1. E19 result Ryuta Kiuchi (SNU)
-- on behalf of E19 collaboration and J-PARC hadron beam line staffs and users
Ryuta Kiuchi (SNU)
“ Korea-Japan workshop on nuclear and hadron physics at J-PARC”
Seoul National University

2. E19 and Pentaquark search
J-PARC aim to search Θ+ pentaquark resonance
via (π-, K-) reaction using high intensity beam line & good mass resolution
### Pentaquark is a hypothetical particle consisting of four quarks and one anti-quark

3. Past experiments of Penta-quark search
LEPS collaboration , Nakano et.al,
K. Miwa et.al.,Phys. Lett. B. 635, 72 (2006)
E552 suggest the existence of Θ+ at 1.53GeV/c2

4. K1.8 Experimental Area SKS Spectrometer K1.8 Beam Spectrometer Q13 Q12D4
Q11
Q10

5. Current Setup ・ Beam spectrometer ・ SKS spectrometer Beam spectrometer
(SKS0 configuration)
・ Beam spectrometer
Trigger Counter :
-- BH1, BH2 (Hodoscope)
-- eGC (e/p ,Cherenkov)
-- BAC (p/K, K/p , Cherenkov)
Tracking Chamber:
eGC
-- BC1, BC2 (MWPC)
-- BC3, BC4 (MWDC)
SKS spectrometer
・ SKS spectrometer
SKS magnet : Typ T (300A) ,
Central Mom. 0.75GeV/c
Trigger PID Counter :
-- TOF wall (32seg.)
-- LC wall (28seg.)
-- AC (p/K , Cherenkov )
Tracking Chamber:
-- SDC1, SDC2, SDC3, SDC4 (MWDC)

6. Data Summary Ʃ+ 1.37 (π+, K+) LH2 2.9 5 Ʃ- (π-, K+) 12 20 Empty 1.92
Term : ~
Mom
[GeV/c]
Reaction
Target
Number of Beam particle
Data taking hours Ʃ+
1.37
(π+, K+)
LH2
2.9 5 Ʃ-
(π-, K+) 12 20
Empty
1.92
(π-, K-) --
4.6 10 Θ+ 78
132
### Empty run == without LH2 but target cell was exist
We have accumulated 10 times more statistics than E522 exp.

7. Vertex reconstructionY
Target cell Z
Beam
Beam

8. Vertex reconstruction -- comparing with empty run dataZ X
LH2 Y
Empty
Target cell Z
Empty target 1.92 GeV/c
~3 % background in the selected region
(Empty data : Normalized by beam flux)

9. Calibration run -- Ʃ+/- production
p(p+, K+)S GeV/c
p(p-, K+)S GeV/c

10. Missing mass resolution
Estimated from S data
& simulation DM
=1.86 MeV/c2
(FWHM) S+
DBeam
DSKS Dq DE DM
MeV S+
0.42
1.66
0.46
0.56
1.86 Q+
0.53
1.17
0.50
0.41
1.44
@ q=5 °
S±: DMS = 1.9 ± 0.1 MeV/c2 (FWHN) ⇒Q+ missing mass resolution DMQ = 1.4 ± 0.1 MeV/c2 (FWMH) (DM ∝ Mtarget/MQ)

11. Missing mass spectrum Preliminary All event sum : 7.8×1010 p-
p- + p → K GeV/c
Preliminary
＊If exists
MQ ~ 1.53 GeV/c2
All event sum : 7.8×1010 p-
With event selection
2°< qscat.< 15°& vertex cut e.t.c
No prominent peak structure observed.

12. Comparison with background simulation
BG reactions
p- p → fn→K- K+ n
(s = 30±8 mb)
p- p → L(1520) K0
→K- K0 p
(s = 21±5 mb)
p- p →K- K+ n
p- p →K- K0 p
(s ~25 mb)
O. I. Dahl et al .
Phys. Rev. B 163, 1377 (1967).
(Bubble chamber data)
Simulation with measured cross section.
Cross section error : 20~30%

13. Comparison with background simulation
Data
BG reactions
p- p → fn→K- K+ n
(s = 30±8 mb)
p- p → L(1520) K0
→K- K0 p
(s = 21±5 mb)
p- p →K- K+ n
p- p →K- K0 p
(s ~25 mb)
Sim (×1.0)
Sim (×1.2)
O. I. Dahl et al .
Phys. Rev. B 163, 1377 (1967).
(Bubble chamber data)
Simulation with measured cross section.
Cross section error : 20~30%

14. Differential cross section
Preliminary
Differential cross section (Averaged 2°-15°)
⇒Obtain 90 % confidence level upper limit
Width : 1.4 MeV/c2 fixed (Estimated S data)

15. Upper limit of cross section
Differential cross section
Scanning region
GeV/c2
BG shape
⇒ 3rd order polynomial
Peak shape
⇒ Gaussian
(s=1.4 MeV/c2 fixed)
Preliminary
Differential cross section (Averaged 2°-15°)
⇒Obtain 90 % confidence level upper limit
Width : 1.4 MeV/c2 fixed (Estimated S data)

16. Upper limit of cross section
Preliminary
Preliminary
Upper limit cross section : < GeV/c2
Cross if MQ = 1.53 GeV/c2
Differential : 100 nb/sr (averaged 2°-15°)
Evaluation of
systematic errors
is ongoing.

17. Summary
・ J-PARC E19 experiment, search for penta-quark state via p- p → K- Q+ reaction, was done in 2010 October/November with 10 times higher statics than E552.
・ Preliminary analysis results shows no remarkable
signals around GeV/c2 .
・ Now we are improving analysis method, and also preparing a paper.
・ We will take data with the incident pion beam
momentum of 2.0 GeV/c again.

23. Present status of Q+ After LEPS collaboration report
⇒Many positive results & Many negative results
Positive results
LEPS new report : g d →p K- K+ n
CLAS(p) : g p→p+ K- Q+→p+ K- K+ n
DIANA : K+ n →Q+→K0 p
Negative results
High energy experiments
CLAS : g d→p K- Q+→p K- K+ n
＊High statistics & high sensitivity
⇒Controversial situation
＊Low energy hadron reaction (p or K beam)
Few data
Expected larger production cross section
⇒ Essential part for the investigation of Q+
DIANA
CLAS

24. Cross section Tracking part Counter, PID part Other part
Target
Beam
Other analysis
SKS
Tracking part
BC1&2, BC3&4, SDC1&2, SDC3&4, K1.8, SKS
Single track selection
Counter, PID part
Beam p selection, TOF, LC, AC, scattered K selection
Other part
Decay, absorption, vertex, matrix trigger, acceptance

25. Cross section Tracking part Counter, PID part Other part
Target
Beam
Other analysis
SKS
Tracking part
BC1&2, BC3&4, SDC1&2, SDC3&4, K1.8, SKS
Single track selection
Counter, PID part
Beam p selection, TOF, LC, AC, scattered K selection
Other part
Decay, absorption, vertex, matrix trigger, acceptance

26. Missing mass S+ S-
Missing mass resolution : ~2 MeV/c2 (FWHM)

27. Missing Mass Resolution