1. May/27/05 Exotic Hadron WS 1 Hypothetical new scaler particle X for  + and its search by the (K +, X + ) reaction T. Kishimoto Osaka University

2. May/27/05 Exotic Hadron WS 2 Contents Current status of  + search Another explanation of  + Could  + be made from K  N? X as a K  bound state Experiment to search for X (KEK-PS E548)

3. May/27/05 Exotic Hadron WS 3 First evidence of   from SPring8  n    K   K  K  n  1.54  0.01 GeV  < 25 MeV Gaussian significance 4.6  Target: neutron in Carbon nucleus Background level is estimated by a fit in a mass region above 1.59 GeV. Assumption: Background is from non-resonant K + K - production off the neutron/nucleus … is nearly identical to non- resonant K + K - production off the proton ++ Phys.Rev.Lett. 91 (2003) 012002 hep-ex/0301020

4. May/27/05 Exotic Hadron WS 4 Positive results (Table: courtesy of A. Airapetian) Mass~1540 MeV Width <10 MeV

5. May/27/05 Exotic Hadron WS 5  + width from the KN database A. Sibirtsev et al., hep-ph/0405099 P K (GeV) The background is smooth (~4 mb). The  + with a narrow width should appear as a bump. If not, a strong limit on the width can be put.  =20 MeV  =1 MeV   < 1 MeV

6. May/27/05 Exotic Hadron WS 6 Negative results (Table: courtesy of A. Airapetian) Consistent explanation?

7. May/27/05 Exotic Hadron WS 7  + : Another explanation Consistent theoretical (quark) model –yet to be worked out K  N bound state  arXiv:hep-ex/0312003 (T.K and T.Sato and others) Mass ~1540 MeV –M(K  N) ~1570 MeV (30 MeV bound) –10 MeV/particle (usual) Spin parity ½+ (original prediction) –K  N system (s-wave) ½+ This conjecture explains all  + properties particularly –Narrow width –Seen in Low Q, unseen in High Q

8. May/27/05 Exotic Hadron WS 8 Could  + be a K  N bound state Known two Body interaction –  N: weakly attractive – KN: weakly repulsive – K  weakly attractive K  int. may have ambiguity –So strong to make K  bound state X (new scaler particle) No bound state

9. May/27/05 Exotic Hadron WS 9 In order  to decay –K  N ! KN (  has to be absorbed in N) –  N (s-wave) !  N (p-wave) –K-  N (s-wave) ! K-  N (p-wave) K  N have to interact simultaneously Width ~  (strong) (R(int)/R(  )) 6 –R(int): Radius of Interaction –R(  ): Radius of  Width of  + in K  N conjecture

10. May/27/05 Exotic Hadron WS 10 How to Decay K  N K  N p p K N p Decay (R(int)/R(  )) 6 ss R(  ) R(int)

11. May/27/05 Exotic Hadron WS 11 Radius of  + (and X) Asymptotic wave function (  ) E B =30 MeV 15 MeV r~ 2 fm r~ 3 fm Extended object Seen only in Low momentum transfer reaction

12. May/27/05 Exotic Hadron WS 12 Width ~  (strong) (R(int)/R(  )) 6 –  (strong) ~ a few 100 MeV –R(int) ~ 1 fm Radius of Interaction –R(  ) ~ 3 fm Radius of   (  ) ~ 300 x (1/3) 6 ~ 0.3 MeV –Consistent with observation Production of  + → low q 2 reaction Width of  + in K  N conjecture

13. May/27/05 Exotic Hadron WS 13 K  interaction may be strong enough to make a bound state: New particle X 0 - + 0 - → 0 + scaler particle Binding energy less than 30 MeV –If deeper than 30 MeV  + decays into N and X –Probably a few MeV bound –Very extended object New hypothetical particle X: K  bound state

14. May/27/05 Exotic Hadron WS 14 X (Why missed) Lowest order decay mode X ! K  –No strong decay M X < M K + M  –No X→K  decay (0 + → 0 - + 1 - L non cons. ) –No X→K e + e - (vec. curr. vs axial charge (0 + → 0 - ) No such decay mode is listed in PDG No experimental searches ever made (Probably) If it exists. –Hard to believe but possibility is there.

15. May/27/05 Exotic Hadron WS 15 Experiment to search for X extended object→Low q 2 reaction –r(X)~4fm: q 2 ~ 50 MeV/c Lowest q 2 reaction p(K -+, X -+ )p @P K ~1 GeV/c –q ~ 50 MeV/c X ! K 

16. May/27/05 Exotic Hadron WS 16 How to measure (KEK-PS-E548) p(K -+, X -+ )p, X! K   –Measure Kaon momentum in coincidence with  rays BG process: p(K -+, K -+  0 ),  0 !   X particle gives highest P K Measure invariant mass of K and two  ‘s –Dedicated detector system Study of K  final state interaction

17. May/27/05 Exotic Hadron WS 17 Cross section P K ~1.05 GeV/c Inelastic  : ~5 mb (  production)  (X) ~  (K  ) x f f: low relative momentum phase space Reaction mechanism  b/sr order (1/1000) KEK-PS E548

18. May/27/05 Exotic Hadron WS 18 K + momentum (P K =1 GeV/c) K + scattering angle (cos  ) K + momentum ( MeV/c ) K + p → X + p K + p → K +  0 p Signal Background Max 950 MeV/c Max 830 MeV/c

19. May/27/05 Exotic Hadron WS 19 Experimental condition (E548) K + beam from K2 beam line at KEK-PS –P K =1.2 GeV/c –50k for 3x10 12 ppp Target: 20cm thick H 2 O and 20 cm thick CH 2 Trigger –(K +, K + ) x NaI(>5 MeV) –Rate ~ 500 ev/spill NaI –Target region: 5x5 top and bottom 10.5 cm from the beam center –Forward counter: 3x4 top and bottom 13cm from the beam center Data taking went well (2 days in this April)

20. May/27/05 Exotic Hadron WS 20 Spectrometer E548 Study of kaonic nuclei by (K-, p) reaction Search for X particle by (K+, K+  ) reaction

21. May/27/05 Exotic Hadron WS 21 Current setup of E548 BAC 2 BAC 1 LC Target(water) BQC NaI 5x5 NaI 3x4 CV VZH K+Beam 1.2GeV/c γ γ K+ FAC KURAMA BS 10.5cm 20cm

22. May/27/05 Exotic Hadron WS 22 Gammas Signal Background  energy (MeV)   invariant mass (MeV/c 2 ) K +   invariant mass (MeV/c 2 ) K +   invariant mass (MeV/c 2 )

23. May/27/05 Exotic Hadron WS 23 K + momentum Tagged by 2γ X particle production π 0 production K+ momentum 2 γ backward P K =1.2 GeV/c

24. May/27/05 Exotic Hadron WS 24 Typical cross section  0 production cross section ~ 5 mb ~10 -3 of  0 –1 MeV bound X (r~ 10 fm) ~10 -2 of  0 –5 MeV bound X (r~ 4 fm) K+K+ X+X+ p p 

25. May/27/05 Exotic Hadron WS 25 Expected yield (Extension requested) N K ： 50 k/spill N T ： 20cm （ water target ） X + cross section ~10 -3 of  0 Beam Time ‥ 18shift ⇒ Xparticle ~1600 ~10fm, BE~1MeV

26. May/27/05 Exotic Hadron WS 26 Summary K  bound system X is hard to believe Might have been missed experimentally Explains almost all  + properties If found, it means we found a new scaler particle (like  strange partner of σ) It is not only a solution of  + but opens new world. Wait for our results