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 z-vertex for reconstructed proton tracks

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%, racetrack holding coil (0.54 T, ΔB/B~0.4%, no polarization loss during spin rotation) no polarization loss during spin rotation)

Repolarization about once per week Target performance design g9a (2008/9) g9b (2010) polarization:±85%+82%+85% -85%-93% relaxation time:500 h2700 h (+)3500 h (+) 1400 h (-)1900 h (-) (~5%/day)(<1.5%/day)(<1%/day) base temp:50 mK30 mK25 mK cooling power at 50 mK:0.01 mW0.8 mW0.8 mW on-beam efficiency: ~80%~90%~95%

Circular and linear photon polarization Hall-B photon tagger: Eγ = 20-95% of E 0 ( Eγ up to ~6 GeV) dE/E ~10 -3 of E 0 Circularly polarized photons from long. polarized electrons (P e >85%) Linearly polarized photons: coherent bremsstrahlung on oriented diamond crystal

Photonuclear cross sections

N*  Baryon resonance spectrum

g9 –FROST experiments γp→KY (K + Λ, K + Σ 0, K 0 Σ + ) E02-112: γp→KY (K + Λ, K + Σ 0, K 0 Σ + ) γp→π 0 p, π + n E03-105/E04-102: γp→π 0 p, π + n γp→ηp E05-012: γp→ηp γp→π + π - p E06-013: γp→π + π - p goal: all 15 polar. observ. for K + Λ, K + Σ 0 statistics ±5-10% (<15% for Σ + ) systematics ±3-7% (beam, target, P, Σ, dilution fac.) ±6-8% E, F, G, H, C x,z, O x,z, L x,z, T x,z from CLAS g1, g8, g11, g13 data FROST FROST (KY)

Event selection (example: γp→π 0 p)

Event selection (timing cut)

Raw asymmetry (γp→π 0 p)

Bound-nucleon subtraction

π 0 beam-target asymmetries (I) helicity asymmetry γp→π 0 p (PhD Hideko Iwamoto, GWU) (PhD Hideko Iwamoto, GWU)

π 0 beam-target asymmetries (II) G asymmetry (lin.pol.beam – long.pol.target) : variation of Σ by P z sin(2φ) Jo McAndrew (U.Edinburgh) → talk today 17:30 on G asymmetry in γp→π + n preliminary

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

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

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

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

Tagger calibration g9b Tagger calibration 2 nd calibration pass done (practically calibrated each run individually) each run individually) Tag_time – RF_time Tcounter bin run 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

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

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

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

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