1 Melynda Brooks, “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

2 Melynda Brooks, “Understanding the Origin of the Nucleon Spin” “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’  )n JLAB provides electron beam of appropriate energy CLAS12 Detector provides target, large acceptance to detector e’, , 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 Question 1

3 Melynda Brooks, “Understanding the Origin of the Nucleon Spin” 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 Melynda Brooks, “Understanding the Origin of the Nucleon Spin” 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. Q – Q1 2011Install JLAB Hall B Monte Carlo, set up geometry and physics event generator Q – Q3 2011Run Monte Carlo with different detector configurations – determine acceptance for physics signal and at the same time start trigger software development Q – Q3 2012Formulate Proposal to CLAS12 – Detector collaboration approval must precede JLAB PAC submission Q (Q4 2013)Formulate Proposal to PAC – iteration may be needed if PAC recommends more work

5 Melynda Brooks, “Understanding the Origin of the Nucleon Spin” 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. Q – Q3 2011Computer Simulations - Examine different possible trigger algorithms using software. Select best algorithm, taking into account ease of FPGA development Q – Q3 2012FPGA Coding– translate C++ code into VHDL code (for FPGAs) Q – Q3 2013Test algorithms with hardware– Install VHDL code into prototype hardware and test

6 Melynda Brooks, “Understanding the Origin of the Nucleon Spin” 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. Q – Q3 2011Layout Trigger Board Q – Q2 2012Test Prototype Hardware – Install VHDL code and test, determine what iterations needed Q – Q Iterate Hardware and Software Design– 2 nd round hardware if needed, evolve FPGA code

7 Melynda Brooks, “Understanding the Origin of the Nucleon Spin” 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 : 1.Full simulations and trigger hardware – Needed to defend proposal 2.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. 3.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 Melynda Brooks, “Understanding the Origin of the Nucleon Spin” Backups

9 Melynda Brooks, “Understanding the Origin of the Nucleon Spin” DVCS and Angular Momentum Quark angular momentum can be extracted if GPDs H q, E q are measured: Measuring pDVCS gives you H q Measuring nDVCS cross sections, asymmetries give you E q GPD: Small for nDVCS

10 Melynda Brooks, “Understanding the Origin of the Nucleon Spin” 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. Elastic Scattering transverse quark distribution in Coordinate space DIS longitudinal quark distribution in momentum space GPDs Fully-correlated quark distribution in both coordinate and momentum space

11 Melynda Brooks, “Understanding the Origin of the Nucleon Spin” Physics Simulation Result Asymmetry measurement, with error bars, compared to different quark angular momenta will be produced. Recommended running conditions will be produced.