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COMPASS plans to measure GPDs

COMPASS plans to measure GPDs. The COMPASS experiment GPDs at COMPASS now: deep r production ≥2010: DVCS and HEMP. Jean-Marc Le Goff DAPNIA/CEA-Saclay 24 Feb 2006, Albuquerque workshop on Orbital Angular Momentum. The COMPASS experiment.

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COMPASS plans to measure GPDs

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  1. COMPASS plans to measure GPDs • The COMPASS experiment • GPDs at COMPASS • now: deep r production • ≥2010: DVCS and HEMP Jean-Marc Le Goff DAPNIA/CEA-Saclay 24 Feb 2006, Albuquerque workshop on Orbital Angular Momentum

  2. The COMPASS experiment

  3. The COMPASS Collaboration(230 Physicists from 12 Countries) Bielefeld, Bochum, Bonn (ISKP & PI), Erlangen, Freiburg, Heidelberg, Mainz, München (LMU & TU) Dubna (LPP and LNP), Moscow (INR, LPI, State University), Protvino CERN Warsaw (SINS), Warsaw (TU) Helsinki Prag Nagoya CEA-Saclay Lisboa Torino(University,INFN), Trieste(University,INFN) Burdwan, Calcutta Tel Aviv

  4. COMPASS fixed target experiment at CERN muons hadrons π/K, p Beam: 2 . 108 µ+/ spill (4.8s / 16.2s) 2 . 108 h/spill Beam polarisation: 80% Beam momentum: 160 GeV/c 150-270 GeV/c COMPASS SPS LHC COMPASS  COmmon Muon and Proton Apparatus for Structure andSpectroscopy

  5. muon beam nucleon spin structure • Quark and Gluon Polarization in (longitudinally) polarized nucleons • transverse spin distribution function Tq(x) • Flavor dependent polarized quark helicity densities q(x) • Lambda polarisation • Diffractive vector-meson production Physics goals hadron beams nucleon spectroscopy • Primakoff-Reactions • polarizability of  and K • Exotics: glueballs and hybrids • charmed mesons and baryons • semi-leptonic decays • double-charmed baryons

  6. Spectrometer 2002  2004 trigger-hodoscopes DW45 straws SM2 dipole Muon-filter2,MW2 HCAL1 RICH_1 Gem_11 SM1 dipole ECAL2,HCAL2 MWPC Gems Scifi Polarised Target Muon-filter1,MW1 Veto straws,MWPC,Gems,SciFi Gems,SciFi,DCs,straws Silicon SciFi Micromegas,DC,SciFi BMS

  7. COMPASS and GPDs

  8. measurement of GPDs γ* Q2 γ x +ξ x -ξ GPDs p p’ t =Δ2 Q2 meson Q2 γ* γ* 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): γ* γ Q2 hard x +ξ x -ξ soft GPDs Q2 large t << Q2 + γ* p p’ t =Δ2 Hard Exclusive Meson Production (HEMP): meson L t =Δ2 Quark contribution

  9. Complementarity of experiments E=190, 100GeV At fixed xBj, study in Q2 Valence and sea quarks and Gluons Valence quarks 0.0001< xBj < 0.01 Gluons HermesPRL87(2001) COMPASS plans JLab PRL87(2001) H1 and ZEUS PLB517(2001) PLB573(2003)

  10. if Nμ 5  Q2 < 17 GeV2 Benefit of a higher muon intensity for GPDs study E=190, 100GeV if Nμ 2  Q2 < 11 GeV2 DVCS limited by luminosity now Nμ= 2.108μ /SPS spill Q2 < 7.5 GeV2  At fixed xBj, study in Q2

  11. m flux at COMPASS in 2010 ?  sharing CNGS/FT  new Linac 4  up to 10 times more p +improve m line COMPASS >>LINAC4 From Lau Gatignon

  12. What can we measure now ?

  13. DVCS, HEMP ? 1/Q6 1/Q4 vector mesonspseudo-scalar • sDVCS small, bckg • HEMP factorization: gL • vector meson decay •  R=sT/sL • ρ0 largest s • ρ0 π+ π- , charged particules Vanderhagen et al.:

  14. Diffractive r0 production μN μ’N’ρ * π+π- Q 2 W N’ N t • Exp (NMC, E665, Zeus, H1, Hermes): • lr ≈ lg S-channel helicity conservation SCHC • exchanged object has natural parity : P=(-1)JNPE

  15. Spin properties of amplitudes • angular dist. of ρ  π+π- : spin density matrix elt • they are bilinear combinations of • helicity amplitudes : • λγ=  1, 0 λρ=  1, 0  9 amplitudes • if NPE  5 amplitudes • T00, T11 >> T01, T10 >> T-11 • SCHC 1 helicity flip 2 flips

  16. r spin density matrix elt 04 00 0.01 < Q² < 0.05 < Q² < 0.3 < Q² < 0.6 < Q² < 2.0 < Q² < 10 GeV2 Distribution : in terms of amplitudes:

  17. Determination of R=sL/sT 2002 2003 + 2004 • If SCHC holds : • sL is dominant at Q2>2 • 2002: high stat • in large Q2 range • 2003 and 2004 data : • - much more stat • - better high Q2coverage

  18. Conclusions on rho • SCHC → R • stot + R → sL • when Q2 > 2 → R > 1 : accurate sL • we have transv. target spin asym → E/H • important for Ji sum rule (∫E+H) • exploratory measurement • (no exclusivity, nuclear target)

  19. Towards a dedicated experiment for DVCS and HEMP

  20. Additions to COMPASS setup μ’ + additional calorimeter at larger angle Recoil detector to insure exclusivity to be designed and built p’ μ 2.5m liquid H2 target to be designed and built L = 1.3 1032 cm-2 s-1  ECal 1 or 2   12° Exclusivity: at high energy dDM2 = d[(mp+mπ)2-mp2] > 1 GeV2 need 0.25 GeV2 for DM cut  hermetic detector

  21. A possible solution 30° ECAL0 12° 4m 2004-2007: Funding by European Union (Bonn-Mainz-Warsaw-Saclay) 45° sector recoil detector - scintillating material studies (200ps ToF Resolution over 4m) - fast triggering and multi-hit ADC/TDC system

  22. DVCS background • not included: • Beam halo • with hadronic contamination • Beam pile-up • Secondary interactions • External Bremsstrahlung • DVCS: μp  μp • with PYTHIA 6.1 simulate: • HEπ°P: μp  μpπ° •   • Dissociation of the proton: • μp  μN*π° •  Nπ • DIS: μp μpX • with 1, 1π°, 2π°,η… • Acceptance cuts: • qgmax= 30° • Egmin= 50 MeV • qchargedmax= 30°

  23. g* γ x +ξ x -ξ TDVCS: GPDs p p’ t =Δ2 GPD measurement • xxB/(2-xB) and t are fixed • loop over x

  24. DVCS + Bethe-heitler μ μ p p  μ’ * θ μ p φ BH calculable Higher energy: DVCS>>BH  DVCS Cross section • Smaller energy: DVCS~BH • Interference term will provide the DVCS amplitude

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

  26. at 100 GeV BCA Q2=40.5 GeV2 x = 0.05 ± 0.02 Model 1: H(x,0,t) ~ q(x) F(t) Model 2: H(x,0,t) = q(x) e t <b2> = q(x) / xα’t • assuming: • L = 1.3 1032 cm-2 s-1 • 150 days • efficiency=25% • 2 bins shown out of 18: • 3 bins in xBj= 0.05, 0.1, 0.2 • 6 bins in Q2 from 2 to 7 GeV2 φ φ BCA x = 0.10 ± 0.03 φ

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

  28. HEMP: filter of GPDs Cross section: Vector meson production (ρ,ω,…) H & E Pseudo-scalar production (π,η…) H & E ~ ~ Hρ0 = 1/2 (2/3Hu + 1/3Hd + 3/8Hg) Hω= 1/2 (2/3Hu – 1/3Hd + 1/8Hg) H = -1/3Hs - 1/8Hg Transverse single spin asymmetry : ~ E/H

  29. HEMP in 2010 • HEMP requires higher Q2 than DVCS • with liq H target and same m flux as now: • r  Q2= 20 GeV2 • w, p, h, f  Q2= 7 GeV2 • if more m  higher Q2

  30. Roadmap for DVCS at COMPASS • 2004-2009: r production: sL and transverse spin asym • 2005 :"Expression of Interest": SPSC-E0I-005 • 2004-2007: recoil detector prototype • 2008 ? : proposal • 2007-2009:construction of the recoil detector • cryogenic target, ECal0 • 2010: dedicated GPD measurement

  31. Measure OAM ? • Ji sum rule relates total quark spin to GPDs H and E : • similar sum rule for gluons • To do : • Measure H and E • Perform flavor decomposition • Extrapolate to t=0 • Integrate over x at fixed x • Sivers asymmetries are also measured at COMPASS

  32. SPARE

  33. Key role of calorimetry ECAL2 from 0.4 to 2°: mainly lead glass GAMS ECAL1 from 2 to 12° : good energy and position resolution for 2-g separation in a high rate environment ECAL0 from 12 to 30°: to be designed for background rejection Careful study of g and π0 production  COMPASS program with hadron beam

  34. ρ° angular distributions W(cosθ, φ, Φ) depends on theSpin density matrix elements 23 (15) observables with polarized (unpolarized) beam φ This analysis: only one-dimensional angular distribution We will use also: ψ= φ - Φ

  35. 0.01 < Q² < 0.05 < Q² < 0.3 < Q² < 0.6 < Q² < 2.0 < Q² Angular distributions 0.01 < Q² < 0.05 < Q² < 0.3 < Q² < 0.6 < Q² < 2.0 < Q² < 10 GeV2 φ Preliminary : - Corrected for Acceptance, smearing and efficiency (MC:DIPSI gen) - Background not subtracted Statistical error only, limited by MC

  36. Measurement of r and Im r 04 1-1 3 1-1 φ Distribution : beam polarisation weak violation Spin density matrices: If SCHC holds

  37. COMPASS 6 angular distributions among 18: 3 bins in xBj=0.05, 0.1, 0.2 6 bins in Q2 from 2 to 7 GeV2 BCA in DVCS projections for 1 year HERMES one single bin <x>=0.11 <Q2>=2.6

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