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Prospects for Generalized Parton Distributions studies at

Prospects for Generalized Parton Distributions studies at. GPDs Experimental Setup Prospects. F.-H. Heinsius (Universität Freiburg/CERN) on behalf of the COMPASS collaboration. DIS 2006, Tsukuba, 21.4.2006. GPDs – a 3-D picture of the partonic nucleon structure.

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Prospects for Generalized Parton Distributions studies at

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  1. Prospects forGeneralized Parton Distributionsstudies at • GPDs • Experimental Setup • Prospects F.-H. Heinsius (Universität Freiburg/CERN) on behalf of the COMPASS collaboration DIS 2006, Tsukuba, 21.4.2006

  2. GPDs – a 3-D picture of the partonic nucleon structure Deep Inelastic Scattering Hard Exclusive Scattering Deeply Virtual Compton Scattering ep eX *  Q² Q²xBj ep ep x+ x- x g* p GPDs p t z p z x P x P r y y x boost x boost Generalized Parton Distribution H( x,,t ) 0 ( Px, ry,z) x 1 Parton Density q ( x ) Px Burkardt,Belitsky,Müller,Ralston,Pire

  3. What do we learn from the 3 dimensional picture (Px,ry,z)? • Lattice calculation (unquenched QCD): • J.W. Negele et al., NP B128 (2004) 170 • M. Göckeler et al.,NP B140 (2005) 399 •  fast parton close to the N center •  small valence quark core •  slow parton far from the N center •  widely spread sea q and gluons mp=0.87 GeV xav 2. Chiral dynamics: Strikman et al., PRD69 (2004) 054012 at large distance, the gluon density is generated by the pion cloud significant increase of the N transverse size if xBj < mπ/mp=0.14 COMPASS domain

  4. GPDs depend on 3 variables: x: longitudinal quark momentum fraction ≠ xBj 2: longitudinal momentum transfer: =xBj/(2-xBj) t: momentum transfer squared to the target nucleon (fourier conjugate to the transverse impact parameter r) Deep Virtual Compton Scattering GPD: H, H̃, E, Ẽ Hard Exclusive Meson Production Vektormeson: E, H Pseudoscalar: Ẽ, H̃ Generalized Parton Distributions * ,r Q² x+ x- µp µp (µpr) p GPDs t p r z x P y x boost

  5. GPDs and Relations to Physical Observables factorization x+ξ x-ξ t The observables are some integrals of GPDs over x Dynamics of partons in the Nucleon Models: Parametrization Fit of Parameters to the data H, H̃, E, Ẽ(x,ξ,t) “ordinary” parton density Elastic Form Factors Ji’s sum rule 2Jq =  x(Hq+Eq)(x,ξ,0)dx x x H(x,0,0) = q(x) H̃(x,0,0) = Δq(x)  H(x,ξ,t)dx = F(t)

  6. Measurement of GPDs g* g Q2 x + ξ x - ξ GPDs p p’ t =Δ2 meson Q2 Q2 g* g* L L L hard x + ξ x - ξ x - ξ x + ξ soft GPDs GPDs p p’ p p’ t =Δ2 Gluon contribution Collins et al. Deeply Virtual Compton Scattering (DVCS): g* g Q2 x + ξ x - ξ hard soft GPDs Q2 large t << Q2 + g* p p’ t =Δ2 Hard Exclusive Meson Production (HEMP): meson L t =Δ2 Quark contribution

  7. DVCS and Bethe Heitler μ p  μ’ * θ μ p φ μ p BH calculable High energy muon beam at COMPASS: Higher energy: DVCS >> BH  DVCS Cross section • Smaller energy: DVCS ≈ BH • Interference term will provide the DVCS amplitude

  8. Advantage of µ+ and µ- for DVCS (+BH)  dσ(μpμp) = dσBH + dσDVCSunpol + PμdσDVCSpol + eμ aBHReADVCS + eμ PμaBHImADVCS μ’ * θ μ p φ  cos nφ sin nφ t, ξ~xBj/2 fixed Pμ+=-0.8 Pμ-=+0.8 Diehl

  9. Advantage of µ+ and µ- for DVCS (+BH)  dσ(μpμp) = dσBH + dσDVCSunpol + PμdσDVCSpol + eμ aBHReADVCS + eμ PμaBHImADVCS μ’ * θ μ p φ  cos nφ sin nφ t, ξ~xBj/2 fixed Pμ+=-0.8 Pμ-=+0.8 Diehl

  10. Advantage of µ+ and µ- for DVCS (+BH)  dσ(μpμp) = dσBH + dσDVCSunpol + PμdσDVCSpol + eμ aBHReADVCS + eμ PμaBHImADVCS μ’ * θ μ p φ  cos nφ sin nφ t, ξ~xBj/2 fixed Pμ+=-0.8 Pμ-=+0.8 Diehl

  11. Polarized beam: Ep=110 GeV → Eµ=100 GeV P(µ+) = -0.8 2.108/spill P(µ-) = +0.8 2.108/spill Experimental Setup: Beam Collimators 1 2 3 4 H V H V scrapers T6 primary Be target Compass target Be absorbers Protons 400 GeV Muon section 400m Hadron decay section 600m 2.108 muons/spill 1.3 1013protons/spill

  12. Experimental Setup: Target & Detektor all COMPASS trackers: SciFi, Si, MM, GEM, DC, Straw, MWPC μ’ 2.5 m Liquid H2 target to be designed and built  ECAL1/2   12° COMPASS equipment with additional calorimetry at large angle (p0 bkg) p’ μ Recoil detector to insure exclusivity to be designed and built L= 1.3 1032 cm-2 s-1

  13. Recoil Detector Design 30° ECAL0 • Detect protons of 250-750 MeV/c • ToF with 200 ps resolution required • 2 concentric barrels of 24 scintillators • read out at both sides, fast multi-hit ADC 12° 4m

  14. Recoil Detector Prototype 4 m • 30° sector design • Test at COMPASS beam this year • Funded by EU FP6 (Bonn, Mainz, Saclay, Warsaw)

  15. Prospects: Kinematical Range if Nμ 5  Q2 < 17 GeV2 for DVCS E=190, 100GeV if Nμ 2  Q2 < 11 GeV2 for DVCS for DVCS  Limitation by luminosity now Nμ= 2.108μper SPS spill Q2 < 7.5 GeV2 At fixed xBj, study in Q2 Limit for r (DVMP) 2 times higher Q²

  16. Simulations with two Models Parametrizations of GPDs Model 1: H(x,ξ,t) ~ q(x) F(t) Model 2: Chiral quark-soliton model:Goeke et al., NP47 (2001) 401 H(x,0,t) = q(x) e t <b2> = q(x) / xα’t (α’slope of Regge traject.) <b2> = α’ln 1/x transverse extension of partons in hadronic collisions considers fast partons in the small valence core and slow partons at larger distance (wider meson cloud) includes correlation between x and t Vanderhaeghen et al., PRD60 (1999) 094017

  17. 6 bins in Q2 from 1.5 to 7.5 GeV2 (1 shown) 3 bins in xBj=0.05,0.1,0.2 (2 shown) Assumptions L=1.3 1032 cm-2s-1 150 days efficiency=25% DVCS Simulations for COMPASS at 100 GeV BCA Q2=40.5 GeV2 x = 0.05 ± 0.02 φ φ BCA x = 0.10 ± 0.03 φ Model 1: H(x,ξ,t) ~ q(x) F(t) Model 2: H(x,0,t) = q(x) e t <b2> = q(x) / xα’t

  18. sensitive to different spatial distributions at different x Advantage of COMPASS kinematics model 1 model 2 Model 1: H(x,ξ,t) ~ q(x) F(t) Model 2: H(x,0,t) = q(x) e t <b2> = q(x) / xα’t COMPASS

  19. Hard Exclusive Meson Production (ρ,ω,…,π,η…) L meson g* x + ξ x - ξ GPDs p p’ t =Δ2 Scaling predictions: hard soft 1/Q6 1/Q4 Collins et al. (PRD56 1997): 1. factorization applies only for g* 2. σT << σL L vector mesons pseudo-scalar mesons ρ0 largest production present study ρ0 π+ π-with COMPASS

  20. Roadmap for GPDs at COMPASS • 2005: Expression of interest SPSC-EOI-005 • 2006: Test of recoil detector prototype • Proposal • 2007-2009: construction of • recoil detector • LH2 target • ECAL0 • ≥ 2010: Study of GPDs at COMPASS • In parallel present COMPASS studies with polarised target • Complete analysis of ρ production • Other channels: , 2π … • GPD E/H investigation with the transverse polarized target

  21. SPARE

  22. Complementarity of Experiments E=190, 100GeV At fixed xBj, study in Q2 0.0001< xBj < 0.01 Gluons Valence and sea quarks and Gluons Valence quarks JLab PRL87(2001) Hermes PRL87(2001) COMPASS plans H1 and ZEUS PLB517(2001) PLB573(2003)

  23. Competing reactions to DVCS DVCS: μp  μp HEπ°P: μp  μpπ°   Dissociation of the proton: μp  μN*π°  Nπ DIS: μp μpX with 1, 1π°, 2π°,η… Beam halo with hadronic contamination Beam pile-up Secondary interactions External Bremsstrahlung Selection DVCS/DIS with PYTHIA 6.1 Tune parameters: -maximum angle for photon detection 30° -threshold for photon detection 50MeV -maximum angle for charged particle detection 30°

  24. Beam or target spin asymmetry contain only ImT, therefore GPDs at x = x and -x Cross-section measurement and beam charge asymmetry (ReT) integrate GPDs over x Quark distribution q(x), -q(-x) M. Vanderhaeghen

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