History: Target

Information about the polarized target of GEn, the geometry of the cells and reference cells, and how to use them in the analysis them (eg: get their temperature to get density, etc.) will go here.

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!!Target Geometry
Aidan's ((Target Glass Thickness Measurements)) page.

The target ladder looked like:
{img src="img/wiki_up/Target2.jpg" width=200}

!!Edna target cell
An early version of Aidan's writeup about the "Edna" target cell, including a description of the full analysis chain to determine the cell's polarization, can be found in [http://hallaweb.jlab.org/experiment/E02-013/mtg/2009nov04/kelleher/target_edna.pdf|target_edna.pdf]

!!Target Polarization:

Target polarization has been entered into the MySQL database. The columns therein are: (1)time of NMR measurement, (2)polarization, (3)error in polarization, (4)target cell. Currently, data only for Edna exists. This will be updated as soon as the other data are analyzed (Dolly and Barbara).

The numbers here are from Aidan's article on polarization numbers.

(A script to get the polarization for any run should be ready soon.)

Nitrogen Densities and Dilution Analysis:

There is about 1.5% nitrogen (by density) in the target cells. The fraction of detected events that come from this nitrogen instead of the ³He is referred to as nitrogen dilution.

Below are two scripts that get the densities of nitrogen in the target (lower) chamber of the target cell Edna and the reference cell. Edna was used for kinematics 3 and 4 and during the second run of kinematic 2. These scripts use the EPICS variables in the mysql database and output the nitrogen densities in amg units. To get densities in atoms/cm3, multiply the amg number by k � 2.6868 � 10¹⁹ for k-atomic molecular gas (e.g. k=2 for nitrogen).

The nitrogen dilution factor can then be calculated as:


D_N2 = 1 - R(Y_N2,ref/Y_N2,3He)


where


R: ratio of nitrogen densities in target chamber and reference cell (obtained by dividing the nitrogen density outputs of the above scripts)

Y: Yields (total number of neutral events after all relevant cuts†) from the reference cell and target cell.

Where does this factor, D_N2, enter the asymmetry calculations?

A_phys = A_ex/(P_eP_nP_tD_N2D_bck),
where A_ex is the experimental raw asymmetry corrected for false asymmetries, P_nP_t is the neutron polarization in the 3He target, P_e is the electron beam polarization and D_bck is the background dilution factor.



(A script that outputs average N2 density and target polarization for a given run should be ready soon. All this could then be put into the MySQL database as well.)

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!! Holding field

Ameya's documents on the target box field measurements can be found here:
http://www.jlab.org/~kolarkar/docs/mag_field_dir.pdf

Pictures are here:
http://www.jlab.org/~kolarkar/compass/