Prajwal T. Mohan Murthy Laboratory for Nuclear Science, MIT νDM Group Spin-Light Polarimeter for the Electron Ion Collider EIC Users Meeting 2014 Jun 2014 Story Brook, NY

Synchrotron Radiation (SR) “Spin-Light” Wiggler Magnets Collimators Ionization Chambers Geant4 Simulations Topic by Topic Case Studies (Only a Few Presented) Summary Outline (CHANGE)

Synchrotron Radiation (SR) “Spin-Light” Wiggler Magnets Collimators Ionization Chambers Geant4 Simulations Topic by Topic Case Studies (Only a Few Presented) Possible Location at mEIC Summary Outline (CHANGE) Quick parts, for details, please refer to: arXiv: arXiv: arXiv:

Synchrotron Radiation (SR) “Spin-Light” Wiggler Magnets Collimators Ionization Chambers Geant4 Simulations Topic by Topic Case Studies (Only a Few Presented) Possible Location at mEIC Summary Outline (CHANGE) Quick parts, for details, please refer to: arXiv: arXiv: arXiv: Latest Updates

Comparative Introduction

What is Synchrotron Radiation? First seen in General Electric Lab, 1947 Angular Distribution

So where is spin dependence? With QED Corrections by A.A.Sokolov and I.M.Ternov (1960s) Spin dependent term Spin flip dependent term Verified at VEPP-4 storage ring in Novosibirsk Belomesthnykh et. al., NIM 227, 173 (1984)

Longitudinal Spin Light

What are Spin-Light Characteristics? Spin light characteristics

Conceptual Design

Won’t all the fans of SR merge? The SR fans may be selected out after each dipole and collimated before being fed into the DIC. Notice only 2 fans are required for polarimetry, 4 fans are for statistics.

What are Spin-Light Characteristics? A differential ionization chamber can be used to measure the asymmetry. SR (+ SpinLight) The ionization chamber can use Xenon A split plane IC can pick out small up- down asymmetries in SR - influx. At the IC, the collimated SR beam spots shall be about 1cm. Notice: Figure on left is only one half of the actual IC. The middle plate is held at an intermediate potential.

A schematic for detection of SR (alternative arrangements are a possible) Detecting the Collimated SR

What will be the signal?

Geant 4 Simulation

Geant 4 Simulation Results Simulation reproduces photon spectrum and asymmetry Only a single DIC is being simulated along with collimators

What about Background Simulations? Background events are mostly Bremsstrahlung events from the collimators

SR Spots from GEANT4? Notice only 2 fans are required for polarimetry, 4 fans are for statistics. Note: The Geant4 simulation plots are all for just one split plane IC, on one side of beamline.

How does this scale with E Beam and I Beam ? Number Spectra

How does this scale with E Beam and I Beam ? Power Spectra

How does this scale with E beam and I beam ? Asymmetry Power output remains to be a challenge for high energy EIC Spin-Light Polarimeter is best suited for: E(e) = [2,20]GeV I(e) < 10mA

Where could this be accommodated in mEIC? Ample real-estate near the 8 dipoles and the fact that the magnets are of 20mrad bend angle (twice as much as initial proposal design) allows for convenient sized collimators.

Updated Geant4 Results Theory Plots: Updated Spectra and Corresponding Asymmetry

Updated Characteristic Plots Theory Plots: Updated Spectra and Corresponding Asymmetry The spectra now is completely in the hard X-ray Spectrum

Updated Geant4 Results Number Spectra for beam energy of 5GeV, magnet pole strength of 0.22T

Updated Geant4 Results Power Spectra for beam energy of 5GeV, magnet pole strength of 0.22T

Updated Geant4 Results Number Spectra for beam energy of 12GeV, magnet pole strength of 0.5T

Updated Geant4 Results Power Spectra for beam energy of 12GeV, magnet pole strength of 0.5T

Updated Geant4 Results But the Geant4 asymmetry for both the energy configurations 0.5T and 0.22T) match within about 5%

Slit Width Effects For 0.22T

Slit Width Effects For 0.5T: Completely resolved even if the e- beam is allowed a 4cm wide passage.

Uncertainties Background and background asymmetry has to be measured with the wiggler on/off Simulation was used to estimate background

SUMMARY Acknowledgements This work is supported by the U.S. Department of Energy under contract number DE-FG02-07ER41528 ‘10 – ’13 and MIT Frank Fellowship. 3 dipole magnet:.1m dipoles separated by 1m. DIC 10m away Asymmetry in SR gives spin light component -> Polarization A non invasive and continuous method Possible location at mEIC zeroed on

Backup

How does the dipole field look like? Central Uniform field BEAM Magnet Face Beam Pipe Edge fringe field Conceptual Design

How does the dipole field look like? Edge fringe field Central Uniform field BEAM Magnet Face Simulated using LANL Poisson EM Code Beam Pipe

Does the asymmetry in B field change anything? For each dipole Magnet: There is a reduction in both the total events and spin-light events (Plot: Events vs. E(MeV) of the light emitted)

Does the asymmetry in B field change anything? For each dipole Magnet: Even though there was a decrease in SR and SpinLight events, the asymmetry remains the same.

Does the Gaussian Beam profile change anything? Point BeamBeam Pipe 2inch SR Profile for Point Cross section of Beam The graph shows events as seen at the DIC For a point beam cross section, the SR profile is “box” like.

Does the Gaussian Beam profile change anything? Finite Beam size Beam Pipe 2inch SR Profile for Gaussian Beam Profile The graph shows events as seen at the DIC For a Gaussian beam profile, the SR profile is “box” with smooth edges. Notice the asymmetry has not changed. 200μ Note: Has been scaled to make it visible

Do the B field and dimensions affect? B field was chosen to be 4T YES! And the corresponding pole length of 10cm. This corresponds to a 10mrad angular beam bend.

What are Spin-Light Characteristics? Beam Energy dependence

How does this scale inclusion of Beam Halo? Asymmetry

Collaboration