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Experiments with Frozen-Spin Target and Polarized Photon Beams.

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Presentation on theme: "Experiments with Frozen-Spin Target and Polarized Photon Beams."— Presentation transcript:

1 Experiments with Frozen-Spin Target and Polarized Photon Beams

2 CEBAF Large Acceptance Spectrometer Torus magnet 6 superconducting coils Gas Cherenkov counters e/  separation, 256 PMTs Time-of-flight counters plastic scintillators, 684 photomultipliers Drift chambers argon/CO 2 gas, 35,000 cells polarized target + polarized target + start counter start counter Electromagnetic calorimeters Lead/scintillator, 1296 photomultipliers DAQ linit ~ 6kHz (~1.5TB/day)

3 polarized photon beams circularly pol. beam (long. pol. electrons) linearly pol. beam (coherent bremsstrahlung) → CLASg8 poster tagged flux ~ 50MHz (for k>0.5 E 0 ) ~10MHz (coh.peak)

4 CLAS polarized targets existing dynamically pol. NH 3 target: P~80%, P~35% (deuterized) pol. magnet: 5.1 T (Helmholtz coils) reduces 4π acceptance to θ<65 o

5 CLAS frozen-spin target target: Ø15mm x 50mm butanol C 4 H 9 OH dilution factor 10/74 eff. density: g/cm 3 operate at ~50mK, repolarize at 0.4K

6 CLAS frozen-spin target longitudinal polarization: solenoidal coil (0.5T; ΔB/B~0.2%) → online NMR transverse polarization: “racetrack” coil (0.3+T; ΔB/B~0.5%) NEW DEVELOPMENT! size: Ø5cmx11cm size: Ø5cmx20cm max. Pol.~96%, average ~80-85% (τ relax ~30d)

7 Proposed Experiments E02-112: γp→KY (K + Λ, K + Σ 0, K 0 Σ + ) E03-105/E01-104: γp→π 0 p, π + n E05-012: γp→ηp in preparation: γp→π + π - p, γp→ωp reactions off neutrons/deuterons ??

8 - resonance parameters - search for missing resonances goal of exp. program

9 determine mass, width, coupling of all resonances up to ~2.0 GeV FROST

10 Experiment and Theory Experiment cross section, spin observables Theory LQCD, quark models, QCD sum rules, … Reaction Theory dynamical frameworks Amplitude analysis →multipole ampl., →phase shifts σ,dσ/dΩ (single) Σ y,P,T Σ p, T 20, T 21,T 22 (beam-target) E, F, G, H, (beam-recoil) C x,C z, O x,O z, (target-recoil) L x,L z, T x,T z, (beam/target-VM) C BV, C TV, C BTV PWA: SES CC: res. param. extraction

11 beam – target polarization 4 (12) complex amplitudes for 0 - (1 - ) meson production ≥ 8 (≥ 68) measurements FROST: all 4 combinations of beam (lin,circ) and target (long,trans) for Λ, Σ 0,+ additionally recoil polar. complete set all observables as fcts of √s and cosθ use algebraic relations to check for systematics from CLAS g1, g8, g11 data

12 beam – target polarization Extraction of spin observables via Fourier analysis of polarized cross section in each (E,cosθ) bin α=orientation of photon polarization β=orientation of target polarization P T =linear photon polarization P o =circular photon polarization P z =longitudinal target polarization P xy =transverse target polarization FROST: 6 polar. observ. for π 0 p,π + n,ηp statistics ±3-5% (<8% for η) systematics ±3-5% (beam, target, E, Σ, eff. dilution fac.) ±6-8% P, F, G, H

13 data extraction estimated from He/H CLAS data and MC FROST: additional carbon target, averaged yields dilution factor: (D but =10/74=0.135) yields for free/bound nucleons: D eff ~ γp→K + Λ γp→πN γp→ηp

14 gp→ηp TAPSGRAALCLASCB-ELSATAPSGRAALCLASCB-ELSA GRAAL  Bonn T GRAAL  Bonn T only 15% pol. data NO double pol.data

15 γp→ηp (dσ/dΩ) solid line: REM (etaMAID) - includes: D13(1520), S11(1535), D15(1675), F15(1680), D13(1700), P11(1710), P13(1720), t-exchange ( ρ,ω) dashed line: χQM (Saghai) - additionally: P11(1440), S11(~1730), P13(1900), F15(2000),

16 γp→ηp (SAID solution) small changes in fit to dσ/dΩ cause large fluctuation of multipoles → fit not well constrained by data → need polarization observables → fit not well constrained by data → need polarization observables

17 γp→π 0 p, π + n said database: hardly any double-pol. obs. FROST: wide coverage: E γ ~ GeV,θ cm ~ o fine binning: ΔE<25MeV, Δθ cm ~10-15 o > 5000 data points single pol. ~2-3x double pol. ~7-8x

18 γp→π 0 p, π + n most cases: only 1 st excited state in PW well known after FROST experiment we expect: red: sample PWA (MC data)

19 γp→π 0 p, π + n (sample PWA) sample PWA using MC data generated from SM02 greatly reduced uncertainties

20 γp→π 0 p, π + n impact on single energy solutions

21 γp→KY (K + Λ, K + Σ 0, K 0 Σ + ) present data insufficient to perform single energy fits

22 γp→KY (K + Λ, K + Σ 0, K 0 Σ + )

23 FROST: all 16 polar. observ. for K + Λ, K + Σ 0, K 0 Σ + statistics ±5-10% (<15% for Σ + ) systematics ±3-5% (beam, target, P, Σ, dilution fac.) ±6-8% E, F, G, H, C x,z, O x,z, L x,z, T x,z

24 γp→ωp dσ/dΩ compared to model (Y.Oh, H.S. Lee) purple: t-channel (Pomeron, π, η) and u-channel (N-pole) green: s-channel black: sum

25 γp→ωp

26 ● 1 st run period in fall 2006 (long.pol.) ● cryostat being tested in test lab ● all polarization observables measurable in CLAS will be extracted from data ● complete set of measurements for KY ● “almost” complete set for πN, ηp ● double/triple pol. obs. for π + π - p, ωp least model dependent extraction of N* parameters & potential for discovery of missing states outlook


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