Kazutaka Nakahara KEK for the G 0 Collaboration: Caltech, Carnegie-Mellon, William&Mary, Grinnell College, Hampton, IPN-Orsay, LPSN-Grenoble, JLab, Kentucky, LaTech, NMSU, TRIUMF, UIUC, U Manitoba, U Maryland, UNBC, U Winnipeg, VPI, Yerevan The G 0 Experiment Strange quark contribution to proton structure SPIN2006 Kyoto 10/6/2006

s quark contribution Proton and neutron EM form factors (assuming charge symmetry): Neutral Weak form factor: Measure G Z,p !!! Flavor Decomposition of Nucleon Form Factors Spin2006 Kyoto 10/6/06 Determine s quark contribution to the charge and magnetization distribution of the proton

Parity Conserving Parity Violating Measure at forward angles (elastic e-p) Measure at backward angles (elastic e-p and quasi-elastic e-d) Parity Violating Electron-Proton Scattering Spin2006 Kyoto 10/6/06

Jefferson Laboratory A B C Injector/Source linacs

Forward Angle Apparatus Forward angle mode: Q 2 = 0.12 ~  A longitudinally polarized beam. 32MHz repetition rate for TOF. Helicity flip at 30 Hz (macro-pulse, MPS), arranged into quartet pattern. High power LH 2 target. Capable of maintaining stable temperature/density with high power deposit. 8 octant superconducting toroidal magnet, array of 16 scintillator pairs per octant. Different scintillator  Different Q 2. Distinguish elastic protons from background through TOF separation. Fast electronics counting individual particle. lead collimators elastic protons detectors target beam Spin2006 Kyoto 10/6/06 Backward angle mode: Q 2 = 0.23 and  A longitudinally polarized beam. 499MHz repetition rate  no TOF Helicity flip at 30 Hz (macro-pulse, MPS), arranged into quartet pattern. High power LH 2 & LD target. 8 octant superconducting toroidal magnet. 8 octant, array of 16 scintillator pairs per octant. Additional detectors (Cerenkov, CED) for background (pion) rejection. FPD-CED matrix electronic/detector package  separate elastics from background. Target Scintillator Detector Superconducting Coils Backward Angle Apparatus

G 0 beam monitoring Superconducting Magnet (SMS) Detectors (Ferris wheel) FPD Spokesman Target service module G0 in Hall C : The key elements Detectors (Mini-Ferris wheel) CED+Cherenkov

Forward Angle Data Successful run in spring 2004 Different components separated by t.o.f. Beam systematics understood: % polarization -small helicity- correlation -effect of leakage beam understood Background under elastic peak is main analysis issue Corresponds to: 701 h at 40  A (100 C) 19 x 10 6 quartets 76 x 10 6 MPS Spin2006 Kyoto 10/6/06

Strange Quark Contribution to Proton

, Q 2 = 0.1 GeV 2 =  GEGE s GMGM s =  0.31 Contours 1 , 2  68.3, 95.5% CL Theories 1.Leinweber, et al. PRL 94 (05) Lyubovitskij, et al. PRC 66 (02) Lewis, et al. PRD 67 (03) Silva, et al. PRD 65 (01) GEGE s GMGM s

., Q 2 = 0.1 GeV 2 GEGE s GMGM s HAPPEx He HAPPEx calculation: Q 2 = 0.1 GeV 2 G M = 0.28 ± 0.20 s G E = ± s

G 0 Backward Angle Status Q 2 = 0.23 and 0.62 GeV 2 /c 2 March 15 – May 1: 0.62 GeV 2 /c hours LH 2, 50 hours LD 2 (at 10  A) - 80 hours “parity quality” data w/ LH2 at 60  A May15-18: 0.23 GeV 2 /c 2 - first look at LD 2 at low beam current - outstanding beam delivery July 19- Sept 1 (0.23) / Sept 22- Dec 22 (0.62) production First hand look at data so far: - Elastic asymmetry near expected - good elastic/inelastic electron separation - pion asymmetry smaller than elastic - Deuterium data shows high background rates in Cerenkov (probably neutrons)

Summary Forward angle production run successfully completed Results published Phys. Rev. Lett. 95, (2005) i.Interesting Q 2 -dependence for the strange quark contribution to the nucleon form factors ii.Agreement at low Q 2 with previous experiments Backward angle measurement has begun! Spin2006 Kyoto 10/6/06

Backup

Summary of Systematic Effects SourceUncertainty Electronics deadtime0.05 ppm Helicity-correlated differences in beam properties 0.01 ppm 499 MHz (2 ns) leakage beam0.14 ppm Beam polarization (Hall C Møller)1 % Transverse beam polarization0.01 ppm Inelastic background subtraction0.2-9 ppm Radiative corrections0.3 % Detector  Q 2  1 %

G0 in Hall C beam monitoring girder superconducting magnet (SMS) scintillation detectors cryogenic supply cryogenic target ‘service module’ electron beamline

Strange Quark Contribution to Proton Armstrong, et al. PRL 95 (2005)

Analysis Overview A phys +  GEGE s GMGM s Blinding Factor Raw Asymmetries, A meas “Beam” corrections: Leakage beam asymmetry Helicity-correlated beam properties Deadtime Beam polarization Background correction Q2Q2 Elastic form factors Unblinding

Helicity-Correlated Beam Parameters 1.How much does the yield change when the beam “moves”?  understood (simulation & data agree) 2.‘Instrumental’ (false) asymmetries –e.g. if beam current changes in helicity-correlated manner –e.g. if beam position on target changes in helicity-correlated manner Helicity-correlated change Correction X position 3  4 nm ~ 1 ppb X angle 1  1 nr ~ few ppb Y position 4  4 nm ~ 1 ppb Y angle 1.5  1 nr ~ 10 ppb Beam energy 29  4 eV ~ 1 ppb Beam current  0.32 ppm ~ 10 ppb False asymmetries from helicity- correlated parameters small (~10 -8 ) compared to physics asymmetry (~10 -5 – )

Strange quark contribution to asymmetry depends on: - A NVS = No vector strange asymmetry - EM form factors (Kelly parametrization) Strange Quark Contribution

Strange Quark Contribution to Proton

Where Were We? From HAPPEX H preprint nucl-ex/ Similar angular kinematics to G 0

Polarized source and beam High polarization has been reached routinely using superlattice GaAs cathodes New Fiber laser for Hall C (adjustable pulse repetition rate) Allows flexible time structure (1-2h for setting) : 32 ns used for Cherenkov study 780 nm is at polarization peak (P ~ 85%) for superlattice GaAs 60  A of low energy beam New optics, beam dump and halo issue handled Moeller polarimeter in Hall C Energy smaller than 800 MeV (design) Need to move quadrupoles closer to target Difficult tune (beam position, magnet settings) Finally successful at 686 MeV 1 um foil = /- 0.36% (stat) 4 um foil = /- 0.33% (stat) Systematic error  2 %, expected to be reduced New features and specificities

Commissioning (I) Beam properties Hall C instrumentation OK Beam properties 35 h IN and 42 h OUT at 60  A (LH 2 ) Adiabatic damping, PITA, RWHP, IA Room for improvement (position feedback) Halo within a 6 mm diameter was determined to be < 0.3 x (spec : ) Target and Lumi detectors LH 2 and LD 2 target (“Flyswatter” and gas target for cell contribution) Target boiling from Lumi detectors Intensity up to 60  A (limitation by window on beam dump) Very flat behavior (rates/beam current) Ratio LD2:LH2:C12 are the ones expected Beam Param. Achieved in G 0 (IN-OUT) Spec s Charge asym.-0.4 ± 0.24 ppm 2 ppm X-Y position diff ± 5 nm40 nm X-Y angle diff.-2 to -4 ± 2 nrad 4 nrad Energy diff.2 ± 4 eV 30 eV

Pions 60  A, LH 2 10  A, LD 2 Particle ID : CED-FPD + Cherenkov (rates in Hz/  A per octant) Electrons

Loss/random issue Fraction (%) of loss  I LH 2 60  A LD 2 10  A Fraction (%) of random  I 2

Asymmetries : Electron plane and LH 2 INOUT

Asymmetries : Electron plane and LH 2 INOUT

Data taking in 2006 (I) First period of running at 682 MeV Commissioning and data taking … in a row !!  As usual a risky business and a scary/tough period !! Many new features handled successfully Beam : low energy … but no compromise on intensity and Parity Quality New settings (polarimeter, target, …) New set-up (CED, Cherenkov, electronics …) Analysis underway (remember this ended … 15 days ago !!) Remained to be fixed for running in the Fall Work/tests underway to reach 60  A with LD 2 Cherenkov (anode current and random coincidences)  Gas flow in diffusion box (Ar (not working), CO 2 ), gain/HV reduction, M > 2 CED-FPD (random/loss)  Use backplane scintillators of FPD counters (factor 10 reduction)

G0 Backward angle … What’s next in 2006 Still a long way to go … and maybe some new challenges at 362 MeV Adiabatic damping Halo issue (if due to processes in residual gas) Test run underway this week at JLab More work on Moeller polarimeter Hopefully by the end of 2006 … +

Lab Update Slides – Sept. 15

G0 362 MeV Update D. Beck UIUC Sept. 06 Hydrogen data taking at 362 MeV completed –86 C out of ~ 120 C possible as scheduled –170 C proposed: 80  A for 30 d 75% polarization proposed, 84% delivered Very clean hydrogen elastic signal –all backgrounds total ~ 5-10% Deuterium test run (May) CED Rate (kHz/  A) Hydrogen data (Aug.) FPD (quasi) elastic electrons

G0 362 MeV: Deuterium Tests High singles rates in Cherenkov detectors with deuterium target –traced to low energy neutrons capturing in boroscilicate glass PMT windows: B(n,  )Li –measurements at NIST, Grenoble confirm effect each  produces 6 p.e. –recalibration of NIST neutron beam flux (10 p.e. → 6 p.e.) –PMTs with quartz windows reduce counting rates for ~thermal neutrons by x100 (NIST, Grenoble) Based on July/August testing –various combinations of 5 in. boroscilicate and 2 in. boroscilicate and quartz tubes –extrapolate from comparison of LH 2 and C targets –with new 5 in. quartz tubes for Cherenkov detectors: bottom line Expect 0.5 – 1.5 x LH 2 rate (→ successful run) Successful reduction of FPD accidentals (x4) –alternate front and back tubes

362 MeV Beam Helicity-correlated beam properties well within spec MeasuredSpec Charge symmetry 0.03±0.12 ppm 2 ppm X position difference -12±4 nm40 nm Y position difference 1±4 nm40 nm Beam polarization –measurement with Moller not feasible std. solenoid field not compatible with beam transport chkd longitudinal polarization –concurrent Hall A, Mott measurements at beginning of run –periodic Mott measurements throughout run individual measurements average ~84±1.5%

G0 362 MeV Online LH 2 Asymmetries Low backgrounds (5-10%), small deadtimes (4-8%) BLINDED online results –fraction of data set –no corrections for h.c. beam parameters, deadtime, …

G0 362 MeV Online LH 2 Asymmetries Elastic Background P R E L I M I N A R Y Octant

Low backgrounds (5-10%), small deadtimes (4-8%) BLINDED online results –fraction of data set –no corrections for h.c. beam parameters, deadtime, … G0 362 MeV Online LH 2 Asymmetries Also measured asymmetry with transverse polarization to correct longitudinal asymmetry –beam angle limited to ~ 50 mr from longitudinal –asymmetry in octant azimuthal scattering angles limited to ~ 20 mr –correction < 0.1 ppm

G0 362 MeV LH 2 Transverse Asymmetry BLINDED online results –no corrections for h.c. beam parameters, deadtime, … Transverse: Elastic P R E L I M I N A R Y Octant

Outlook for 687 MeV Direct resumption of production data-taking as soon as halo/background from April restored Lower accidental rates in FPDs (as in summer run) Expect switch to LD 2 near end of October (as soon as tubes arrive –possible LD 2 test (~ 2 days) in early October to finalize plans for trigger with new Cherenkov tubes Expect near 100 C of data for both LH 2 and LD 2 at 687 MeV assuming –Cherenkov tubes arrive before end of October –rate projections for LD 2 correct