Presentation on theme: "Robert J. Feuerbach Jefferson Lab Constructed from contributions from the HAPPEX Collaboration Hall A Collaboration Meeting December 5, 2005 HAPPEX-II."— Presentation transcript:
Robert J. Feuerbach Jefferson Lab Constructed from contributions from the HAPPEX Collaboration Hall A Collaboration Meeting December 5, 2005 HAPPEX-II Status Report
Strange-form factors At Q 2 =0.11 GeV 2, A PV can access Hydrogen: (G s E G s M ) Helium:G s E
How is the PV Asymmetry Measured? Beam Helicity - 30 Hz 1 ppm: 5% measurement > 4x10 14 counts PV asymmetry between window pair is measured. 34M (He) and 24M (H) good pairs collected.
Beam Asymmetries A raw = A det - A Q + E + i x i natural beam jitter (regression) beam modulation (dithering) Slopes from
Target Spectrometer: QQDQ Hall A Cherenkov cones PMT Compton Moller Polarimeters
The Goal 2004: Helium A PV : ~ 0.84 ppm (11.2%) Hydrogen A PV : ~ 0.24 ppm (17%) The goal was to improve on the error bars of last year by a factor of ~3. This required higher luminosity similar to the previous years tight control over systematics uncertainties.
Some Improvements for this year Sweeper Magnet –I b He :28uA to 36uA –I b H :35uA to 58uA S0 trigger Beam quality In development: –Integrating Compton –Cavity monitors
Run Summary Helium E b =2.75 GeV Scheduled: 48 days Actual: 55 days July 9 – Aug 7 Aug 7 – Aug 31 July 28 – Sept 1 Sept 9 – Sept 27 Late start due to installation sweeper/septum and spectrometer commissioning beamline commissioning Hydrogen E b =3.18 GeV Scheduled: 39 days Actual: 36 days Oct 15 – Nov 23 Oct 16 – Nov 21 Last day for PREx tests ~18 day parasitic extension (to Hall C) was very important
Auxiliary Studies Al (target wall) Backgrounds: ~1.8% (He), ~0.7% (H) Inelastics (quasi-elastic) Rescattering probability with dipole scan He: Prelim estimate: <2% He QE, ~1.8% Al, <0.6% rescatter H: Prelim estimate: ~0.7% Al, <0.2% rescatter Q 2 measurement (scans, Counting DAQ, optics, angle) Polarimetry: Compton and Moller in good agreement
Optics with Sweeper Sweeper induces ~simple shifts of phi and Z. Angle found with nuclear-recoil method.
Polarimetry Results Helium Discrepancy of ~0.6% in the transfer function (LvsR) compared to last year and last absolute measurement in Will be opening up the Compton to re-measure the transfer function to understand the effect.
New Challenges Electronics pickup between an (unconnected) helicity module and magnet controls –100nm beam-position difference Transverse asymmetry –~3% vertical polarization, He A T ~ 13 ppm -> suggests 0.8 ppm difference –A L – A R is large (0.9 ppm), with correct sign! Compton power dropped 1200W ->300W –cleaning optics brought it to 500W –excellent beam quality resulted in ~20 S/B
Physics Asymmetry Hydrogen Helium A PV : ~ 0.21 ppm (3.5%) G E s : ~ : A PV : ~ 0.84 ppm (11.2%) G E s : ~ A PV : ~ 0.12 ppm (8%) G E s G M s : ~ : A PV : ~ 0.24 ppm (17%) G E s G M s : ~ NOTE: Statistical error only! Systematic error will likely increase Helium error bar by ~40%, and Hydrogen by about 25%
Impact of the Measurement 2 = 1 95% c.l. He: nucl-ex/ (reviewed and recommended for PRL) H: nucl-ex/ (under revision for submission to PL)
Future Analysis is beginning (continuing). Knowledge transfer to next generation of students Next collaboration meeting in late February P-REX and HAPPEX-3 will benefit greatly from high current/high beam polarization now available: 80% vs. 71% Manpower needed for the Compton upgrade. –data in ~2008, graduate 2009?