S pin A symmetries of the N ucleon E xperiment

SpinAsymmetries of the NucleonExperiment( E07-003)

Anusha Liyanage

Hall C User Meeting(January 25, 2013)

Analysis Updates

Proton Form Factor Ratio, GP

E/GPM

From Double Spin Asymmetries

Outline

Introduction Physics Motivation Experiment SetupPolarized TargetElastic Kinematic Data Analysis & MC/SIMC SimulationConclusion

2

The four-momentum transfer squared,

2

sin4 222 EEqQ

MQEE 22

IntroductionNucleon Elastic Form Factors

• Defined in context of single-photon exchange.• Describe how much the nucleus deviates from a point like

particle.• Describe the internal structure of the nucleons.• Provide the information on the spatial distribution of electric

charge (by electric form factor,Gp

E) and magnetic moment ( by magnetic form factor, Gp

M) within the proton.• Can be determined from elastic electron-proton scattering.• They are functions of the four-momentum transfer squared, Q2

3

At low || 2q Fourier transforms of the charge, and magnetic moment, distributions in Breit Frame

)(r

)(r

At 02 q

1pM

pEG

G

General definition of the nucleon form factor is

Sachs Form Factors ; ;

F1 – non-spin flip (Dirac Form Factor) describe the charge distributionF2 – spin flip (Pauli form factor) describe the magnetic moment distribution

4

Form Factor Ratio Measurements

1. Rosenbluth separation method.• Measure the electron - unpolarized proton elastic

scattering cross section at fixed Q2 by varying the scattering angle, θe.

• Strongly sensitive to the radiative corrections.

Y = m X + CThe gradient = ,

The Intercept = ,

E - Incoming electron energyE/ - Outgoing electron energyθe- Outgoing electron’s scattering angleMp - Proton mass 5

2. Polarization Transfer Technique.• Measure the recoil proton polarization components from

elastic scattering of polarized electron-unpolarized proton.

• Ratio insensitive to absolute polarization, analyzing power.

• Less sensitive to radiative correction.

Polarization along q

Polarization perpendicular to q (in the scattering plane) Polarization normal to scattering plane.

E - Incoming electron energyE/ - Outgoing electron energyθe– Outgoing electron’s scattering angleMP - Proton mass

6

3. Double-Spin Asymmetry.• Measure the double asymmetry between even (++, --)

and odd (+-, -+) combinations of electron and proton polarization.

• Different systematic errors than Rosenbluth or proton recoil polarization methods.

• The sensitivity to the form factor ratio is similar to that of the Polarization Transfer Technique.

r = GpE

/GpMa, b, c = kinematic factors

, = pol. and azi. Angles between and Ap = The beam - target asymmetry

*

Here,

crabrAP

2

*** coscossin

7

• Dramatic discrepancy between Rosenbluth and recoil polarization technique.• Multi-photon exchange considered the best candidate for the explanation

• Double-Spin Asymmetry is an independent technique to verify the discrepancy

Physics Motivation

Dra

mat

ic

disc

repa

ncy

!RSS (Jlab)Q2 = 1.50 (GeV/c)2

5.17

6.25

SANE2.06 Q2 (GeV/c)2 8

Elastic (e , e’p) scattering from a polarized NH3 target using a longitudinally polarized electronbeam(Data collected from Jan – March, 2009)

• HMS for scattered proton or electron detection• Central angles are 22.3° and 22.0°• Solid angle ~10 msr

Hall C at Jefferson Lab

• BETA for coincidence electron detection• Central scattering angle: 40 °• Over 200 msr solid angle coverage

Experiment Setup

9

Polarized TargetThe Polarized Target Assembly • C, CH2 and NH3

• Dynamic Nuclear Polarization (DNP) polarized the protons in the NH3 target up to 90% at

1 K Temperature 5 T Magnetic Field• Temperature is maintained by immersing the entire target in a liquid He bath • Used microwaves to excite spin flip transitions (55 GHz - 165 GHz) • Polarization measured using NMR coils• To maintain reasonable target polarization, the beam current

was limited to 100 nA and uniformly rastered. 10

• Used only perpendicular magnetic field configuration for the elastic data• Average target polarization is ~ 70 %• Average beam polarization is ~ 73 %

ΘB = 180°

ΘB = 80°

( 80 and 180 deg )

Polarized Target Magnetic Field

11

Spectrometer mode

Coincidence

Coincidence

Single Arm

HMS Detects

Proton Proton Electron

E BeamGeV

4.72 5.89 5.89

PHMSGeV/c

3.58 4.17 4.40

ΘHMS(Deg)

22.30 22.00 15.40

Q2

(GeV/c)25.17 6.26 2.06

Total Hours(h)

~40(~44 runs)

~155(~135 runs)

~12 (~15 runs)

Elastic Events

~113 ~1200 ~5x104

Elastic Kinematics( From HMS

Spectrometer )

12

Electrons in HMS

E’

E

Θ

e- p e- p

By knowing, the incoming beam energy, , scattered electron energy, and the scattered electron angle,

)(2222 EEMQMW

2

sin4 22 EEQ

Data Analysis

13

Momentum Acceptance

The elastic data are outside of the usual delta cut +/- 8%

Use -8% < <10%

P -Measured momentum in HMSPc-HMS central momentum

Invariant Mass, W (GeV/c2)

hsde

lta

(%)

&

Use 10% < <12% 14

Extract the electrons

Here,

- Total measured shower energy of a chosen electron track by HMS Calorimeter - Detected electron momentum/ energy at HMS - Relative momentum deviation from the HMS central momentum

shE

• Used only Electron selection cuts. # of Cerenkov photoelectrons > 2 - Cerenkov cut -8% < < 10% and 10% < <12% - HMS Momentum Acceptance cuts

> 0.7 - Calorimeter cut

3.5 x 104

1.5 x 104

-8% < < 10%

10% < < 12%

15

Extracted the Asymmetries …..The raw asymmetry, Ar N+ / N- = Charge and live time

normalized counts for the +/- helicities ∆Ar = Error on the raw asymmetry

NNNNAr

)()(2

NNNNNNAr

-8% < < 10%

10% < <12%

16

Extracted the Asymmetries …..

Needdilution factor, f

in order to determine the physics

asymmetry,

and GpE/Gp

M

(at Q2=2.2 (GeV/c)2 )

CTB

rp N

PfPAA

PBPT = Beam and target polarization Nc = A correction term to eliminate the contribution from quasi-elastic scattering on polarized 14N under the elastic peak (negligible in SANE)

Use MC/DATA comparison for NH3 target to extract the dilution factor…..17

Srast x offset=-0.4 cmSrast y offset=0.1 cm

MC for C run

18

MC with NH3 Generated N, H and He separately. Added Al coming from target end caps and 4K shields

as well. Calculated the MC scale factor using the data/MC

luminosity ratio for each target type.

Added all targets together by weighting the above MC scale factors.

Used 60% packing fraction. Adjusted acceptance edges in Y and Y’ by adjusting

the horizontal beam position. Adjusted the vertical beam position to bring the

elastic peak to GeV.

srastx = -0.40 cmsrasty = 0.10 cm

19

Determination of the Dilution FactorWhat is the Dilution Factor ?The dilution factor is the ratio of the yield

from scattering off free protons(protons from H in NH3) to that from the entire target (protons from N, H, He and Al)

Invariant Mass, W (GeV/c2)

Each target type contributions (Top target)

20Invariant Mass, W (GeV/c2)

Dilution Factor,

-8% < < 10%

MC Background contributions (Only He+N+Al)

Calculate the ratio of YieldData/YieldMC for the region 0.7 < W <0.85 and MC is normalized with this new scaling factor. Used the polynomial fit to N+ He+Al in MC and Subtract the fit function from data

21Invariant Mass, W (GeV/c2)

Each target type contributions (Top target)

Invariant Mass, W (GeV/c2)

10% < < 12%

Invariant Mass, W (GeV/c2)

Invariant Mass, W (GeV/c2)

22

The relative Dilution Factor

Dilution Factor,

• We have taken data using both NH3 targets, called NH3 top and NH3 bottom.

• NH3 crystals are not uniformly filled in each targets which arise two different packing fractions and hence two different dilution factors.

Invariant Mass, W (GeV/c2)

The relative dilution factor for two different targets, top and

bottom for two different delta regions, -8% < <

10% and 10% < <12%

23

Beam /Target Polarizations

COIN dataSingle arm electron data

24

The Physics Asymmetry -8% < < 10%

10% < < 12%

Invariant Mass, W (GeV/c2)

Invariant Mass, W (GeV/c2)

Phys

. As

ym.,

A P

Phys

. As

ym.,

A P

25

The beam - target asymmetry, Ap

crabrAP

2

*** coscossin

ca

crbAP

*** coscossin

From the HMS kinematics, r2 << c

Error propagation from the experiment

r = GE /GMa, b, c = kinematic factors

, = pol. and azi. Angles between and

*

Here,

Where , μ – Magnetic Moment of the Proton=2.79

26

Preliminary …..-8 < < 10

10 < < 12

Top Ap±eAp -0.212±0.0

22

-0.150±0.0

32Bot Ap±eAp -

0.216±0.027

-0.161±0.0

40Avg. Ap±eAp

-0.213±0.0

17

-0.154±0.0

25 (Deg) 45.68 (Deg) 190.49Q2 (GeV/c)2 2.2 1.927μGE/GM 0.477±0.1

900.928±0.2

79

Pred. μGE/GM

0.75 0.775

Pred. Ap -0.188 -0.174

Q2 (GeV/c)2 2.06Wei. Avg. μGE/GM

0.62±0.157

*

27

ΘP

Xclust

Yclust

e

e’

P

Definitions :X/Yclust - Measured X/Y positions on the BigCal • X = horizontal / in-plane coordinate• Y = vertical / out – of – plane coordinate Eclust - Measured electron energy at the BigCalBy knowing the energy of the polarized

electron beam, EB and

the scattered proton angle, ΘP

We can predict the • X/Y coordinates - X_HMS, Y_HMS and ( Target Magnetic Field Corrected)• The Energy - E_HMS of the coincidence electron on the BigCal

Coincidence Data(Electrons in BETA and Protons in HMS)

28

Spectrometer mode

Coincidence

Coincidence

Single Arm

HMS Detects

Proton Proton Electron

E BeamGeV

4.72 5.89 5.89

PHMSGeV/c

3.58 4.17 4.40

ΘHMS(Deg)

22.30 22.00 15.40

Q2

(GeV/c)25.17 6.26 2.06

Total Hours(h)

~40(~44 runs)

~155(~135 runs)

~12 (~15 runs)

e-p Events ~113 ~1200 ~5 x 104

Elastic Kinematics( From HMS Spectrometer )

29

Fractional momentum difference

PHMS – Measured proton momentum by HMSPcal - Calculated proton momentum by knowing the beam energy, E and the proton angle,ΘPcent – HMS central momentum

DataMC

MPCal 22

MQ2

2

222

2222

sin2cos4EMEM

EMQ

30

X/Y position difference

DataMC

X position difference

X_HMS-Xclust/ cm

Y_HMS-Yclust/ cm

Y position difference

31

Applied the coincidence cuts

X_HMS-Xclust/ cm

Y_HMS-Yclust/ cm

Abs( )<0.02

abs(X_HMS-Xclust)<7

abs(Y_HMS-Yclust)<10

32

Elastic Events

X_HMS-Xclus/ cmt

Y_H

MS-

Yclu

st/ c

m4.72 GeV data

Raw

# o

f Yie

lds

Run Number

5.89 GeV data

X_HMS-Xclus/ cmt

Y_H

MS-

Yclu

st/ c

m

Run Number

Raw

# o

f Yie

lds

33

Extract the Raw Asymmetries

Needdilution factor, f

in order to

determine the physics

asymmetry,

and GpE/Gp

M

CTB

rp N

PfPAA

Raw yields are normalized with• Total Charge• charge average +/-

life times

34

Determine The Dilution Factor• Estimate The

Background

• Get the ratio of data/SIMC_C for the region of 0.03 < < 0.08. (ratio=2.73893)

• Normalized the SIMC_C with that ratio (2.73893) for the region of -0.1 < < 0.1 and added SIMC_H3 to it. Compare with the data.

Data/SIMC(H3+2.73893*C) = 0.991536 • Used the Gaussian fit for the SIMC_C (normalized with 2.73893)

and subtract it from the data• Get the relative dilution factor by taking the ratio of SIMC_C

substracted data to data. the relative df. = (data-SIMC_C)/data

35

• Get The Relative Dilution Factor

Two different target cups

(NH3 Top and NH3 Bottom)

Two different packing fractions

NeedTwo different

dilution factors 36

• The Relative Dilution Factors ForTop Target

Bottom Target

37

• The Relative Dilution Factor (Used the Integration Method)• Because of the low statistics, It is hard to correct the raw asymmetry

for the df as a function of • Just integrate over the region of +/- 0.02 for the top and

bottom.

The relative D.F = (data-SIMC_C)_top/data_top = 606-130/606 = 0.785

= (data-SIMC_C)_bot/data_bot= 541-92/541= 0.830

Top Target Bottom Target

Similarly, the relative D.F for 4.72 GeV beam energy is 0.816

38

Beam and Target Polarizations

• Used the runs of beam polarization > 60 % and abs(target polarization) > 55 %

• Used the charge average target and beam polarizations to calculate the physics asymmetries

39

Extract the Physics AsymmetriesBeam

Energy(GeV)

4.72 5.89

Ap±eAp 0.184±0.136

-0.006±0.0

77Dilution Factor, f

0.816 Top (0.785)

Bot. (0.830)

(Deg) 102 102 (Deg) 0 0

Q2 (GeV/c)2

5.17 6.26

μGE/GM -0.032±0.6

68

0.875±0.424

Q2 (GeV/c)2 5.72

Wei. Avg. μGE/GM

0.614±0.35840

*

Extract the Proton Form Factor Ratio, Gp

E/GpM

Q2 (GeV/c)2

2.06 5.72

μGE/GM 0.620±0.15

7

0.614±0.358

Q2 (GeV/c)2 41

Preliminary …..

Measurement of the beam-target asymmetry in elastic electron-proton scattering offers an independent technique of determining the Gp

E/GpM ratio.

This is an ‘exploratory’ measurement, as a by-product of the SANE experiment.

Extraction of the GpE/Gp

M ratio from single-arm electron and coincidence data are shown.

The preliminary data point at Q2=2.06 (GeV/c)2 is very consistent with the recoil polarization data.

The preliminary weighted average data point of the coincidence data at Q2=5.72 (GeV/c)2 has large error due to the lack of elastic events.

Conclusion

42

SANE Collaborators:Argonne National Laboratory, Christopher Newport U., Florida International U., Hampton U., Thomas Jefferson National Accelerator Facility, Mississippi State U., North Carolina A&T State U., Norfolk S. U., Ohio U., Institute for High Energy Physics, U. of Regina, Rensselaer Polytechnic I., Rutgers U., Seoul National U., State University at New Orleans , Temple U., Tohoku U., U. of New Hampshire, U. of Virginia, College of William and Mary, Xavier University of Louisiana, Yerevan Physics Inst.

Spokespersons: S. Choi (Seoul), M. Jones (TJNAF), Z-E. Meziani (Temple), O. A. Rondon (UVA)

44

Packing Fraction.

• Packing fraction is the actual amount of target material normalized the nominal amount expected for the target volume.

• Determined by taking the ratio of data to MC as a function of W.

• Need to determine the packing fractions for each of the NH3 loads used during the data taking.Hoyoung Kang’s work

45

Determine the Packing Fraction • Compared data to SIMC simulation for the NH3 target

for 3 different Packing Fractions.• Normalized MC_NH3 by 0.93 which is the factor that

brings C data/MC ratio to 1.

Pf (%) 50 60 70Data/MC Ratio

1.00 0.88 0.78

Data/MC Ratio/0.93

1.075 0.95 0.84

• Determined the packing fraction which brings Data/MC ratio to 1 from the plot.

• Packing Fraction=56.3 %

Consistent with Hoyoung kang’s packing fraction determinations !!!! 46