Spin structure of the nucleon Delia Hasch introduction to polarised DIS prerequisites quark polarisation gluon polarisation the (spin) structure of the nucleon

fascinated by spin …. N. Bohr W. Pauli “You think you understand something? Now add spin…” -- R. Jaffe W. Pauli N. Bohr preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

what is spin ? Stern-Gerlach (1921): Uhlenbeck, Goudsmit: (1925) [www.markusehrenfried.de/science/physics/whatisspin.html] Stern-Gerlach (1921): Uhlenbeck, Goudsmit: (1925) explanation of atomic spectra quantum number: ms=1/2 Pauli : exclusion principle preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

how to study the nucleon structure ? … deep-inelastic scattering (DIS)  Q2 determines the resolution “deep” high resolution:  nucleon has a structure “inelastic” preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

the nucleon spin structure gluons are important ! DG sea quarks: Dqs don’t forget the orbital angular momentum! QPM: EMC 1988: DS=0.123 ± ... Spin Puzzle SLAC, CERN, DESY: DS 0.2-0.4 preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

helicity densities Dq because of helicity conservation, the virtual photon can couple only to a quark of opposite helicity by changing the orientation of target nucleon spin or the helicity of incident lepton beam we can select q+(x) or q-(x)  Dq preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

experimental prerequisites (Hermes) resolution: dp/p~2%, dq<1 mrad particle ID: lepton ID with e~98%, hadron contamination <1% RICH: p, K, p ID within 2<Eh<15 GeV Stern-Gerlach separation self-polarised electrons: e 27.5 GeV (e+/e-) <Pb>~ 0.53±0.03 Stern-Gerlach separation pure nuclear-polarised atomic gas, flipped at 90s time intervals, <Pt>~0.85 ±0.04 preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

DIS cross section leptonic part of the cross section hadronic part of the cross section  contains information on nucleon structure  cannot be calculated from first principles leptonic part of the cross section  independent of nucleon structure  can be calculated explicitely preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

hadronic tensor parametrised by structure functions (symmetry considerations, conservation laws) momentum distribution of quarks QPM: helicity distribution of quarks preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

how to measure cross sections / asymmetries q = const. E’ = const. preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

quark helicity distributions preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

Dq and DG from inclusive data (QCD fit) one step further (evolution equations): parameterised minimisation : evaluate parameters preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

Dq and DG from inclusive data Duv and Ddv (quite) well determined: Duv >0, Ddv <0 Dq and DG weakly constraint by data preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

how to further proceed ? unpolarised DIS Dq and DG from inclusive DIS data: via evolution equations requires wide kinematic range in Q2 and x only fixed target spin experiments so far … need polarised collider to extend kinematic coverage need more direct probes preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

polarised semi-inclusive DIS , z=Eh/n probability that struck quark of flavour f fragments into hadron of type h with energy fraction z flavour tagging p+ ud fragmentation function K- us p- ud distribution function preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

polarised quark distributions flavour separation by flavour tagging flavour content of final state hadrons related to flavour of struck quark via fragmentation functions Dqh not well known at √s~5-20 GeV of current polarised DIS experiments  preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

particle identification double radiator RICH for p / K / p separation aerogel: n=1.03 C4F10: n=1.0014 Cerenkov light emission: Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

purity analysis @ HERMES Delia Hasch Physics at Hermes Trieste (Italy), 12-10-2004

measured hadron asymmetries proton HERMES incl p+ h+ deuteron HERMES p- h+ h- p+ p- K+ K- incl h- h- p- K- us all sea objects x x preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

purities p+ p- u u d d s s K+ K- probability that g* hit a quark of flavour q when hadron of type h was detected u u d d s s p+ K+ p- K- preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

quark/anti-quark helicity distributions [HERMES, PRL92(2004), PRD71(2005)] u quarks large positive polarisation d quarks negative polarisation sea quarks (u, d, s ,s) compatible with 0 - first direct 5-flavour separation of polarised PDFs new data from COMPASS/RHIC coming preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

how to measure the gluon polarisation DG …reminder: from scaling violation preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

direct measurement of DG method: photon-gluon fusion q t  ħ/2mq open charm production (hard scale: mass of c-quark)  theoretically very clean: c g g* D cc-bar  D* , D0 g*p  D0 D0-bar X   experimentally very challenging:  vertex reconstruction inside massive target  S/B preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

direct measurement of DG method: photon-gluon fusion q t  ħ/2mq hadron pairs with high transv. momenta (hard scale: PT)  experimentally very clean g g* h1 h2  highly model dependent preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

G from high-pT hadron pairs 3 main contributions to *p  h+h- X : h2 h2 h2 * q q * * q V q g p g q q h1 h1 QCDC VMD PGF h1 AQCDC ~ q/q AVDM = 0 APGF  G/G Contributions shown from paper: Pythia 5 … ! Infinite systematic error ! :-o  applicable at HERMES (COMPASS) ? : kine / resolved photons / intrinsic k_T  new Pythia 6 tuned to HERMES multiplicities: f_PGF much smaller  first time: sys. error estimated (Patty thesis) -- new paper in preparation  HERMES: quasi-real photoproduction estimate their relative contributions: Monte Carlo… 0.5 -1 preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

G from high-pT hadron pairs 3 main contributions to *p  h+h- X : h2 h2 h2 * q q * * q V q g p g q q h1 h1 QCDC VMD PGF h1 AQCDC ~ q/q AVDM = 0 APGF  G/G Contributions shown from paper: Pythia 5 … ! Infinite systematic error ! :-o  applicable at HERMES (COMPASS) ? : kine / resolved photons / intrinsic k_T  new Pythia 6 tuned to HERMES multiplicities: f_PGF much smaller  first time: sys. error estimated (Patty thesis) -- new paper in preparation  HERMES: quasi-real photoproduction [PRL84(2000)] preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

G from high-pT hadron pairs first glimpse: preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

G from high-pT hadron pairs first glimps: complementary measurement @RHIC preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

pp  p0X is sensitive to gg gg and gq gq G from p0 at RHIC pp  p0X is sensitive to gg gg and gq gq STAR preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

pp  p0X is sensitive to gg gg and gq gq G from p0 at RHIC pp  p0X is sensitive to gg gg and gq gq fractional contributions: uncertainty still large ... dramatic improvement by lumi and beam polarization (~70%) preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

future G measurements (2010) COMPASS :  open charm  high PT first glimps: HERMES :  high PT on d RHIC :  p0  jets  prompt g  charm/bottom preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05

Gluon Polarization at RHIC Longitudinal double spin asymmetry in : Dominant processes:  or  photon  or  (heavy flavor) Direct photon production Di-jet production

? ? where do we stand the nucleon puzzle is going to be completed the (spin) structure of the nucleon … HERMES: first glimpse NMC,BCDMS,E665, H1, ZEUS COMPASS RHIC HERMES COMPASS RHIC JLab KEK …ecc. exclusive processes first results: HERMES JLab transversity ? HERMES (SMC, SLAC)  Compass  RHIC seminar by its own ? seminar by its own preface | introduction to polarised DIS | prerequisites | quark polarisation | gluon polarisation | the (spin) structure of the nucleon Delia Hasch spin structure of the nucleon GK: Freiburg-University 06/07/05