Today's Progress 11. Nov. 2006 (updated every moment)

(stopped K^-, n onNT:p/&pi onTC) coincidence spectrum and VcaVn selection

Method

Until now, the PID on the trigger counter system has been developed. Here, we classify the neutron spectrum by means of TC/VDC-related quantities, and search for possible signal. Note that all the spectra shown here are under the requirements of

1. light output of over 7MeVee, and

2. VDCVETO,

if no special statement is given. Note that other VETO hits are NOT included into the VETO condition, at least softwarewise.

(stopped K^-, n onNT:p onTC) spectra

It is already known that (stopped K^-, n onNT:p onTC) spectrum can be classified with

1. VcVn (Vc:direction vector of proton. i. e. selection by the cos of direction vectors of p(on TC) and n(on NT),

2. dE/dx on TC (for the proton momentum slection).

Now, let we call the p tagged events with dE/dx on A < 7.5 MeVee as "fast p", while "slow p" if it is > 7.5 MeVee. The value is corresponding to proton momentum 400 MeV/c, obtained from the Monte-Carlo simulation previously shown for TC analysis.

Distribution of VcVn for (stopped K^-, n onNT:p onTC) events.

(stopped K^-, n onNT:p onTC) spectrum

(stopped K^-, n onNT:fast p onTC) spectrum.

(stopped K^-, n onNT:slow p onTC) spectrum.

(stopped K^-, n onNT:&pi onTC) spectra

It is already known that (stopped K^-, n onNT:&pi onTC) spectrum can be classified with

1. VcaVn,

2. pion momentum.

First, just VcaVn selection is applied to the &pi-tagged spectrum.

pi-tagged VcaVn spectrum.

(stopped K^-, n onNT:&pi onTC) spectrum

(stopped K^-, n onNT:&pi on TC) spectra classified by VcaVn. For the top, green:-60~-25, red:-25~-5, black:-5~-2. For the bottom, green:25~60, red:5~25, black:2~5.

(stopped K^-, n onNT:&pi onTCtop:&pi onTCbottom) spectra

Here, 2-&pi coincidence neutron spectrum is shown for 5, 7, 10 Mevee threshold values. As is already known, non-pionic components all vanish.

(stopped K^-, n onNT:&pi onTCtop:&pi onTCbottom) spectra by 5(black)/7(red)/10(green) threshold values.

(stopped K^-, n onNT:slow &pi onTC) spectra

Now, slow&pi tagged neutron spectrum is shown. The definition of slowpi is given by dE/dx(A)-vs-dE/dx(B) as shown just below. It is defined to set the cutting momentum to be 125 MeV/c.

Definition of slow-pi.

slowpi-tagged VcaVn spectrum.

(stopped K^-, n onNT:slow&pi onTC) spectrum

(stopped K^-, n onNT:slow&pi on TC) spectra classified by VcaVn. For the top, green:-60~-25, red:-25~-5, black:-5~-2. For the bottom, green:25~60, red:5~25, black:2~5.

(stopped K^-, n onNT:fast &pi onTC) spectra

Now, fast&pi tagged neutron spectrum is shown. The definition of fastpi is given by dE/dx(A)-vs-dE/dx(B) as shown just below. It is defined to set the cutting momentum to be 125 MeV/c.

Definition of fast-pi.

fastpi-tagged VcaVn spectrum.

(stopped K^-, n onNT:fast&pi onTC) spectrum

(stopped K^-, n onNT:fast&pi onTC) spectrum with -2. < VcaVn < 2. to search for possible hypernuclear two-body decay 4HeLambda -> 3He + n at around 510 MeV/c.

(stopped K^-, n onNT:fast&pi on TC) spectra classified by VcaVn. For the top, green:-60~-25, red:-25~-5, black:-5~-2. For the bottom, green:25~60, red:5~25, black:2~5.

Backword(top)/Forward(bottom) comparison of the variation of the spectra related to VcaVn value.

(stopped K^-, n onNT_L:n onNT_R:p/&pi onTC) spectra

Here, (stopped K^-, n onNT_L:n onNT_R:p/&pi onTC) spectra are shown. Since we have intense accidental neutrons, we need some event selections to purify the spectrum. The event selection criteria related to detected neutral particles are as follows:

1. neutral hit on both arm,

2. 7MeVee threshold for counted(i.e. sampled to construct the spectrum) neutron,

3. 3MeVee threshold for counter-detected neutral particle,

4. 1.5 < 1/&beta < 8.0 for counter-detected neutral particle,

and note that not necessarily both neutrons are included in the spectrum, then. It is classified by cos(nn) and counter-detected neutron momentum, and shown below.

Neutron 1/&beta spectrum and cos(nn) distribution under 3 MeVee thresold value if counter-detected neutron has light output larger than 7 MeVee.

(stopped K^-, n onNT_L:n onNT_R:X onTC) spectra. On the first, the spectrum is classified by cos(nn), while by counter-detected-neutron momentum on the second.

(stopped K^-, n onNT L:n on NT R:X on TC) spectra selected by counter-detected-neutron momentum AND cos(nn). The first/second/third spectra are with p_n > 300/400/500 MeV/c, respectively. Black/Red/Green/Yellow are all/cos(nn).le.-0.90/cos(nn).le.-0.95/cos(nn).le.-0.98, respectively.)

Now, we study trigger-particle dependence of the spectrum.

(stopped K^-, n onNT_L:n onNT_R:&pi onTC) spectra. On the first, the spectrum is classified by cos(nn), while by counter-detected-neutron momentum on the second.

(stopped K^-, n onNT_L:n onNT_R:p onTC) spectra. On the first, the spectrum is classified by cos(nn), while by counter-detected-neutron momentum on the second.