The G 0 Experiment Strange quark contribution to proton structure

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The G 0 Experiment Strange quark contribution to proton structure. Kazutaka Nakahara KEK for the G 0 Collaboration: - PowerPoint PPT Presentation

Text of The G 0 Experiment Strange quark contribution to proton structure

  • Kazutaka NakaharaKEK

    for the G0 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 G0 ExperimentStrange quark contribution to proton structureSPIN2006 Kyoto 10/6/2006

  • Proton and neutron EM form factors (assuming charge symmetry):Flavor Decomposition of Nucleon Form FactorsSpin2006 Kyoto 10/6/06Determine s quark contribution to the charge and magnetization distribution of the proton

  • Parity Violating Electron-Proton ScatteringSpin2006 Kyoto 10/6/06

  • Jefferson LaboratoryABCInjector/Sourcelinacs

  • Forward Angle ApparatusForward angle mode: Q2 = 0.12 ~ 1.040A longitudinally polarized beam. 32MHz repetition rate for TOF. Helicity flip at 30 Hz (macro-pulse, MPS), arranged into quartet pattern. High power LH2 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 Q2. Distinguish elastic protons from background through TOF separation. Fast electronics counting individual particle.Spin2006 Kyoto 10/6/06

  • G0 beammonitoring Superconducting Magnet (SMS) Detectors (Ferris wheel)FPDSpokesmanTarget service moduleG0 in Hall C : The key elements Detectors (Mini-Ferris wheel)CED+Cherenkov

  • Forward Angle DataSuccessful run in spring 2004Different components separated by t.o.f.Beam systematics understood:73.7 % polarizationsmall helicity-correlationeffect of leakage beam understoodBackground under elastic peak is main analysis issueCorresponds to:701 h at 40 A (100 C)19 x 106 quartets76 x 106 MPSSpin2006 Kyoto 10/6/06

  • Strange Quark Contribution to Proton

  • , Data @ Q2 = 0.1 GeV2 -0.013 0.028 = +0.62 0.31 Contours

    1s, 2s 68.3, 95.5% CL

    TheoriesLeinweber, et al. PRL 94 (05) 212001Lyubovitskij, et al. PRC 66 (02) 055204Lewis, et al. PRD 67 (03) 013003Silva, et al. PRD 65 (01) 014016

  • HAPPEx calculation: Q2 = 0.1 GeV2

    . , Data @ Q2 = 0.1 GeV2HAPPEx He

  • G0 Backward Angle StatusQ2 = 0.23 and 0.62 GeV2/c2 March 15 May 1: 0.62 GeV2/c2 - 200 hours LH2, 50 hours LD2 (at 10 A) - 80 hours parity quality data w/ LH2 at 60 A May15-18: 0.23 GeV2/c2 - first look at LD2 at low beam current - outstanding beam delivery July 19- Sept 1 (0.23) / Sept 22- Dec 22 (0.62) productionFirst 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, 092001 (2005)Interesting Q2-dependence for the strange quark contribution to the nucleon form factorsAgreement at low Q2 with previous experiments

    Backward angle measurement has begun!Spin2006 Kyoto 10/6/06

  • Backup

  • Summary of Systematic Effects

    SourceUncertaintyElectronics deadtime0.05 ppmHelicity-correlated differences in beam properties0.01 ppm499 MHz (2 ns) leakage beam0.14 ppmBeam polarization (Hall C Mller)1 %Transverse beam polarization0.01 ppmInelastic background subtraction0.2-9 ppmRadiative corrections0.3 %Detector Q21 %

  • G0 in Hall Cbeammonitoring girdersuperconducting magnet (SMS)scintillation detectorscryogenic supplycryogenic target service moduleelectron beamline

  • Strange Quark Contribution to Proton Armstrong, et al. PRL 95 (2005) 092001

  • Analysis Overview

  • Helicity-Correlated Beam ParametersHow much does the yield change when the beam moves? understood (simulation & data agree)Instrumental (false) asymmetriese.g. if beam current changes in helicity-correlated mannere.g. if beam position on target changes in helicity-correlated mannerFalse asymmetries from helicity-correlated parameters small (~10-8) compared to physics asymmetry (~10-5 10-6)

    Helicity-correlated changeCorrectionX position3 4 nm~ 1 ppbX angle1 1 nr~ few ppbY position4 4 nm~ 1 ppbY angle1.5 1 nr~ 10 ppbBeam energy29 4 eV~ 1 ppbBeam current-0.14 0.32 ppm~ 10 ppb

  • Strange Quark ContributionStrange quark contribution to asymmetry depends on:- ANVS = No vector strange asymmetry- EM form factors (Kelly parametrization)

  • Strange Quark Contribution to Proton

  • Where Were We?From HAPPEX H preprint nucl-ex/0506011Similar angular kinematics to G0

  • 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 mA of low energy beam New optics, beam dump and halo issue handledMoeller 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 = -86.36 +/- 0.36% (stat) 4 um foil = -85.94 +/- 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 mA (LH2) Adiabatic damping, PITA, RWHP, IA Room for improvement (position feedback) Halo within a 6 mm diameter was determined to be < 0.3 x 10-6 (spec : 10-6 ) Target and Lumi detectors LH2 and LD2 target (Flyswatter and gas target for cell contribution) Target boiling from Lumi detectors Intensity up to 60 mA (limitation by window on beam dump) Very flat behavior (rates/beam current) Ratio LD2:LH2:C12 are the ones expected

    Beam Param.Achieved in G0(IN-OUT)Specs Charge asym. -0.4 0.24 ppm2 ppmX-Y position diff.20-24 5 nm40 nm X-Y angle diff.-2 to -4 2 nrad4 nrad Energy diff.2 4 eV30 eV

  • Pions 60 mA, LH210 mA, LD2Particle ID : CED-FPD + Cherenkov(rates in Hz/mA per octant)Electrons

  • Loss/random issueFraction (%) of loss ILH260 mALD210 mAFraction (%) of random I2

  • Asymmetries : Electron plane and LH2

  • Asymmetries : Electron plane and LH2

  • 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 mA with LD2 Cherenkov (anode current and random coincidences) Gas flow in diffusion box (Ar (not working), CO2), gain/HV reduction, M > 2 CED-FPD (random/loss) Use backplane scintillators of FPD counters (factor 10 reduction)

  • G0 Backward angle Whats next in 2006Still 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 polarimeterHopefully by the end of 2006 +

  • Lab Update Slides Sept. 15

  • G0 362 MeV UpdateHydrogen data taking at 362 MeV completed86 C out of ~ 120 C possible as scheduled170 C proposed: 80 mA for 30 d75% polarization proposed, 84% delivered

    Very clean hydrogen elastic signalall backgrounds total ~ 5-10%D. Beck UIUCSept. 06Deuterium test run (May)CEDRate (kHz/mA)Hydrogen data (Aug.)FPD(quasi) elastic electrons

  • G0 362 MeV: Deuterium TestsHigh singles rates in Cherenkov detectors with deuterium targettraced to low energy neutrons capturing in boroscilicate glass PMT windows: B(n,a)Limeasurements at NIST, Grenoble confirm effecteach a produces 6 p.e.recalibration of NIST neutron beam flux (10 p.e. 6 p.e.)PMTs with quartz windowsreduce counting rates for ~thermal neutrons by x100 (NIST, Grenoble)

    Based on July/August testingvarious combinations of 5 in. boroscilicate and 2 in. boroscilicate and quartz tubesextrapolate from comparison of LH2 and C targetswith new 5 in. quartz tubes for Cherenkov detectors: bottom lineExpect 0.5 1.5 x LH2 rate ( successful run)Successful reduction of FPD accidentals (x4)alternate front and back tubes

  • 362 MeV BeamHelicity-correlated beam properties well within specBeam polarizationmeasurement with Moller not feasiblestd. solenoid field not compatible with beam transportchkd longitudinal polarizationconcurrent Hall A, Mott measurements at beginning of runperiodic Mott measurements throughout runindividual measurements average ~841.5%

  • G0 362 MeV Online LH2 AsymmetriesLow backgrounds (5-10%), small deadtimes (4-8%)BLINDED online results fraction of data setno corrections for h.c. beam parameters, deadtime,

  • G0 362 MeV Online LH2 AsymmetriesElasticBackgroundP R E L I M I N A R YOctantOctant

  • G0 362 MeV Online LH2 AsymmetriesLow backgrounds (5-10%), small deadtimes (4-8%)BLINDED online results fraction of data setno corrections for h.c. beam parameters, deadtime,

    Also measured asymmetry with transverse polarization to correct longitudinal asymmetrybeam angle limited to ~ 50 mr from longitudinalasymmetry in octant azimuthal scattering angles limited to ~ 20 mrcorrection < 0.1 ppm

  • G0 362 MeV LH2 Transverse AsymmetryBLINDED online results n