Presentation on theme: "Measuring the Proton Spin Polarizabilities in Real Compton Scattering Philippe Martel – UMass Amherst Advisor: Rory Miskimen TUNL (Triangle Universities."— Presentation transcript:
Measuring the Proton Spin Polarizabilities in Real Compton Scattering Philippe Martel – UMass Amherst Advisor: Rory Miskimen TUNL (Triangle Universities Nuclear Lab) Bosen 2009
May 2, 2015P. Martel - Bosen Table of Contents Concerning spin-polarizabilities What are they? Where do they come from? What is currently known? Concerning the sensitivities to them Observe changes in asymmetries after perturbing one Smearing of effects from multiple perturbations Concerning the fitting method Constructing asymmetries and partials Minimization checks Results
May 2, 2015P. Martel - Bosen Nuclear Compton Scattering Compton scattering refers to scattering a photon off of a bound electron (atomic) or off of a nucleon (nuclear). Below about 20 MeV, this process is described by the Hamiltonian: * Above 20 MeV, the photon begins to probe the nucleon structure. To second order, an effective Hamiltonian can be written: Here, E1 represents the electric, and M1 the magnetic, dipole (scalar) polarizabilities. * *B. Holstein, GDH Convenor’s Report: Spin polarizabilities (2000)
May 2, 2015P. Martel - Bosen Spin Polarizabilities These scalar polarizabilities have been measured for the proton through real Compton scattering experiments. * Advancing to third order, four new terms arise in the eff. Hamiltonian: * These terms are the spin (vector) polarizabilities. The subscript notation denotes their relation to a multipole expansion. *R.P. Hildebrandt, Elastic Compton Scattering from the Nucleon and Deuteron (2005) - Dissertation thesis
May 2, 2015P. Martel - Bosen S.P. Measurements The GDH experiments at Mainz and ELSA used the Gell-Mann, Goldberger, and Thirring sum rule to evaluate the forward S.P.: The Backward S.P. was determined from dispersive analysis of backward angle Compton scattering: *B. Pasquini et al., Proton Spin Polarizabilities from Polarized Compton Scattering (2007)
May 2, 2015P. Martel - Bosen S.P. Theoretical Values O(p 3 )O(p 4 ) LC3LC4SSEBGLMNHDPVKSDPVExperiment E1E No data M1M No data E1M No data M1E No data 0 ±0.08 ±0.10 ± 1.8 The pion-pole contribution has been subtracted from the experimental value for Calculations labeled O(p n ) are ChPT LC3 and LC4 are O(p 3 ) and O(p 4 ) Lorentz invariant ChPT calculations SSE is small scale expansion Other calculations are dispersion theory Lattice QCD calculation by Detmold is in progress
May 2, 2015P. Martel - Bosen Dispersion Analysis Program The theoretical cross sections used here are produced in a fixed-t dispersion analysis code, provided to us by Barbara Pasquini. For further information, see B. Pasquini, D. Drechsel, M. Vanderhaeghen, Phys. Rev. C (2007). The program was run for three different experimental runs: Transversely polarized target with a circularly polarized beam Longitudinally polarized target with a circularly polarized beam Unpolarized target with a linearly polarized beam The former two return cross sections for unpolarized, left helicity, and right helicity beams. The latter returns the beam asymmetry.
May 2, 2015P. Martel - Bosen Asymmetries After producing tables of cross sections with various values for the polarizabilities (their HDPV values, and those + 1 unit we construct the asymmetries: Using the counts, the statistical errors can be propagated through:
May 2, 2015P. Martel - Bosen 2x – 0 and Constrained
May 2, 2015P. Martel - Bosen 2z – 0 and Constrained
May 2, 2015P. Martel - Bosen 3 – 0 and Constrained
May 2, 2015P. Martel - Bosen 2x – All Four Multipole S.P.s
May 2, 2015P. Martel - Bosen 2z – All Four Multipole S.P.s
May 2, 2015P. Martel - Bosen 3 – All Four Multipole S.P.s
May 2, 2015P. Martel - Bosen
May 2, 2015P. Martel - Bosen
May 2, 2015P. Martel - Bosen
May 2, 2015P. Martel - Bosen Fitting Program Cross sections → Counts → Asymmetries Solid Angle of Detector Real/Effective Polarization Energy Bin Width Partials with Respect to Polarizabilities Pseudodata 300 hours 2x, 300 hours 2z, 100 hours 3 Fitting 2 Construction Minimization
May 2, 2015P. Martel - Bosen Solid Angle The solid angle for the chosen polar angle bin is given by: In order to tag the event (as likely described before), the reaction requires a proton recoil energy of at least 40 MeV, limiting our minimum forward angle of acceptance to: This, however, neglects the different events that different parts of the detector observe for a given run configuration, which will be corrected for in the next section.
May 2, 2015P. Martel - Bosen Real/Effective Polarization The cross sections produced in the code assume 100 % beam and target polarization (if applicable). The cross sections with a real polarization: Transversely LongitudinallyUnpolarized Where red is target polarization, and gray is beam polarization direction For 2x and 3
May 2, 2015P. Martel - Bosen Real/Effective Polarization The effective polarizations can then be written as: With the expected experimental polarizations, the resulting effective polarizations are:
May 2, 2015P. Martel - Bosen Minimization Partials The energy bin averaged counts can be written in a linear expansion: Where k max, k min, and k 0 are the energy bin max, min, and centroid respectively, i is the S.P. perturbation, and F is the flux factor: The C i term represents the partials of the counts with respect to the S.P.s
May 2, 2015P. Martel - Bosen Construction The fitting program uses a minimization routine on 2, defined as: The algorithm is actually the summation of various 2 components, including the selected constraints for the particular run. Is it reasonable, however, to assume that the theoretical component can be approximated by a linear expansion? Run a 2 check.
May 2, 2015P. Martel - Bosen S.P. Fitting – 280 MeV (no con.)
May 2, 2015P. Martel - Bosen Con. Values – 280 MeV (no con.)
May 2, 2015P. Martel - Bosen Results The tabulated results for running with both the 0 and constraints: The tabulated results for running with no constraints:
May 2, 2015P. Martel - Bosen Conclusions By simply plotting the changes in the asymmetries, the sensitivities to the polarizabilities is seen to be appreciable. Checks of the fitting method being used demonstrates reasonable behavior (near linearity and containment) Fitting results are very promising: Running the full program with 2x, 2z, and 3 appears to be sufficient to extract the S.P.s without invoking the 0 or constraints. This would provide the first set of experimental values for these important quantities!