Jefferson Lab PAC 30 1 August 23, 2006 PR (Hall A) ● PR (Hall C) Measuring the Neutron g 2 and d 2 at 12 GeV PR (Hall A) ● PR (Hall C) Goal:  Clearly map out Q 2 evolution of neutron g 2 for x > 0.5  Determine the neutron d 2 at = 3, 4, 5 GeV 2 An Experiment in Hall A: (approved by the Hall A Collaboration)  A polarized electron beam of 6.6, 8.8 GeV and polarized 3 He target  Measure unpolarized cross section for reaction in conjunction with the transverse asymmetry and the parallel asymmetry for 0.2 < x < 0.9 with 2.5 < Q 2 < 9 GeV 2. An Experiment in Hall C:  A polarized electron beam of 11.0 GeV and polarized 3 He target  Measure, for reaction for 0.2 < x < 0.9 with 2 < Q 2 < 6 GeV 2. Spokespeople:  Hall A: T. Averett, J.P. Chen, W. Korsch, B. Sawatzky  Hall C: T. Averett, W. Korsch, Z.E. Meziani, B. Sawatzky

Jefferson Lab PAC 30 2 August 23, 2006 PR (Hall A) ● PR (Hall C) Polarized deep inelastic cross sections

Jefferson Lab PAC 30 3 August 23, 2006 PR (Hall A) ● PR (Hall C) g 2 and Quark-Gluon Correlations QCD allows the helicity exchange to occur in two principle ways

Jefferson Lab PAC 30 4 August 23, 2006 PR (Hall A) ● PR (Hall C) Moments of Structure Functions (Extracted from neutron and hyperon weak decay measurements)

Jefferson Lab PAC 30 5 August 23, 2006 PR (Hall A) ● PR (Hall C) Moments of Structure Functions (continued) To extract f 2, d 2 needs to be determined first. Both d 2 and f 2 are required to determine the color polarizabilities 3

Jefferson Lab PAC 30 6 August 23, 2006 PR (Hall A) ● PR (Hall C) Color “polarizabilities”

Jefferson Lab PAC 30 7 August 23, 2006 PR (Hall A) ● PR (Hall C) World Data on on g 2 n However, Q 2 values for these data range from 0.1 – 15 GeV 2

Jefferson Lab PAC 30 8 August 23, 2006 PR (Hall A) ● PR (Hall C) World Data on d 2 (nucleon elastic contribution suppressed) Projected JLab E06-014

Jefferson Lab PAC 30 9 August 23, 2006 PR (Hall A) ● PR (Hall C) Model evaluations of d 2

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) The proposal for Hall A and BigBite A 6.6 and 8.8 GeV polarized electron beam scattering off a polarized 3 He target Measure unpolarized cross section for reaction in conjunction with the parallel asymmetry and the transverse asymmetry for 0.2 < x < 0.9 with 2.5 < Q 2 < 9 GeV 2.  Asymmetries measured by BigBite for two kinematic settings:  E beam = 6.6 GeV and  = 40 °, E beam = 8.8 GeV and  = 30°  Absolute cross sections measured simultaneously by L-HRS Determine d 2 n and g 2 n using the relations where, I beam = 10 μA P beam = 0.8 P targ = 0.5  = angle between scattering plane and transverse target pol.

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) Floor layout for Hall A HRS used to measure at 10 momentum settings for each beam energy.  will also reverse the field to monitor  - /  + and e - /e + asymmetries BigBite measures and with single configuration at each beam energy. Hall A Two beam energies  6.6, 8.8 GeV 200 hours for 6.6 GeV data set  175 hrs transverse  25 hrs parallel 400 hours for 8.8 GeV data set  360 hrs transverse  40 hrs parallel

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) BigBite in Hall A GeN electron detector package (upper left) will modified by increasing the MWDC spacing to improve the high momentum position resolution (lower left). The Gas Cerenkov (currently under construction for E06-014) will be used to suppress pion backgrounds.

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) Kinematics for Hall A HRS used to measure at 10 momentum settings for each beam energy.  will also reverse the field to monitor  - /  + and e - /e + asymmetries BigBite measures and with single configuration at each beam energy.  Optimized to minimize error on extracted g 2 as well as d 2 Ratio of Transverse to Parallel hours is ~8:1 Hall A: 200 hours for 6.6 GeV data set hours for 8.8 GeV data set BigBite Rates/backgrounds computed using multiple parametrizations: MRST2001LO, CTEQ61, H12000LO, and Wiser fit of SLAC data. Results cross-checked against previous JLab data.

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) Kinematics for Hall A (cont...)

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) Projected x 2 g 2 (x,Q 2 ) results from Hall A g 2 for 3 He is extracted directly from L and T spin-dependent cross sections measured within the same experiment. Strength of BigBite: large x coverage per setting (but large Q 2 variation)

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) Systematic Error Contributions to g 2 n and d 2 n ● Systematics comparable for Halls A & C ● Radiative correction uncertainty cross-checked with E (Spin Duality) experiment  worst case: 4.4% ● Pion rejection ratio of  1000:1 (minimum)  10000:1 (achievable)

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) TAC Comments for Hall A Background from the downstream beamline and dump?  GeN (E02-013) observed dominant background was from target area  Increase in soft neutrons from dump at higher beam energy (~3x) can only affect scintillator plane (shielded by Pb-glass). Scaling from GeN suggests worst case still OK. Pion asymmetry was measured in Spin-Duality (~0.1). The combination of a gas Cerenkov and the Pb-Glass system in BigBite should easily provide 1000:1 rejection ratio, 10000:1 with some work  raw pion uncertainty contribution at the few percent level  we will also have a direct measure of the contribution by sampling the pion background  final correction will reduce uncertainty further

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) Electron and pion rates computed using multiple parametrizations and cross checked against JLab data using the same 3 He target design.  e+ cross sections will be explicitly measured in HRS (should be <3%)  lowest momentum bin will be driven by observed e-/e+ ratio  expectation is that this will be around x = 0.25 BigBite momentum and acceptance derived from a full Monte Carlo that included the modified detector stack. TAC Comments for Hall A, (cont...)

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) The proposal for Hall C and SHMS/HMS An Experiment in Hall C:  A polarized electron beam of 11.0 GeV and polarized 3 He target  Measure, for reaction using both the SHMS and HMS running in parallel for 3 kinematic settings each  SHMS: (p 0 = 8.0 GeV/c,  = 11.0 °), (p 0 = 7.0 GeV/c,  = 13.3°), (p 0 = 6.3 GeV/c,  = 15.5°)  HMS: (p 0 = 4.2 GeV/c,  = 13.5°), (p 0 = 5.0 GeV/c,  = 16.4°), (p 0 = 3.4 GeV/c,  = 20.0°) Determine d 2 n and g 2 n using the relations: I beam = 10 μA P beam = 0.8 P targ = 0.5

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) Floor layout for Hall C SHMS collects data at Θ = 11 °, 13.3 ° and 15.5 ° for 200 hrs each  data from each setting divided into 4 bins HMS collects data at Θ = 13.5°, 16.4 ° and 20.0 ° for 200 hrs each Hall C One beam energy  11 GeV Each arm measures a total cross section independent of the other arm. Experiment split into three pairs of 200 hour runs with spectrometer motion in between.

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) Kinematics in Hall C (E beam = 11 GeV) SHMS collects data at Θ = 11 °, 13.3 ° and 15.5 ° for 200 hrs each  data from each setting divided into 4 bins HMS collects data at Θ = 13.5°, 16.4 ° and 20.0 ° for 200 hrs each Ratio of Transverse to Parallel hours is ~11:1  Hall C: SHMS and HMS collect data in parallel  Total time: 600 hours Rates/backgrounds computed using multiple parametrizations: MRST2001LO, CTEQ61, H12000LO, and Wiser fit of SLAC data. Results cross-checked against previous JLab data.

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) Kinematics for Hall C (cont...)

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) Projected x 2 g 2 (x,Q 2 ) results from Hall C g 2 for 3 He is extracted directly from L and T spin-dependent cross sections measured within the same experiment. Strength of SHMS/HMS: nearly constant Q 2 (but less coverage for x < 0.3) Projected points are vertically offset from zero along lines that reflect different (roughly) constant Q 2 values from 2.5—6 GeV 2.

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) Systematic Error Contributions to g 2 n and d 2 n ● Systematics comparable for Halls A & C ● Radiative correction uncertainty cross-checked with E (Spin Duality) experiment  worst case: 4.4% ● Pion rejection ratio of ~10000:1 should be achievable with standard SHMS/HMS detectors.

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) TAC Comments for Hall C A 2x2 mm rectangular raster has been tested with the polarized 3 He target in Hall A. The planned Hall C fast raster system will be sufficient. Systematic estimates for Hall C may be conservative in a few areas  beam current, acceptance cuts  not dominant contributors, smaller is always better! Radiative correction uncertainty estimate is comparable to final Spin-Duality results (4.4% in the worst case)

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) Combined Kinematics from both Halls

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) Q 2 evolution of d 2 (both Halls) Directly measure Q 2 evolution of g 2 at constant x

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) Q 2 evolution of d 2 (both Halls) Lines of integration for d 2 at Q 2 = 3, 4, 5 GeV 2

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) Expected Error on d 2 Proposal (both Halls) The proposed measurements are at constant Q 2 The dominant E155x point includes data evolved down from as far as 15 GeV 2 !

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) PAC30 'Contribution' requirement Hall A Proposal (PR ): 2 FTE manpower from Temple, W&M, Kent. 1-2 FTE manpower from USTC and CIAE ➔ Chinese collaborators (now official) Upgraded HRS DAQ systems Moeller polarimeter Compton polarimeter Polarized 3 He target Hall C Proposal (PR ): 2 FTE manpower from Temple, W&M, Kent. 1-2 FTE manpower from USTC and CIAE ➔ Chinese collaborators (now official) Compton polarimeter Moeller polarimeter ARC beam energy measurement Double fast-raster system Polarized 3 He target Manpower devoted to construction and commissioning of listed items in collaboration with Jefferson Lab staff.

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) Summary We propose a pair of complementary measurements in Hall A and Hall C to  map out g 2 with unprecedented x, Q 2 coverage and precision  precisely measure the neutron d 2 n at Q 2 = 3, 4, and 5 GeV 2.  precisely measure Q 2 evolution of g 2 n (x) for x > 0.5 Provide a rigorous test for theory (lattice QCD).  we can achieve a statistical uncertainty of ∆d 2 n ~ 5 x  measurements done at constant Q 2 (never been done before!) Dramatically improve our knowledge of g 2 n (x)  vastly improve the available data for x > 0.2, all with better precision and with an optimized distribution in x and Q 2 Uses standard equipment in Hall A and Hall C (plus polarized 3 He target) We request Hall A: 700 hours of polarized beam divided between 6.6 and 8.8 GeV.  ~ 600 hours of production, ~100 hours of overhead and calibration Hall C: 700 hours of polarized beam at 11 GeV.  ~ 600 hours of production, ~100 hours of overhead and calibration

Jefferson Lab PAC August 23, 2006 PR (Hall A) ● PR (Hall C) d 2 and g 2 evolution (both Halls) Lines of integration for d 2 at Q 2 = 3, 4, 5 GeV 2 Directly measure Q 2 evolution of g 2 at constant x