1. 平岩聡彦 京都大学 On behalf of the J-PARC E15 collaboration

2. Outline Introduction J-PARC E15 experiment
experiment & theory of K-pp
J-PARC E15 experiment
method
setup
background
Possibility of E15 30kW
Summary & outlook
2010/12/2-4
ストレンジネス研究会2010

3. Introduction
2010/12/2-4
ストレンジネス研究会2010

4. Low-energy KN interaction
K-nucleon interaction
Low energy Kp scattering
Kaonic hydrogen level shift (KEK-PS E228)
Kaonic nuclei
Kaon bound states with a few nucleons
Extract the information about KN interaction below KN threshold
M.Iwasaki et al. , PRL 78, 3067(1997)
Attractive (I=0)
How strong?
2010/12/2-4
ストレンジネス研究会2010

5. Experimental results on K-pp
FINUDA
Invariant mass of back-to-back Lp pairs in K- absorptions
B = 115±6(stat)±4(syst) MeV G = 67±14(stat)±3(syst) MeV
DISTO
pp  K+X+, X+ pL
B = 105±2(stat)±5(syst) MeV G = 118±8(stat)±10(syst )MeV
Several experimental searches for K-pp bound states have been done so far.
FINUDA group reported the indication of K-pp bound states in the invariant mass
spectra of back-to-back Lambda p pairs from Kaon absorption
They claimed that the binding energy and the width are 115 MeV and 67 MeV, respectively.
Very recently, DISTO collaboration re-analysised the old data and found the broad structure
in the lambda p invariant mass spectra, which corresponds to the biding energy of 105 MeV and
the width of 118 MeV.
T.Yamazaki et al. , PRL 104, (2010)　
M.Agnello et al. ,
PRL 94, (2005)
2010/12/2-4
ストレンジネス研究会2010

6. Theoretical study on K-pp
B.E [MeV]
G [MeV]
Method
Yamazaki and Akaishi 48
61 (mesonic)
Variational Method (ATMS)
Shevchenko, Gal, and Mares
55-70
(mesonic)
Coupled Channel Faddeev Calculation
Ikeda and Sato
60-95
45-80
(mesonic)
Nishikawa and Kondo
~126
Skyrme Model
Dote, Hyodo, and Weise
20±3 (s-wave)
(mesonic)
Chiral SU(3) Variational Method
Arai, Oka, and Yasui
depend on gΛ*Λ*σ
Variational Method (as Λ*p state)
Theoretical studies on K-pp are also advancing. Here we listed the recent results.
All calculation support the existence of K-pp bound states.
But we don’t know whether it is a deep state or shallow states and the decay width is sufficiently narrow or not.
K-pp bound states should exist!
A deep state or shallow state?
Decay width is sufficiently narrow?
2010/12/2-4
ストレンジネス研究会2010

7. Formation spectra : in-flight 3He(K-,n)
K- + 3He  “K-pp” + PK=1GeV/c, q=0º
YA potential
quasi-free
Signal can be clearly seen!
bound
K- conversion
K- escape
Integrated production cross section amounts to 3.5 mb/sr.
2010/12/2-4
ストレンジネス研究会2010
T.Koike and T.Harada. , PLB652 (2007) 262

8. Search for K-pp bound states at J-PARC
E15 experiment via in-flight (K-, n) reaction 　on 3He.
E27 experiment via d(p+, K+) reaction.
2010/12/2-4
ストレンジネス研究会2010

9. J-PARC E15 collaboration
2010/12/2-4
ストレンジネス研究会2010

10. J-PARC E15 experiment L neutron 3He K- p p- We can observe both the
Experimental search for K-pp bound states using in-flight (K-, n) reaction on 3He
K-pp
cluster
neutron K-
3He
Formation
1 GeV/c
Missing mass
Spectroscopy via neutron
Decay L p p-
Mode to decay charged particles
We can observe both the
“Formation” and “Decay”
of K-pp bound state
Invariant mass reconstruction
2010/12/2-4
ストレンジネス研究会2010

11. Experimental Setup J-PARC K1.8BR Neutron 1.0 GeV/c K- TOF length 15m
Invariant mass resolution for K-pp (B.E. 100 MeV)
s ~ 13 MeV/c2 (sCDC=200mm, B=0.7T)
Neutron counter
Beam sweep magnet
Cylindrical Detector System
Neutron
1.0 GeV/c K-
TOF length 15m
Missing mass resolusion for K-pp (B.E. 100 MeV )
s ~ 9.2 MeV/c2 (Pn~1.3GeV/c, sTOF=150ps)
Beamline Spectrometer
2010/12/2-4
ストレンジネス研究会2010

12. Identification of Lpn final state by CDS & NC
Possible background - S0pn final state g missing - QF-L + p missing - QF-S, SL conv p missing
Other processes can be clearly separated!!
2010/12/2-4
ストレンジネス研究会2010

13. Background?? : two nucleon absorption
2NA + LN rescattering / SL conversion looks like a “signal” ??
(2NA itself is not a problem.)
1GeV/c
De Broglie wave 1 GeV/c ~ 1.2 fm
NN distance in 3He ~ 2.25 fm
Proc. Jpn. Academy, Series B83 (2007) 144.
12C(K-,p)
These probabilities are expected to be very small ...
Anyway, let’s see how they look like!
2NA is very small
2010/12/2-4
ストレンジネス研究会2010
T. Kishimoto et al., Prog.Theor.Phys. 118(2007)181.

14. Signal(DISTO) vs Background(2NA+SL conv.)
2NA and S-L conversion
(B.E.=100MeV G=100MeV)
2NA and S-L conversion
2010/12/2-4
ストレンジネス研究会2010

15. Signal(DISTO) vs Background(2NA+rescattering)
2NA and s-wave scattering
2NA and s-wave scattering
2010/12/2-4
ストレンジネス研究会2010

16. Possibility of the E15 experiment with 30kW PS operation
2010/12/2-4
ストレンジネス研究会2010

17. Yield estimation (1week run @30kW)
Yield = NKaon x t x (ds/dW)q=0º x R x r x A x e x e
Nkaon : kaons per spill  300k /spill
t : target  0.08 [g/cm3] / 3 [g/mol] x 6.02x1023 [mol-1] x 9.3 [cm] ~ 1.4 x 1023 [cm-2]
(ds/dW)q=0º : differential cross q=0º  3 [mb/sr]
R : Kpp decay branch (Lp)  0.5
r : branching ratio (L  p-p)  0.63
A : acceptance (NC + CDS)  5.3 [msr]
e : NC efficiency  0.3
e : overall efficiency (trigger, detector, ana etc...)  0.7
PLB 652 (2007) 262.
PRC80 (2009)
4.5 x103 signals can be collected in 1 week run with 30kW operation.
2010/12/2-4
ストレンジネス研究会2010

18. Missing mass of 3He(K-, n)
Lp / S0p decay branches stand on same mass!
4,500 signals (Lp)
+ 4,500 signals (S0p)
~ Total 9,000 signals
( [Lp] : [S0p] = 0.5 : 0.5 )
2010/12/2-4
ストレンジネス研究会2010

19. Improvement of statistics
Statistical improvement can be achieved by “one proton missing”.
Missing proton resolution: 28  0.3 MeV/c2 (s)
Acceptance (NC+CDS)
3body phase space  0.079% (all detected)  0.12% (one proton missing)
K-pp (B=100MeV, G=100MeV)  0.042%(all detected)  0.098% (one proton missing) x2
Lpn final state still can be identified!
2010/12/2-4
ストレンジネス研究会2010

20. Summary & outlook J-PARC E15 experiment
search for a K-pp bound state using in-flight (K- n) reaction on 3He
measure the missing mass in (K-, n) reaction and the invariant mass via the decay of K-pp, simultaneously.
E15 30kW operation
Enough statistics for the first physics data can be collected within a week if the cross section is ~ 3 mb/sr. (2% of the requested beam time)
We wish to start E15 exp. as soon as possible . (after E17)
2010/12/2-4
ストレンジネス研究会2010