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E-158 : A precise measurement of at low

E-158 : A precise measurement of at low. Antonin VACHERET CEA SACLAY PAVI 2004, June 10. The 2 miles long LINAC at SLAC. Physics Motivation Apparatus Control of systematics Analysis Run I+II preliminary results Conclusion. Extracting the weak charge at low.

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E-158 : A precise measurement of at low

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  1. E-158 : A precise measurement of at low Antonin VACHERET CEA SACLAY PAVI 2004, June 10 The 2 miles long LINAC at SLAC

  2. Physics Motivation • Apparatus • Control of systematics • Analysis • Run I+II preliminary results • Conclusion

  3. Extracting the weak charge at low Møller scattering : - Sensitive to: e, Qw Parity violation asymmetry : Tree level Moller asymmetry : Qw

  4. Radiative corrections • 1 loop corrections change the relation between Aee and : 3% corrections to

  5. Projection Sensitivity Aim to measure to 0.001 level 6.5s significance level to radiative corrections effect. 1. Precise measurement away from Z pole complementary to e-e+ colliders 2. Sensitive to new physics scenarii : Z’ (GUT) boson MZ’ ~ 0.8 TeV Electron compositness L ~ 10 TeV

  6. SLAC E158 • SLAC • Smith College • Syracuse • UMass • Virginia • UC Berkeley • Caltech • Jefferson Lab • Princeton • Saclay SLAC A-line Sep 97: EPAC approval 1998-99: Design and Beam Tests 2000: Funding and construction 2001: Engineering run 2002: Physics Runs I, II 2003: Physics Run III ESA

  7. 2,7 GHz scattered Møller • Ee= 45 GeV Flux integration • High Polarization Pe=85% • Aee=PeAexp High density target , see=12 mb L ~ 1038 cm-2s-1 • High intensity • 5x1011 e-/pulse 4 Months to achieve 10% statistical precision • Fast polarization reversal • 120 Hz Experiment principle Raw Asymmetry =1.3x10-7 (130 ppb) D(Apv) = 10-8 (10 ppb) Need 1016 electrons DETECTOR BEAM N+,N- TARGET 4-7 mrad LH2

  8. QE (%) Polarization (%) Wavelength (nm) Polarized beam • Optical pumping : • Helicity sequence : Quadruplet RLLR,LLRR,… Very high-charge polarized electron beams are possible (Pe~85%) • Beam helicity is chosen pseudo-randomly at 120 Hz • Data analyzed as “pulse-pairs”

  9. Liquid Hydrogen target Length 1.54 m Refrigeration capacity 1 kW Beam heat deposit 800W Operating temperature 20K Flow rate 5 m/s

  10. Spectrometer e-e 60 m • Dipole Magnetic chicane cut particles < 10 GeV • Quadrupoles focus Møller electrons • Synchrotron light blocked with Collimators.

  11. Basic Idea: light guide :quartz : copper air shielding PMT Electron Detector • Full Azimuthal acceptance • Radiation hard • Fast pure Cerenkov signal • Insensitive to low energy backgrounds

  12. Statistics and systematics • Integrating counting rate : 1. Additional random fluctuations : affect statistical precison 2. Constant shift : false asymmetry • Origin : beam parameters variations (E,X,Y, qx,qy) Physics backgrounds Electronic crosstalk Pulse pair width ~ 200 ppm Raw asymmetry ~ 150 ppb

  13. Energy dithering region Agreement (MeV) BPM24 X (MeV) energy ~1 MeV BPM12 X (MeV) Precise beam diagnostics • High resolution BPM cavity monitors (energy position, angle) • Toroids (beam current) BPM~2 microns toroid~30 ppm

  14. Minimizing beam asymmetries Natural pulse to pulse jitter : AI~0.5% AE~0.1% Feedback loop (Cumulative) : (run I data) Cumulative asymmetries with feedback on : AI< 200 ppb +/- 5 ppb AE< 20 ppb +/- 3 ppb

  15. Backgrounds controls Flux integration includes various residual backgrounds : False asymmetry eP ring eP asymmetry Dilution effect Flux Radial and azimuthal scans Pion flux and asymmetry

  16. Scattered flux profile • Very good agreement between Flux scans and MC (run I) • Q2 determination : <Q2> = 0.0266 GeV-2 Flux vs radial distance agreement Radial and azimuth agreement e-e e-p

  17. Corrections method Run I: DAPV(regression-dithering) = (3.1 ± 11.8) ppb Run II: DAPV(regression-dithering) = (4.8 ± 4.2) ppb Very good agreement !

  18. Analysis • Blinded asymmetry Raw asymmetry distribution byruns Raw asymmetry distribution by pairs Gaussian over 5 orders of magnitude

  19. Slow reversal Split data in four exclusive states : 1. Insertable Half Wave Plate 2. Energy change 45 -> 48 GeV g-2 precession in A-Line

  20. Systematics summary

  21. Run I+II Preliminary Q2 = 0.027 GeV2): Official Run I result : PRL : hep/ex:0312035 First observation of parity violation in Møller scattering ~ 5 s Run I APV = -175  30 (stat)  20 (syst) ppb Run II APV = -144  28 (stat)  23 (syst) ppb APV = -161  21 (stat)  17 (syst) ppb Run I + II (preliminary)

  22. E158 projected The Weak Mixing Angle sin2eff(Q2=0.026 GeV2) =0.2379 ± 0.0016 ±0.0013 (Run I + II, preliminary) Agreement with theory at the level of uncertainty prediction: 0.2386 ± 0.0006 (stat) (syst) sin2(MZ2)

  23. Physics implication • Parity is violated in Møller scattering • Limit on LL : L+LL >= 7,4 TeV L-LL >= 6,4 TeV • Limits on extra Zs at the level of 700 GeV

  24. Toward the final result • Run III data analysis is being finalized • Preliminary result on full data set very soon • Systematics will improve • Significant complementary constraint on new physics

  25. Conclusion • Preliminary result on APV: -161 ± 21 ± 17 ppb • sin2Weff = 0.2379 ± 0.0016 ± 0.0013 (preliminary) • Inelastic e-p asymmetry at low Q2 consistent with quark picture • First measurement of e-e transverse asymmetry • Preliminary result for all three runs soon ! - 10 ppb statistical error - Systematic error will be less than statistical error

  26. Physics Runs Run 1: Apr 23 12:00 – May 28 00:00, 2002 Run 2: Oct 10 08:00 – Nov 13 16:00, 2002 Run 3: July 10 08:00 - Sep 10 08:00, 2003 • One g-2 flip in each run • /2 flip roughly once in two days • Run I data divided into 24 “slugs” Run 1: Spring 2002 Run 2: Fall 2002 Run 3: Summer 2003 1020Electrons on Target

  27. Higher orders • Beam spotsize : higher moment in residual polarisation effect at the photocathode. • Beam sub pulse fluctuations - Evidences in Run II analysis - monitored during Run III in order to estimate the systematics. - affect the OUT only

  28. Source Photocathode New photocathode from NLC R&D effort. (T. Maruyama et al., Nucl.Instrum.Meth.A492:199-211,2002 ) High doping for 10-nm GaAs surface overcomes charge limit. Low doping for most of active layer yields high polarization. QE (%) Polarization (%) Gradient-doped cathode structure. Wavelength (nm) New cathode Electrons per pulse Old cathode Laser Power (µJ) No sign of charge limit! Very high-charge polarized electron beams are possible. Small anisotropy in strain results in ~3% analyzing power for residual linear polarization.

  29. End Station A setup Target chamber Quadrupoles Detector Cart Concrete Shielding Dipoles Drift pipe 60 m

  30. Regression Dithering Results of corrections cxp pxp cxc pxc Asym width goes form ~500 ppm to 200 ppm Run I: DAPV(regression-dithering) = (3.1 ± 11.8) ppb Run II: DAPV(regression-dithering) = (4.8 ± 4.2) ppb

  31. from APV to sin2qWeff where: is an analyzing power factor; depends on kinematics and experimental geometry. Uncertainty is 1.7%. (y = Q2/s) Fbrem= (0.90 ± 0.01) is a correction for ISR and FSR; (but thick target ISR and FSR effects are included in the analyzing power calculation from a detailed MonteCarlo study) qWeffis derived from an effective coupling constant, geeeff , for the Zee coupling, with loop and vertex electroweak corrections absorbed into geeeff

  32. “ep” Detector Data • Radiative tail of elastic ep scattering is dominant background • 8% under Moller peak • Additional 1% from inelastic e-p scattering • Coupling is large: similar to 3 incoherent quarks • Reduced in Run II with additional collimation

  33. Backgrounds

  34. Polarized Source Laser System IA Feedback Loop POS Feedback Loop IA cell applies a helicity-correlated phase shift to the beam. Piezomirror can deflect laser beam on a pulse-to-pulse basis. The cleanup polarizer transforms this into intensity asymmetry. Can induce helicity-correlated position differences. CID Gun Vault

  35. rf Cavity BPMs for E-158 476 MHz RF Cavity BPM Mixer Rf cavities resonate at 2856 MHz X cavity is TM210 Y cavity is TM120 Q cavity is TM010 “ANALYSIS OF AN ASYMMETRIC RESONANT CAVITY AS A BEAM MONITOR” (David H. Whittum (SLAC), Yury Kolomensky (Caltech). SLAC-PUB-7846; published in Rev.Sci.Instrum.70:2300-2313,1999.)

  36. Beam Performance Delivered (May 2002) Quantity All proposal goals achieved or exceeded

  37. Luminosity Monitor Data • Null test at level of 20 ppb • Target density fluctuations small • Limits on second order effects

  38. Collimators

  39. Pion Detector • ~ 0.5 % pion flux • ~ 1 ppm asymmetry • < 5 ppb correction

  40. Qweak ~4 years Møller Jlab 12 GeV DIS Jlab 12 GeV Future Possibilities Part per billion measurements are now feasible: future measurements could improve sensitivity Challenging experiments E158 (projected) Interest will depend on discoveries (or lack thereof) over the next few years, including LHC

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