K2KOFFICIAL: 7/99 Official Plots

SK candidate events

Last Update: 15 Feb, 2000

K2K news release(1999.06.28)
Kate-san's report on entering events(1999.06.26)
Mark-san's online display views (1999.07.02)
Ed-san's superscan display views (1999.06.28)
Tomasz-san's tscan display views (1999.08.26)
/Far/ Close/ Stereo/ Stereo Freeview/
UCI tscan page: Nice SK event views are available.

Released: Thu, 15 Jul 1999 23:07:09 +0900
Updated : Sat, 17 Jul 1999 12:19:08 +0900

From: Koichiro Nishikawa
To: e362real@neutrino.kek.jp
Subject: exec. and convener meeting

Hi,

We have discussed about SK event candidates. Kaneyuki-san explained event selection and event itself. Here I have copied a part of Kaneyuki-san's E-mail.

1) Event selections and candidates

The official list of selection criteria for the ID events:

(1) HE trigger
(2) No OD trigger
(3) No event exist in 30 micro second timing window before the candidate
(4) total number of p.e. in 300 nano second timing window > 200 p.e.
(5) total number of p.e. < 50000 p.e.

Event display with reconstructed rings and vertices:

skcand.afit-pmom.ps

The timing window for the March data were 25 micro second shifted, (from -525 micro second to 475 micro second). Thus, we made figure for +- 450 micro second. But, there was no other event in the 1 mili second timing window around the beam time.

tdiff_flasher.ps ( +- 450 micro seconds )
candidate_4ev.ps ( +- 50 micro seconds )

The upper figure of tdiff_flaser.ps shows all F.C. candidates. Event (2) (Kate's entering event) is not in this figure. The middle figure shows 4 F.C. candidates and 1 off-timing e-like neutrino event. The lower figure shows flashers or very low energy events. As for candidate_4ev.ps, there is no flasher event if ev (1) is not flasher.

------------+--------------------------------------------------- | (1) (2) (3) (4) (5) ------------+--------------------------------------------------- date | 06/06 06/15 06/19 06/24 06/26 time | 14:14:30 14:29:12 18:42:49 5:00:36 16:12:18 ------------+--------------------------------------------------- SK run# | 7404 7428 7436 7447 7450 SK subrun# | 145 115 259 86 9 SK ev# | 7819547 6257637 14054126 4677921 445602 ------------+--------------------------------------------------- beam run# | 1752 1810 1826 1909 1937 spill# | 18637 21385 21522 12925 9952 CT (E12 PPP)| 3.88 4.64 4.72 4.68 4.44 ------------+--------------------------------------------------- GPS T(u sec)| 0.0759 0.150 0.493 0.889 0.894 ------------+--------------------------------------------------- total p.e. | 540.9 2760.9 1018.1 1547.2 413.5 max p.e. | 131.0 39.6 20.9 116.5 18.5 Nring | 1 1 2 1 1 decay-e | 2+(0)#1 1+(0)#2 0+(1) 0+(0) 0+(0) ------------+--------------------------------------------------- pos X (cm) | -485 -497 -775 520 -690 Y | -889 1615 -1201 1576 -1355 Z | -1784 1679 1570 -293 -953 Dwall (cm) | 26 0.63 240 30 169 ------------+--------------------------------------------------- dir X_1 | 0.587 0.153 -0.499 0.409 0.597 Y_1 | 0.693 -0.935 -0.856 -0.540 -0.800 Z_1 | -0.419 -0.319 0.132 -0.735 0.064 ------------+--------------------------------------------------- X_2 | 0.450 Y_2 | -0.821 Z_2 | 0.352 ------------+--------------------------------------------------- C_ang_1 | 34.8 40.5 29.5 39.0 29.5 _2 | 37.7 ------------+--------------------------------------------------- goodness | 0.818 0.774 0.846 0.768 0.660 ------------+--------------------------------------------------- MS_1 | mu mu mu,pi,p mu mu _2 | e,pi ------------+--------------------------------------------------- mom_e_1 (MeV/c) 38 262 34 131 21 _2 | 13 ------------+--------------------------------------------------- mom_mu_1 | 208 >459 204 >324 175 _2 | 152 ------------+--------------------------------------------------- cos th_kek | -0.264 0.860 0.444 0.662 0.997 ------------+---------------------------------------------------

Dwall : distance from the inner detector wall C_ang : opening angle of cherenkov ring MS : We applied the standard mu/e analysis for single ring events. For event (3), the possibilities for the pi and p are checked additionally. mom_e : momentum for electron mom_mu : momentum for muon th_kek : opening angle between the beam direction and the highest energy ring decay-e : decay electron candidates. N+(M) : M candidates in the same gate with the parent event N candidates as different event #1: decay-e_1 pos=(-455,-871,-1758) dir=(0.582,-0.747,-0.322) goodness=0.658 delay time from parent event = 2.30 micro sec decay-e_2 pos=(-453,-908,-1753) dir=(0.305,-0.935,0.179) goodness=0.602 delay time from parent event = 4.54 micro sec #2: decay-e_1 pos=(-517,1468,1614) dir=(0.996,0.06,0.06) goodness=0.706 delay time from parent event = 8.30 micro sec

Comments

(1) The probability to be flasher is very small. The reason is as follows,
- i) the accidental coincidence probability in +-1 micro seconds from the flasher is 1%. (we obtained 4 or 5 flashers in +-500micro seconds).
- ii) this event has two decay electron candidates, and directions of these events are different. If these events are caused by the flasher, these events should have a similar cherenkov ring pattern.
- iii) here was no flasher event, which have a similar vertex position, in run 7404 subrun 145.
So, this event is mu-like event caused by the neutrino coming from KEK. This event is expected to have invisible pi, because this event has two decay electron candidates.
(2) Kate's entering event (mu-like event with one decay electron candidate). The accidental coincidence rate from the cosmic ray muon is 4%. (See Kate's report.)

(3) Two ring + decay electron event. Official 1st event.

                       |    e      mu     pi    proton
   --------------------+---------------------------------------------------
   ring 1 momemtum     |   33.4   204    261    1342
          exp'd angle  |   42     32.9   31.5   24.4       29.5+-2(fitted)
   ring 2 momentum     |   12.8   152    358    1191       ~~~~~~~~~~~~~~~
          exp'd angle  |   42     24.9   36.2   18.2       37.7+-2(fitted)
                       |                                   ~~~~~~~~~~~~~~~
   --------------------+---------------------------------------------------

Ring 1 is identified as mu or pi or p, and ring 2 is identified as e or pi. This event is in the 2m fiducial volume.

(4) At the previous summary, this event was mis-identified to be electron by the auto-fit. Thus, the vertex position is shifted inside. The results in this summary are obtained by the manual-fit and normal atm/pd reconstruction programs. This event is identified to be mu-like, and Dwall is 30cm. (vertex resolution for Sub-GeV mu-like is 27cm) Following the usual S.K. atm/pd definition, this event is the partially contained event. Because there were more OD clusters than the threshold. So, this event is the entering event which occurred just outside the inner detector, or the event which occurred in the inner detector and one particle (for example, gamma from pi0) exited from the detector.
(5) This event is the low energy mu-like event. The direction of this event is close to the expected neutrino direction. However, it is accidental, because the expected momentum for muon of this event is 175MeV/c.

2) Discussion

- event#1 : the probability to be a flasher event is much less than 1%, based on the flasher around that time period. The PMT pattern is not like 'normal' flasher event. There is a associted decay electron-like activity.
  We think it is a KEK beam associte event. It is outside 22.5kton fiducial volume, but inside 32kton.
- event#2 : Kate's entering event. There is several % background probability.
- event#3 : official event inside fiducial volume
- event#4 : outside 22.5kton fiducial volume, but inside 32kton
- event#5 : outside 22.5kton fiducial volume, but inside 32kton
Inside the 22.5kton fiducial volume, we have 1 event.
The probability of 10^-4 is for the event#3 (in the 22.5kton fid. vol.) For the other 3 events, (#1,#4,#5), we did not discussed the background probabilities in the meeting. But if we have to quote the number, we (Kaneyuki-san and myself) think as follows;
By the selection criteria (given above), we left with 9 events in +-500 microsec., including (possible) flasher events.
(1)Thus 5 background events in 1 msec. in this criteria, we expect 5x10^-3 in 1microsec. The probability for 4 events ocurr in 1microsec. therefore 10^-4 (for #3) x (5x10^-3)**3.
(2)The expected fully contained neutrino event candidate in 32kton is 1.7x10^-4 in 1 micorsec. Thus the probability for 4 events ocurr in 1microsec. therefore 10^-4 (for #3) x (2x10^-4)**3.
The difference is handling of possible flasher events. Estimate (1) is more conservative, I will vote for it.
For presentations, we can show event displays event#3 (our official only one event in the fiducial volume. In addition, we can also show other(1,4,5) displays, but it may cause unneccesary speculation, due to the fact that all of them are low energy events.
We should explain event#3, upto vector level information (vertex position, direction, PE). But PID, Cherenkov angle etc. should not be mentioned, because we are not in the stage of discussing physics( with single event).

For the analysis, the conveners will meet on July 22 10:00 with results from each detector analysis. Especially, profile (low E, high E), Evis, Eneutrino, theta-muon, and Far/Near estimate from pion monitor should be ready along with Monte Carlo. The Monte Carlo, we will use Cho's parametrization with 200kA for now.

K.Nishikawa

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