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Measuring the Spin-Polarizabilities of the Proton T HI S at Hiγs

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Measuring the Spin-Polarizabilities of the Proton T HI S at Hiγs Measuring the Spin-Polarizabilities of the Proton at HIγS Rory Miskimen University of Massachusetts, Amherst • Nucleon polarizabilities: What are they, and what’s still to be accomplished • Spin-polarizabilities of the proton • The experiment in preparation at HIGS Proton electric and maggpnetic polarizabilities from real Compton scattering† α = (12.0 ± 0.6)x10−4 fm3 −4 3 β = (1.9 m 0.6)x10 fm Some observations… i. the numbers are small: the proton is very “stiff” ii. the magnetic polarizability is around 20% of the electric polarizability Cancellation of positive paramagnetism by negggative diamagnetism † M. Schumacher, Prog. Part. and Nucl. Phys. 55, 567 (2005). The spin-polarizabilities of the nucleon •At O(ω3) four new nucleon structure terms that involve nucleon spin-flip operators enter the RCS expansion. (3),spin 1 ⎛ r r r& r r r& ⎞ H = − 4π⎜γ σ ⋅ E × E + γ σ ⋅ B × B − 2γ E σ H + 2γ H σ E ⎟ eff 2 ⎝ E1E1 M1M1 M1E2 ij j j E1M2 ij j j ⎠ • The classical Faraday effect is a spin polarizability effect • Spin-polarizabilities cause the nucleon spin to ppggrecess in rotating electric and magnetic fields Spin polarizatibilities in Virtual Compton Scattering Contribution of spin polarizabilities in the VCS response functions Experiments The GDH experiments at Mainz and ELSA used the Gell-Mann, Goldberger, and Thirring sum rule to evaluate the forward S.-P. γ0 γ0 = −γE1E1 − γE1M2 − γM1M1 − γM1E2 ∞ 1 σ1 2 − σ3 2 γ0 = dω 4π2 ∫ ω3 mπ −4 4 γ0 = (−1.01 ± 0.08 ± 0.10) × 10 fm Backward spin polarizability from dispersive analysis of backward angle Compton scattering γ π = −γE1E1 − γE1M2 + γM1M1 + γM1E2 −4 4 γ π = (−38.7 ± 1.8) ×10 fm Experiment versus Theory Experiment121,2 SSE3 Fixed-t DR4 γ0 -1.01 ±0.08 ±0.10 .62 ± -0.25 -0.7 γπ 8.0 ± 1.8 8.86 ± 0.25 9.3 1. Ahrens, et. al., Phys. Rev. Lett . 87, 022003 (2001) 2. Schumacher, Prog. Part. Nucl. Phys. 55, 567 (2005) 3. Hildebrandt, et. al., Eur. Phys. J. A 20, 293 (2004) 4. Drechsel, et. al., Phys. Rep. 378, 99 (2003) Theory versus Theory HBCHPT Fixed-t dispersion analyses O(p3)1 O(p4)2 O(p4)3 SSE2 HDPV4 BGLMN5 DPV6 KS7 γE1E1 -5.7 -1.8 -1.4 -5.7 -4.3 -3.4 -3.8 -5.0 γM1M1 -111.1 292.9 333.3 313.1 292.9 272.7 292.9 343.4 γE1M2 1.1 .7 0.2 .98 -0.01 0.3 0.5 -1.8 γM1E2 1.1 1.8 1.8 .98 2.1 1.9 1.6 1.1 1. Hemmert et. al., Phys. Rev. D 57, 5746 (1998) 2. Gellas, et. al., Phys. Rev. Lett. 86, 3205 (2001) 3. Kumar, et. al., Phys. Lett. B 479, 167 (2000) 4. Holstein, et. al., Phys. Rev. C 61, 034316 (2000) Lattice calculations 5. Babusci, et. al., Phys. Rev. C 58, 1013 (1998) are in progress 6. Drechsel, et. al., Phys. Rep. 378, 99 (2003) 7. Kondratyuk, et. al., Phys. Rev. C 64, 024005 (2001) Experiments in progress to measure nucleon spin- polibilitilarizabilities in RCS • Mainz (J. Ahrens) rr γp → γp circularly polarized photons, longitudinal and transversely polarized target Crystal ball detector, ≈ 4π detection Eγ≈ 200 MeV (large sensitivity to γ’s) Possible problem with γ C → π 0 C and γ C →γ C • HIγS Compton scattering with polarized beam and target r 3 r 3 γrp → γp γt He →γ He Experimental concept for HIγS: 7 •Iγ = 10 photons/s, monochromatic Eγ ≥ 100 MeV, 100% circular polarization • ≈ 800 hours combbdined running on lldlongitudinal and transversely polarized target • HINDA NaI de tec tor array •Polarized scintillating target, 5 cm long, 80% polarization GEANT-4 Simulation Polarized Target Transverse Coil γrr → γ 100 MeVp CM energyp longitudinal polarized target, 110 MeV Longitudinal target polarization 45 40 +z steradian +z+z no spin pol er er -z+z no spin pol. Sensitivity 35 -z no spin pol -z-z no spin pol. to γ’s obarns p 30 Projected errors for anan n 200 hours running 25 20 15 10 5 0 20 40 60 80 100 120 140 160 angle (degrees) r 100γr MeV→ CM energyγ Transversep targetp polarizationtransverse polarized target, 110 MeV 30 ianian r sterad +x+x 25 +x no spin pol. pe pe -x+x no spin pol -x-x no spin pol. -x no spin pol Sensitivity nobarns Projected errors for 20 to γ’s nana 200 hours running 15 10 5 20 40 60 80 100 120 140 160 angle (degrees) rr γp → γp transverse polarized target, 130 MeV E= 120 MeV Transverse Target Pol. 35 +X +X no spin pol. 30 -X Sensitivity -X no spin pol. to γ’s 25 PjtdProjected errors for 200 hours running srsr nbnb 20 σσ ΩΩ dd dd 15 10 5 20 40 60 80 100 120 140 160 θ (degrees) Projected Uncertainties: 800 hours @ 100 MeV S.-P. Value* (10-4 fm3) Fitting error Δγ † Δγ/γ -4.3 .21 5 % γΕ1Ε1 2.9 .16 6 % γΜ1Μ1 -.01 .25 2500 % γΕ1Μ2 2.1 .25 12 % γΜ1Ε2 † Statistical errors only, no systematic * B. Pasquini Sc in tilla ting polidlarized tttarget • Coherent Compton scattering from complex nuclei in butanol (C4H10O) is orders of magnitude larger than the proton Compton scattering Tag Compton events on proton by observing scintillation light from recoil protons • Eliminate backgrounds in the NaI detectors by timing cut Light capture with wavelength shifting fibers APD or SSPM Transparent shell BCF-92 blue to green wavelength Polarized scintillating disks 5 mm thick, shifting fiber, 1 mm square, double BC-490 doped with Tempo clad, wrapped around clear shell, 7% capture efficiency Overall light transport efficiency ≈ 2% Trues:Accidentals = 35:1 Cryogenic capable photo-detectors for the polarized target 1. Hamamatsu Si-APD (commercially available) 2. SS-PMT from Radiation Monitoring Devices operating in proportional mode • Phase I SBIR proposal approved and completed • Phase II SBIR proposal submitted. If approved, this SBIR will ppprovide experiment-ready detectors for HIγS. Quantum Efficiency of Hamamatsu Si-APD Gain ≈ × 200 † † Erik Johnson, RMD, DOE SBIR DE-FG02—7ER84752 Low temperature performance of the RMD SS-PMT QE ≈ 30% Gain = 103 to 104 Target material: the problems Use dynamic nuclear polarization with chemical doping to polarize the target. There are problems, 1. the paramagnetic dopant must survive the process of making the target 2. the target should be reasonably efficient for producing scintillation light 3. the target should be reasonably transparent to blue scintillation light If we can do all that, then we still must obtain high proton polarization, ≈ 80%. Tools for testinggg target materials include: • Electron Polarization Resonance (EPR) for counting paramagnetic centers in target material (Paul Lahti, UMass Chemistry) • Helium dilution refrigerator, high field magnet, RF, and NMR system for polarizing target samples. (Don Candela, UMass Physics) Polarized-Scintillating Target: Possible materials 1. PSI technique • Dissolve polystyrene scintillator in toluene • Dope the scintillator mixture with a paramagnetic doping agent, tempo, at 2×1019 p.c.’s /cc • Pour out thin films of the scintillator mixture and let the toluene evaporate • Press the thin films together to form scintillating blocks several mm thick 2. Dope a castable polyethylene scintillator resin, BC-490, with tempo and use a peroxide setting agent to harden the scintillator. 3. Prepare a liquid scintillator doped with tempo, then freeze it in liquid nitrogen • Xylene mixed with ≈1% PPO and ≈0.05% POPOP • Mineral oil based liquid scintillator, e.g. BC-517S • BC-490 polyethylene scintillator resin Summary: • Spin-polarizabilities parameterize the long distance spin-structure of the nucleon, in the limit where π’s and Δ’s are the relevant degrees of freedom. The pion clou d is one of the key ingredi ent s in deci ph eri ng the proton “spin crisis”. • There exist no measurements of individual nucleon spin-polarizabilities • Can measure the polarizabilities at HIGS with an uncertainty of ≈ 0.2 x 10-4 fm4 . This will be sufficient to test and differentiate between theoretical models. rr γp → γp longitudinal polarized target, 130 MeV E = 120 MeV 50 Longitudinal Target Pol. +Z +Z no spin pol. -Z 40 -Z no spin pol. PjtdProjected errors for Sensitivity 200 hours running srsr nbnb 30 to γ’s σσ ΩΩ dd dd 20 10 0 20 40 60 80 100 120 140 160 θ (degrees).
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