[A1n_d2n] Abstract for the A1n talk in DIS2022

[JPChen]

Hi, Mingyu and Murchhana,

Thanks for the draft abstracts.
The abstract submission deadline is now extended to Feb 20, which gives us more time to give you feedback.

Best regards.

Jian-ping

> On Feb 11, 2022, at 1:48 PM, mingyu at jlab.org wrote:
> 
> Hi All,
> Here is my draft for the abstract for the A1n talk in the upcoming
> DIS2022. Feel free to leave comments and suggestions. (in LaTex math
> formulae for indico.cern.ch abstract submittion)
> 
> The virtual photon asymmetry $A_1$ is one of the fundamental quantities
> that provide information on the spin structure of the nucleon.  The value
> of A1 at high $x_{Bj}$ is of particular interest because valence quark
> dominate in this region, which makes it a relatively clean region to study
> the nucleon spin structure.  There are several theoretical calculations
> that apply to the high x valence quark region, and here we will focus on
> the neutron $A_1^n$. The neutron $A_1^n$ is predited to be 0 in the naive
> SU(6) quark model, while both relativistic constituent quark model (RCQM)
> and perturbative QCD (pQCD) predict $A_1^n$ to be 1 at $x$=1. Predictions
> for the quark polarization in the nucleon also exist: $\Delta d/d$ is
> predicted to approach $+1$ in pQCD while RCQM prediction remains negative
> at the $x\to 1$ limit. The $A_1^n$ experiment during the 6 GeV JLab era
> showed that $a_1^n$ indeed turns positive at $x\sim 0.5$, while $\Delta
> d/d<0$ at $x=0.61$. Subsequent theoretical studies based on our 6 GeV
> results claimed that quark orbital angular momentum or non-perturbative
> nature of the strong interaction plays a significant role in the valence
> quark region.
> With the 12 GeV upgrade of JLab, a new experiment on $A_1^n$
> (E12-06-110)$^1$ was carried out using a 10.4 GeV beam, a polarized $^3$He
> target, and the HMS and the Super-HMS (spectrometers) in Hall C. This
> measurement reached a deeper valence quark region: $x\sim 0.75$. And once
> combined with expected data from the upgraded CLAS12 experiment on the
> proton $A_1^p$, we will finally be able to reveal whether $\Delta d/d$
> turns positive (as in pQCD) or remain negative at high $x$ (as in RCQM).
> We will present the physics of $A_1^n$ and report the analysis results
> from the $A_1^n$  experiment. Performance of an upgraded polarized $^3$He
> target will be presented.
> $^1$ This work is supported in part by the U.S. Department of Energy,
> Office of Nuclear Physics, under Contract No. DE-FG02-94ER4084.
> 
> Sincerely,
> Mingyu Chen
> 
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