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Results from HERMES in view of future  pp experiments

Results from HERMES in view of future  pp experiments. Michael Düren Universität Gießen. —  pp- QCD Workshop, ECT* Trento, July 3-7, 2006 —. HERMES physics: Modest aims and rich harvest HERMES technology: polarization and novel techniques Physics results: Spin structure of the nucleon

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Results from HERMES in view of future  pp experiments

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  1. Results from HERMESin view of futurepp experiments Michael Düren Universität Gießen —pp-QCD Workshop, ECT* Trento, July 3-7, 2006—

  2. HERMES physics: Modest aims and rich harvest HERMES technology: polarization and novel techniques Physics results: Spin structure of the nucleon Hard exclusive reactions Quarks in nuclei Future prospects for pp Conclusions Outline Some transparencies are stolen from Aschenauer, Hasch, Nowak, Ji, … M. Düren, Univ. Giessen

  3. HERMES physics

  4. In 1987 we discovered in the EMC the “spin puzzle”: Violation of the Ellis Jaffe sum rule A large negative strange sea polarization Both results were based on inclusive DIS data and validity of SU(3)f Original physics program of HERMES: In 1989 we decided to solve the “spin puzzle” with a semi-inclusive DIS experiment doing a flavor decomposition of the quark spin Re-measure inclusive polarized DIS on proton and neutron: Ellis-Jaffe sum rule Bjorken sum rule g1, g2 Measure semi-inclusive polarized DIS on p and n: u(x), d(x), s(x) Why HERMES?A historical review

  5. Results (in short): Ellis-Jaffe sum rule: is really broken Bjorken sum rule: is fine (fortunately) g1, g2 are well known nowadays u(x) is large and positive d(x) is smaller and negative s(x) is approx. zero i.e. SU(3)f is broken and only ~30% of the spin of the nucleon is due to the spin of the quarks Why HERMES?A historical review up down u d strange M. Düren, Univ. Giessen

  6. Spin of the nucleon Latest results! ~30% up and down quark contributionin valence region <3% strange quark contribution M. Düren, Univ. Giessen

  7. Flavor decomposition of quark spin (done) Gluon spin contribution (first result but large errors) Transversity, Collins and Sivers functions (first non-zero results) Orbital angular momentum of quarks (first results, but model dependent) Generalized parton distributions (first results on BCA, BSA, TTSA,…) Fragmentation process in vacuum and nuclear medium Spin matrix elements of vector meson production Positive Pentaquark signal ... Physics program at HERMES today: In many areas HERMES contributed as a pioneering experiment M. Düren, Univ. Giessen

  8. HERMES technology

  9. HERMES requires: Large polarization of beam and target; pure target Relatively large luminosity (Much larger than EMC) Relatively high beam energy (Q²>1 GeV²; larger than Jlab) Relatively large acceptance (Much larger than SLAC) Strangeness identification (kaons) Recoil protons (for exclusive reactions) Solution: High HERA beam polarization (pushed by HERMES) and ABS Storage cell technique (new at that time) HERA fixed target Polarization and novel techniques • Standard open spectrometer • RICH upgrade in 2000 (well working RICH) • Recoil upgrade in 2006 (for GPD program) M. Düren, Univ. Giessen

  10. Polarized target M. Düren, Univ. Giessen

  11. The spectrometer M. Düren, Univ. Giessen

  12. Recoil detector M. Düren, Univ. Giessen

  13. Scintillating fiber detector M. Düren, Univ. Giessen

  14. Guide to success: • Novel technologies (at time of proposal) • Unique facility (energy, luminosity, precision, …) • Polarization (that is where one can falsify models) • Flexibility for upgrades • Electromagnetic processes that can be directly related to QCD My message: Panda at Fair will also measure completely different things compared to what is in the proposal today! M. Düren, Univ. Giessen

  15. HERMES physics: Modest aims and rich harvest HERMES technology: polarization and novel techniques Physics results: Spin structure of the nucleon Hard exclusive reactions Quarks in nuclei Future prospects for pp Conclusions Outline M. Düren, Univ. Giessen

  16. Quark density Helicity distribution Transversity Transverse spin distribution of quarks • The transverse polarization of quarks in a transversely polarized proton is not identical with the longitudinal polarization of quarks in a longitudinally polarized proton(Rotation and boost do not commute) • There are three leading-twist structure functions: M. Düren, Univ. Giessen See talk by Anselmino

  17. Transverse spin distribution of quarks • The azimuthal angular distributions of hadrons from a transversely polarized target show two effects: • Collins asymmetry in +s • Sivers asymmetry in -s Target spin M. Düren, Univ. Giessen

  18. Transverse spin distribution of quarks • The azimuthal angular distributions of hadrons from a transversely polarized target show two effects: • Collins asymmetry in +sProduct of the chiral-odd transversity distribution h1(x)and the chiral-odd fragmentation function H1(z) related to the transverse spin distribution of quarks • Sivers asymmetry in -s First results from Belle Target spin M. Düren, Univ. Giessen

  19. Transverse spin distribution of quarks • The azimuthal angular distributions of hadrons from a transversely polarized target show two effects: • Collins asymmetry in +sProduct of the chiral-odd transversity distribution h1(x)and the chiral-odd fragmentation function H1(z) related to the transverse spin distribution of quarks • Sivers-Asymmetrie in -s:Product of the T-odd distribution function f1T(x)and the ordinary fragmentation function D1(z) related to the orbital angular momentum of quarks First results from Belle Target spin M. Düren, Univ. Giessen See talk by Metz

  20. Collins asymmetries • at HERMES(H) significantly positive/negative for +/- • at COMPASS(D)compatible with zero

  21. Sivers asymmetries • at HERMES(H)positive/zero for +/- • at COMPASS(D)compatible with zero The results are unexpected but not inconsistent

  22. Collins and Sivers Kaon asymmetries • at HERMES (H) and • at COMPASS (D) are similar except for the Sivers K+ asymmetry M. Düren, Univ. Giessen

  23. Perspectives for futurepp experiments:Drell Yan processes • Parton distributions accessible -similar (complementary) to DIS • Asymmetries of polarized beam and/or target experiments give access to transversity • if the energy is sufficient(energy scale ~√(x1x2s)) • if the beam polarizations are sufficient • No knowledge of polarized fragmentation functions needed! (Contrary to DIS) M. Düren, Univ. Giessen See talk by Anselmino

  24. Hard exclusive reactions Quantum phase-space „tomography“ of the nucleon

  25. Quantum phase-space Wigner distribution • A classical particle is defined by its coordinate and momentum (x,p): phase-space • A state of classical identical particle system can be described by a phase-space distribution f(x,p). The time evolution of f(x,p) obeys the Boltzmann equation. • In quantum mechanics, because of the uncertainty principle, the phase-space distributions seem useless, but… • Wigner introduced the first phase-space distribution in quantum mechanics (1932) • Wigner function: M. Düren, Univ. Giessen

  26. Wigner function • When integrated over x, one gets the momentum density. • When integrated over p,one gets the probabilitydensity. • Any dynamical variable can be calculated from it! ! The Wigner function contains the most complete (one-body) infoabout a quantum system. • A Wigner operator can be defined that describes quarks in the nucleon • The reduced Wigner distribution is related toGeneralized parton distributions (GPDs) M. Düren, Univ. Giessen

  27. What is a GPD? • A proton matrix element which is a hybrid of elastic form factor and Feynman distribution • Depends on x: fraction of the longitudinal momentum carried by parton t=q2: t-channel momentum transfer squared ξ: skewness parameter There are 4 important GPDs (among others): Limiting cases: • t0: Ignoring the impact parameters leads to ordinary parton distributions • Integrating over x: Parton momentum information is lost, spatial distributions = form factors remain

  28. z by bx 3-D contours of quark distributions for various Feynman x values Fits to the known form factors and parton distributions with additional theoretical constraints (e.g. polynomiality) and model assumptions M. Düren, Univ. Giessen

  29. Conclusions: Quarks in the quantum mechanical phase-space • Elastic form factors charge distribution (space coordinates) • Parton distributions momentum distribution of quarks (momentum space) • Generalized parton distributions (GPDs) are reduced Wigner functions correlation in phase-space  e.g. the orbital momentum of quarks: • Angular momentum of quarks can be extracted from GPDs: Ji sum rule: • GPDs provide a unified theoretical framework for various experimental processes M. Düren, Univ. Giessen

  30. Hard exclusive reactions at

  31. Kinematic coverage M. Düren, Univ. Giessen

  32. Experimental Access to GPDs • QCD handbag diagram Deeply virtual Compton scattering (DVCS) Hard exclusive meson production (HEMP) M. Düren, Univ. Giessen

  33. DVCS is the cleanest way to access GPDs: *N N Factorization theorem is proven! Handbag diagram separates hard scattering process (QED & QCD) and non-pertubative structure of the nucleon (GPDs) Deeply virtual Compton scattering (DVCS) x+x: longitudinal momentum fraction of the quark -2x: exchanged longitudinal momentum fraction t :squared momentum transfer GPDs = probability amplitude for N to emit a parton (x+x) and for N’ to absorb it (x-x) M. Düren, Univ. Giessen

  34. DVCS and BH Interference (epe‘p) FF DVCS Bethe-Heitler (BH) Kinematics: • x[-1,1] xB/(2- xB) • t=(q-q‘)2 Q2=-q2 DVCS-BH interferenceIgives non-zero azimuthal asymmetry Use BH as a vehicle to study DVCS.

  35. Laser and nucleon holography (Belitsky/Mueller) M. Düren, Univ. Giessen

  36. Azimuthal asymmetries in beam spin and beam charge Fourier decomposition of interference term: charge spin • Access to real and imaginary part of helicity conserving amplitude M1,1 • (GPDs enter in linear combinations in amplitudes) • beam spin asymmetry (BSA) • beam charge asymmetry (BCA) HERMES is the only experiment which measures BCA M. Düren, Univ. Giessen

  37. Results: BSA and BCA on proton BSA: Significant sin() dependence BCA: Significant cos() dependence

  38. HERMES results and projected error-bars of the recoil running BCA and BSA on proton M. Düren, Univ. Giessen

  39. DVCS: Transverse Target Spin Asymmetry first model dependent extraction of Ju possible Code: VGG Jdassumed to be zero M. Düren, Univ. Giessen

  40. HERMES can constrain the total angular momentum of up and down quarks (Ju+Jd)! same statistics with electron beam on tape independent data set to constrain (Ju+Jd) M. Düren, Univ. Giessen

  41. Generalized EMC-Effect in nuclear DVCS • Beam spin asymmetries in nuclear DVCS (Neon) • More to come: 2H,4He,14N,20Ne,82-86Kr,129-134Xe: A-dependence of coherent DVCS processes to study quarks in nuclei M. Düren, Univ. Giessen

  42.  Pion form factor  Dq First results for Hard Exclusive Meson Production (HEMP) from HERMES: Pseudoscalar Mesons HEMP cross section ep  e’n p+ GPD Model: Vanderhaeghen, Guichon, Guidal

  43. First results for HEMP from HERMES:Vector Mesons (r0,f,w) -Clean signal without background subtraction;-DIS-background well described by MC; HEMP target spin asymmetry ep  e’p r0 M. Düren, Univ. Giessen

  44. M. Düren, Univ. Giessen

  45. Quarks in nuclei

  46. Study fragmentation in nuclei   understanding of the space-time evolution of the hadron formation process K p M. Düren, Univ. Giessen

  47. 2-hadron production in nuclei  disentangle absorption and energy loss models leading hadron: z1 >0.5 subleading hadron: z2< z1 M. Düren, Univ. Giessen

  48. Hard exclusive reactions and GPDs in futurepp experiments

  49. For exclusive processes, „crossing“ allows to measure the same matrix elements with completely different experiments and probes Instead of having an initial electromagnetic process, a final state electromagnetic process is selected Perspectives for futurepp experiments Example: Compton scattering Annihilation M. Düren, Univ. Giessen

  50. Experimental difficulty: the total cross section of a hadronic beam is typically much larger than the one of the exclusive electro-magnetic process The experiment needs a huge background suppression factor as the majority of events have a hadronic final state Perspectives for futurepp experiments Example: Compton scattering Annihilation M. Düren, Univ. Giessen

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