Compton Scattering from Deuterium above the Pion Production Threshold Collaboration  Duke University Luke Myers  Luke Myers  Seth Henshaw  Henry Weller  University of Kentucky  Mike Kovash  University of Illinois  Al Nathan  George Washington University Jerry Feldman  Jerry Feldman  Lund University  Kevin Fissum  Lennart Isaksson  Bent Schröder  Jason Brudvik  Kurt Hansen  Magnus Lundin

Outline  Current Compton scattering program at MAX-Lab  Proton data at higher energies  lack of comparable deuteron data  Motivation  EFT considerations  exploit approved expt. on  – photoproduction  Proposed Experiment  run plan (energies, angles, etc.)  NaI detectors  beamtime estimate  Summary

Compton Scattering at Lund E  = MeV using tagged photons  energies: E  = MeV using tagged photons  two tagger settings: and MeV  bin data in 7-8 MeV energy bins   = 60°, 120°, 150°90°  angles:   = 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 (E  /E  ~ 2%) BUNI: Boston Univ. CATS: Mainz Univ. UK: Univ. of Kentucky UK CATS BUNI 120 o

Kinematic Coverage x present work (18) SAL – Hornidge (5) Lund – Lundin (18) Illinois – Lucas (6)

79 MeV 87 MeV 70 MeV 96 MeV 105 MeV 112 MeV (,) = 11.3, 3.2 (= 2, = 2) 

Proton Compton Scattering Data  fit with N,, up to N 3 LO  note unitarity cusp at MeV McGovern09

World Data Set  Lucas – Illinois (1994) E  = 49, 69 MeV  Hornidge – SAL (2000) E  = MeV  Lundin – Lund (2003) E  = 55, 66 MeV  Myers – Lund (2010) E  = MeV   = 60 º, 120 º, 150 º

Motivation  Lack of higher-energy deuteron data  need analogous data to the proton data  Theoretical considerations  increased contribution from pion degrees of freedom  importance of spin polarizabilities  opening of new channel  imaginary part  sensitivity to pion production multipoles  Exploit NaI detector setup already well tested  commissioned and used extensively for neutron pol.  Exploit  – photoproduction expt. already approved  proposal by K. Fissum matches energy range

Calculated Proton Cross Sections

Calculated Neutron Cross Sections

Experimental Plan  measure at E  = MeV  bin data in 5 MeV energy bins  measure at 3 angles    = 60°, 150° + 1 other angle  additional considerations  tagging efficiency measurements  lineshape measurements of NaI detectors (in-beam)

    MeV Compton events can be identified above 138 MeV

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

CATS NaI Detector 48 cm 27 cm Front View 64 cm Side View 2 MeV E  = 100 MeV

Count Rate Estimate  differential cross section ()  12 nb/sr  average value between 30° and 150°  photon beam intensity: R  = 450 kHz/MeV  based on 750 kHz/channel and 20% tagging efficiency  target thickness: t = xN 0 /A = 8.04  cm -2  LD 2 target linear thickness x = 16 cm  solid angle:  = 41 msr  target-detector distance = 70 cm  NaI entrance collimator diameter = 16 cm Count rate = () R   t

Beam on Target Estimate  need 1100 counts (foreground) for 3% statistics  requires 314 hrs of running  background from Kapton target windows  measure with stack of 100 Kapton foils, then scale  requires 24 hrs of running Count rate = 3.5 counts/hour/(5 MeV)

Beamtime Request DescriptionHours Measurements with LD Measurements with Kapton24 Detector setup/commission48 Tagging efficiency28 Lineshape measurements36 TOTAL450

Summary  higher-energy Compton scattering from deuterium  E  = MeV in 5 MeV steps  measure 3 angles  Provide benchmark data for EFT calculations  need data to match extensive proton results  Exploit favorable circumstances  existing NaI setup is well understood  expt. with identical requirements is already approved  Needed 450 hrs of beamtime (4 weeks – Already approved!)