1. N* Program at COSY
April 19, | Hans Ströher (FZ-Jülich)

2. Selected recent results
COSY N* Program: Outline
COSY-facility
Detection systems
Selected recent results 2 2

3. COSY N* Program: Facility
WASA
COSY
ANKE
p, d
TOF 3

4. COSY N* Program: Detectors
ANKE 4 4

5. COSY N* Program: Detectors
WASA 5 5

6. COSY N* Program: Detectors
TOF
Target Tracking
Detectors 6 6

7. Focussing and defocussing of hydrogen or deuterium hyperfine states
COSY N* Program: Targets
Cooled Laval nozzle
Operation principle:
Focussing and defocussing of hydrogen or deuterium hyperfine states
Condensation point
Virtual target point
Skimmer
Cluster jet
Pellet
Polarized (ABS) 7 7

8. COSY COSY N* Program: Overview N N  N N*  [N N] X (= g, p, h, …)
Mostly: no resonance structure, but
3(4)b-phase space & final state IA
& resonances
difficult to extract resonance
parameters
But: p N(+)  (N N*)+(+)  d X(+)
Special cases, e.g. p p  p p p0p0
Roper
COSY
WASA at CELSIUS 8 8

9. COSY N* Program: Recent Results
pp  p K+ L 9 9

10. COSY-TOF experiment: pp  p K+ L
COSY N* Program: Recent Results
COSY-TOF experiment: pp  p K+ L K+ p
Strangeness trigger:
charged multiplicity (2  4)
Delayed vertex reconstruction: K+ N p p
L (1116) p-
M(pp-) 10 10

11. COSY N* Program: Recent Results
COSY-TOF experiment: pp  p K+ L
Data (3.06 GeV/c)
Dalitz plot
Contributions of resonances
Which resonances contribute ? 11 11

12. = + COSY N* Program: Recent Results COSY-TOF experiment: pp  p K+ L
Full Model
N* only
FSI only = +
Result:
Change of different N* contributions
as function of beam momentum 12 12

13. COSY N* Program: Future Plans
COSY-TOF experiment: pp  p K+ L
Data (cross sections)  ambiguities
Counts Ay
cos(Θp)
cos(Θp)
Cross sections not sufficient; polarization data needed ! 13 13

14. COSY N* Program: Recent Results
pp  N K+ S ? 14 14

15. COSY-11 vs. ANKE experiment: pp  n K+ S+
COSY N* Program: Recent Results
COSY-11 vs. ANKE experiment: pp  n K+ S+
COSY-11 (n K+)
COSY-11:
 S+ cross section near threshold
larger than for L !
 Contribution of D++* (1620) ?
COSY-11 threshold enhancement (K+S+) 15 15

16. COSY-11 vs. ANKE experiment: pp  n K+ S+
COSY N* Program: Recent Results
COSY-11 vs. ANKE experiment: pp  n K+ S+
ANKE: pp  K+p X
contributions: L, S0, S+
5 new energies
COSY-11 (n K+)
ANKE (K+p, K+p)
COSY-11 threshold enhancement (K+S+): No confirmation ! 16 16

17. COSY N* Program: Recent Results
pp  p K+ S*(1480)
(…)
(…) 17 17

18. COSY N* Program: Recent Results
ANKE-COSY experiment: pp  p K+ (p+- X-+)0
Missing mass distributions
Y* (1480) needed in both channels w/ same parameters (M,G) 18 18

19. COSY N* Program: Recent Results
pp  p K+ S*(1385) / L*(1405) 19 19

20. COSY N* Program: Recent Results
ANKE-COSY experiment: pp  p K+ (p- p) X
Missing mass distributions
L (1405)
L-tag !
 Separation of L* / S*
S (1385)
Unambiguous separation of L(1405) and S(1385)  Lineshape of L(1405) 20 20

21. (Isospin, Strangeness)
COSY N* Program: Future Plans
WASA-at-COSY experiment: pp  p K+ L p0 (g)
Decay scheme for L* / S* L*
1405
-0 +
S*0
1385
Mass (MeV/c2) p0
-0 + p0 S
1190 g L
1116 p-
0 +
940
(0, -1)
(½ , 0)
(1, -1)
(Isospin, Strangeness)
Direct observation with WASA: Strangeness tag needed 21 21

22. 2p production dominated by resonance excitation
COSY N* Program: Recent Results
pp  p p p0p0
s N* D N double D
2p production dominated by resonance excitation 22 22

23. COSY N* Program: Recent Results
WASA-at-COSY experiment: pp  p p p0p0
p in forward det´s
2p0 reconstructed from 4g in EMC
(pp) invariant mass vs.
(ppp) Invariant mass
Enhancement at D(1232) and N(1440) observed 23 23

24. DD model does not reproduce p0p0 data ( PRL 102, 052301)
COSY N* Program: Recent Results
ABC-Effect
ABC:
2p (~ 310 MeV)
strong enhancement
over phase space
no pp-resonance
conventional view:
excitation + decay
of DD-excitation in
relative s-wave
DD model does not reproduce p0p0 data ( PRL 102, ) 24 24

25. COSY N* Program: Recent Results
WASA-at-COSY experiment: pn  d p0 p0
ABC-effect
WASA at CELSIUS:PRL 102
Energy dependence of p0p0 cross section 25 25

26. COSY N* Program: Recent Results
WASA-at-COSY experiment: pn  d p0 p0
ABC-effect
WASA at CELSIUS:PRL 102
WASA-at-COSY
preliminary
Striking energy dependence of p0p0 cross section ( ABC-resonance ? ) 26 26

27. COSY N* Program: Recent Results
ANKE-COSY experiment: pp  (pp)s (pp)0
WASA-at-COSY
pn  d p0p0
INN = 0
Ipp = 0
ANKE-COSY
pp  (pp)s (pp)0
INN = 1
Ipp = 0,2
Could ANKE be missing the point ? Strong spin-isospin dependence ! 27 27

28. COSY N* Program: Summary, Outlook
N* activities at COSY-Jülich – recent results:
- higher lying N* resonances
- Y*(1480)
- L (1405)
- ABC (DD)  What about: pp  {nn}s p+p+ ?
Future:
- ANKE: special cases – no extended program
- TOF: hyperon resonances program; polarization
- WASA: N* not highest priority; strangeness tag for Y*
- Theory support (PWA) 28 28

29. Thank you
for your
attention 29