17 June 2004HAPPEX-II ExperimentsK. Paschke The Second Generation HAPPEX Experiments Kent Paschke...
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Transcript of 17 June 2004HAPPEX-II ExperimentsK. Paschke The Second Generation HAPPEX Experiments Kent Paschke...
17 June 2004 HAPPEX-II Experiments K. Paschke
The Second Generation HAPPEX Experiments
Kent Paschkefor
The HAPPEX Collaboration
California State University, Los Angeles - Syracuse University -DSM/DAPNIA/SPhN CEA Saclay - Thomas Jefferson National Accelerator
Facility - INFN, Rome - INFN, Bari - Harvard - Indiana University -University of Virginia - University of Massachusetts - Florida
International University - University of New Hampshire - MassachusettsInstitute of Technology - College of William and Mary in Virginia
(Thanks to Rich Holmes for .ppt from PAVI ’04)
17 June 2004 HAPPEX-II Experiments K. Paschke
● Spin
● Longitudinal momentum
● Strange mass
● Strange vector FF
Strangeness in the Nucleon
17 June 2004 HAPPEX-II Experiments K. Paschke
PVES
Leading contribution to parity-violating scattering asymmetry is from interference of EM and weak exchange amplitudes
17 June 2004 HAPPEX-II Experiments K. Paschke
PVES and strange form factorsFor hydrogen:
=> Measurement of APV yields linear combination of Gs
E, Gs
M
Related at Q2=0 to s,
s.
17 June 2004 HAPPEX-II Experiments K. Paschke
The HAPPEX Experiments
● A look back: HAPPEX, ep Q2=0.5 (GeV/c)2
● HAPPEX-H: ep, Q2=0.1 (GeV/c)2
● HAPPEX-He: e 4He, Q2=0.1 (GeV/c)2
● PREX: ePb, Q2=0.01 (GeV/c)2
17 June 2004 HAPPEX-II Experiments K. Paschke
A look back: HAPPEX
Hall A Proton Parity Experiment (E91-010)
ep at Q2=0.5 (GeV/c)2, 12.3 degrees
GsE + 0.392Gs
M = 0.014 ± 0.020 (exp) ± 0.010 (FF)
Phys. Rev. Lett. 82:1096-1100,1999;Phys. Lett. B509:211-216,2001;
Detailed paper accepted for PRC - arXiv nucl-ex/0402004
17 June 2004 HAPPEX-II Experiments K. Paschke
HAPPEX results
APV = -14.92 ppm ± 0.98 (stat) ppm ± 0.56 (syst) ppm
17 June 2004 HAPPEX-II Experiments K. Paschke
The next step
● Increase sensitivity● Choose different Q2 range
● Separate GsE , Gs
M
=> Two new experiments at smaller Q2
17 June 2004 HAPPEX-II Experiments K. Paschke
HAPPEX-H (JLAB E99-115)
● Polarized e- on 1H● Q2 = 0.1 (GeV/c)2, LAB = 6● APV = 1.6 ppm
● A = 5% (stat) + 2.5% (syst)
=> 80 ppb (stat) + 40 ppb (syst)
17 June 2004 HAPPEX-II Experiments K. Paschke
Helium and strange form factors
For helium:
=> APV sensitive only to GsE
17 June 2004 HAPPEX-II Experiments K. Paschke
HAPPEX-He (JLAB E00-114)
● Polarized e- on 4He● Q2 = 0.1 (GeV/c)2, LAB=6● APV = 8.4 ppm
● A = 2.2% (stat) + 2.1% (syst)
=> .18 ppm (stat) + .18 ppm (syst)
17 June 2004 HAPPEX-II Experiments K. Paschke
Tough new measurement: How do you do it?
•Small forward angle => new Septum magnets
•High statistical precision => Thick new targets, high current, rad-hard integrating detectors, improved DAQ, new photocathode
•High relative accuracy => improved polarimetry, new integrating focal plane profile scanner
•High systematic accuracy => improved polarized source, close attention to beam optics, lumi monitor.
17 June 2004 HAPPEX-II Experiments K. Paschke
Septum magnets
● Minimum scattering angle 12.5° -> 6.0°● Installed and commissioned 2003-2004
17 June 2004 HAPPEX-II Experiments K. Paschke
100 x 600 mm
12 meter dispersion sweeps away inelastic events
‘L’ geometry design Hydrogen geometryCerenkov detectors overlap the elastic
line above the focal plane :
HAPPEX-H Detector geometry
He detector = (H detector) / 2 !
17 June 2004 HAPPEX-II Experiments K. Paschke
Brass-quartz stack
Light guide Filter box
PMT
Assembly at Saclay
17 June 2004 HAPPEX-II Experiments K. Paschke
Luminosity monitors● Target boiling● Beam parameters● Electronics noise
Tested to ~200 ppm resolution,expecting about ~100 ppm
Current A
pp
m
17 June 2004 HAPPEX-II Experiments K. Paschke
Target cells"Beer can" – 15 cm, worked well for HAPPEX-I
New "race track" design – 20 cm, boiling untested
17 June 2004 HAPPEX-II Experiments K. Paschke
Luminosity Fluctuations● Beer can cells good enough, as measured in HAPPEX● “Racetrack” cells never tried (Transverse flow good,
curvature of window bad)● Cold (6.6K), dense (230 psi) cryogenic 4He gas target…
“boils”!
Widths go down with increasing raster…
… and UP with increasingcurrent!
17 June 2004 HAPPEX-II Experiments K. Paschke
● Møller: Main uncertainty is foil polarization; p/p = 3 – 3.4% expected
● Compton: Added electron recoil detector since HAPPEX-I; p/p = 2% in ~1 hour seen – 1.3% probably achievable at 3 GeV
Polarimetry
● Big challenge for PREX – high current, low energy. Plan to upgrade Compton with green laser => 1% in ~16 hours
Compton GEANT4 monte carlo
17 June 2004 HAPPEX-II Experiments K. Paschke
Main Challenge: extreme requirements on halo/tail are necessary to reduce background
100 Hz / A at 5mm from the beam centroid (10-10)!
Compton Polarimeter
Photon detector Electron detector
17 June 2004 HAPPEX-II Experiments K. Paschke
Profile scannersQ2 measured at low current with VDCs...
... verified and monitored at high current with scanners.
17 June 2004 HAPPEX-II Experiments K. Paschke
Beam Requirements
Property Nominal Jitter (30 Hz) Hel corr (run)Energy 3.2 GeV < 80 ppm < 13 ppbCurrent 100 A < 1000 ppm < 600 ppbPosition 0 < 12 m < 2 nmAngle 0 < 12 rad < 2 nradHalo <100 Hz/A @ 5 mm
Specifications driven by sensitivities and estimates of quality of corrections.
CASA and EGG have worked closely with HAPPEX to meet these requirements
17 June 2004 HAPPEX-II Experiments K. Paschke
Polarized source● Pockels cell voltage (PITA) used to tune AQ, x● Intensity Attenuator (IA)● PZT mirror● IHWP for slow helicity reversal● RHWP for control of position/intensity asymmetries● Superlattice photocathode: >80% polarization, 100 A
17 June 2004 HAPPEX-II Experiments K. Paschke
Controlling Position Differences
Identify and control sources of position differences● Intrinsic birefringence gradient in the Pockels cell● Steering from distortions due to piezo-electric
deformation of the Pockels cell ● Analyzing power gradients
Lisa Kaufman, Brian Humensky, Gordon Cates, Ryan Snyder, Kent
Paschke, and the EGG.
17 June 2004 HAPPEX-II Experiments K. Paschke
ITS Laser Room
Studies in the laser room conducted over the past year have been crucial in developing our understanding of the sources of position differences.
● Characterization of Pockels cells on parameters relevant to sources of position differences
● Identification and characterization of the history effect in optical properties of the Pockels cells
● Development of alignment techniques to reduce effects from Pockels cell steering
17 June 2004 HAPPEX-II Experiments K. Paschke
Injector Beam Studies● Electron beam studies allows studies of
effects from the photocathode, as well as other idiosyncratic elements such as vacuum windows.
● Set points for source elements (PC voltages, rotating waveplate angle) can only be determined from beam data.
● Injector transmission becomes an important issue in getting the well-tuned beam to the Hall.
17 June 2004 HAPPEX-II Experiments K. Paschke
Phase Trombone• Goal: vary betatron phase while preserving the shape and orientation of the phase space ellipse
• implemented with eight existing quads at the beginning of the Hall A arc• Allows for independent betatron phase control in horizontal and vertical planes
• Uses:• Allows one to trade off position and angle differences• Periodic phase changes can be used to randomize or reverse the sign of position differences
Phase TromboneSetpoint (x , y)
x (m)0.3 m
y (m)0.3 m
x(rad)0.01 rad
y (rad)0.02 rad
(0o,0o) 2.9 2.0 -0.08 -0.19
(30o,0o) 2.7 1.2 -0.07 -0.22
(-30o,0o) 2.8 3.2 -0.07 -0.16
(30o,30o) 1.0 1.2 -0.12 -0.21