The 𝑔2𝑝

ExperimentToby Badman

The University of New HampshireOn Behalf of the E08-027 Collaboration

Inclusive Electron Scattering

𝑑𝜎

𝑑Ω𝑑𝐸′= 𝜎𝑀𝑜𝑡𝑡

1

𝜈𝐹2 𝑥, 𝑄

2 +2

𝑀𝐹1 𝑥, 𝑄

2 𝑡𝑎𝑛2𝜃

2

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Unpolarized nucleon structure functions.

ee’

P

W𝛾∗

Inclusive Electron Scattering

𝑑𝜎

𝑑Ω𝑑𝐸′= 𝜎𝑀𝑜𝑡𝑡

1

𝜈𝐹2 𝑥, 𝑄

2 +2

𝑀𝐹1 𝑥, 𝑄

2 𝑡𝑎𝑛2𝜃

2+ 𝛾𝑔1 𝑥, 𝑄

2 + 𝛿𝑔2(𝑥, 𝑄2)

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Polarized nucleon spin structure functions.

ee’

P

W

Polarized target

Polarized 𝑒− beam𝛾∗

Inclusive Electron Scattering

∆𝜎∥ =𝑑2𝜎↑⇑

𝑑Ω𝑑𝐸−𝑑2𝑑↓⇑

𝑑Ω𝑑𝐸∝ 𝛼𝑔1 𝑥, 𝑄

2 − 𝛽𝑔2 𝑥, 𝑄2

∆𝜎⊥ =𝑑2𝜎↑⇒

𝑑Ω𝑑𝐸−𝑑2𝑑↓⇒

𝑑Ω𝑑𝐸∝ 𝛾𝑔1 𝑥, 𝑄

2 + 𝛿𝑔2 𝑥, 𝑄2

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Inclusive Electron Scattering

𝑔1 𝑥, 𝑄2 ∝ ∆𝜎∥ + tan

𝜃

2∆𝜎⊥

𝑔2 𝑥, 𝑄2 ∝ −∆𝜎∥ +

1 + 1 − 𝑦 cos 𝜃

1 − 𝑦 sin 𝜃∆𝜎⊥

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• ∆𝜎∥ is highly suppressed in the kinematic range where we are measuring 𝑔2 (2-8% of total contribution to 𝑔2).

• For kinematic settings where we will not measure ∆𝜎∥, EG4 data will be combined with our ∆𝜎⊥ data to calculate 𝑔2.

Motivation

• Measure the proton structure function, 𝑔2, in the low 𝑄2 region for the first time.

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SLAC JLAB SANE

Motivation

• Measure the proton structure function, 𝑔2, in the low 𝑄2 region for the first time.

• Provides a unique opportunity to test the Burkhardt-Cottingham Sum Rule in the low 𝑄2 region.

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Motivation

The 0𝑡ℎ moment of 𝑔2 should

satisfy (for all 𝑄2):

01𝑔2 𝑥, 𝑄

2 𝑑𝑥 = 0

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Brown: SLAC E155xRed: Hall C RSSBlack: Hall A E94-010Green: Hall A E97-110Blue: Hall A E01-012

• Good agreement with existing Neutron data.

• Some disagreement with existing proton data.

• More proton data is needed.

Motivation

• Measure the proton structure function, 𝑔2, in the low 𝑄2 region for the first time.

• Provides a unique opportunity to test the Burkhardt-Cottingham Sum Rule in the low 𝑄2 region.

• Benchmark test of Chiral Perturbation Theory by extracting the generalized longitudinal-transverse spin polarizability.

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Spin Polarizability

𝛿𝐿𝑇 𝑄2 =

16𝛼𝑀2

𝑄6

0

𝑥0

𝑑𝑥 𝑥2 𝑔1 𝑥, 𝑄2 + 𝑔2 𝑥, 𝑄

2

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• Neutron data shows deviations from 𝜒𝑃𝑇calculations.

• No proton data yet!

Neutron

Motivation

• Measure the proton structure function, 𝑔2, in the low 𝑄2 region for the first time.

• Provides a unique opportunity to test the Burkhardt-Cottingham Sum Rule in the low 𝑄2 region.

• Benchmark test of Chiral Perturbation Theory by extracting the generalized longitudinal-transverse spin polarizability.

• Improve calculations of Proton Hyperfine Splitting.

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Experimental Setup

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Continuous Electron Beam Accelerator Facility (CEBAF)• Maximum Energy 12GeV• 200𝜇𝐴 current• Electron polarization ~85%

Thomas Jefferson National LaboratoryNewport News, Virginia

You are here

Experimental Setup

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Beam Current

Monitors

Beam Rasters

Chicane

Beam Position Monitor

Scattering Chamber

Local Dump

Septum Magnet

High Resolution Spectrometers

• New beamline equipment installed for low current running (<100nA)

• Chicane installed for transverse target field requirements.

• Rotatable 2.5T/5T scattering chamber.

• Local dump and septum magnets

Kinematics and Projections

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0.02 < 𝑄2 < 0.2𝐺𝑒𝑉2

Beam Energy (GeV)

Target Field (T)

1.158 2.5

1.706 2.5

2.254 2.5

2.254 5.0

3.352 5.0

Kinematics and Projections

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LT Spin PolarizabilityBC Sum Integral

Analysis Progress

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Completed• Run DB• HRS Optics

• Field Measurement Analysis• VDC t0 calibration• Simulation Package• Optics Reconstruction

• Detector Calibrations/Efficiencies• Scalers

• Helicity Decoding• BCM calibrations• Deadtime calculations

• Target Polarizations• BPM calibrations• Raster size calibration

In Progress• Packing fraction/dilution analysis• Elastic PBPt check• Radiative corrections• Acceptance study

Online Results

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Courtesy R. Zielinski

Online Results

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Summary

• The 𝑔2𝑝

Experiment ran very successfully in spring, 2012.

• New instrumentation and beam requirements (and fires) introduced many challenges to the running and analysis.

• A first pass of production data is complete and analysis is well underway!

• We hope to have offline asymmetries and cross-sections by spring of next year

• 𝑔2 calculation shortly after, possibly by summer, 2015.

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E08-027 Collaboration

SpokespeopleAlexander CamsonneJ.P. ChenDon CrabbKarl Slifer

Post DocsKalyan AlladaEllie LongJames MaxwellVince SulkoskyJixie Zhang

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Graduate StudentsToby BadmanMelissa CummingsChao GuMin HuangJie LiuPengjia ZhuRyan Zielinski

Thank You!