[Sbs] A JLab12 GeV proposal for PAC42, SIDIS reaction with SBS+BB double-spin asymmetry measurements for nucleon spin-flavor decomposition.

[Xiaodong Jiang]

Dear Collaborators,

  As Andrew briefly discussed last Wednesday at the SBS weekly phone
meeting.

  Andrew, Nilanga  and myself have been developing a proposal to PAC42 on
measuring SIDIS beam-target double-spin asymmetries on a longitudinally
polarized 3He target (A_1n^h on neutron), for nucleon spin-flavor
decomposition, with the SBS+BB combination.  The key features of the
experiments are:

  1. High luminosity, high polarization, pin down A_1n^h extremely well on a
dense grid of (x, Q2, z) and vs hadron p_t. The precision data set will feed
into DSSV NLO QCD global fit, which will include DIS, SIDIS  as well as
inclusive pi^0, jet, and W boson asymmetries from RHIC p+p.  The high
precision data set will put tight constraints on  valence quark
polarization, sea quark polarization, and indirectly on gluon polarization.

  2. Accessing polarized neutron information,  have a much better F.O.M
compared to  CLAS12 with ND3, NH3 combination.
BigBiet at 30 degree as electron arm, to reach the highest possible Q^2
coverage for SIDIS at JLab12 GeV, complementary to SoLID's kinematic
coverage.  

  3. Well controlled hadron particle identification, by RICH, for a clear
pion/Kaon separation. Straight-line tracking in the detector package.

  4. Identical phase space for positive and negatively charged pion, so that
we can pin down A_{1He}^{\pi^+ - \pi^-} very well. This flavor non-singlet
observable is of special interest,  gluon density, gluon polarization, and
gluon fragmentation functions drop out to all orders in QCD.   Under the
assumption of SU(2) symmetry,  only valence quark's polarization
contributes to this special asymmetry combination, sea quarks drops out.
Thus, a better way to achieve spin-flavor decomposition, without requiring
detailed knowledge of quark to pion fragmentation functions.

  5. On a polarized neutron (3He) target,  we are more sensitive to \Delta
d, \Delta dbar. In addition to access valence quark polarization, we can
also access sea quark polarization, \Delta ubar, \Delta dbar, and polarized
sea flavor asymmetry (\Delta ubar - \Delta dbar).  Recent STAR W asymmetry
data strongly favors a positive sea up-quark polarization at x=0.05-0.2. A
precision measurement in SIDIS reaction is very urgently needed to verify
the apparent positive ubar polarization, and to provide the first
information on dbar polarization. The results will strongly impact EIC's
physics program.

  6. We can pin down valence quark polarization very well,  from x=~0.15 to
x=~0.7.   This is one of the major physics program that drove the Jlab-12
GeV upgrade.

  7. Experimental set up is very similar to that of SBS+BB Transversity,
with longitudinally polarized 3He target, can fit into the same run group.

  8. SIDIS multiplicities will also be measured in the same setup, using
reference cells.

  we  have a  working draft of a proposal for pac42 (deadline June 2nd),
please take a  look  at:

 https://userweb.jlab.org/~puckett/PAC42_deltad/main_Deltaq.pdf
 
Several plots and sections are still under construction,   references are
not all fixed yet.

We very much appreciate your supports.  Please consider to join this
proposal. 
Please email us a list of collaborators from your institution.

  Thank you very much,

Andrew, Nilanga and Xiaodong

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 Xiaodong Jiang
 P25 group, MS H846,                     Tel. 505 606 0437
 Los Alamos National Laboratory
 Los Alamos, NM 87545
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