HERa MEasurement of Spin Collaboration of 180 phys., 33 Inst., 12 Countries Introduction to polarised DIS Prerequisites Polarised structure functions The Spin of the Nucleon Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

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 | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

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 Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

What is Spin ? Spin and Symmetry: [S.Hawkins: A brief history of time] 2x360o spin: 2 spin: 1 math: antisymmetric wave function 180o 360o Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

is spin important ? Pauli principle … MATTER FORCES obey Pauli principle antisymmetric under exchange of identical particles Fermi-Dirac statistics: Fermions half integer SPIN MATTER don’t care for Pauli principle symmetric Bose-Einstein statistics: Bosons integer SPIN FORCES Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

how to study the proton spin ? … deep-inelastic scattering (DIS) “deep” high resolution: “inelastic”  proton has structure Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

DIS cross section leptonic part of the xsection hadronic part of the xsection  contains info on proton structure + strong interaction effects leptonic part of the xsection  independent of proton structure  can be calculated explicitely Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

hadronic tensor parametrised by structure functions (Lorentz symmetry, current conservation, parity, ecc.) momentum distribution of quarks QPM: helicity distribution of quarks Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

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 | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

the nucleon spin structure gluons are important ! don’t forget the orbital angular momentum! QPM: EMC (‘88) DS=0.123 ± ... Spin Puzzle SLAC, CERN, DESY: 0.2-0.4 Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

polarised deep inelastic scattering inclusive dis exclusive dis inclusive hadrons polarised beam and/or polarised target semi-inclusive DIS flavour separation Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

Hermes @ DESY Stern-Gerlach separation self-polarised electrons: e Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

how to measure xsections / asymmetries q = const. E’ = const. Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

how to measure g1 virtual photon asymmetry: Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

how to measure g1 Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

the integral of g1 helicity distributions (polarised quark distributions) Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

sum rules for g1 violated Bjorken sum rule: (isospin symmetry) Bjorken sum rule confirmed @ 8% C.L. violated Ds=0 Bjorken sum rule: (isospin symmetry) fundamental QCD prediction related to axial charges of proton: measured in weak baryon decays Ellis-Jaffe sum rule: Ds=0 Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

Dq from g1(x,Q2) parameterised one step further: evaluate parameter minimisation : evaluate parameter Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

Dq and DG from g1(x,Q2) Duv Du Ds Ds Ddv Dd Duv and Ddv (quite) well determined Duv Du Ds Ds Ddv Dd Dq and DG weakly constraint by data need more direct probes flavour separation DG Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

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 | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

polarised semi-inclusive DIS polarised parton distribution functions ! known quantities hadron asymmetries to be measured Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

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________

quark/anti-quark helicity distributions PURITY is an unpolarised quantity needs at least six independent asymmetry sets A1h(x) to determine six unknown helicity distributions: Du, Du, Dd, Dd, Ds, Ds Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

measured hadron asymmetries proton incl p+ h+ deuteron p- h+ h- p+ p- K+ K- incl h- h- p- K- us all sea objects x x Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

purities conditional probability that g* hits 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 | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

quark/anti-quark helicity distributions u quarks large positive polarisation d quarks negative polarisation sea quark (u, d, s ,s) compatible with 0 no indication for Ds < 0 - Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

? where do we stand the (spin) structure of the nucleon … HERMES: first glimpse H1, ZEUS,++ HERMES CERN RHIC SLAC ? HERMES, ++ Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

don’t forget the orbital angular momentum hard exclusive processes… exclusive dis polarised beam and/or polarised target g Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

missing mass technique: Mx2=(p+q-Pg,p )2  s(Mx)~0.8 GeV exclusivity @HERMES 2005++ e+ detected missing mass technique: Mx2=(p+q-Pg,p )2  s(Mx)~0.8 GeV NOT detected Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

? ? where do we stand the nucleon puzzle is going to be completed the (spin) structure of the nucleon … HERMES: first glimpse H1, ZEUS,++ HERMES CERN RHIC SLAC HERMES CERN RHIC JLab KEK …ecc. transversity ? UPCOMING: HERMES JLab lecture by its own ? HERMES, ++ Preface | Introduction to polarised DIS | Prerequisites | polarised Structure Functions | the Spin of the Nucleon ___Delia Hasch _______________________________________________________________Spin Physics at HERMES________

outlook to further HERMES activities what happens in a nuclear medium:

outlook to further HERMES activities what happens in a nuclear medium: reduction of multiplicity of fast hadrons  hard partonic + soft hadron interaction cold hot nuclear matter

outlook to further HERMES activities exotic states

template Thank you !