Today's Progress 18. May. 2007

Fine tune of NT slewing correction function with (stopped K^-, X^+-&gamma) events : E570

Part-by-part study of offset on time diff-to-y conversion function with (stopped K^-, X^+-) events

Since it is now very important to know the direction of neutron motion exectly related to YN correlation analysis, we check the TDC top-bottom difference to y position conversion function part-by-part, by using charged events, although, the improvement of neutron momentum resolution is expected to be tiny.

The conversion function, Y(T) is defined as a linear function of the Top-Bottom difference, T(T-B):

Y(T) = a * T(T-B) + b,

where a and b are determined to fulfill the relationship,

Y(PDC) = a * T(T-B) + b,

where X(PDC) is the PDC-detected y position on the NT segment. Note that the slope, a, is the half of the effective light velocity inside the segment. The convertion function is once defined for stopped K⁺ run, and the stability is checked segment-by-segment part-by-part below.

Part-by-part segment-by-segment check of Time diff to y conversion function.

For several counters, position offset originates from the time walk is considerable, so that we introduce the part-by-part position correcation term, and define y on NT segment i by

Y_i(T) = (a_i * T_i(T-B) b_i) - c_i(idpart),

where c_i is defined by the part-by-part Gaussian center of the distribution of Y(T)-Y(PDC) as plotted above.

Fine tune of NT slewing correction function with (stopped K^-, X^+-&gamma) events

Adopting the updated time difference to y conversion function, we study the time residual from (stopped K^-, X^+-&gamma) events here.

Method

For the 100% production runs, we study the time residual,

deltaT(T0->NT) = Tnt - Tt0 -TOFkstop-TOF_&gamma ,

for neutral particles. Firstly, charged-particle-defined Tnt is examined.

Result with Kmu2-defined correction functions

T0->NT 1/beta resolution defined as the Gaussian &sigma to fit the peak of Compton-like &gamma when Kmu2-determined correction functions and offsets are applied as they are.

T0->NT 1/beta Gaussian center when Kmu2-determined correction functions and offsets are applied as they are for Compton-like &gammma.

T0->NT 1/&beta resolution defined as the Gaussian &sigma to fit the peak of shower-like &gamma when Kmu2-determined correction functions and offsets are applied as they are.

T0->NT 1/&beta Gaussian center when Kmu2-determined correction functions and offsets are applied as they are for shower-like &gamma.

As already reported, following two facts are clearly found when Kmu2-determined corrections are applied for GAMMA RAY as they are:

1/&beta center is deviated to the faster side in segment-dependent scale.

Substantial correlation between energy and time still remains.

Note that they are still open problem whether they are also true for neutron, or not.

Nextly, the results AFTER the re-tunning of the offset and correction function to optimize for Compton-like GAMMA RAY, are shown.

T0->NT 1/&beta resolution defined as the Gaussian &sigma to fit the peak of Compton-like &gamma-ray when &gamma-determined correction functions and offsets are applied.

T0->NT 1/&beta Center of Gaussian to fit the peak of Compton-like &gamma-ray when &gamma-determined correction functions and offsets are applied.

T0->NT 1/&beta resolution defined as the Gaussian &sigma to fit the peak of NOT shower-like &gamma-ray when &gamma-determined correction functions and offsets are applied.

T0->NT 1/&beta Center of Gaussian to fit the peak of shower-like &gamma-ray when &gamma-determined correction functions and offsets are applied. Substantial deviation from 1.0 is seen.

A substantial deviation of 1/&beta center is found for shower-like &gamma-ray, and the tendency of the deviation is opposite to the expected from the possible overcounting of the TOF distance. This fact is known since E471.

Energy dependence of 1/&beta peak center and Gaussian &sigma/Layer-by-layer resolution plot are exhibitted below, for Compton-like &gamma-ray with Compton-&gamma-determined slewing correction function.

Arm-by-arm energy dependence of Gaussian &sigma(left)/center(right) of 1/&beta distribution from Compton-like &gamma-ray events. Left and right arm results are plotted by black and red, respectively.

Layer-by-layer resolution for 5 (black),7 (red), and 10 (red) MeVee th values for Compton-like &gamma.

Layer-by-layer Gaussian center of 1/&beta distribution for 5 (black),7 (red), and 10 (red) MeVee th values for Compton-like &gamma.

Run-by-run arm-by-arm stability of Gaussian mean and &sigma fitted to 1/&beta distribution obtained from Compton-like &gamma. Black/red/green are used for 5MeVee/7MeVee/10MeVee, respectively.