The Parity Violation A4 Experiment at forward and backward angles

May 17, 2006 Sebastian Baunack, PAVI06

The Parity Violation A4 Experiment at forward and

backward angles

•Strange Form Factors

•The Mainz A4 Experiment

•Result at forward angles

•A look at backward angles

Sebastian Baunack

for the A4 collaboration


Structure of the Nucleon

dContribution of s-quarks to the vector current

NssN ||

Constituent Quarks

QCD: sea quarks, gluons…

e-

e-

Z0

p

2NCEM MM

•Electromagnetic interaction

•Weak interaction


PV Asymmetry

56

2

2

1010~~

Z

EM

NC

LR

LRPV

M

Q

M

MA

Weak interaction: Parity violation

Flavour Decomposition of form factors:

sME

dME

uME

pME GGGG ,,,,, 3

1

3

1

3

2

sMEW

dMEW

uMEW

ZpME GGGG ,

2,

2,

2,, )sin

3

1

4

1()sin

3

1

4

1()sin

3

2

4

1(

•Universality of quark distribution, charge symmetry…


Extraction of Strange FF

SAVPV AAAA

22

22

)()(

))sin41(

24 pM

pE

nM

pM

nE

pE

wF

V GG

GGGGQGA

22

222

)()(

))1(1)sin41(24 p

MpE

pA

pMwF

A GG

GGQGA

22

2

)()(

)

24 pM

pE

sM

pM

sE

pEF

S GG

GGGGQGA

0A : No strangeness

Strangeness contribution

Strange FF

extractable!

Standard model

calculation


A4 Kinematics

sM

sE GG

p-Target

35º

Detector Detector

rotated

Forward angles: sensitive to

with Q2 [in GeV/c)2]

E=854.3 MeV

Q2= 0.23 (GeV/c)2

A0= -6.30 ppm

E=570.4 MeV

Q2= 0.11 (GeV/c)2

A0= -2.08 ppm

e-


A4 Kinematics

p-Target

145º

Detector Detector

rotated

Backward angles: sensitive to

sMG (and the axial term)

E=315.1 MeV

Q2= 0.23 (GeV/c)2

A0= -16.2 ppm

(AV=-13.6 ppm , AA=-2.6 ppm)

e-


Statistics

total

PVStat

NPA

1

NN

NNAPV

with NNN total

Count elastic events N+, N-

5% Accuracy:

Q2= 0.11 (GeV/c)2 forward: Ntotal=1 x 1014

Q2= 0.23 (GeV/c)2 forward: Ntotal=1 x 1013

Q2= 0.23 (GeV/c)2 backward: Ntotal=1 x 1012

A4: Large solid angle (0.6 sr) PbF2 calorimeter

Meas. Time

1100 h

400 h

600 h


A4 Experiment at MAMI

Forward angle configuration

Polarized GaAs

electron source

I=20 A, P=80%

MAMI

E=854.3 MeV

E=570.4 MeV

Compton Laser

Backscatter

Polarimeter

10 cm liquid

hydrogen

target

PbF2

Calorimeter

Luminosity

monitors

Transmisson

Compton

Polarimeter


A4 Experiment at MAMI

Backward angle configuration

Polarized GaAs

electron source

I=20 A, P=80%

MAMI

E=854.3 MeV

E=570.4 MeV

Compton Laser

Backscatter

Polarimeter

20 cm liquid

hydrogen

target

PbF2

Calorimeter

Luminosity

monitors

Transmisson

Compton

Polarimeter

Scintillator


Polarized electron source

•Superlattice GaAs Photocathode

•Pockels cell: Rapid helicity flip every 20 ms

•Rotatable halfwave plate: Current asymmetry < 10 ppm

•Insertable halfwave plate:Slow helicity reversal every 50-80 h, systematic check

=> K. Aulenbacher, May 20, 18:00


Compton Backscatter Polarimeter

=> J. Diefenbach, May 20, 16:30


PbF2 Calorimeter

•1022 PbF2 crystals in 7 rings and 146 frames

•Pure Cerenkov radiator, intrinsically fast

•Solid angle:

=0.6 sr,

or

•Total rate MHz

•Sum of 3x3 crystals


Luminosity monitors

•8 Integrating water Cerenkov detectors

•Measurements every 20ms

•Small forward angles, 4.4°10°, optimized for Moller electrons


Transmission Compton Polarimeter (TCP)

•Relative measurement of polarization

•Determination of electron spin angle

•Control of halfwave plate statusA

sy

mm

etry

/1

0-3 10

5

0

-5

-10Asy

mm

etry

/10-5


Forward angle measurements

PbF2 Energy spectrum

Single channel, =34.1°

E=854.3 MeV

Q2=0.23 (GeV/c)2

I = 20A, t = 2.5minFit: Double Gaussian plus

exponential

Calc. energy resolution



•Calculate low ADC cut:

RCut kEE

0

From fitCan be choosen,

We use k=1.6

•High ADC cut:

No difficulty

Elastic events

N+, N-





E = 570.4 MeV

Q2 = 0.11 (GeV/c)2

I = 20A, t = 2.5min

Also clean extraction of elastic events


Analysis

1022

1

1022

1

,c

cc

c NNNN

For each 5min run:

2044 spectra (+/-)


Analysis

1022

1

1022

1

,c

cc

c NNNN

NN

NN

Aex•Experimental Asymmetry: with target density

ii

iphysex XaAPA

6

1

•Elastic events for one run:

P: Beam polarisationX1: Current asymmetryX2: Horiz. position diff.X3: Verti. Position diff.

X4: Horiz. angle diff.X5: Verti. angle diff.X6: Energy diff.

•Determination of ai via multiple linear regression

May 17, 2006

A4@MAMI, forward angle

Q2= 0.23 (GeV/c)2

APV=(-5.44±0.54stat±0.26syst) ppm 036.0039.0225.0 s

MsE GG

036.0071.0106.0 sM

sE GG

Q2= 0.11 (GeV/c)2

APV=(-1.36± 0.29stat±0.13syst) ppm

F.E. Maas et al., Phys.Rev.Lett.93:022002 (2004)

F.E. Maas et al., Phys.Rev.Lett.94:152001 (2005)


To the backward measurements

p-Target

145º

Detector

e-

p-Target

35ºe-

Detector

=> B. Gläser, May 17, 18:30


PbF2 spectrum



E=315.1 MeV

Q2=0.23 (GeV/c)2

I = 20A, t = 2.5minCoincidence spectrum

Backward angle


Backward anglePbF2 Energy spectrum


E=315.1 MeV

Q2=0.23 (GeV/c)2

I = 20A, t = 2.5min

PbF2 spectrum

Coincidence spectrum

•A4 Standard fit possible

•Elastic events extractable


N+back, N-

back:Background analysis

Backward angle

coinccoinc

coinccoinccoinc NN

NNA

N+coinc, N-

coinc:used for the preliminary analysis


Noncoincidence spectrum

backback

backbackback NN

NNA


Background subtraction

•In development

Estimate background dilution factor

Subtract background:

Coincsub(ADC)=Coinc(ADC)-

×Back(ADC)


Background subtraction

•Good estimation of background dilution


Coincidence spectrum with

background substracted

•fit possible


Backward angle, beam parameter

Beam current Asymmetry

Mean: -0.31 ppm

: 4.36 ppm

N: 8037

Asymmetries and differences in current, position, angle, energy: The smaller, the better


Backward angle, beam parameter

Current Asymmetry AI -0.31 ppm

Horiz. position diff. X -0.10 m

Verti. position diff. Y -0.04 m

Horiz. angle diff. X‘ -7.41 nrad

Verti. angle diff. Y‘ -3.00 nrad

Energy diff. E -0.21 eV

0.31 ppm0.15 ppm

0.06 ppm0.03 ppm

0.01 ppm0.00 ppm

Beam parameter False Asymmetry |AFalse|

(Estimation)


A look at luminosity

Luminosity asymmetry vs time

Luminosity asymmetry smaller than 1 ppm


Spin angle determination1. E=315.1 MeV

2. Rotate electron spin with Wienfilter

3. Asymmetry in TCP polarimeter sensitive to longitudinal spin

S=(1.6±6) °


Backward asymmetriesDone:

•Extraction of elastic events with standard A4 method

•Partly corrections of helicity correlated false asymmetries

•Polarization correction (based on a preliminary analysis)

Ongoing:

•Development of new fit and background subtraction

•Full analysis of helicity correlated false asymmetries

•Target density analysis

•Systematic check of energy spectra (more than 25x106 so far)

•And so on…


Very preliminary

Q2=0.23 (GeV/c)2 backward

About 550h of data

Nelastic=1.6x1012

Aout = (-14.0 ± 1.9) ppm

Ain = (+17.2 ±1.8) ppm

Acoinc= (-15.8 ± 1.3) ppm

Coincidence data

•Halfwave plate sign flip observable

•In/Out asymmetries consistent

•Asymmetries have expected magnitude



Nbackground=3.1x1012

Aout = (-4.6 ± 1.4) ppm

Ain = (+3.2 ±1.3) ppm

Aback= (-3.9 ± 0.9) ppm

Noncoincidence data

•Bg. asmmytries by a factor of 4 smaller than coinc. asymmetries

Very preliminary



Some speculation:

BackPVcoinc AAA )1(

Acoinc= (-15.8 ± 1.3) ppm

Aback= (-3.9 ± 0.9) ppm

Assume dilution factor =0.1

APV= (-17.1 ± 1.4) ppm

No strangeness: A0=-16.2 ppm

=> Not very strange……

But: Analysis very preliminary!!


Summary and Outlook

•PVA4 setup successfully rearranged for backward measurements

•550 hours of backward data taken at Q2=0.23 (GeV/c)2

•First results look reasonable

•Analysis in ongoing

•Measurements at Q2=0.23 (GeV/c)2 will continue soon

(June 2006)

Documents

The Parity Violation A4 Experiment at forward and backward angles