first measurement of the beam normal single spin asymmetry in Δ resonance production by q-weak...

First Measurement of the Beam Normal Single Spin Asymmetry in Δ Resonance Production by Q-weak

Nuruzzaman(https://userweb.jlab.org/~nur/)

for the Q-weak Collaboration

https://userweb.jlab.org/~nur/

https://userweb.jlab.org/~nur/

Outline

CIPANP 2015Nuruzzaman 2

Beam Normal Single Spin Asymmetry

Experimental apparatus

Overview of the dataset

Overview of analysis and preliminary result

Comparison with a theory calculation



Bn = σ − σσ + σ

• Beam Normal Single Spin Asymmetries (Bn) are generated when transversely polarized electrons scatter from unpolarized targets

• Bn is parity conserving and is time-reversal invariant

spin UP

spin DOWN



Bn = 2T1γ × Im T2γ

|T1γ|σ − σσ + σ =

γ + γ γ



• Bn provides direct access to the imaginary part of the two-photon exchange amplitude

Bn arises from the interference of 2-photon exchange with 1-photon

exchange in e-N scattering

T1γ – amplitude for 1-photon exchangeT2γ – amplitude for 2-photon exchange

spin UP

spin DOWN




|T1γ|σ − σσ + σ =

T1γ – amplitude for 1-photon exchangeT2γ – amplitude for 2-photon exchange

Contains information about the Intermediate states of the nucleon

γ + γ γ



• Bn provides direct access to the imaginary part of the two-photon exchange amplitude

Bn arises from the interference of 2-photon exchange with 1-photon

exchange in e-N scattering

spin UP

spin DOWN

Bn in the Production of the Δ Resonance


Measuring Bn in e + p e + Δ

Bn in the Production of the Δ Resonance


• Proton EM FF well known. N→Δ EM transition FF fairly well known

• Unique tool to study *ΔΔ form factors

• Potential to constrain charge radius and magnetic moment of Δ !

Physics Motivation:

For p and Δ intermediate hadrons, vertices are known - except for *ΔΔ electromagnetic (EM) vertex

Measuring Bn in e + p e + Δ

More details by M. Dalton on Wed

Asymmetry Measurement


Measured asymmetry

ϵM(ϕ) = N − NN + N

e-

protonθK

K'

Detect

or

S S

Bn is also known as transverse asymmetry

Can be measured with a transversely polarized beam to determine the magnitude

Asymmetry Measurement


Measured asymmetry

ϵM(ϕ) = N − NN + N = − BnS.n = BnS sin(ϕ-ϕ0) = Bn [PVcos(ϕ) - PHsin(ϕ)]

∧

n =∧ k × k’

|k × k’|

Measured asymmetry has a small azimuthal dependence

e-

protonθK

K'

Detect

or

S S

• Horizontal : PH = S cos(ϕ0)

• Vertical : PV = S sin(ϕ0)

Bn is also known as transverse asymmetry

Can be measured with a transversely polarized beam to determine the magnitude

Jefferson Lab and Q-weak Setup


CA B

D

Q-weak experiment ran in Hall-C at the Thomas Jefferson National Laboratory in Newport News, Virginia from Jan 2010 – May 2012

Q-weak setup inside Hall-C (during construction)

Aerial view of Jefferson Lab

Transverse measurements were taken from 16 - 20 February, 2012

Bn Measurement Using Q-weak Apparatus


• Ebeam = 1.16 GeV• <θ> ~ 8.3°• Q2 = 0.021 (GeV/c)2

• ϕ coverage ~ 49% of 2π• Current = 180 μA• Polarization = 88%

Kinematics

Bn Measurement Using Q-weak Apparatus


3

7

51

2 4

8 6

ϕ (octant # − 1) x 45o

• Ebeam = 1.16 GeV• <θ> ~ 8.3°• Q2 = 0.021 (GeV/c)2

• ϕ coverage ~ 49% of 2π• Current = 180 μA• Polarization = 88%

Kinematics

Transverse Dataset


Δ peak

Simulation at E = 1.16 GeV

elastic peak

Toroidal magnet spectrometer current [A]

Data on 3 types of targets • Hydrogen• Aluminum• Carbon

Transverse polarization: • Horizontal• Vertical

Transverse Dataset




Δ peakThis talk: Inelastic e-p

scattering with a Δ(1232) final state at E = 1.16 GeV


elastic peak


Transverse Dataset


Data on both side of the inelastic peak were taken to

study the elastic dilution

Δ peakThis talk: Inelastic e-p

scattering with a Δ(1232) final state at E = 1.16 GeV


elastic peak




Transverse Dataset


Δ peak

Other datasets: • in the →Δ region (Al, C)𝑁• in the →Δ region (H𝑁 2, 0.877 GeV) • elastic scattering (H2, Al, C)

• elastic Møller scattering (H2)• in the DIS region (3.3 GeV) • in pion photoproduction

This talk: Inelastic e-p scattering with a Δ(1232)

final state at E = 1.16 GeV


elastic peak

Data on both side of the inelastic peak were taken to

study the elastic dilutionToroidal magnet spectrometer current [A]



Asymmetries from Main Detector Signals


Not corrected for• False beam asymmetries• Polarization• Backgrounds

ϵR

ϵL

ϵraw = ϵL + ϵR

2

~0.6 V

Right PMT

Left PMT

e-Integrating signal

Correction for False Beam Asymmetries


Correcting for the helicity correlated changes in beam position, angle and energy using linear regression

Ti = X, X´, Y, Y´ & Eϵreg = ϵraw - ∂ϵraw ∂Ti

∆Ti ∑i

Not corrected for• Polarization• Backgrounds





∆Ti ∑i

∆X∂ϵraw ∂X


0° 45° 90° 135° 180° 225° 270° 315°

example: ~2hr measurement




ϵreg = ϵraw - ∂ϵraw ∂Ti

∆Ti ∑i


Small corrections (<1%), compared to the size of the asymmetry

example: ~2hr measurement

Regressed Transverse Asymmetries

11Nuruzzaman CIPANP 2015

Fit function for horizontal: ϵreg

H sin(ϕ)

Regressed asymmetries Not corrected for polarization and backgrounds

0° 45° 90° 135° 180° 225° 270° 315°



Fit function for horizontal: ϵreg

H sin(ϕ)vertical: ϵreg

V cos(ϕ)

~90o phase offset

Regressed asymmetries Not corrected for polarization and backgrounds

0° 45° 90° 135° 180° 225° 270° 315°



ϵreg = 5.1 ± 0.4 (stat) ppmMeasured asymmetry

Error weighted (H and V) regressed asym. Corrected for detector acceptance Not corrected for polarization and backgrounds

Summary of Uncertainties on ϵreg


dominated by statistics

systematics are under control

Error weighted (H and V) regressed asym. Corrected for detector acceptance Not corrected for polarization and backgrounds

ϵreg = 5.1 ± 0.4 (stat) ± 0.1 (sys) ppmMeasured asymmetry

Extraction of Physics Asymmetry






Extracting Bn from the experimental measured asymmetry by removing false asymmetries

ϵreg = ϵraw -∂ϵraw

∂Ti ∆Ti, cor. for det. acpt.∑

i




Extracting Bn from the experimental measured asymmetry by removing false asymmetries correcting for the beam polarization



i




Extracting Bn from the experimental measured asymmetry by removing false asymmetries correcting for the beam polarization removing background asymmetries

Bbi = Background asymmetries

fbi = dilution factors



i

• Al : aluminum window backgrounds

• BB : scattering from the beamline• QTor: neutral particles in the magnet acpt.• el : elastic radiative tail




Extracting Bn from the experimental measured asymmetry by removing false asymmetries correcting for the beam polarization removing background asymmetries correcting for radiative tails and other

kinematic correction • Al : aluminum window backgrounds

• BB : scattering from the beamline• QTor: neutral particles in the magnet acpt.• el : elastic radiative tail

Bbi = Background asymmetries

fbi = dilution factors

Mkin = kinematic correction



i

Extraction of Physics Asymmetry and Uncertainties



at kinematics• <E> = 1.16 GeV• <W> = 1.2 GeV• <θ> = 8.3°• <Q2> = 0.021 GeV2

~ 38% measurement of beam normal single asymmetry in Δ resonance production

Bn = 43 ± 16 ppmPreliminary

Summary of Uncertainties




Bn = 43 ± 16 ppmPreliminary




Bn = 43 ± 16 ppm


Preliminary




Biggest contribution is from elastic radiative tail

Bn = 43 ± 16 ppm


Preliminary

Elastic Radiative Tail


Preliminary BNSSA in elastic e-p scattering using Q-weak apparatus isBn

el = -5.35 ± 0.07 (stat) ± 0.15 (sys) ppmat kinematics• <E> = 1.16 GeV• <θ> = 7.9°• <Q2> = 0.025 GeV2

Background Corrections Elastic radiative tail


At similar kinematics• ϵreg

in has opposite sign to the ϵregel

• Bnin is much larger than the absolute

value Bnel

Asymmetry



Bel = -5.1 ± 0.5 ppm

Scaled elastic asym. (Bn

el~√Q2) to inelastic kinematics, additional 10% uncertainty for scaling

Preliminary BNSSA in elastic e-p scattering using Q-weak apparatus isBn

el = -5.35 ± 0.07 (stat) ± 0.15 (sys) ppmat kinematics• <E> = 1.16 GeV• <θ> = 7.9°• <Q2> = 0.025 GeV2



At similar kinematics• ϵreg

in has opposite sign to the ϵregel

• Bnin is much larger than the absolute

value Bnel

Asymmetry

Background asymmetry from elastics





Δ peak

Bel = -5.1 ± 0.5 ppm

Dilution

elastic peak




fel = 0.70 ± 0.07



This prelim. analysis takes10% additional uncertainty due to discrepancy between data and simulation (incomplete)

Residual =(data – sim.)

data

Bel = -5.1 ± 0.5 ppm

Dilution

elastic peak

Δ peak

elastic peak

Δ peak

Toroidal magnet spectrometer current [A] Toroidal magnet spectrometer current [A]

Asymmetry is Diluted by Elastic Radiative Tail


Simplifying* the extraction equation(* for illustrative purposes)

0.214×43 ppm = 9.2 ppm ≈ (5.1/0.875) - 0.70×(-5.1) - 0.3 = 5.8 - (-3.6) - 0.3 ppm



Plot to illustrate the dependence of Bn on fel


0.214×43 ppm = 9.2 ppm ≈ (5.1/0.875) - 0.70×(-5.1) - 0.3 = 5.8 - (-3.6) - 0.3 ppm



• The extraction of Bn depends strongly on the elastic dilution• Careful study is ongoing to reduce uncertainty in fel

Plot to illustrate the dependence of Bn on fel


0.214×43 ppm = 9.2 ppm ≈ (5.1/0.875) - 0.70×(-5.1) - 0.3 = 5.8 - (-3.6) - 0.3 ppm

Comparison of Bn to Theory Calculation


• sensitive to γ*ΔΔ form factors

In the calculation there is lattice QCD parameterizations for γ*ΔΔ form factors which are not so well known

large asymmetries in the forward region

Comparison of Bn to Theory Calculation


• sensitive to γ*ΔΔ form factors• Q-weak transverse dataset along with world data has potential to

constrain models and study charge radius and magnetic moment of Δ

Measured Bn agrees with theoretical calculation

0° 45° 90° 135° 180° 225° 270° 315°

Summary


Q-weak has measured Bn in the N-to-Δ transition on H2

43 ± 16 ppm<E> = 1.16 GeV, <W> = 1.2 GeV, <θ> = 8.3°, <Q2> = 0.021 GeV2

• preliminary result shows agreement with a theoretical calculation

• physics implications of the model needs investigation

• sensitive to γ*ΔΔ form factors• working towards the improvement in systematic

uncertainty

Data for Bn at low Q2 in elastic and inelastic scattering with a Δ(1232) final state from several targets and energy are available.

• looking for model predictions !• Q-weak transverse dataset along with world

data has potential to constrain models and study charge radius and magnetic moment of Δ

Δ peak


elastic peak

Acknowledgement


Q-weak Collaboration

Special thanks to Babara Pasquini for providing theory predictions at Q-weak kinematics

D.S. Armstrong, A. Asaturyan, T. Averett, J. Balewski, J. Beaufait, R.S. Beminiwattha, J. Benesch, F. Benmokhtar, J. Birchall, R.D. Carlini1, J.C. Cornejo, S. Covrig, M.M. Dalton, C.A. Davis, W. Deconinck, J. Diefenbach, K. Dow, J.F. Dowd, J.A. Dunne, D. Dutta, W.S. Duvall, M. Elaasar, W.R. Falk, J.M. Finn1, T. Forest, D. Gaskell, M.T.W. Gericke, J. Grames, V.M. Gray, K. Grimm, F. Guo, J.R. Hoskins, K. Johnston, D. Jones, M. Jones, R. Jones, M. Kargiantoulakis, P.M. King, E. Korkmaz, S. Kowalski1, J. Leacock, J. Leckey, A.R. Lee, J.H. Lee, L. Lee, S. MacEwan, D. Mack, J.A. Magee, R. Mahurin, J. Mammei, J. Martin, M.J. McHugh, J. Mei, R. Michaels, A. Micherdzinska, K.E. Myers, A. Mkrtchyan, H. Mkrtchyan, A. Narayan, L.Z. Ndukum, V. Nelyubin, Nuruzzaman, W.T.H van Oers, A.K. Opper, S.A. Page1, J. Pan, K. Paschke, S.K. Phillips, M.L. Pitt, M. Poelker, J.F. Rajotte, W.D. Ramsay, J. Roche, B. Sawatzky,T. Seva, M.H. Shabestari, R. Silwal, N. Simicevic, G.R. Smith2, P. Solvignon, D.T. Spayde, A. Subedi, R. Subedi, R. Suleiman, V. Tadevosyan, W.A. Tobias, V. Tvaskis, B. Waidyawansa, P. Wang, S.P. Wells, S.A. Wood, S. Yang, R.D. Young, S. Zhamkochyan

1Spokespersons 2Project Manager Grad Students


Backup Slides

Δ Elastic Form Factors

CIPANP 2015Nuruzzaman

There are 4 elastic form factors (spin 3/2)

GE0(Q2), GM1(Q2), GE2(Q2), GM3(Q2)

J. Segovia et. al. arXiv:1308.5225 (2013)

Q2 = 0 define dimensionless multipole moments• GE0(0) = eΔ charge• GM1(0) μ∝ Δ magnetic moment• GE2(0) D∝ Δ dipole moment• GM3(0) O∝ Δ octopole moment

Summary of Measurements


N + πN + 2π

D13

F15

...

PVA4Q-weakSOLID

Higher beam energies allow more intermediate states

Two Photon Exchange


Form factors:

Δp, Δ, Xp

e- e-

γ γ

pp

γ

Δp

γ

Xp

γ+ + +

Δp

γ

ΔΔ

γ+ +

FF TFF

TFF

Don’t know

This measurement

will help

Δp, Δ, Xp

e- e-

γ γp(n)

π0(π+)

Don’t know XΔ

γ

Why Bn=0 at θ=0 ?


σ − σ ∝2me

QεL

ε(1-ε) =2me

QQν(1-ε)

1/2

Qν

=2me

ν(1-ε)

νel = 0.013νin = 0.348νmin = 300 MeV + K. E.

Private communication with Carl Carlson

(1-ε) = ε(1/ε-1)

ε-1 = 1+ 2 ν2

Q21+ tan2θe

2

= 2ε ν2

Q21+ tan2θe

2


|T1γ|σ − σσ + σ =

ν = KP

K is the average incoming four-momenta of the electronP is the average outgoing four-momenta of the proton

=ν2

Q21+ tan2θe

2ν4meε

Regression Scheme Dependence


Horizontal transverseCorrections were small

(0.15% <<10% stat error)

Vertical transverseCorrections were small (1.7% <<18% stat error)

Regression scheme dependence is ~ 0.005 ppm (0.1%)

Horizontal

Vertical

Regression Scheme Dependence


Horizontal transverseCorrections were small

(0.15% <<10% stat error)

Vertical transverseCorrections were small (1.7% <<18% stat error)

Regression scheme dependence is ~ 0.005 ppm (0.1%)

Summary of Uncertainties on ϵreg

ϵreg = 5.07 ± 0.44 (stat) ± 0.08 (sys) ppm

Nuruzzaman CIPANP 2015

uncertainty is dominated by statistics

All other systematics are under control

corrected for detector acceptance

Measured asymmetry

Fit Scheme Dependence


Horizontal Transverse

Vertical Transverse

Fit Function ϵregH [ppm] ϵreg

H(n) – ϵregH(1)

[ppm]1 ϵreg

H sin(ϕ+ϕ0) + C 5.343 ± 0.532 0.000

2 ϵregH

sin(ϕ+ϕ0) 5.344 ± 0.532 +0.001

3 ϵregH

sin(ϕ) + C 5.303 ± 0.533 −0.040

4 ϵregH

sin(ϕ) 5.304 ± 0.533 −0.039

Fit Function ϵregV [ppm] ϵreg

V(n) – ϵregV(1)

[ppm]1 ϵreg

V cos (ϕ+ϕ0) + C 4.525 ± 0.806 0.000

2 ϵregV

cos(ϕ+ϕ0) 4.510 ± 0.806 −0.015

3 ϵregV

cos (ϕ) + C 4.458 ± 0.807 −0.067

4 ϵregV

cos (ϕ) 4.442 ± 0.807 −0.083

• Small fit scheme dependence for horizontal transverse, slightly higher for vertical transverse. Probably low statistics!

• The PV contamination to the transverse asymmetry is buried under this uncertainty.

Fit scheme dependence is ~0.05 ppm (1.0%)

C = APV + background

Detector Acceptance Correction

Nuruzzaman CIPANP 2015

• A single detector measures the average asymmetry over 49% of azimuth

• Transverse measurement uses octant asymmetries and need to correct for the octant coverage

cosϕ = cosϕ0

sin ΔϕΔϕ

1/Mϕ

ϵreg = Mϕϵinreg

Detector Acceptance Correction

ϵreg = 5.1 ppm

Cancellation of HCBA with IHWP


An Insertable Half Wave Plate (IHWP) can flip the electron spin. Inserting IHWP: • sign of some helicity correlated (HC) false asymmetries remains unchanged

Horizontal Transverse

cancellation of HC false asym.

Fit function: ϵregIN/OUT sin(ϕ)

physics asym. changes sign

Regression Corrections


Small corrections, compared to the size of the asymmetry

Corrections:∂ϵraw

∂Ti ∆Ti






∆Ti ∑i

first measurement of the beam normal single spin asymmetry in Δ resonance production by q-weak...

Documents

n n n n ee

b n s sin

photon exchange amplitude

unpolarized targets

en scattering t

timereversal invariant

kk detector s s b n

b n p v cos p h sin