Sieve Slit Calibration

Procedure

In HKS experiment, although the Splitter field smears the one to one correspondence between target angles and sieve slit hole position and introduces additional momentum dependence. particle trajectories scattered from a point target with given momenta still have a fixed target angle when they pass a given hole. The angle in this case is also a function of particle momentum, and depend on splitter optics. Based on this observation, the Sieve slit calibration procedure is:

1. Fit function $F_{s2t}$: target angles as a function of SS positions and momentum based on Splitter optics.

2. Separate events of the SS calibration run data hole by hole, thus determine corresponding SS hole center position for each event.

3. Using function $F_{s2t}$, calculate corrected target angles ($xptar$, $yptar$) for each event from SS center position and momentum.

4. Fit transfer matrix from focal plane to target: ($xfp$, $xpfp$, $yfp$, $ypfp$) $\longrightarrow$($xptar$, $yptar$).

A simulation of the SS calibration procedure with initial inaccurate Splitter, Enge optics reaches final resolution for e' (Enge) target angles ($\sigma$): $xptar$: 1.8 mr, $yptar$: 1.1 mr, for Kaon (HKS) angles: $xptar$: 0.4 mr, $yptar$: 2.4 mr.

Code

The codes are written in Perl script, which calls a series of Fortran programs. Currently, they work on simulated data. All the codes start from the directory:jlabs1:/home/yuan/HKS/optics/

• .enge/fsv2tarang: Perl script to fit target angles as function of sieve slit positions ($X_{sv}$, $Y_{sv}$) and momentum by 6-order polynomials.

• .enge/opticscalib: Perl script to fit target angles as 6-order polynomials of focal plane quantities.
• Nominal electron arm Raytrace data card:.enge/hksearm_tilt.dat
• nominal electron arm reconstruction matrix:.enge/enge_recon_coeff.dat