Experiments with Frozen-Spin Target and Polarized Photon Beams.

Experiments with Frozen-Spin Target and Polarized Photon Beams

CEBAF Large Acceptance Spectrometer

Torus magnetTorus magnet6 superconducting coils

Gas Cherenkov countersGas Cherenkov counterse/ separation, 256 PMTs

Time-of-flight countersTime-of-flight countersplastic scintillators, 684 photomultipliers

Drift chambersDrift chambersargon/CO2 gas, 35,000 cells

polarized target +polarized target + start counterstart counter

Electromagnetic calorimetersElectromagnetic calorimetersLead/scintillator, 1296 photomultipliers

DAQ linit ~ 6kHz (~1.5TB/day)DAQ linit ~ 6kHz (~1.5TB/day)

polarized photon beams

circularly pol. beam (long. pol. electrons)

linearly pol. beam (coherent bremsstrahlung)→ CLASg8 poster

tagged flux ~ 50MHz (for k>0.5 Etagged flux ~ 50MHz (for k>0.5 E00) ~10MHz (coh.peak)) ~10MHz (coh.peak)

CLAS polarized targets

existing dynamically pol. NH3 target:

P~80%, P~35% (deuterized)pol. magnet: 5.1 T (Helmholtz coils)

reduces 4π acceptance to θ<65o

CLAS frozen-spin target

target: Ø15mm x 50mmbutanol C4H9OH

dilution factor 10/74eff. density: 0.611 g/cm3

operate at ~50mK,repolarize at 0.4K

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: Ø

5cmx11cm

size: Ø5cmx20cm

max. Pol.~96%, average ~80-85% (τrelax~30d)

Proposed Experiments

• E02-112: γp→KY (K+Λ, K+Σ0, K0Σ+)• E03-105/E01-104: γp→π0p, π+n

• E05-012: γp→ηp• in preparation: γp→π+π-p, γp→ωp • reactions off neutrons/deuterons ??

- resonance parameters

- search for missing resonances

goal of exp. program

determine mass, width, couplingof all resonances up to ~2.0 GeV

FROST

Experiment and Theory

Experimentcross section,

spin observables

TheoryLQCD,

quark models,QCD sum rules,

…

Reaction Theorydynamical frameworks

Amplitude analysis→multipole ampl.,→phase shifts

σ,dσ/dΩ(single) Σy,P,T Σp, T20, T21,T22

(beam-target) E, F, G, H,(beam-recoil) Cx,Cz, Ox,Oz,(target-recoil) Lx,Lz, Tx,Tz,(beam/target-VM) CBV, CTV, CBTV

PWA: SESCC: res. param. extraction

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, Σ0,+ 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

beam – target polarizationExtraction of spin observables Extraction of spin observables

via Fourier analysis via Fourier analysis of polarized cross sectionof polarized cross section

in each (E,cosθ) binin each (E,cosθ) bin

α=orientation of photon polarization

β=orientation of target polarization

PT=linear photon polarization

Po=circular photon polarization

Pz=longitudinal target polarization

Pxy=transverse target polarization

FROST: 6 polar. observ. for π0p,π+n,ηpstatistics ±3-5% (<8% for η)systematics ±3-5% (beam, target, E, Σ, eff. dilution fac.)

±6-8% P, F, G, H

data extraction

estimated from He/H CLAS data and MC

FROST: additional carbon target,

averaged yields

dilution factor: (Dbut=10/74=0.135)yields for free/bound nucleons: Deff~0.3-0.5

γp→Kγp→K++ΛΛγp→πNγp→πN

γp→ηpγp→ηp

gp→ηpTAPS TAPS

GRAALGRAALCLASCLAS

CB-ELSACB-ELSA

TAPS TAPS GRAALGRAALCLASCLAS

CB-ELSACB-ELSAGRAAL GRAAL

Bonn TBonn TGRAAL GRAAL

Bonn TBonn T

only 15% pol. dataonly 15% pol. dataNO double pol.dataNO double pol.data

γp→ηp (dσ/dΩ)

solidsolid line: line: REMREM (etaMAID) - includes: D13(1520), S11(1535), D15(1675), F15(1680), D13(1700), P11(1710), (etaMAID) - includes: D13(1520), S11(1535), D15(1675), F15(1680), D13(1700), P11(1710), P13(1720), P13(1720),

t-exchange (t-exchange (ρ,ω)ρ,ω)

dasheddashed line: line: χQMχQM (Saghai) - additionally: P11(1440), S11(~1730), P13(1900), F15(2000), (Saghai) - additionally: P11(1440), S11(~1730), P13(1900), F15(2000),

γp→ηp (SAID solution)

small changes in fit to dσ/dΩ cause large fluctuation of multipolessmall changes in fit to dσ/dΩ cause large fluctuation of multipoles

→→ fit not well constrained by data fit not well constrained by data → need polarization observables→ need polarization observables

γp→π0p, π+n

said database: hardly any double-pol. obs.FROST: wide coverage: Eγ~0.6-2.0 GeV,θcm~15-150o

fine binning: ΔE<25MeV, Δθcm~10-15o

> 5000 data points single pol. ~2-3x double pol. ~7-8x

γp→π0p, π+n

most cases: only 1st excited state in PW well known

after FROST experiment we expect:

redred: sample PWA (MC data): sample PWA (MC data)

γp→π0p, π+n (sample PWA)

sample PWA using MC datagenerated from SM02

greatly reduced uncertainties

γp→π0p, π+nimpact on single energy solutions

γp→KY (K+Λ, K+Σ0, K0Σ+)

present data insufficient to perform single energy fits

γp→KY (K+Λ, K+Σ0, K0Σ+)

γp→KY (K+Λ, K+Σ0, K0Σ+)

FROST: all 16 polar. observ. for K+Λ, K+Σ0, K0Σ+

statistics ±5-10% (<15% for Σ+)systematics ±3-5% (beam, target, P, Σ, dilution fac.)

±6-8% E, F, G, H, Cx,z, Ox,z, Lx,z, Tx,z

γp→ωpdσ/dΩ compared to model (Y.Oh, H.S. Lee)

purple: t-channel (Pomeron, π, η) and u-channel (N-pole)green: s-channelblack: sum

γp→ωp

● 1st 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