Lara De Nardo DIS 2007 Measurement of the spin structure functions g 1 and g 1 at HERMES Lara De Nardo TRIUMF/DESY pd Lara De Nardo DIS 2007 Inclusive Deep Inelastic Scattering is exact in QED in LO QCD Lara De Nardo DIS 2007 Inclusive Deep Inelastic Scattering is exact in QED in LO QCD Lara De Nardo DIS 2007 param. kin. fact. measuredparam. kinematic factors Measured Inclusive Asymetries measured DIS cross section inclusive asymmetry: P zz =0.830.03 A zz ~0.01 Lara De Nardo DIS 2007 The HERMES Spectrometer Reconstruction: Reconstruction: p/p < 2%, < 1 mrad Particle ID: Particle ID: TRD, Preshower, Calorimeter : Cherenkov, 1998: RICH Internal Gas TargetH, D, Internal Gas Target: unpol: H 2, D 2, He, N, Ne, Kr, Xe, He, H, D, H Lara De Nardo DIS 2007 The data The cut at Q 2 =1GeV 2 identifies the DIS region P beam ~(531.8)% Full analysis published in Phys.Rev.D75 (2007) P beam ~(531.0)% Lara De Nardo DIS 2007 Unfolding of radiative corrections Measured events have to be corrected for: Background tail (radiation from (quasi)-elastic) Radiation from DIS and detector smearing full detector descriptionmodel for the cross-section The smearing of events is simulated through a MonteCarlo which includes a full detector description and a model for the cross-section independent The approach is independent on the model for the asymmetry in the measured region The correction for the systematic effect introduces statistical correlations Lara De Nardo DIS 2007 g 1 results Statistical uncertainties are diagonal elements of covariance matrix Systematic unc. are dominted by target and beam polarization Lara De Nardo DIS 2007 g 1 results Statistical uncertainties are diagonal elements of covariance matrix Systematic unc. are dominted by target and beam polarization Lara De Nardo DIS 2007 Neutron results g 1 n negative everywhere except at very high-x Low-Q 2 data tends to zero at low-x Does not support earlier conjecture of strong decrease for Lara De Nardo DIS 2007 theoryIntegrals Saturation in the deuteron integral is assumed Q 2 =5 GeV 2, NNLO in MS scheme from hyperon beta decay ( a 8 =0.5860.031) theory D =0.050.05 from neutron beta decay a 3 =1.2690.003 (use only Q 2 >1GeV 2 data) Use only deuteron data! Lara De Nardo DIS 2007 Comparisons Integrals provide a fair comparison of the accuracies of various experiments (all correlations taken into account) Proton data comparable with SLAC and CERN expts. most precise Deuteron data is the most precise so far (*): integrals re-calculated in a smaller x range, to match HERMES Lara De Nardo DIS 2007 HERMES has measured g 1 for proton and deuteron for