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Understanding the Origin of the Nucleon Spin

Understanding the Origin of the Nucleon Spin Andi Klein, P-23, Melynda Brooks P-25 , Pat McGaughey, P-25, Matt Stettler, ISR-3. Question 1. “ Explain your development schedule in detail and describe what contingencies exist in case of problems.” Reiteration of goals:

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Understanding the Origin of the Nucleon Spin

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  1. Understanding the Origin of the Nucleon Spin • Andi Klein, P-23, Melynda Brooks P-25, Pat McGaughey, P-25, Matt Stettler, ISR-3

  2. Question 1 • “Explain your development schedule in detail and describe what contingencies exist in case of problems.” • Reiteration of goals: • Neutron Deeply Virtual Compton Scattering (nDVCS) measurement gives direct access to quark angular momentum in the nucleon. D(e, e’g)n • JLAB provides electron beam of appropriate energy • CLAS12 Detector provides target, large acceptance to detector e’, g, recoil p. • Needed:Upgraded trigger to allow collection of data, full physics simulation to support proposal to JLAB PAC • Development Needed: • Physics Simulations – Quantitatively determine kinematic acceptance and resolution to allow precise sensitivity plots to be produced, determine optimum running conditions. • Trigger Simulations – Develop tracking trigger algorithms in software • Build Hardware – Build and test trigger hardware • Submit Proposal – Submit experimental proposal to CLAS12 and JLAB PAC

  3. Physics Motivation Reiterated • NSAC Long Range Plan: • “..and if we are to claim any understanding of QCD, we must be able to identify how this value [the nucleon spin] arises from the nucleon’s internal structure.” • NSAC specifically gave JLAB #1 priority for its Long Range Plan: • “We recommend completion of the 12 GeV CEBAF Upgrade at Jefferson Lab. The Upgrade will enable new insights into the structure of the nucleon, the transition between the hadronic and quark/gluon descriptions of nuclei, and the nature of [quark] confinement.”

  4. Question 1 continued • “Explain your development schedule in detail and describe what contingencies exist in case of problems.” • Physics Simulation Development: • Challenges/Contingency: Physics simulations straight-forward, but will take some time. PAC presentation main challenge. Contingency – allow time for 2 presentations if needed.

  5. Question 1 continued • “Explain your development schedule in detail and describe what contingencies exist in case of problems.” • Trigger Algorithm Development: • Challenges/Contingency – implementing efficient • tracking algorithm in FPGA. Plan to test several • different algorithms in software first, allow time for • iteration in hardware testing.

  6. Question 1 continued • “Explain your development schedule in detail and describe what contingencies exist in case of problems.” • Hardware Development: • Challenges/Contingency – If density of boards becomes too challenging, would need to move to more front-end boards and adapt back-end trigger boards accordingly. Need to be able to accommodate different size FPGAs, to be determined by what is needed by tracking algorithm of choice.

  7. Question 2 • “If this development project is successful, what is the probability of being accepted for a real JLAB experiment? What steps are involved in the approval process?” • Steps Involved: • Full simulations and trigger hardware – Needed to defend proposal • Present proposal to CLAS - Collaboration must sanction before proposing to PAC. Do not see any issues as this is an important measurement, we will provide trigger bandwidth. • Present proposal to JLAB PAC - PAC meets each year in January and July. Ratings of A, B, or deferred are given. Often deferred comes with homework assignments so want to have time to present twice if needed. • Chances for being approved – excellent: • DVCS is one of the main thrusts of JLAB • We have already received strong endorsement from CLAS12 management • Trigger contribution is already recognized as important by JLAB - LANL involvement in trigger considered highly desirable by JLAB • Our proposed DVCS measurement can be carried out with existing detector - With trigger upgrade, no new detector development is needed for CLAS12

  8. Backups

  9. DVCS and Angular Momentum • Quark angular momentum can be extracted if GPDs Hq, Eq are measured: • Measuring pDVCS gives you Hq • Measuring nDVCS cross sections, asymmetries give you Eq GPD: Small for nDVCS

  10. Generalized Parton Distribution Functions (GPDs) • What we need is the correlation of momentum and space: • Wigner quantum mechanical phase space distribution correlates momentum and space, non-relativistic. In classical limit, goes to classical phase-space distribution. • GPD can be thought of as the relativistic extension to quarks and gluons. They are related to the more well known quantities F1: Dirac, F2: Pauli, F3: axial and F4: pseudo-scalar Form factors . GPDs Fully-correlated quark distribution in both coordinate and momentum space Elastic Scattering transverse quark distribution in Coordinate space DIS longitudinal quark distribution in momentum space

  11. Physics Simulation Result • Asymmetry measurement, with error bars, compared to different quark angular momenta will be produced. • Recommended running conditions will be produced.

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