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Compton@MAX-Lab Collaboration

Explore the latest results on Compton scattering on deuterium for improved neutron electromagnetic polarizabilities. Collaboration between MAX-Lab and University of Kentucky, along with relevant researchers. Understand the fundamentals, measurements of proton and neutron polarizabilities, and the challenges involved in the experiments. Delve into the latest experiments, theory support, and the status of nucleon polarizability findings. Discover the advancements made in elastic Compton scattering on deuterium and the ongoing efforts to enhance the research further.

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Compton@MAX-Lab Collaboration

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  1. New Results for Compton Scattering on Deuterium: A Better Determination of the Neutron Electromagnetic Polarizabilities Compton@MAX-Lab Collaboration University of Kentucky

  2. Compton@MAX-Lab Collaboration • University of Kentucky • Mike Kovash • KhayrulloShoniyozov • Duke University • Sean Stave • Seth Henshaw • University of Glasgow • John Annand • George Washington University • Jerry Feldman • Lund University • Bent Schröder • Lennart Isaksson • Kevin Fissum • Magnus Lundin • Kurt Hansen • Jason Brudvik • University of Illinois • Alan Nathan • Luke Myers • Theory support • H. Griesshammer (GWU) • J. McGovern (Manchester) • D. Phillips (Ohio)

  3. q , m 1st order response • , b 2nd order response (lowest order response of internalstructure) Introduction • polarizability – measure of induced dipole moment in external field electric magnetic D= aE M= bB De= –d·E – ½a|E|2 De= –m·B – ½b|B|2 • for the free nucleon: • fundamental structure constants (and not so well known) • test of models of nucleon structure

  4. + paramagnetic polarizability: moments align with B electric polarizability: separation of charge D= 0 M= 0 M=bdiaB diamagnetic polarizability: induced current opposes B M=bparaB D=aE

  5. Measuring Nucleon Polarizability • Proton • Compton scattering sp(w) r02 – 2r0apw2 • Neutron • difficulties • no free neutron targets • neutron is uncharged (no Thomson scattering) • techniques • neutron scattering by heavy nucleus • quasi-free Compton scattering: D(g,gn)p • elastic Compton scattering: D(g,g)D sn(w) an2w4 sD(w) r02 – 2r0(ap+an)w2

  6. Proton Polarizability

  7. an = 12.6  1.5(stat)  2.0(syst) +1.1 –0.6 an = 12.5  1.8(stat) (syst)  1.1(model) +0.6 –1.1 bn = 2.7 1.8(stat) (syst) 1.1(model)   Neutron Polarizability Experiments nscattering D(g,gn)p

  8. Elastic Compton Scattering on D • Motivation • sum of proton and neutron polarizabilities • sD(w) r02 – 2r0(ap + an)w2 • Requirements • must separate elastic from breakup! • monoenergetic (tagged) photons • high-resolution photon detector (DE/E < 2% at 100 MeV) • Data • Lucas – Illinois (1994) Eg = 49, 69 MeV • Hornidge – SAL (2000) Eg = 85-105 MeV • Lundin – Lund (2003) Eg = 55, 66 MeV • Theory • diagrammatic approach (Levchuk/L’vov) • EFT (Griesshammer, McGovern, Phillips)

  9. World Data Set • Lucas – Illinois (1994) Eg = 49, 69 MeV • Hornidge – SAL (2000) Eg = 85-105 MeV • Lundin – Lund (2003) Eg = 55, 66 MeV • Myers – Lund (2014) Eg = 65-115 MeV qg = 60º, 120º, 150º

  10. Status of Nucleon Polarizability proton neutron • deuteron data set is much smaller than proton • 29 vs. 170 data points • deuteron data covers much narrower energy range • 49-95 MeV vs. 40-170 MeV

  11. 120o BUNI UK CATS Experiment at Lund • energies: Eg = 65-115 MeV using tagged photons • two tagger settings: 65-97 and 81-115 MeV • bin data in DE = 8 MeV energy bins • angles: qg = 60°, 120°, 150° (plus recent 90°) • with 3 NaI detectors simultaneously • detectors: 3 large-volume (50 cm  50 cm) NaI’s • excellent photon energy resolution (DEg/Eg ~ 2%) BUNI: Boston Univ. CATS: Mainz Univ. UK: Univ. of Kentucky

  12. Kinematic Coverage (23) (5) (18) (6)

  13. Washington Location of MAX-Lab

  14. Nuclear Physics • Upgrade to double linac in 2002-04 • Install SAL tagger magnet in 2005 • First beam delivered in Sept. 2005 MAX1 PSR MAX3 MAX2 125 MeV Linacs

  15. Experimental Area at MAX-Lab Tagging Spectrometer CATS 60° BUNI 120° DIANA 150°

  16. NaI Detectors

  17. Front View Side View 48 cm 27 cm 64 cm Eg = 100 MeV 2 MeV CATS NaI Detector

  18. Timing Cuts

  19. Carbonvs. Deuterium 1 day 15 days!!

  20. Background Subtraction

  21. Data Analysis • Extraction of yields • subtraction of cosmics • subtraction of accidentals • Determination of photon flux • tagging efficiency (Ng = etag Ne ) • Simulation of expt. geometry and NaI response • effective solid angle and target thickness • overall detector efficiency • Corrections for rate-dependent effects • stolen coincidences • ghost events in tagger focal plane • beam time structure profile

  22. Rate-Dependent Corrections Myers et al. (2013) Preston et al. (2014)

  23. ds/dW (nb/sr) Eg (MeV) Myers et al. (2014)

  24. Lucas ●Myers ds/dW (nb/sr) • Lundin  Hornidge Eg (MeV) Myers et al. (2014)

  25. Lundin Lucas ds/dW (nb/sr) Myers 0 30 60 90 120 150 0 30 60 90 120 150 qg (deg) qg (deg) Myers et al. (2014)

  26. Myers Hornidge ds/dW (nb/sr) 0 30 60 90 120 150 0 30 60 90 120 150 qg (deg) qg (deg) Myers et al. (2014)

  27. Summary and Outlook • New elastic Compton scattering data on deuterium • roughly doubles world data set (first new data since 2003) • extends data to higher energy, more backward angles • reduces statistical uncertainty by 30%for an and bn • More data coming! (Shoniyozov – Kentucky) • concentrate on measurements in the 81-115 MeV range • greater sensitivity to polarizabilities • more angles covered (60º, 90º, 120º, 150º) • better statistics, smaller rate-dependent corrections

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