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Compton@MAX-Lab Collaboration

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

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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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