17 June 2004HAPPEX-II ExperimentsK. Paschke The Second Generation HAPPEX Experiments Kent Paschke for The HAPPEX Collaboration California State University, Los Angeles - Syracuse University - DSM/DAPNIA/SPhN CEA Saclay - Thomas Jefferson National Accelerator Facility - INFN, Rome - INFN, Bari - Harvard - Indiana University - University of Virginia - University of Massachusetts - Florida International University - University of New Hampshire - Massachusetts Institute of Technology - College of William and Mary in Virginia (Thanks to Rich Holmes for.ppt from PAVI 04)

17 June 2004HAPPEX-II ExperimentsK. Paschke Spin Longitudinal momentum Strange mass Strange vector FF Strangeness in the Nucleon

17 June 2004HAPPEX-II ExperimentsK. Paschke PVES Leading contribution to parity-violating scattering asymmetry is from interference of EM and weak exchange amplitudes

17 June 2004HAPPEX-II ExperimentsK. Paschke PVES and strange form factors For hydrogen: => Measurement of A PV yields linear combination of G s E, G s M Related at Q 2 =0 to s, s.

17 June 2004HAPPEX-II ExperimentsK. Paschke The HAPPEX Experiments A look back: HAPPEX, ep Q 2 =0.5 (GeV/c) 2 HAPPEX-H: ep, Q 2 =0.1 (GeV/c) 2 HAPPEX-He: e 4 He, Q 2 =0.1 (GeV/c) 2 PREX: ePb, Q 2 =0.01 (GeV/c) 2

17 June 2004HAPPEX-II ExperimentsK. Paschke A look back: HAPPEX Hall A Proton Parity Experiment (E91-010) ep at Q 2 =0.5 (GeV/c) 2, 12.3 degrees G s E G s M = ± (exp) ± (FF) Phys. Rev. Lett. 82: ,1999; Phys. Lett. B509: ,2001; Detailed paper accepted for PRC - arXiv nucl-ex/

17 June 2004HAPPEX-II ExperimentsK. Paschke HAPPEX results A PV = ppm ± 0.98 (stat) ppm ± 0.56 (syst) ppm

17 June 2004HAPPEX-II ExperimentsK. Paschke The next step Increase sensitivity Choose different Q 2 range Separate G s E, G s M => Two new experiments at smaller Q 2

17 June 2004HAPPEX-II ExperimentsK. Paschke HAPPEX-H (JLAB E99-115) Polarized e - on 1 H Q 2 = 0.1 (GeV/c) 2, LAB = 6 A PV = 1.6 ppm A = 5% (stat) + 2.5% (syst) => 80 ppb (stat) + 40 ppb (syst)

17 June 2004HAPPEX-II ExperimentsK. Paschke Helium and strange form factors For helium: => A PV sensitive only to G s E

17 June 2004HAPPEX-II ExperimentsK. Paschke HAPPEX-He (JLAB E00-114) Polarized e - on 4 He Q 2 = 0.1 (GeV/c) 2, LAB =6 A PV = 8.4 ppm A = 2.2% (stat) + 2.1% (syst) =>.18 ppm (stat) +.18 ppm (syst)

17 June 2004HAPPEX-II ExperimentsK. Paschke Experimental impact

17 June 2004HAPPEX-II ExperimentsK. Paschke Experimental impact

17 June 2004HAPPEX-II ExperimentsK. Paschke Tough new measurement: How do you do it? Small forward angle => new Septum magnets High statistical precision => Thick new targets, high current, rad-hard integrating detectors, improved DAQ, new photocathode High relative accuracy => improved polarimetry, new integrating focal plane profile scanner High systematic accuracy => improved polarized source, close attention to beam optics, lumi monitor.

17 June 2004HAPPEX-II ExperimentsK. Paschke Overview Hall A CEBAF Injector Polarized source

17 June 2004HAPPEX-II ExperimentsK. Paschke Septum magnets Minimum scattering angle 12.5° -> 6.0° Installed and commissioned

17 June 2004HAPPEX-II ExperimentsK. Paschke 100 x 600 mm 12 meter dispersion sweeps away inelastic events L geometry design Hydrogen geometry Cerenkov detectors overlap the elastic line above the focal plane : HAPPEX-H Detector geometry He detector = (H detector) / 2 !

17 June 2004HAPPEX-II ExperimentsK. Paschke Brass-quartz stack Light guide Filter box PMT Assembly at Saclay

17 June 2004HAPPEX-II ExperimentsK. Paschke Luminosity monitors Target boiling Beam parameters Electronics noise Tested to ~200 ppm resolution, expecting about ~100 ppm Current A ppm

17 June 2004HAPPEX-II ExperimentsK. Paschke Target cells "Beer can" – 15 cm, worked well for HAPPEX-I New "race track" design – 20 cm, boiling untested

17 June 2004HAPPEX-II ExperimentsK. Paschke Luminosity Fluctuations Beer can cells good enough, as measured in HAPPEX Racetrack cells never tried (Transverse flow good, curvature of window bad) Cold (6.6K), dense (230 psi) cryogenic 4 He gas target… boils! Widths go down with increasing raster… … and UP with increasing current!

17 June 2004HAPPEX-II ExperimentsK. Paschke Møller: Main uncertainty is foil polarization; p/p = 3 – 3.4% expected Compton: Added electron recoil detector since HAPPEX-I; p/p = 2% in ~1 hour seen – 1.3% probably achievable at 3 GeV Polarimetry Big challenge for PREX – high current, low energy. Plan to upgrade Compton with green laser => 1% in ~16 hours Compton GEANT4 monte carlo

17 June 2004HAPPEX-II ExperimentsK. Paschke Main Challenge: extreme requirements on halo/tail are necessary to reduce background 100 Hz / A at 5mm from the beam centroid ( )! Compton Polarimeter Photon detector Electron detector

17 June 2004HAPPEX-II ExperimentsK. Paschke Profile scanners Q 2 measured at low current with VDCs verified and monitored at high current with scanners.

17 June 2004HAPPEX-II ExperimentsK. Paschke Beam Requirements PropertyNominalJitter (30 Hz)Hel corr (run) Energy3.2 GeV< 80 ppm< 13 ppb Current100 A< 1000 ppm< 600 ppb Position0< 12 m< 2 nm Angle0< 12 rad< 2 nrad Halo<100 Hz/ 5 mm Specifications driven by sensitivities and estimates of quality of corrections. CASA and EGG have worked closely with HAPPEX to meet these requirements

17 June 2004HAPPEX-II ExperimentsK. Paschke Polarized source Pockels cell voltage (PITA) used to tune A Q, x Intensity Attenuator (IA) PZT mirror IHWP for slow helicity reversal RHWP for control of position/intensity asymmetries Superlattice photocathode: >80% polarization, 100 A

17 June 2004HAPPEX-II ExperimentsK. Paschke Controlling Position Differences Identify and control sources of position differences Intrinsic birefringence gradient in the Pockels cell Steering from distortions due to piezo-electric deformation of the Pockels cell Analyzing power gradients Lisa Kaufman, Brian Humensky, Gordon Cates, Ryan Snyder, Kent Paschke, and the EGG.

17 June 2004HAPPEX-II ExperimentsK. Paschke ITS Laser Room Studies in the laser room conducted over the past year have been crucial in developing our understanding of the sources of position differences. Characterization of Pockels cells on parameters relevant to sources of position differences Identification and characterization of the history effect in optical properties of the Pockels cells Development of alignment techniques to reduce effects from Pockels cell steering

17 June 2004HAPPEX-II ExperimentsK. Paschke Injector Beam Studies Electron beam studies allows studies of effects from the photocathode, as well as other idiosyncratic elements such as vacuum windows. Set points for source elements (PC voltages, rotating waveplate angle) can only be determined from beam data. Injector transmission becomes an important issue in getting the well- tuned beam to the Hall.

17 June 2004HAPPEX-II ExperimentsK. Paschke Phase Trombone Goal: vary betatron phase while preserving the shape and orientation of the phase space ellipse implemented with eight existing quads at the beginning of the Hall A arc Allows for independent betatron phase control in horizontal and vertical planes Uses: Allows one to trade off position and angle differences Periodic phase changes can be used to randomize or reverse the sign of position differences Phase Trombone Setpoint ( x, y ) x ( m) 0.3 m y ( m) 0.3 m x ( rad) 0.01 rad y ( rad) 0.02 rad (0 o,0 o ) (30 o,0 o ) (-30 o,0 o ) (30 o,30 o )

17 June 2004HAPPEX-II ExperimentsK. Paschke HAPPEX Has Started Installation started June 4, optics commissioning done June 9 Luminosity limited by septum heating, improvement possible Progress on beam conditions (Helicity-correlated, Compton halo), spectrometers, detectors, target