E12 07 108 gmp precision measurement of the proton elastic cross section at high q 2
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E12-07-108 : ( GMp ) Precision Measurement of the Proton Elastic Cross Section at High Q 2 PowerPoint PPT Presentation

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E12-07-108 : ( GMp ) Precision Measurement of the Proton Elastic Cross Section at High Q 2. Vincent Sulkosky Massachusetts Institute of Technology f or the E12-07-108 Collaboration Spokespeople: J. Arrington, E. Christy, S. Gilad , B. Moffit , V. Sulkosky , B. Wojtsekhowski

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E12-07-108 : ( GMp ) Precision Measurement of the Proton Elastic Cross Section at High Q 2

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E12-07-108: (GMp)Precision Measurement of theProton Elastic Cross Sectionat High Q2

Vincent Sulkosky

Massachusetts Institute of Technology

for the E12-07-108 Collaboration

Spokespeople: J. Arrington, E. Christy, S. Gilad, B. Moffit,

V. Sulkosky, B. Wojtsekhowski

Hall A CollaborationMeeting

December 10th, 2012


Goals forGMp

  • Accurately measure e-p elastic cross section in

    kinematics similar to other JLab form factor


  • Improve accuracy of the cross section by as much as a

    factor of 4 (< 2%) over previous measurements

  • Key input to all form factors and many of other

    experiments, where elastic scattering is a background

  • Provide measurement of power scaling for GMp

    in the range Q2 = 7-14 GeV2

  • Approved for 24 PAC days



PAC Approved 24 days

Control of Systematics

Planned improvements

  • Tracking efficiency

    • Include front chambers of FPP as third wire chamber

      with VDCs

  • Target density

    • Use precise optics to provide software cuts on vertex

    • Use race-track cell targets with vertical flow to

      minimize fluctuations

  • Solid Angle

    • A benefit of improved optics

    • Precise determination of target location using

      swing arm

HRS Detector Stacks

Use standard detectors including one plane of FPP

for additional tracking

FPP (front chambers)

Problems: gas consumption

> 50 l/h HV trips often

due to gas, many dead

wires/some electronics

Done: repair of dead electronics

built parallel gas

distribution tests of each

wire/disconnect dead

Still to do: HV distribution in one

layer; gas distribution

should be as wide as a

straw block; tension test

for each wire

~ 100 wires need to

be restrung

VDC Improvements

  • Upgrade electronics to use

    1877S, which allows sparsification

  • Replace aging A/D cards and will reuse MAD cards

  • Provide very good stability against

    oscillations and rate capability

    of 8 MHz (in full chamber)

Gas Cherenkov Improvements

  • Reflectivity measurements of HRS GCC mirrors will begin this month

  • After initial measurements, recoating of mirrors

  • Check and replace PMTs as needed

  • Cosmic mirror calibration

Target Configuration

LH2: 15 cm Racetrack:

  • Vertical flow design

  • Dedicated studies of density

  • Luminosity monitors in


    Solid Al Foils (Dummy):

    Endcap subtraction

    Carbon Optics Targets:

    1-2 cm spacing along zvertex for extended target acceptance

Solid targets/Endcaps measured with x-ray attenuation

HRS Optics and Angle

Wire target on strong arm, reproducibility of 100 microns sufficient, 20 microns is likely achievable

Expected Precision

Systematic Uncertainties

Systematic Uncertainties

Tasks & Responsibilities

Tasks & Responsibilities (cont.)

Commitments in Manpower

  • FPP work: Albert Shahinyan, GalustSargsyan and Karen (YerPHI)

  • HRS detectors:

    • Milan Dukic (NCCU technician) for three weeks

    • HamzaAtac (Temple) for two weeks

    • NSU student for one month

    • LongwuOu (MIT student) for one month

    • Kai Pan (UVa student) for two weeks

    • PuneetKhetarpal (FIU postdoc) for two weeks

    • John LeRose (JLab) part time

    • Mohamed NuhHashirRashad (ODU); DVCS graduate student

    • JinJin Pan (HU); graduate student (potential GMp student)

    • Yang Wang (WM); graduate student (potential GMp student)

Potential Physics Prospects


  • Firstexperiment to run in the 12-GeV era with DVCS.

  • GMp will provide a baseline for the 21st century level of accuracy in form factor measurements by precisely measuring the cross section at Q2 up to 14 GeV2.

  • It is the only measurement of the cross section; key input to all form factors and many of other experiments

  • The DVCS luminosity × HRS-R solid angle (1/8 of GMpproposal) and restricted angle range of HRS-R allows for some parallel running of GMp during DVCS data taking.

  • Collaborators are welcome to participate; much work is required before 2014.

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