Today's Progress 16. July. 2006

Study of (stopped K^-, X^0) spectrum with T0-NT (3)

Now, we have following two kinds of slewing correction functions.

stopped K^+ -Kmu2 detrmined, then NT run-by-run offsets has been tuned by stoppedK^- Kmu2 events.

NT run-by-run offsets has been tuned by above scheme, but finally tuned with Compton-like gamma-ray.

T0 run-by-run offset is tuned by T0-PA-PB iteration for both. Until now, we do not have rigid solution for the best correction for neutron, hence, we examine which correction is more relevant for NEUTRON here.

Study of stoppedSigma^+ -> pi^+ n

We study the monochromatic neutron from

stoppedSigma^+ -> pi^+ n (p_n = 185.02 MeV/c, 1/beta = 5.176(n) / 1.253(pi^+) ),

with Kstop-PAPB trigger. Adopting the Kstop-PAPB triggered events, 5 times larger monochromatic neutron yield is expected compared to the case that Kstop-VTC-NT trigger is adopted. At the same time,

stoppedSigma^- -> pi^- n (p_n = 193.09 MeV/c, 1/beta = 4.968(n) / 1.234(pi^-) ),

is investigated. As shown below, our mometum resolution is better than 2 MeV/c at the region below 200 MeV/c - hence, momentum binning should be smaller than 2 MeV/c.

Neutron momentum VS momentum resolution for several constant 1/beta resolution values. On the neutron measurement, 1/beta resolution depends on beta - hence, this is no more than an approximated dependence. For the proton measurement, 1/beta resolution does not depend on beta, and this is the accurate one for the momentum after PA. The resolution for the momentum at the production stage is convoluted one with the resolution of the energy-loss correction.

Event selections

We start with event selection. In order to select the neutron from stoppedSigma decay,

1) inverse-velocity of the charged particle going to the opposite arm,

2) correlation between emission angles of charged particle / neutron,

are available. 1) is realized by selecting the charged particle 1/beta 1.20~1.40, and 2) is selected by inner-product between two direction cos < -0.985 . The arm-by-arm neutron 1/beta spectra with 3MeVee from stopped K^- are shown below. Conditions are :

black:all

red: 1/beta 1.20~1.40 (condition A)

green: (1/beta.LT.1.20).OR.(1/beta.GT.1.40) (condition Abar)

magenta: (1/beta 1,20~1.40).AND.(cos .LE.-0.985) (condiion A and B)

sky-blue:(1/beta 1.20~1.40).AND.(cos.GT.-0.985) (condition A and Bbar)

Neutron 1/beta spectrum detected by Larm under various selection conditions described in the text.

Neutron 1/beta spectrum detected by Rarm under various selection conditions described in the text.

To study the slewing correction functions, we adopt the cut condition A.AND.Bbar and 3 MeVee software threshold value.

The comparison of neutral particle spectra

The arm-by-arm comparison of the compton-like gamma (top)/neutron from stopped Sigma decay (bottom) is shown below, with Kmu2(red) and Compton(black) - determined slewing correction. We observe the systematic tendencies as listed below:

For Compton-like gamma, Compton-determined slewing correction gives confidently better result, as already known (but here confirmed under the identical event selection with those applied to neutron).

On both arms, systematic deviation of peak positions are observed. Kmu2-determined function returns higher velocity, but the peak center position is more accurate by Compton-determined one considering the presence of the Sigma^+ stopping time(91/280 psec for 100/160 MeV/c momentum, respectively) + life time(80 psec exponential), while we do not see any significant difference in the width.

Now, we conclude that Compton-determined slewing correction parameter gives a better result to low-energy neutron.

1/beta local spectra detected by Larm under the selection conditions described in the text.

1/beta local spectra detected by Rarm under the selection conditions described in the text.

Global spectrum of neutral particles detected by L/Rarm under the selection conditions described in the text.

The correlation between 1/beta and light output is shown below. The monochromatioc neutrons exist at 1/beta~5.0/5.2 up to 10 MeVee, and they show no correlation between 1/beta and light output.

1/beta VS light output for neutral particles detected by Larm under the condition A.AND.Bbar. Compton-like-photon-defined slewing correction is applied.

1/beta VS light output for neutral particles detected by Larm under the condition A.AND.Bbar. Kmu2-defined slewing correction is applied.

1/beta VS light output for neutral particles detected by Rarm, under the condition A.AND.Bbar. Compton-like-photon-defined slewing correction is applied.