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

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

measurements

- 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

- Include front chambers of FPP as third wire chamber
- 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

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

- 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)

- 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

LH2: 15 cm Racetrack:

- Vertical flow design
- Dedicated studies of density
- Luminosity monitors in
datastream

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

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)

Summary

- 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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