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XVIII SEMINARIO NAZIONALE di FISICA NUCLEARE E SUBNUCLEARE

XVIII SEMINARIO NAZIONALE di FISICA NUCLEARE E SUBNUCLEARE. Fisica dello Spin. Mauro Anselmino Torino University and INFN . Why spin ….?.

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XVIII SEMINARIO NAZIONALE di FISICA NUCLEARE E SUBNUCLEARE

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  1. XVIII SEMINARIO NAZIONALE di FISICA NUCLEARE E SUBNUCLEARE Fisica dello Spin Mauro Anselmino Torino University and INFN

  2. Why spin ….? Spin is one of the most fundamental concepts in physics, deeply rooted in Poincaré invariance and hence in the structure of space-time itself. All elementary particles we know today carry spin, among them the particles that are subject to the strong interactions, the spin-1/2 quarks and the spin-1 gluons. Spin, therefore, plays a central role also in our theory of the strong interactions, Quantum Chromodynamics (QCD), and to understand spin phenomena in QCD will help to understand QCD itself. Research Plan for Spin Physics at RHIC, 2005

  3. Polarized Deep Inelastic Scattering: exploring the proton longitudinal spin structure • Helicity distributions- Δq, Δg -and their QCD evolution • Polarized structure functions: g1, g2 • Data and “spin crisis” (not a real crisis) • The spin carried by the gluons • Flavour separation • Weak interactions • Missing information

  4. Surprises:Transverse Single Spin Asymmetries(unintegrated polarized parton distributions) • Single Spin Asymmetries (SSA) in elastic processes • Single Spin Asymmetries in pQCD and in data • Parton intrinsic motion and spin • Spin - Transverse Momentum Dependent distribution and fragmentation functions • Phenomenology of SSA in inclusive processes • Mysteries: spin asymmetries in pp → pp processes

  5. The last missing piece of the proton structure:transversity • The partontransverse spindistribution,h1 • A partner for h1 • Transversity inDrell-Yanprocesses • Transversity inSIDISprocesses • Collins function from e+e- data • Hunting strategies forh1

  6. Polarized Deep Inelastic Scattering What do we know, and how, about the proton structure? l’ l,s Main source of information is DIS q p,S X l’,E’ θ p, S l,E,s X

  7. parity conserving case (one photon exchange) current conservation

  8. measuring dσ one extracts information on the structure functionsF1, F2, g1andg2 F1,2related toq(x,Q2), g(x,Q2 ) quark, gluon distributions g1 related to∆q(x,Q2), ∆g(x,Q2)quark, gluonhelicity distributions

  9. l’ l QCD parton model q q p,S X

  10. scheme dependent coefficient functions helicity distributions at LO

  11. QCD evolution splitting functions

  12. de Florian, Navarro, Sassot

  13. Dirk Ryckbosh, DIS 2005

  14. Research Plan for Spin Physics at RHIC February 11, 2005 Figure 11: Left: results for Δg(x,Q2 = 5GeV2) from recent NLO analyses [1, 2, 36] of polarized DIS. The various bands indicate ranges in Δg that were deemed consistent with the scaling violations in polarized DIS in these analyses. The rather large differences among these bands partly result from differing theoretical assumptions in the extraction, for example, regarding the shape of Δg(x) at the initial scale. Note that we show xΔg as a function of log(x), in order to display the contributions from various x-regions to the integral of Δg. Right: the “net gluon polarization” Δg(x,Q2)/g(x,Q2) at Q2 = 5 GeV2, using Δg of [2] and its associated band, and the unpolarized gluon distribution of [82].

  15. Spin(Jz)sum rule de Florian, Navarro, Sassot Direct measure of Δg needed • large pT di-hadron production in SIDIS, • high pT pions and jets at RHIC, • direct photon production at RHIC, • charm production at RHIC, • role of orbital angular momentum

  16. large pT di-hadron production in SIDIS

  17. (collinear configurations) factorization theorem X c a b X FF PDF pQCD elementary interactions

  18. RHIC

  19. polarized case: measure X c a b X Δq, Δg FF pQCD elementary asymmetries

  20. RHIC proposal 2005

  21. prompt photon production at RHIC

  22. Flavour separation -W production at RHIC X parity violating longitudinal single spin asymmetry a b X

  23. Flavour decomposition in SIDIS, DIS SIDIS Unknowns:

  24. large x behaviour

  25. Charged–Current Deep-Inelastic Scattering (neutrino factory) S. Forte, M. Mangano, G. Ridolfi p,S X

  26. LO QCD parton model results Some combinations of the polarized structure functions are of particular interest. For example:

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