Upload
isi
View
48
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Spin Polarization in d g → n p. Chang Ho Hyun Daegu University Work with S. Ando ( Daegu ) Y.-H. Song (South Carolina) K. Kubodera (South Carolina). HNP2011, Pohang, Korea February 21-24. Outline Motivation Formalism Spin polarization P’ y Results Conclusion. Motivation. - PowerPoint PPT Presentation
Citation preview
Spin Polarization in d g → n p
Chang Ho HyunDaegu University
Work withS. Ando (Daegu)
Y.-H. Song (South Carolina)K. Kubodera (South Carolina)
HNP2011, Pohang, KoreaFebruary 21-24
Outline
• Motivation
• Formalism
• Spin polarization P’y
• Results
• Conclusion
MotivationNN force well understood at Elab ≤ 300 MeV
Nevertheless many discrepancies in the polarization
observables
Puzzles with spin
- Spin crisis: origin of the nucleon spin
- P’y in deuteron photo-disintegration
- Ay puzzle in neutron-deuteron scattering
Spin is still an open problem in few-body systems
Spin polarization P’y
- Experiments: 1961-1983 (John61, Jewell65, Nath72, Holt83)
- Jewell65 Jewell et al., PR 139, B71 (1965)
- SNPA (standard nuclear physics approach) R. Schiavilla, PRC 72, 034001 (2005)
“New and more accurate measurements of the induced polar-ization in the 2H(γ,n)1H reaction are needed to establish un-equivocally whether there is a discrepancy between theory and experiment.”
Need to investigate the problem with modern theories
- Effective field theories (EFTs) provide proper tools
Our choice: Pionless EFT with dibaryon fields
Formalism
NN force with chiral perturbation theory Meson-exchange currents with systematic expansion rules - Integrate out heavy degrees of freedom Pionless theory - Integrate out the pion - NN contact interactions - Low energy constants determined by low-energy data Dibaryon fields - Nucleon bubbles summed infinitely, the deuteron pole re-produced successfully - Ensure fast convergence with only a few leading terms
Lagrangians
- si, ti : dibaryon fields in 1S0 and 3S1 states, respectively- Bi : external photon fields
Low energy constants- ys, yt : dNN coupling constants. Fitted to effective range
parameters- L1, L2 : ddV coupling constants. Fitted to np capture cross
section at threshold and deuteron magnetic moment- Total np capture cross section
Definition
Spin polarization P’y
p
n
g z’y’
s+,-(q) : differential cross section with parallel and anti-parallel neu-tron spin
Py’ becomes non-zero due to the interference of even and odd transition amplitudes
Amplitudes and cross sections- Feynman diagrams
- Amplitudes
- Cross section for unpolarized neutron
- Projection operator for the neutron spin
- Cross section for polarized neutron
- Result for P’y
ResultsDifferential cross section of unpolarized neu-
tronEg = 19.8MeV De Pascale et al. PRC 32, 1830 (1985)
Our work SNPA
P’y at Eg = 2.75 MeV
Our work SNPA
P’y at q = 45
P’y at q = 90
P’y at q = 135
Conclusion What is the correct answer? Experiment side - Large errors - Data do not converge (q = 90) - Revival of the measurement at modern facilities and instruments is absolutely necessary Theory side - Results for unpolarized cross section show good agreement - SNPA results are discrepant from pionless EFT - Systematic investigation at higher orders are in-evitable works in the future
Possible scenarios - New measurements or other theories consistent with SNPA - New measurements or other theories consistent with pionless EFT - New measurements still inconsistent with any the-ory Spin is still an open and active subject in the nuclear
physics P’z ∝ cosq : Parity-violating effect. In progress with
Ando and Shin