1. Understanding the low-energy kaon-nuclei interactions: the AMADEUS program
A. Scordo on behalf of the AMADEUS collaboration
52° International Winter Meeting on Nuclear Physics
Bormio, January 2014

2. The key role of L(1405) in low energy QCD
K-p threshold = 1432 MeV

3. The unexplained nature of L(1405)
1) three quark state:
expected mass ~ 1700 MeV
2) penta quark:
more unobserved excited baryons
3) KN bound state
Only at rest events
(cut at mass limit)

4. The 2 poles picture of L(1405)
Is there any evidence?

5. The 2 poles picture of L(1405)
Line-shape also depends on the decay channel :
S*(1385)
Pure I=0
(free from S(1385) background)

6. Latest results: CLAS & HADES
No direct Kp production to enhance the higher mass pole
First parallel measurement of L(1405) lineshape in all 3 Sp channels
Measurement of the Isospin interference contribution via the S+p- / S-p+ ratio and of the S*/L* ratio

7. Testing the higher mass pole: K- absorption on light nuclei
(H, 4He, 8Be, 12C)
Reactions:
K- 'p' → S0p0 (non resonant) OR K- 'p' → L(1405) → S0p0 (resonant)
K- 'p' → S+p- (non resonant) OR K- 'p' → L(1405)/S(1385) → S+p- (resonant)
K- ‘p' → Lp0 (non resonant) OR K- 'p' → S(1385) → Lp0 (resonant)
K- ‘n' → Lp- (non resonant) OR K- ‘n' → S(1385) → Lp- (resonant)
'p' , 'n' BOUND nucleons
AT-REST (K- absorbed from atomic orbit) or IN-FLIGHT

8. The AMADEUS experiment
Target: A gaseous He target for
a first phase of study
First 4p fully dedicated
setup!
Monochromatic beam of low momentum
K- (pk = 127 MeV/c)

9. Meanwhile….KLOE 2005 data MC simulations show that :
~ 0.1 of K- stopped in the DC gas (90% He, 10% C4H10)
~ 2% of K- stopped in the DC wall (750 mm c. f. , 150 mm Al foil).
Possibility to use KLOE materials as an active target
Advantage:
unprecedent resolution : sp/p ~ 0.4 MeV/c
4p-geometry with ~ 96% acceptance
Calorimeter optimized for g : sm ~ 18 MeV/c2
Vertex position resolution ~ 1 mm (in DC)
Disadvantage:
Non dedicated target → different nuclei contamination → complex interpretation .. but → new features .. K- in flight absorption. K- K+

10. KLOE 2005 data
The reaction can be studied on several different materials: H, 4He, 8Be, 12C
DC entrance wall (C+H)
DC wall (C+H)
Beam Pipe inner part (Be)
Beam Sphere (Be+Al)
Very different kinematics between the different materials; MC is needed for understanding !!!
DC gas (C+H+4He)

11. Pure Carbon target inside KLOE (2012)
AMADEUS step-0:
Pure Carbon target inside KLOE (2012)
Dedicated run in november/december 2012 with a Carbon target 4/6 mm thickness
Advantages:
gain in statistics
(~90 pb-1; analyzed 37 pb-1, x1.5 statistics)
K- absorptions occur in Carbon
absorptions at-rest.
BP (Be+Al)
DC wall (C+H)
DC gas (C+H+4He)
2005 data: at-rest + in-flight events
Carbon target (C)
2012 data: ONLY at-rest events

12. The neutral channel in 12C: S0p0
N.U.
2005 data
2012 data
A higher invariant mass region is opened!!!
First evidence of an in-flight component !!!
N.U.
2005 data
2012 data
Momentum (MeV/c)
Mass limit
on 12C at rest
The hydrogen contribution can not be separated and MC is needed to include it into a fit
Invariant Mass (MeV/c2)

13. Which model could we use for MC input?
Lack of collaboration with the theoreticians
We developed our model for the simplest case (4He)

14. Lp- ; the pure S* channel
Only charged particles => excellent resolution

17. The charged channel: S+p-

18. Reactions in DC gas (4He): at rest / in flight
Total H
IF 4He
AR 4He
Removing the H component is fundamental since it behaves like a high mass pole!!!
Total H
IF 4He
AR 4He
The ratio between IF and AR can be calculated
Rif/ar = 2.9 ± 0.3 (stat. + contam.)
Total H
IF 4He
AR 4He
Carbon is still there….

19. 2005 VS 2012 data
2005 Data
hydrogen
Carbon Target 2012
hydrogen
‘’not at rest’’
‘’carbon at rest’’
2005 data
2012 data
Excluding the H component, 2005 and 2012 data can be compared
The final mS+p-, pS+p- and qS+p-spectra, confirms the presence of an in-flight component in the 2005 data

20. Reactions in DC wall : at rest / in flight
Total
IF H
IF 12C
AR 12C
Total
IF H
IF 12C
AR 12C
Total
IF H
IF 12C
AR 12C
The ratio between IF and AR can be calculated
Rif/ar = 1.16 ± 0.05 (statistic)

21. Future perspectives: neutrons!
The possibility to detect neutron is fundamental for the S-p+ --> np-p+ but is also very useful
to increase the statistics in the S+p- --> np+p-

22. …waiting for the AMADEUS experiment!!!
Final messages…
AMADEUS provides a unique opportunity for L(1405) investigation
Very promising results have been already obtained with the KLOE 2005 data
Possibility to study in-flight and at-rest reactions individually
New perspectives with the new MC simulations
…coming soon (hopefully with some help with the models)…
MC simulations for all the possible materials and acceptance correction
MC simulations for (all possible) background evaluation (undergoing…)
MC simulations for the carbon target data
Global fit of the data with all the possible components
…to extract…
L(1405) lineshape on light atoms for all possible channels (second pole?)
Resonant and Non-Resonant formation Branching Ratios for different materials
S* / L* branching ratios for different materials
Cross sections for KN interactions for different materials
Precise measurement of L(1116) mass (to publish in PDG)
…waiting for the AMADEUS experiment!!!

23. (really) concluding… The war is not over……
Follow the spirit of this (wonderful) conference

24. Thanks for your attention

25. Spare slides

26. S0 p0 channel
L(1405) signal searched by K- interaction with a bound proton in Carbon
K- p → S0p0 detected via: (Lg)(gg)
Strategy : K- absorption in the DC entrance wall, mainly 12C with H contamination (epoxy)
N.U.
N.U.
2005 data
2012 data
2005 data
2012 data
Mass limit
on 12C at rest
Invariant Mass (MeV/c2)
Momentum (MeV/c)

27. S0 p0 channel
Invariant mass spectra with mass hypotesis on S0 and p0 non resonant misidentification background subtracted (left)
sm ≈ 17 MeV/c2 (12C) sm ≈ 15 MeV/c2 (4He)
Similar m(S0p0) shapes due to the similar kinematical thresholds for 4He and 12C.
2005 data
12C
4He
n.r.m. 12C
n.r.m. 4He
12C
4He

28. Reactions in DC wall and Carbon target data : at rest / in flight
hydrogen
Carbon Target 2012
2005 Data
2005 Data
hydrogen
hydrogen
‘’not at rest’’
‘’carbon at rest’’
No hydrogen and in-flight events in Carbon Target data !!!
Carbon target data can be used, untill new MC simulations, to disentangle between ‘’Not at rest’’ data and ‘’at rest data’’

29. S0 p0 channel : the p0 momentum
P(p0) resolution: sp ≈ 12 MeV/c
mlim 12C at-rest
mlim 12C in-flight
At-rest
In-flight
Counts/(10MeV/c)
Counts/(10MeV/c)
In-flight component
M(S0p0) (MeV/c2)
M(S0p0) (MeV/c2)
P(p0) (MeV/c)
P(p0) could be used for in-flight/at-rest separation
P(p0) (MeV/c)

30. Reactions in DC gas (4He): at rest / in flight
From the scatterplot of the reconstructed mS+ and mp0, the 2 particles can be identified with a resolution of :
dm(p0 ) ~11.9 MeV/c2 , dm(S+)~13.4 MeV/c2
Using the kinetic energy information, a smaller contamination between in-flight and at-rest events is left.
The measured contaminations are
3.0 % ± 0.2 % (AR in IF MC)
5.3 % ± 0.2 % (IF in AR MC)
MC IF
MC AR
Superposition zone

31. 2005 VS 2012 data
2005 data
2012 data
2005 data
2012 data
Excluding the H component, 2005 and 2012 data can be compared
The final mS+p-, pS+p- and qS+p-spectra, confirms the presence of an in-flight component in the 2005 data
2005 data
2012 data

32. Lp- : the best resolution channel

33. Hydrogen contamination
In the DC gas and DC wall, there is also a non-negligible component related to events occuring on hydrogen.
DC gas is a mixture of helium and isobuthane, while in the DC wall the hydrogen comes from the carbon fiber
Hydrogen in DC gas
The hydrogen contamination
(after selection) in DC gas is 22 ± 7 %
The hydrogen contamination
(after selection) in DC wall is 21 ± 1 %
Hydrogen in DC wall