: a parity violation experiment

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• a parity violation experiment
• (with electrons)
• Outline
• Parity violation as a tool.
• Strange quark form factors why, how, who ?
• The G0 project
• How to perform a parity violation experiment ?
• The G0 peculiars, some results
• Outlook.
• J. Roche (JLab/HallC)

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From asymmetries of cross-sections to asymmetries
of counts the experimental challenge.
All the game is to maintain the quality of the
beam and the response of the detector equal at
the helicity R and helicity L. If not
order of magnitude for G0 for AF1 A, one
needs DXlt10 nm
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Parity violation experiment the basic HOW-TO

• Maintain small random noise
• Measure detectors sensitivities to beam helicity
  correlated properties
• Reduce beam helicity correlated properties
• Measure the beam polarization
• Check..

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Parity violation experiments are based on
statistic
G0 elastic rate in one detector one octant 0.5
MHz Beam helicity window (right or left) 66
ms N30 000 events gt sA 4062 ppm for one
measurement
Take M measurements order of magnitude
assume A10 ppm DA10 M1.6 107 measurements
575 hours 24 days Necessity of high
luminosity, large solid angle and long data
taking..
G0 Octant 7 detector 11
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• Improving the measurements sensitivity
• Assume your are given a time T to perform your
  experience.
• What are the most efficient knobs to get the best
  precision ?

• Work on increasing the beam polarization first
• GaAS maximal polarization 50
• strained GaAS average polarization 75
• super lattice GaAS 85 (but also better QE 1,
  small analyzing power)
• http//www.jlab.org/accel/inj_group/
• Then increase beam intensity, target thickness,
  acceptance
• (careful to second order effect target
  boiling, high rates)
• Both advances are major
  improvement for the field since 74

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Parity violation experiments are based on
statisticYes, but does it work ?
1 det smeasured 4000 ppm gt 8 det
smeasured4000/81/21414 ppm order of magnitude
for G0 all octants summed smeasured 1.1
sstatistic
The case of the target boiling
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Random noise contribution target boiling
1 det smeasured 4000 ppm gt 8 det
smeasured4000/81/21414 ppm order of magnitude
for G0 all octants summed smeasured 1.1
sstatistic
The case of the target boiling
Also consider beam charge monitor noise (300
ppm)
importance of limiting random noise for a good
statistical convergence
Attention these are not helicity correlated
effect !!! They are random effects.
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Random noise contribution the quick reversal
strategy
experimental area
Accelerator
Apparatus slow drifts
optic fiber
retardation box (9 quartets)
HV
Can act like an antenna that shifts pedestals,
thresholds (etc..) around

• How to check the efficiency of those strategy ?
• Measure pedestals asymmetries when no beam
• Measure batteries asymmetries
• Use a fake Pockels cell
• .

quick reversal of the helicity (here at 15
Hz) on a pseudo random pattern ( - - )(-
-) (- -) .
1/4
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Parity violation experiment the basic HOW-TO

• Maintain small random noise
• Measure detectors sensitivities to beam helicity
  correlated properties
• Reduce beam helicity correlated properties
• Measure the beam polarization
• Check..

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Sensitivity of the detectors to beam
characteristics

• Two ways to measure the
• detectors sensitivities
• natural beam motion
• forced beam motion (coil pulsing)
• Effects are correlated
• to correct need to inverse
• a 6X6 matrix
• Good data have
• reduced det. sensitivities
• reduced helicity correlated
• beam characteristics

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Advantage of the azymuthal symmetric geometry
The G0 spectrometer is made up of 8 azimuthally
symmetric octants. ? Diametrically opposing
octants should have opposite (in sign) slopes for
position and angle.

• Slopes show an octant dependence.
• False asymmetries are suppressed for
  position/angle motion when summed over octants.
• Attention this is still not an helicity
• correlated effect

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Helicity correlated beam characteristics
The case of G0 running for the forward angle
production (Winter 04) 700 h
These are helicity correlated results
(Dont wory about the two colors for now) Why
are those results remarkable and essential for
the success of such experiments ?
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Parity violation experiment the basic HOW-TO

• Maintain small random noise
• Measure detectors sensitivities to beam helicity
  correlated properties
• Reduce beam helicity correlated properties
• Measure the beam polarization
• Check..

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Every things happen back in the injectorthe
example of the PITA effect
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Source of Helicity Correlation in Beam
IA cell
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Beam Feedback (G0-Hardware)
Each system is calibrated AIeV -gt Vnew Vold
AI/e System calibration multiple time a
week IA voltage changed each 5mn PZT voltages
changed each 30mn caution both devices
include charge asymetry and positions
differences. Cross-coupling terms must be taken
into account Insertable half-wave plate changed
each other day.
1/2
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Injector

• PV experiments present special
• challenges
• high currents and high polarization
• minimization of the
• helicity properties of the beam
• close collaboration
• between the injector group and
• the PV physicists.

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Beam Feedback Results
SAMPLE example
G0 example
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Parity violation experiment the basic HOW-TO

• Maintain small random noise
• Measure detectors sensitivities to beam helicity
  correlated properties
• Reduce beam helicity correlated properties
• Measure the beam polarization
• Check..

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Polarimetry
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Parity violation experiment the basic HOW-TO

• Maintain small random noise
• Measure detectors sensitivities to beam helicity
  correlated properties
• Reduce beam helicity correlated properties
• Measure the beam polarization
• Check..

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How to check that you are doing a good job ?

• Insertable Half-wave plate

G0

• Statistical distribution of the asymmetries
• measurements

• Luminosity detectors
• at very small angle AF-gt0

G0
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Parity violation experiment the basic HOW-TO

• Maintain small random noise
• Measure detectors sensitivities to beam helicity
  correlated properties
• Reduce beam helicity correlated properties
• Check..
• All of the above apply to G0 and some more

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A specific effect to counting experiment deadtime

• But in a counting experiment one should also take
  into account deadtime effects
• no readout deadtime
• readout while the helicity flips
• helicity window 33 ms
• flip window 500 us
• electronic deadtime (each event)
• 4 signals to sign a particle
• (1,2,3 signals gt 30 ns dt)
• encoding into the histograms
• ( 4 signals gt 30 ns)

N/I
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Helicity correlated deadtime
Use the IA cell to induce a large AI Apply the
deadtime correction before forming the
asymmetry Use linear regression to
further suppress the deadtime effect
Before linear regression ltAIgt 1 ppm
AFlt0.02ppm DAstatistic 0.5 ppm
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A specific to G0 background contribution.
To fully correct the effect, the dilution factor
and the asymmetry are needed

• background contributions to elastic
• ep-gtep quasielastic on Al cell
• (measured with dummy targets)
• dilution 5
• asymmetry -20 ppm
• ep-gtepX inelastic on LH2
• cannot be measured
• independanlty from the elastics !

elastic cuts
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The LH2 inelastic background contribution.
within elastic cut dilution factor is 1-20
(known at 10) asymmetry is
opposite sign of LH2 elastic !
Current projected errors
Up to now extrapolate the inelastic
asymmetry with smaller and larger ToF.. Somewhat
uncertain method, gives larger final errors Need
to do better !! Most difficult part of the G0
analysis
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Systematics From raw asymmetry to physics
results
Form raw measured asymmetry from the detector
yields
Correct for false asymmetries from
helicity-correlated beam properties

• deadtime corrections (20on yield)
• helicity-correlated beam properties

Correct for background and its asymmetry

• background dilution factor correction

Correct for beam polarization and radiative
corrections

• electron beam polarization (0.77)
• SO FAR WE STOPED HERE
• electromagnetic radiative corrections

Correct for measured Q2 and EM form factors

• ltQ2gt determination
• electromagnetic form factors

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Asymmetry results from Jan. 2003 running

• Based on 51 hours
• of data at 40 ?A
• Includes
• false asymmetry corrections
• deadtime corrections
• background corrections
• beam polarization correction
• Full Data taking
• 700 h of data
• DA 0.5 ppm

!!! OLD RESULTS !!!
increasing Q2
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The total G0 error budget
known if you know the EM form factors of the
proton and the neutron

• 3 measurements
• LH2 elastic forward angle all Q2 at once
• LH2 elastic backward angle
• LD2 quasi-elastic backward angle

3 beam energies
designed to be statistic only (need a careful
analysis)
even though the Q2 are small these still carry
errors
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Outlook on ep parity violating experiments.

• Parity violation is a fundamental property of
  the weak interaction
• Amplified by its interference with the
  electromagnetic interaction,
• it has been /will be used for
• testing the standard model mixing angle
• measuring strange quark form factors
• other applications
• (2-photons exchange, D, nuclear effects)

• Major experimental
• improvements
• high luminosity
• high polarization

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Outlook on experimental techniques.
PV experiments are table-top experiments with the
table being the whole accelerator and the
experimental hall.

• Most of the false asymmetries
• effects arise from the interactions
• injector-detectors
• Need
• feedbacks between the hall and
• the injector
• electric isolation between the hall
• and the injector
• low noise detectors
• Some says that the success of a PV
• experiment resides more in its
• preparation than its analysis.

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Outlook on the G0 project
G0 is the last parity violation data taking to
date, but the field is very active (Happex2 data
taking in summer 04, E158 paper to appear very
soon) A dedicated large apparatus has been built
for the sole purpose of the experiment. It is
used in two different configurations -forward
angle running protons are detected, large range
in Q2 at once -backward angle running electrons
are detected, three runs for three Q2
LH2, LD2
LH2
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Outlook on the G0 expected physics results
Lattice S.J. Dong, K.F. Liu and A.G. Williams,
Phys. Rev. D58074504, 1998 ChiPT T. Hemmert,
B. Kubis and U. Meissner, Phys. Rev.
C60044401,1999 Zhu at al. Phys. Rev.
D62033008(2000) Sample T. Ito, et al., PRL 92
(2004) 102003 Nice reviews of the subject KS.
Kumar and P.A. Souder, PPNP 45(2000) 333-395 D.H.
Beck and R.D. McKeown, ARNPS 51(2001) 189-217