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Recent results from lepton proton scattering on the spin structure of the nucleon. Hall B. Hall A. Two high-resolution 4 GeV spectrometers. Large acceptance spect. electron/photon beams. Beam: 160 GeV m ; 75% polarization Target: 6 LiD; 50% polarization. Hall C.
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Recent results from lepton proton scattering on the spin structure of the nucleon
Hall B Hall A Two high-resolution 4 GeV spectrometers Large acceptance spect. electron/photon beams Beam: 160 GeV m; 75% polarization Target: 6LiD; 50% polarization Hall C Beam: 27.5 GeV e±; <50>% polarization Target: (un)-polarized gas targets; <85%> polarization Beam: ≤6 GeV e-; 85% polarization Target: polarized targets 3He, 6LiD, NH3 7 GeV spectrometer, 1.8 GeV spectrometer, large installation experiments The contemporary experiments
Naïve parton model Unpolarised structure fct. Gluons are important ! BUT Full description of Jq and Jg needs orbital angular momentum 1989 EMC measured S = 0.120 0.094 0.138 ± ± DG Spin Puzzle Sea quarksDqs News on the spin structure of the nucleon
FF DF Deep Inelastic Scattering Important kinematic variables: q cross section: Spin 1
How to measure Quark Polarizations • Virtual photon g* 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 Asymmetry definition: inclusive DIS: only e’ info used semi-inclusive DIS: e’+h info used
(Hall-A) Proton Deuterium A1n from 3He CLAS PLB 641, 11 (2006) COMPASS PRD75(2007)012007 World data on inclusive DIS • New data from COMPASS, • HERMES & JLab very precise • high x-behaviour consistent with • A1 with x1 • A1d consistent with zero • for x < 0.05
World data on inclusive DIS Combine p and d to get n: or 3He • What can we learn on the PDFs Compass: hep-ex/0609038 Hermes: hep-ex/0609039
Q2=5 GeV2, NNLO in MS scheme HERMES: Integrals • Saturation in deuteron integral is assumed • use only deuterium From hyperon beta decay a8=0.586±0.031 From neutron beta decay a3=1.269±0.003 • COMPASS:
CLAS: Dq • Using:
In LO-QCD: Polarised quark distributions Correlation between detected hadron and struck qf “Flavor – Separation” Inclusive DIS: Semi-inclusive DIS:
COMPASS: Valence PDFs • For LO: • Assuming: • Gv is 2.5sstat away from flavour • symmetric sea scenario
In LO-QCD: MC Polarised quark distributions Correlation between detected hadron and struck qf “Flavor – Separation” Inclusive DIS: Semi-inclusive DIS: Extract Dqby solving:
Du(x), Dd(x) ~ 0 • In measured range (0.023 – 0.6) • No indication forDs(x)<0 Polarised opposite to proton spin Polarised parallel to proton spin Polarized Quark Densities • First complete separation of • pol. PDFs without assumption on • sea polarization Dd(x) < 0 • Du(x) > 0 good agreement with NLO-QCD
c2DIS c2SIDIS Duv Ddv Du Dd Ds Dg DS Kretzer -0.049 -0.051 206 225 0.94 -0.34 -0.055 0.68 0.28 KKP -0.11 -0.045 0.57 206 231 0.70 -0.26 0.087 0.31 NLO FIT to DIS & SIDIS Data D. De Florian et al. hep-ph/0504155 NLO @ Q2=10 GeV2 • SIDIS data improves description of allDq, especially light sea • Kretzer FF favor SU(3) symmetric sea, not so for KKP • DS ~30%in all cases
DG>0 DG>0 DG<0 DG<0 Several more fits • using mainly only inclusive data or a combination of inclusive and • some semi-inclusive data • Results for DG still completely all over the place • Need a consistent approach for fit and uncertainty determination • with all world data taken into account Lets measure DG more directly
Isolate the photon gluon fusion process (PGF) • Open Charm production • Reaction: LO-MC: Aroma The golden channels Idea: Direct measurementofDG
+ + + .. less sub-processes contributing h±h± higher statistics more sub-processes contributing q q higher statistics qg less sub-processes contributing g h± g more sub-processes contributing The golden channels Idea: Direct measurement ofDG Isolate the photon gluon fusion process • detection of hadronic final states with high pT • high pT pairs of hadrons • single high pT hadrons • Several possible contributions to the measured asymmetry • MC needed to determine R and aLL Important at Q2<0.1
Dg/g=0.016±0.058(stat.)±0.055(syst.) m2=3.0GeV2 10% of statistics COMPASS Results h±h± • Channel: • Cuts: Q2 > 1 GeV2 • RPGF = 0.34 +/- 0.07 xF > 0.1 z > 0.1 m(h1,h2) > 1.5 GeV 2(scale) ~ 3 GeV2<xG> ~ 0.13 Q2 < 1 GeV2 & used for Dg/g extraction
HERMES Results Subprocess Fractions h±h±, h± • Channels: Subprocess Asymmetries (using GRSV std.)
World Data on DG/G x Long way to go till Dg(x)
exclusive: all products of the reaction are detected missing energy (DE) and missing Mass (Mx) = 0 from DIS: ~0.3 The Hunt for Lq Study of hard exclusive processes leads to a new class of PDFs Generalized Parton Distributions possible access to orbital angular momentum
unpolarized polarized quantum numbers of final state select different GPD vector mesons pseudo-scaler mesons DVCS AUT,sr,F,w AUT,sp+ AC,ALU,AUT, AUL GPDs Introduction What does GPDs charaterize? conserve nucleon helicity flip nucleon helicity not accessible in DIS
HERMES / JLAB kinematics: BH >> DVCS p + D DVCS Bethe-Heitler (BH) isolate BH-DVCS interference term non-zero azimuthal asymmetries DVCS two experimentally undistinguishable processes:
~ DsC~cosf∙Re{ H+ xH +… } ~ DsLU~sinf∙Im{H+ xH+ kE} DsUT polarization observables: ~ DsUL~sinf∙Im{H+ xH+ …} beam target DVCS ASYMMETRIES different charges: e+ e-(only @HERA!): H H ~ H DsUT~sinf∙Im{k(H- E) + … } H, E kinematically suppressed x = xB/(2-xB ),k = t/4M2
<-t> = 0.18 GeV2 <-t> = 0.30 GeV2 <-t> = 0.49 GeV2 <-t> = 0.76 GeV2 CLAS: DVCS - BSA Accurate data in a large kinematical domain Integrated over t
Neutron obtained combining • deuterium and proton • F1 small u & d cancel in Away to E and Ju-Jd Hermes DVCS-TTSA: Hall A nDVCS-BSA: x=0.36 and Q2=1.9GeV2
Can we constrain (Ju - Jd) • first model dependent extraction of Ju - Jd possible • VGG-Code: GPD-model: LO/Regge/D-term=0
std. FF Sivers DFF quarks left left left photon proton photon right right right Access to Lq in semi-inclusive scattering • New structure function accessible with SSA Side view Front view • The presence of spin can distort the distribution of quarks in transverse space (orbital angular momentum of quarks is required) NOTE: QCD tells us that the FSI has to be attractive, since quark and remnants form a color antisymmetric state • A distortion in the distribution of quarks in transverse space can give rise to a nonzero Sivers function
HERMES & COMPASS Measuremnets • Proton: • Sivers moment: • p+ > 0 p- ~ 0 • K+ > 0 K- ~ 0 • K+ > p+ • sea quarks important • Deuterium ~ 0 • u and d quark cancel Deuterium Proton
Results from theory Lattice QCD: Sivers Pheno. analysis from data: negative for up quarks Anselmino et al., hep-ph/0511017 [20] Anselmino et al., PRD72 (05) [21] Vogelsang, Yuan, PRD72 (05) [23] Collins et al., hep-ph/0510342 positive for down quarks QCDSF/UKQCD Collab. (hep-ph/05110032)
DG Lq Dq Dq dq Lg Lq Lg DG dq Summary
Spin is fascinating Thank you for your attention
angle of hadron relative to initial quark spin (Sivers) peculiarity of f^1T chiral-even naïve T-odd DF related to parton orbital momentum violates naïve universality of PDF (Sivers) (Collins) different sign of f^1T in DY Azimuthal angles and asymmetries angle of hadron relative to final quark spin (Collins)