G2p other optics plan

Normal HRS optics + Target Field optics

I think there is an important factor to find out: How large is the effective magnetic field region. If it is small, or quantitatively

typical length * bending angle (rad) * 4% (acceptance) < 1mm, (1)

then the optics can be decoupled to two parts with small mixing: 1. normal HRS optics from an effective target 2. bending in the target region Otherwise, the question will be more complex.

I will continue assuming Eq (1) is valid, then here is my PRELIMINARY thinking on optics runs.

1. Calibrate part I, HRS optics w/ septum at 1GeV momentum. Start with an initial optics database like PREX or APEX for replay. Target field is turned off here. Single C foil target is used

      1.1 Sieve OUT, Raster OFF then ON (as large as possible), take data

at quasi-elastic kinematics. This step is for vertex calibration of full acceptance, which is going to be used for clean up sieve pattern with vertex cut.

      1.2 Sieve IN, set beam at elastic kinematics, perform delta scan, dp

= +4% -> -4%, 2% per step. 1.1 & 1.2 calibrate dp, th & ph for full acceptance.

      1.3 Large Raster ON. repeat 1.2, dp = 0%. This is to calibrate the

raster correction. If the correction have strong correlation with dp (traditionally not), then dp scan will also be needed.

2. Calibrate part II

      2.1 Scan target field strength 0T -> 5T. Take elastic data, dp = 0%

with Sieve IN, raster off. The goal is to get a correction function on dp, th & ph, which is a function of TargetField/HRS_p0 to leading order. You may need a target field simulation to help you get the function. Note: correlation between optics observables introduced by the target field is small for your case of small scattering angle.

      2.2 You may need to scan dp and/or raster for step 2.1, depending on

how strong the correction function is correlated to dp/beam position, relative to your precision. A calculation/simulation before the experiment will tell.

3. Repeat calibration at 2GeV. The calibration will be easier since you already have a good optics database to start with. You can reduce the number of data point. Then build the optics as a function of (HRS_p0, TargetField/HRS_p0)

4. repeat for the 12 degree case.

Above might not be a full list. Someone will need to look carefully into this business.

The above calibration is mainly relative to HRS central. It will be important to get the absolute horizontal angle which is related to Q^2. Multiple-target-mass method might not be enough since the momentum transfer is small (need to calculate). 2GeV beam with proton and Ta target might be just enough to give a 1% precision for 5 degree scattering angle. I GUESS good survey on Sieve and beam position may give a precision of 1mrad.

Hope this note helps. I am also glad to answer questions if needed.

Cheers,

Jin