1 / 26

Prospects for Generalized Parton Distributions Studies at DIS 2006

Explore the intricate details of Generalized Parton Distributions (GPDs) and their impact on the partonic nucleon structure through Deep Virtual Compton Scattering and Hard Exclusive Meson Production studies. Learn about the experimental setup and prospects for future research in this field.

silviaw
Download Presentation

Prospects for Generalized Parton Distributions Studies at DIS 2006

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  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

More Related