The g 2^pExperiment - Thomas Jefferson National...

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

Toby Badman DNP 2014 2

Unpolarized nucleon structure functions.

ee’

P

W𝛾∗


𝑑𝜎

𝑑Ω𝑑𝐸′= 𝜎𝑀𝑜𝑡𝑡

1

𝜈𝐹2 𝑥, 𝑄

2 +2

𝑀𝐹1 𝑥, 𝑄

2 𝑡𝑎𝑛2𝜃

2+ 𝛾𝑔1 𝑥, 𝑄

2 + 𝛿𝑔2(𝑥, 𝑄2)


Polarized nucleon spin structure functions.

ee’

P

W

Polarized target

Polarized 𝑒− beam𝛾∗


∆𝜎∥ =𝑑2𝜎↑⇑

𝑑Ω𝑑𝐸−𝑑2𝑑↓⇑

𝑑Ω𝑑𝐸∝ 𝛼𝑔1 𝑥, 𝑄

2 − 𝛽𝑔2 𝑥, 𝑄2

∆𝜎⊥ =𝑑2𝜎↑⇒

𝑑Ω𝑑𝐸−𝑑2𝑑↓⇒

𝑑Ω𝑑𝐸∝ 𝛾𝑔1 𝑥, 𝑄

2 + 𝛿𝑔2 𝑥, 𝑄2



𝑔1 𝑥, 𝑄2 ∝ ∆𝜎∥ + tan

𝜃

2∆𝜎⊥

𝑔2 𝑥, 𝑄2 ∝ −∆𝜎∥ +

1 + 1 − 𝑦 cos 𝜃

1 − 𝑦 sin 𝜃∆𝜎⊥


• ∆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.


SLAC JLAB SANE

Motivation


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


Motivation

The 0𝑡ℎ moment of 𝑔2 should

satisfy (for all 𝑄2):

01𝑔2 𝑥, 𝑄

2 𝑑𝑥 = 0


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



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


Spin Polarizability

𝛿𝐿𝑇 𝑄2 =

16𝛼𝑀2

𝑄6

0

𝑥0

𝑑𝑥 𝑥2 𝑔1 𝑥, 𝑄2 + 𝑔2 𝑥, 𝑄

2


• Neutron data shows deviations from 𝜒𝑃𝑇calculations.

• No proton data yet!

Neutron

Motivation



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

• Improve calculations of Proton Hyperfine Splitting.


Experimental Setup


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


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


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


LT Spin PolarizabilityBC Sum Integral

Analysis Progress


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


Courtesy R. Zielinski

Online Results


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.


E08-027 Collaboration

SpokespeopleAlexander CamsonneJ.P. ChenDon CrabbKarl Slifer

Post DocsKalyan AlladaEllie LongJames MaxwellVince SulkoskyJixie Zhang


Graduate StudentsToby BadmanMelissa CummingsChao GuMin HuangJie LiuPengjia ZhuRyan Zielinski

Thank You!

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