The FROST ExperimentThe FROST Experiment

Franz Klein for the g9 (FROST) run group

CLAS Collaboration Meeting/CLAS12 Workshop Paris 2011

The target: C4H9OH

butanol beads in liq N2 bath

additional calibration targets:1mm Carbon at z=6.15cm2.7mm Polyethylene at z=16cm

z-vertex for reconstructed proton tracks

Longitudinal and transverse polarization

2 run periods:2 run periods:g9a (Nov.2007 – Feb. 2008; ~10B evts):g9a (Nov.2007 – Feb. 2008; ~10B evts):solenoidal holding coil (0.56 T, solenoidal holding coil (0.56 T, ΔΔB/B~0.2%)B/B~0.2%)

g9b (March – Aug.2010; ~14B evts):g9b (March – Aug.2010; ~14B evts):racetrack holding coil (0.54 T,racetrack holding coil (0.54 T, ΔΔB/B~0.4%,B/B~0.4%, no polarization loss during spin rotation)no polarization loss during spin rotation)

Repolarization Repolarization about once per weekabout once per week

Target performancedesign design g9a (2008/9) g9b g9a (2008/9) g9b

(2010)(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%

Circular and linear photon polarizationCircular and linear photon polarization

Hall-B photon tagger:Hall-B photon tagger:EEγγ = 20-95% of E = 20-95% of E0 0 ((EEγγ up to ~6 GeV)up to ~6 GeV)

dE/E ~10dE/E ~10-3-3 of E of E00

Circularly polarized photons from Circularly polarized photons from long. polarized electrons (Plong. polarized electrons (Pee>85%)>85%)

2

2

344

4

kk

kkPP e

Linearly polarized photons: Linearly polarized photons: coherent bremsstrahlung on coherent bremsstrahlung on oriented diamond crystaloriented diamond crystal

Photonuclear cross sections

N*N*

Baryon resonance spectrum

g9 –FROST experiments

E02-112: γγpp→→KYKY (K(K++ΛΛ, K, K++ΣΣ00, K, K00ΣΣ++))E03-105/E04-102: γγpp→π→π00p, p, ππ++nn E05-012: γγpp→η→ηppE06-013: γγpp→π→π++ππ--pp goal: all 15 polar. observ. for Kgoal: all 15 polar. observ. for K++ΛΛ, K, K++ΣΣ00

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

from CLAS g1, g8, g11, g13 data

FROST

FROST (KY)

Event selection (example: γp→π0p)

Event selection (timing cut)

Raw asymmetry (γp→π0p)

Bound-nucleon subtraction

ππ00 beam-target asymmetries (I)beam-target asymmetries (I)ππ00 beam-target asymmetries (I)beam-target asymmetries (I)

helicity asymmetry helicity asymmetry γγpp→π→π00pp (PhD Hideko Iwamoto, GWU)(PhD Hideko Iwamoto, GWU)

ππ00 beam-target asymmetries (II)beam-target asymmetries (II)ππ00 beam-target asymmetries (II)beam-target asymmetries (II)

G asymmetry (lin.pol.beam – long.pol.target)G asymmetry (lin.pol.beam – long.pol.target): variation of : variation of ΣΣ by P by Pzz sin(2 sin(2φφ))

Jo McAndrew (U.Edinburgh)Jo McAndrew (U.Edinburgh)→ → talk talk today 17:30today 17:30

on G asymmetry in on G asymmetry in γγpp→π→π++nn

preliminary

γγpp→π→π++n n helicity asymmetryhelicity asymmetryγγpp→π→π++n n helicity asymmetryhelicity asymmetry

S. Strauch (SC)

γγppKK++ΛΛ helicity asymmetry E helicity asymmetry E

additionally: Lx, Lzadditionally: Lx, Lz

Liam Casey (CUA) → talk on Thursday (Hadron Spectroscopy Working Group)

γγppKK++ΛΛ beam-target asymmetry G beam-target asymmetry G

G asymmetryG asymmetry: variation of beam asymmetry : variation of beam asymmetry ΣΣ by P by Pzz sin(2 sin(2φφ))

Stuart Fegan (Glasgow) → talk on Thursday (Hadron Spectroscopy Working Group)

coherent edge at 1.7 GeV

g9b ((March – August 2008)March – August 2008)

linearly (~10B evts) & circularly (~4.5B evts) polar. photons linearly (~10B evts) & circularly (~4.5B evts) polar. photons on transversely polar. targeton transversely polar. target

pass0 calibration underwaypass0 calibration underway

Beam positionBeam position

number of hit-based tracks per eventnumber of hit-based tracks per event

reconstructed protons per eventreconstructed protons per event

g9b Tagger calibrationTagger calibration

22ndnd calibration pass done calibration pass done

(practically calibrated(practically calibrated each run individually)each run individually)

Tag

_tim

e –

RF

_ti

me

Tcounter bin

run 63340run 63340

issue: occasionally too high rates on Tcounters (in coherent peak)

→ PMT response unstable in most cases only one of the 2 PMTs per Tcounter unstableotherwise event-dependent correction

Tag_time – RF_time Tag_time – RF_time for Tcounter 54for Tcounter 54

g9b SC calibrationg9b SC calibration

22ndnd iteration done for 3 runs … needs additional runs to calibrate! iteration done for 3 runs … needs additional runs to calibrate!

example:fit of effectivepropagationvelocity

g9b ST calibrationg9b ST calibration

22ndnd calibration pass done calibration pass done

timewalk correction

time offset relative to tagger

g9b DC calibrationg9b DC calibration

great improvement in 2great improvement in 2ndnd calibration pass calibration passDC SigmaDC 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 subtractionstudies 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 correctionmomentum correction

analysis of single & double-pion, eta, omega, and Kanalysis of single & double-pion, eta, omega, and KΛΛ channels channels (g9a: 6 students ; g9b: 4 students)(g9a: 6 students ; g9b: 4 students)