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The FROST Experiment

The FROST Experiment. Franz Klein for the g9 (FROST) run group CLAS Collaboration Meeting/CLAS12 Workshop Paris 2011. The target: C 4 H 9 OH. butanol beads in liq N 2 bath. additional calibration targets: 1mm Carbon at z=6.15cm 2.7mm Polyethylene at z=16cm.

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The FROST Experiment

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  1. The FROST Experiment Franz Klein for the g9 (FROST) run group CLAS Collaboration Meeting/CLAS12 Workshop Paris 2011

  2. The target: C4H9OH butanol beads in liq N2 bath additional calibration targets: 1mm Carbon at z=6.15cm 2.7mm Polyethylene at z=16cm z-vertex for reconstructed proton tracks

  3. Longitudinal and transverse polarization 2 run periods: g9a (Nov.2007 – Feb. 2008; ~10B evts): solenoidal holding coil (0.56 T, ΔB/B~0.2%) g9b (March – Aug.2010; ~14B evts): racetrack holding coil (0.54 T,ΔB/B~0.4%, no polarization loss during spin rotation)

  4. Target performance design g9a (2008/9) g9b (2010) polarization: ±85% +82% +85% -85% -93% relaxation time: 500 h 2700 h (+) 3500 h (+) 1400 h (-) 1900 h (-) (~5%/day) (<1.5%/day) (<1%/day) base temp: 50 mK 30 mK 25 mK cooling power at 50 mK: 0.01 mW 0.8 mW 0.8 mW on-beam efficiency: ~80% ~90% ~95% Repolarization about once per week

  5. Circular and linear photon polarization Hall-B photon tagger: Eγ = 20-95% of E0 (Eγup to ~6 GeV) dE/E ~10-3 of E0 Linearly polarized photons: coherent bremsstrahlung on oriented diamond crystal Circularly polarized photons from long. polarized electrons (Pe>85%)

  6. Photonuclear cross sections

  7. Baryon resonance spectrum N* D

  8. g9 –FROST experiments E02-112: γp→KY(K+Λ, K+Σ0, K0Σ+) E03-105/E04-102: γp→π0p, π+n E05-012: γp→ηp E06-013: γp→π+π-p goal: all 15 polar. observ. for K+Λ, K+Σ0 statistics ±5-10% (<15% for Σ+) systematics ±3-7% (beam, target, P, Σ, dilution fac.) ±6-8% E, F, G, H, Cx,z, Ox,z, Lx,z, Tx,z FROST FROST (KY) from CLAS g1, g8, g11, g13 data

  9. Event selection (example:γp→π0p)

  10. Event selection (timing cut)

  11. Raw asymmetry(γp→π0p)

  12. Bound-nucleon subtraction

  13. π0beam-target asymmetries (I) helicity asymmetry γp→π0p (PhD Hideko Iwamoto, GWU) preliminary

  14. π0beam-target asymmetries (II) G asymmetry (lin.pol.beam – long.pol.target): variation of Σ by Pz sin(2φ) Jo McAndrew (U.Edinburgh) → talk today 17:30 on G asymmetry in γp→π+n preliminary

  15. γp→π+n helicity asymmetry preliminary S. Strauch (SC)

  16. γpK+Λ helicity asymmetry E preliminary additionally: Lx, Lz Liam Casey (CUA) → talk on Thursday (Hadron Spectroscopy Working Group)

  17. γpK+Λ beam-target asymmetry G G asymmetry: variation of beam asymmetry Σ by Pz sin(2φ) Stuart Fegan (Glasgow) → talk on Thursday (Hadron Spectroscopy Working Group) coherent edge at 1.7 GeV

  18. g9b (March – August 2008) linearly (~10B evts) & circularly (~4.5B evts) polar. photons on transversely polar. target pass0 calibration underway number of hit-based tracks per event Beam position reconstructed protons per event

  19. g9b Tagger calibration run 63340 2nd calibration pass done (practically calibrated each run individually) Tag_time – RF_time Tcounter bin issue: occasionally too high rates on Tcounters (in coherent peak) → PMT response unstable in most cases only one of the 2 PMTs per Tcounter unstable otherwise event-dependent correction Tag_time – RF_time for Tcounter 54

  20. g9b SC calibration 2nd iteration done for 3 runs … needs additional runs to calibrate! example: fit of effective propagation velocity

  21. g9b ST calibration 2nd calibration pass done time offset relative to tagger timewalk correction

  22. g9b DC calibration great improvement in 2nd calibration pass DC Sigma

  23. Ongoing projects • next iteration of pass0 cooking of g9b will start soon • (wait for DC alignment) • studies on improving the bound-nucleon subtraction • tracking with integrated energy loss • (due to heavy target material & holding field) • momentum correction • analysis of single & double-pion, eta, omega, and KΛ channels • (g9a: 6 students ; g9b: 4 students)

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