12/8/2011

9. PREX @ FEL Parity Violating Electron Scattering Measurements of Neutron Densities atFEL Accelerator Complex (R. Michaels, S. Ban, C.J. Horowitz) Map out For several nuclei, 48Ca, 208Pb, … Est. Error in RN for 48Ca, 208Pb Assumptions: 200 MeVe- beam ½ mA 35 msr 1% resolution Polarization = 0.8 10% RL target 30 days / point

10. DarkLight: A Search for Dark Forces at the Jefferson Lab FEL Experiment requires 10 mA of 100 MeV (1 MWatt) beam from the FEL. MIT, JLab, U.C. Berkeley, LANL University of Maryland, Hampton University, Arizona State University, Catholic University

11. DarkLight: A Search for Dark Forces at the Jefferson Lab FEL