Measurement of Flavor Separated Quark Polarizations at HERMES Polina Kravchenko (DESY) for the collaboration  Motivation of this work  HERMES experiment  HERMES data.  DSA. A 1 (x)  NEW!!! A 1 (p T )  RESULTS  Structure function g 1  5 flavor purity extraction  Isoscalar method  Conclusion 12 September DIFFRACTION 2008

Polina Kravchenko2 Introduction The Spin Structure of the Nucleon Quark spin Gluon spin Orbital angular momentum

Polina Kravchenko3 Quark Parton Model Formalism Partons γ*γ* Nucleon Selects quarks with spin anti-parallel to the nucleon Introduction The Spin Structure of the Nucleon Virtual photon can only couple to quarks of opposite helicity Select q - (x) or q + (x) by changing the orientation of target nucleon spin or helicity of incident lepton beam

4 Quark Parton Model Formalism Partons γ*γ* γ*γ* Virtual photon can only couple to quarks of opposite helicity Select q - (x) or q + (x) by changing the orientation of target nucleon spin or helicity of incident lepton beam Nucleon Selects quarks with spin parallel to the nucleon Spin Independent Structure Function F 1 Spin Dependent Structure Function g 1 ΔqΔq Introduction The Spin Structure of the Nucleon Virtual photon asymmetry:

Polina Kravchenko5 HERMES experiment Polarized lepton beam of The HERA ring ~ 54% Polarized gas target ~ 85% Hermes spectrometer Resolution: Δp/p~2%, ΔΘ<1 mrad PID: 98% lepton identification with <1% hadron contamination Excellent separation of π, K and p via RICH

Polina Kravchenko6 Deep Inelastic Scattering Inclusive scattering: detected scattered lepton Virtual-photon kinematics: Fraction of nucleon momentum carried by struck quark: Semi-inclusive scattering: detected scattered lepton and produced hadrons Fraction of virtual-photon energy carried by produced hadron h:

Polina Kravchenko7 HERMES DATA

8 Partons γ*γ* γ*γ* Nucleon HERMES DATA Asymmetries N : number of DIS events L: luminosity P b P t : beam and target polarizations Measured longitudinal cross section asymmetry: In the QCD parton model: A || and A 1 are related by depolarization and kinematic factors Unfolding of radiative corrections: Measured events have to be corrected for: Background tail (radiation from (quasi)-elastic) Background tail (radiation from (quasi)-elastic) Radiation from DIS and detector smearing Radiation from DIS and detector smearing The smearing of events is simulated through a Monte Carlo which includes a full detector description and a model for the cross-section The approach is independent on the model for the asymmetry in the measured region

Polina Kravchenko9 HERMES DATA Inclusive asymmetries Structure function g 1 result on

Polina Kravchenko10 HERMES DATA Semi inclusive asymmetries 5 flavor Δ q/q(x) extraction: Purity method Published asymmetries from HERMES paper fit with: A1h (x) = C1 + C2 x When covariance is taken into account (gray band) fit uncertainties are reduced.

Polina Kravchenko11 HERMES DATA K +,K - asymmetry Isoscalar method : With these asymmetries and the integrated fragmentation functions computed from the kaon multiplicities, ΔQ(x) and ΔS(x) have been extracted

Polina Kravchenko12 NEW !!! A1(p h T )

Polina Kravchenko13 HERMES DATA A 1 (p h T ) Theoretical paper : M.Anselmino, A. Efremov, A.Kotzinian and B. Parsamyan Phys.Rev.D74:074015,2006 p h T is interesting and important for TMDs (transverse momentum dependences) BUT complicated it is a convolution of fragmentation and intrinsic quark transverse momentum x bj and p h T are not completely independent variables… apparent p h T dependence can result from different in each p h T bin

Polina Kravchenko14 HERMES DATA NEW!!! A1(,x) HERMES DATA NEW!!! A1(p h T,x) P   P   d   d   d  K d  K No significant p h T dependence observed

Polina Kravchenko15 HERMES RESULTS

Polina Kravchenko16 Measurement of g 1 : inclusive DIS Measurement of g 1 : inclusive DIS param.measured kin. fact. param. kinematic factors structure function g 1 : D data is the most precise so far Statistical uncertainties are diagonal elements of covariance matrix Systematic unc. are dominated by target and beam polarization

Polina Kravchenko17 g 1 Integrals. Q 2 =5 GeV 2, NNLO in MS scheme Assuming saturation in the deuteron integral theory from hyperon beta decay (a 8 =0.586±0.031) from neutron beta decay (a 3 =1.269±0.003) x Assuming SU(3) symmetry

Polina Kravchenko18 Measurement of Δq : Semi-Inclusive DIS Use correlation between detected hadron and struck quark -> ‘Flavor separation’ D q h is a measure of the probability that a quark of flavor q will fragment into a hadron of type h Purity is a conditional probability that a hadron of type h observed in the final state originated from a struck quark of flavor q

Polina Kravchenko19 Method of Δq extraction

Polina Kravchenko20 Method of Δq extraction Measured Asymmetry vector contains an asymmetry for each hadron from each target

Polina Kravchenko21 Simulated Purities extracted from LUND string model MC simulation (LEPTO+JETSET) tuned to HERMES unpolarized data Method of Δq extraction

Polina Kravchenko22 Method of Δq extraction Extracted System of asymmetries and purities solved through  2 minimization of polarizations

Polina Kravchenko23 The published HERMES 5-flavor Δq extraction First complete separation of pol.PDFs without assumption on sea polarization Δu(x) > 0 polarized parallel to the proton spin orientation Δd(x) < 0 polarized anti-parallel to the proton Δu(x) and Δd(x) good agreement with LO-QCD fit to inclusive data All the sea quark polarizations are consistent with zero in the measured region

Polina Kravchenko24 Isoscalar extraction of ΔS Isoscalar extraction of ΔS Need a longitudinally polarized deuterium target - strange quark distribution in proton and neutron identical - fragmentation simplifies All needed information can be extracted from HERMES data alone: - inclusive A 1d (x,Q 2 ) and kaon A 1d K (x,Q 2 ) double spin asymmetries - kaon multiplicities Only assumptions used: - isospin symmetry between proton and neutron - charge-conjugation invariance in fragmentation ⇒ large sensitivity to the strange quark polarization

Polina Kravchenko25 Isoscalar extraction of ΔS: Isoscalar extraction of ΔS: Extract isoscalar combinations of ΔQ(x) and ΔS(x)

Polina Kravchenko26 Isoscalar extraction of ΔS: Isoscalar extraction of ΔS: Extract isoscalar combinations of ΔQ(x) and ΔS(x) Inclusive asymmetry A 1,d and kaon asymmetries A 1K + +K -

Polina Kravchenko27 Isoscalar extraction of ΔS: Isoscalar extraction of ΔS: Extract isoscalar combinations of ΔQ(x) and ΔS(x) Inclusive asymmetry A 1,d and kaon asymmetries A 1K + and A 1K - Inclusive purities are simple combinations of unpolarized PDFs. Kaon purities can be computed from the unpolarized kaons multiplicity assuming only charge symmetry in fragmentation

Polina Kravchenko28 Isoscalar extraction of ΔQ and ΔS: Inclusive DIS Leader et al. Kaon multiplicity Multiplicity Data CTEQ for S(x) New Fit Q(x) Contribution S(x) Contribution

Polina Kravchenko29Conclusions Hermes has measured g 1 for proton and deuteron for <x<0.9 and 0.18<Q 2 <20GeV 2 Proton data precision is comparable with CERN and SLAC Deuteron data is the most precise so far The deutron integral is observed to saturate Phys.Rev.D75(2007) complete separation of pol.PDFs without assumption on sea polarization HERMES did complete separation of pol.PDFs without assumption on sea polarization Δu(x) and Δd(x) good agreement with LO-QCD fit to inclusive data Δu(x) and Δd(x) good agreement with LO-QCD fit to inclusive data All the sea quark polarizations are consistent with zero All the sea quark polarizations are consistent with zero In measured range 0.023<x<0.6 : In measured range 0.023<x<0.6 : Phys.Rev.D71(2005) Phys.Rev.D71(2005) Isoscalar method on d target provides an extraction of strange sea No dependence on MC simulation Result is consistent with full 5 flavor extraction No hint of negative strange sea in measured range PLB. (in press) arXiv: PLB. (in press) arXiv: Inclusive DIS Semi-inclusive DIS No MC