E-158 : A precise measurement of sin 2 W at low Q 2 Antonin VACHERET CEA SACLAY PAVI 2004, June 10 The 2 miles long.
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E-158 : A precise measurement of sin 2 W at low Q 2 Antonin VACHERET CEA SACLAY PAVI 2004, June 10 The 2 miles long LINAC at SLAC Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 • • • • • • Physics Motivation Apparatus Control of systematics Analysis Run I+II preliminary results Conclusion Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Extracting the weak charge at low Q 2 Møller scattering : - Sensitive to: e, Qw Parity violation asymmetry : R L M M Z APV R L M 2 Tree level Moller asymmetry : GF 16sin 2 1 2 Aee mE si n W 2 2 (3 c o s ) 4 2 7 Aee (Q 0.03) 3.2 10 2 Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 Qw (320 ppb) PAVI 2004 Radiative corrections • 1 loop corrections change the relation between 2 Aee and sin W: GF 16sin 2 1 2 2 Aee mE (Q ) sin W ... 2 2 2 (3 cos ) 4 1.00122 (Q2 0) 1.03 0.0025 (mZ ) 3% corrections to sin 2 W (M Z )MS Aee 40% !!! Aee Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Sensitivity 2 Aim to measure sin W to 0.001 level 6.5 significance level to radiative corrections effect. Projection 1. Precise measurement away from Z pole complementary to e-e+ colliders 2. Sensitive to new physics scenarii : Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 Electron compositness L ~ 10 TeV Z’ (GUT) boson MZ’ ~ 0.8 TeV PAVI 2004 SLAC E158 •UC Berkeley •Caltech •Jefferson Lab •Princeton •Saclay SLAC Sep 97: 1998-99: 2000: 2001: 2002: 2003: Antonin VACHERET, CEA-Saclay Dapnia/SPhN •SLAC •Smith College •Syracuse •UMass •Virginia EPAC approval Design and Beam Tests Funding and construction Engineering run Physics Runs I, II Physics Run III SLAC E-158 A-line ESA PAVI 2004 Experiment principle Raw Asymmetry =1.3x10-7 (130 ppb) (Apv) = 10-8 (10 ppb) Need 1016 electrons 2,7 GHz scattered Møller BEAM • Ee= 45 GeV TARGET LH2 • High Polarization Pe=85% Aee=PeAexp DETECTOR N+,N4-7 mrad Flux integration High density target , ee=12 mb L ~ 1038 cm-2s-1 • High intensity 5x1011 e-/pulse •Fast polarization reversal 120 Hz Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 4 Months to achieve 10% statistical precision PAVI 2004 • Optical pumping : QE (%) Polarization (%) Polarized beam Wavelength (nm) Very high-charge polarized electron beams are possible (Pe~85%) • Helicity sequence : Quadruplet RLLR,LLRR,… Beam helicity is chosen pseudo-randomly at 120 Hz •Data analyzed as “pulse-pairs” Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Liquid Hydrogen target Length 1.54 m Refrigeration capacity 1 kW Beam heat deposit 800W Operating temperature 20K Flow rate 5 m/s Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Spectrometer e-e 60 m • Dipole Magnetic chicane cut particles < 10 GeV • Quadrupoles focus Møller electrons • Synchrotron light blocked with Collimators. Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Electron Detector Basic Idea: light guide : quartz : copper air shielding • • • • PMT Full Azimuthal acceptance Radiation hard Fast pure Cerenkov signal Insensitive to low energy backgrounds Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Statistics and systematics • Integrating counting rate : Aexp NR NL NR NL Pulse pair width ~ 200 ppm Raw asymmetry ~ 150 ppb 1. Additional random fluctuations : affect statistical precison 2. Constant shift : false asymmetry • Origin : beam parameters variations (E,X,Y, x,y) Physics backgrounds Electronic crosstalk Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Precise beam diagnostics Aexp AN AI AE i X i Energy dithering region BPM24 X (MeV) • High resolution BPM cavity monitors (energy position, angle) • Toroids (beam current) BPM ~2 microns toroid ~30 ppm Agreement (MeV) energy ~1 MeV BPM12 X (MeV) Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Minimizing beam asymmetries Natural pulse to pulse jitter : AI~0.5% Feedback loop (Cumulative) : AE~0.1% (run I data) Cumulative asymmetries with feedback on : AI< 200 ppb +/- 5 ppb Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 AE< 20 ppb +/- 3 ppb PAVI 2004 Backgrounds controls Flux integration includes various residual backgrounds : APV 1 Araw fbkg Abkg Pb fnorm False asymmetry eP ring Dilution effect Flux Radial and azimuthal scans Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 eP asymmetry Pion flux and asymmetry PAVI 2004 Scattered flux profile • Very good agreement between Flux scans and MC (run I) Flux vs radial distance agreement e-e Radial and azimuth agreement e-p • Q2 determination : <Q2> = 0.0266 GeV-2 Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Corrections method Run I: APV(regression-dithering) = (3.1 ± 11.8) ppb Run II: APV(regression-dithering) = (4.8 ± 4.2) ppb Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 Very good agreement ! PAVI 2004 Analysis Raw asymmetry distribution by runs Raw asymmetry distribution by pairs Gaussian over 5 orders of magnitude • Blinded asymmetry Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Slow reversal 1. Insertable Half Wave Plate Split data in four exclusive states : 2. Energy change 45 -> 48 GeV g-2 precession in A-Line Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Systematics summary Source Run I + II DA (ppb) Dilution Beam 1st order 0 +/- 2 - Beam 2nd order 0 +/- 9 - Transverse polarization -12 +/- 2 - eP Background -30 +/- 5 0.071 +/- 0.008 High energy 3 +/- 3 0.004 +/- 0.002 Synchrotron 0 +/- 2 0.0015 +/- 0.0005 Neutrons -2.5 +/- 1.5 0.0015 +/- 0.0005 Pions 0.5 +/- 0.8 0.0014 +/- 0.0011 Normalization factors Polarimetry 0.847 +/- 0.046 Geometry 0.989 +/- 0.011 Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 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 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) Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 The Weak Mixing Angle sin2eff(Q2=0.026 GeV2) = 0.2379 ± 0.0016 ±0.0013 (syst) (Run I + II, preliminary) (stat) Agreement with theory at the level of uncertainty prediction: 0.2386 ± 0.0006 sin2(MZ2) E158 projected Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Physics implication • Parity is violated in Møller scattering • Limit on LLL : L+LL >= 7,4 TeV L-LL >= 6,4 TeV • Limits on extra Zs at the level of 700 GeV Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 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 Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Conclusion – Preliminary result on APV: -161 ± 21 ± 17 ppb – sin2Weff = 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 Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 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 1020 Electrons on Target Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 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 Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Source Photocathode New photocathode from NLC R&D effort. (T. Maruyama et al., Nucl.Instrum.Meth.A492:199-211,2002 ) Electrons per pulse QE (%) Low doping for most of active layer yields high polarization. Gradient-doped cathode structure. Polarization (%) High doping for 10-nm GaAs surface overcomes charge limit. Wavelength (nm) New cathode No sign of charge limit! Very high-charge polarized electron beams are possible. Old cathode Antonin VACHERET, CEA-Saclay LaserDapnia/SPhN Power (µJ)SLAC E-158 Small anisotropy in strain results in ~3% analyzing power for residual linear polarization. PAVI 2004 End Station A setup Target chamber Quadrupoles Concrete Shielding Detector Cart Dipoles Drift pipe 60 m Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Results of corrections Regression c xp pxp c xc pxc Dithering Asym width goes form ~500 ppm to 200 ppm Run I: APV(regression-dithering) = (3.1 ± 11.8) ppb Run II: APV(regression-dithering) = (4.8 ± 4.2) ppb Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 from APV to sin2Weff APV GF Q 2 1 y 2 eff F 1 4 sin brem W 4 4 2 1 y 4 1 y where: is an analyzing power factor; depends on GF Q 2 1 y 4 kinematics and experimental geometry. 4 2 1 y 4 1 y 2 Uncertainty is 1.7%. (y = Q /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) Weff is derived from an effective coupling constant, geeeff , for the Zee coupling, with loop and vertex electroweak corrections absorbed into geeeff Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 “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 Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Backgrounds Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Polarized Source Laser System IA Feedback Loop IA cell applies a helicity-correlated phase shift to the beam. The cleanup polarizer transforms this into intensity asymmetry. Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 POS Feedback Loop Piezomirror can deflect laser beam on a pulse-to-pulse basis. Can induce helicity-correlated position differences. PAVI 2004 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.) Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Beam Performance Quantity Delivered (May 2002) Quantity Run 1 Achieved AQ Alcove: 219 ± 319 ppb (AQ) -8.4 ± 7.8 ppb* Electrons / pulse 6 x 1011 @ 45 GeV, 3.5 x 1011 @ 48 GeV Rep. rate 120 Hz Intensity jitter 0.5% AE -0.1 ± 1.4 keV -1.2 ± 14.8 ppb Position jitter 50 µm (AE) -0.01 ± 0.24 keV 0.05 ± 2.6 ppb Spot size jitter 5% of spot size (x, y)target (-16.6 ± 5.6 nm, -3.1 ± 4.0 nm) Energy jitter 0.03% rms (x, y)target (1.0 ± 0.6 nm, -0.01 ± 0.9 nm) Energy spread 0.1% rms (x, y)angle (15.9 ± 9.4 nm, 4.8 ± 2.7 nm) Polarization (85 ± 5)% (x, y)angle (-2.7 ± 2.0 nm, 0.9 ± 1.0 nm) Efficiency ~(65-70)% (x, y)spotsize (0.7 ± 1.9 nm, -1.7 ± 1.9 nm) All proposal goals achieved or exceeded Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Luminosity Monitor Data •Null test at level of 20 ppb • Target density fluctuations small • Limits on second order effects Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Collimators Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Pion Detector •~ 0.5 % pion flux •~ 1 ppm asymmetry •< 5 ppb correction Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 PAVI 2004 Future Possibilities Part per billion measurements are now feasible: future measurements could improve sensitivity Challenging experiments Interest will depend on discoveries (or lack thereof) over the next few years, including LHC Antonin VACHERET, CEA-Saclay Dapnia/SPhN SLAC E-158 Qweak E158 ~4 years (projected) Møller Jlab 12 GeV DIS Jlab 12 GeV PAVI 2004