1 Elementary Reactions at LEPS/SPring-8 J. K. Ahn Pusan National University Oct. 11, 2006

2 Research Center for Nuclear Physics, Osaka University ： D.S. Ahn, M. Fujiwara, T. Hotta, Y. Kato, K. Kino, H. Kohri, Y. Maeda, N. Muramatsu, T. Nakano, M. Niiyama, T. Sawada, M. Sumihama, M. Uchida, M. Yosoi, T. Yorita, R.G.T. Zegers Department of Physics, Pusan National University ： J.K. Ahn, S.H. Hwang School of Physics, Seoul National University ： H.C. Bhang Department of Physics, Konan University ： H. Akimune Japan Atomic Energy Research Institute / SPring-8 ： Y. Asano, A. Titov Institute of Physics, Academia Sinica ： W.C. Chang, J.Y. Chen, B.R. Lin, D.S. Oshuev Japan Synchrotron Radiation Research Institute (JASRI) / SPring-8 ： S. Date', H. Ejiri, N. Kumagai, Y. Ohashi, H. Ohkuma, H. Toyokawa Department of Physics and Astronomy, Ohio University ： K. Hicks, T. Mibe Department of Physics, Kyoto University ： K. Imai, H. Fujimura, M. Miyabe, Y. Nakatsugawa, T. Tsunemi Department of Physics, Chiba University ： H. Kawai, T. Ooba, Y. Shiino Wakayama Medical University ： S. Makino Department of Physics and Astrophysics, Nagoya University ： S. Fukui Department of Physics, Yamagata University ： T. Iwata Department of Physics, Osaka University ： S. Ajimura, K. Horie, M. Nomachi, A. Sakaguchi, S. Shimizu, Y. Sugaya Department of Physics and Engineering Physics, University of Saskatchewan ： C. Rangacharyulu Laboratory of Nuclear Science, Tohoku University ： T. Ishikawa, H. Shimizu Department of Applied Physics, Miyazaki University ： T. Matsuda, Y. Toi Institute for Protein Research, Osaka University ： M. Yoshimura National Defense Academy in Japan ： T. Matsumura The LEPS Collaboration

3 Outline 1.Introduction 2.LEPS Facility 3.Selected Recent Results 4.Status of the  + Study 5.LEPS2 Future Facility

4 Resonances and Coupled Channels (A. Hosaka)

5 t-Channel Process dominates in the forward angles. can access to a baryon below MB. Linearly polarized photon as a parity filter. NB M M’ 

6 Key Items are 1.linearly polarized beam. 2.good forward acceptance.

7 Compton-Backscattered Photon Beam 8 GeV electrons in SPring nm Ar laser (3.5eV ）  maximum 2.4 GeV photons E  measured by tagging a recoil electron  E  >1.5 GeV,  E  ~10 MeV Laser Power ~6 W  Photon Flux ~1 Mcps Laser linear polarization % ⇒ Highly polarized  beam PWO measurement tagged Linear Polarization of  beam photon energy [GeV]photon energy [MeV]

8 LEPS Spectrometer TOF Dipole Magnet 0.7 Tesla Target Start CounterDC2DC3 DC1SVTX AC(n=1.03) Charged particle spectrometer with forward acceptance PID from momentum and time-of-flight measurements Photons Momentum [GeV/c] K/  separation K+K+ ++ Mass/Charge [GeV/c 2 ]  P ~6 MeV/c for 1 GeV/c,  TOF ~150 ps,  MASS ~30 MeV/c 2 for 1 GeV/c Kaon

9  Photoproduction near threshold Titov, Lee, Toki PR C59(1999) 2993 P 2 : 2 nd pomeron ~ 0 + glueball (Nakano, Toki (1998)) Data from: SLAC('73), Bonn(’74),DESY(’78) Decay asymmetry helps to disentangle relative contributions ⊥ ⊥

10 Differential Cross Sections at -|t| min Phys. Rev. Lett. 95, (2005) Pomeron + π/η exchange

11 Polarization Observables Decay Plane ||  Natural parity exchange (-1) J (Pomeron, Scalar glueball or mesons)  meson rest frame Decay Plane  Unnatural parity exchange -(-1) J (Pseudoscalar mesons  ) Relative contributions from natural, unnatural parity exchanges Decay angular distribution of 

12 Decay Angular Distributions -0.2 < t+|t| min <0. GeV 2 K ＋ polar angle at φ rest frameK ＋ azimuthal angle relative to pol. vector Contribution from Natural Parity Exchange is dominant. T. Mibe et. al., PRL 95 (2005),

Coherent  D   D Reaction Coherent production from deuterons, iso-scalar target, where iso-vector  -exchange is forbidden. Stronger asymmetry

14  and  Photoproduction from p/d LH 2 data LD 2 data p( , K + ) GeV/c 2  00  (1520)   (1405)  (1385)  (1405)  0 (1385)  - (1385) 0, -0, - N( , K + ) GeV/c 2 Hyperons are identified in the K+ missing-mass spectrum Differential cross sections & photon beam asymmetry R.G.T. Zegers et. al., PRL 91 (2003), M. Sumihama et. al., PRC 73 (2006), New!

15 Differential cross sections W (GeV) LEPS SAPHIR CLAS Resonance-like structure W (GeV) Phys. Rev. C68, (2003)

16 Beam asymmetry for  and  0  K+K*-exchange (K*-exchange is dominant) by M. Guidal  Isobar + Regge by T. Mart and C. Bennhold.  Gent isobar model by T. Corthals Positive sign data nucl-th / SNP2004 Phys. Rev. C68, (2003)

17  - photoproduction from LD 2 Differential cross sections Enhancement in K +  0 relative to K +  - around W=2 GeV  P 31  * ? Beam Asymmetries Large asymmetries in K +  -  K* exchange in t- channel. Large difference of asymmetries in K +  - and K +  0 channels.  Inclusion of  * resonance ? Or inclusion of additional effects ? Blue : K +  - Green: K +  0 Lines: Regge model Kohri et. al., PRL 97 (2006)

18 The Nature of the  (1405)

19 Two poles near 1405 MeV       i (KN) i (  ) Jido-Oller-Oset-Ramos-Meissner, Nucl.Phys.A725, 181 (2003) KN or  quasi-bound state KN ~ 8 x 8 = 1, 8, 8, 10, 10, 27 attractive repulsive Two Poles near the  (1405)

20 Lineshape of the  (1405)

21  p  K *  (1405) The first data will be taken next year. K - must be virtual because  (1405) is lighter than pK -. K - exchange can be enhanced by selecting events where  is perpendicular to K *. z1= i z2= i by Hyodo

22  (1405) Photoproduction with TPC  (1405)  (1520)  +  - and  -  + E (200 V/cm) B (2 Tesla)  beam charged particle target  electron drift Momentum×charge [GeV/c] dE/dx [arbitrary unit]  p            nK K Kp )1405( Missing mass p ( , K + ) (GeV/c 2 )

23 u-Channel Process dominates in the backward angles (forward angles in terms of a nucleon). is sensitive to g NNM. M N g NNM

24 Missing-Mass Distribution for ( , p) t (GeV 2 ) Missing mass(GeV/c 2 ) η´ η ω π0π0 cosθ ω Missing mass(GeV/c 2 ) η’peak is clearly identified by requiring t < -0.6 ~9000 events in the 2001 data

25 First Evidence from LEPS  n  K + K - n Phys.Rev.Lett. 91 (2003) ++ Low statistics: but Tight cut: 85% of events are rejected by the f exclusion cut. Unknown background: BG shape is not well understood. Events from a LH2 target were used to estimate it. Possible kinematical reflections. Correction: Fermi motion correction is necessary.

26 LEPS LD 2 Runs Collected Data (LH 2 and LD 2 runs) Dec.2000 – June 2001 LH 2 50 mm ~5×10 12  published the first result May 2002 – Apr 2003 LH mm ~1.4×10 12  Oct – June 2003 LD mm ~2×10 12  #neutrons × #photons in K ＋ K － detection mode LD 2 runs = 5mm-thick STC in short LH 2 runs × ~5

27   Search in  d   (1520)KN Reaction  ＋ is identified by K － p missing mass from deuteron. ⇒ No Fermi correction is needed. K - n and pn final state interactions are suppressed. If ss(I=0) component of a  is dominant in the reaction, the final state KN has I=0. (Lipkin)  p n ＋＋ K－K－ p  detected

28 A Possible Reaction Mechanism  + can be produced by re-scattering of K +. K momentum spectrum is soft for forward going  (1520). γ p/n n/p  K + /K 0  Missing Momentum Formation momentum LD2 P miss GeV/c LEPS acceptance has little overlap with CLAS acceptance. t-channel K exchanged is possible and an exchanged kaon can be on-shell.  A. Titov et. al., nucl-th/ , accepted for PRC

29 Background Processes Quasi-free  (1520) production is the major background. The effect can be estimated from the LH2 data. γ p n  K+K+ n The other background processes which do not have a strong pK - invariant mass dependence can be removed by side-band subtraction.

30 A. Titov et. al., nucl-th/ Enhancement at Forward Angle Theoretical prediction for forward peaking  D  

31 K － p Missing-Mass Spectrum MM d( ,K － p) GeV/c 2 sideband * * sum Counts/5 MeV An Excess of Events is seen at 1.53 GeV and at 1.6 GeV above the background level GeV peak: 5  statistical significance preliminary Normalization of  * is obtained by fit in the region of MMd < 1.52 GeV. No Structure in Sidebands! ++

32 Is the peak really associated with  *? BG level  1/10  *  1/5 Total # of events  1 / < M(K-p) < < M(K-p) < MMd(γ,K － p) GeV/c 2

33 Focusing on the  + at LEPS Just started new data taking with LD 2 target and a forward spectrometer. Photon beam intensity is twice with two 355nm lasers. Aim at 10 times higher statistics

34 The LEPS2 Future Facility Backward Compton Scattering a) SPring-8 SR ring b) Laser hutch c) Experimental hutch 8 GeV electron Recoil electron (Tagging) the BNL-E949 detector 5 m GeV  -ray Inside building Outside building 30m long line （ LEPS 7.8m)  detector （ Tohoku U. ） Large decay spectrometer Forward spectrometer New DAQ system Laser or re-injected X-ray High intensity ： Multi-laser LRNB, round-beam ~ 10 7 photons/s （ LEPS ~ 10 6 ） High energy ： Re-injection of X-ray from undulator E  < 7.5GeV (LEPS < 3GeV) modify ： JASRI Acc. group

35 LEPS2 Working Group Beam upgrade Energy --- Laser with short (>200nm), re-injected Soft X-ray,, Compact accelerator, XFEL Intensity --- High power laser, Multi laser, LRNB --- Round beam 10 6  10 7 /sec Detector upgrade Scale & --- General-purpose 4  detector Flexibility --- Coincidence measurement of charged particles and neutral particles (photons) (e.g.,  0   ) DAQ --- High speed for the minimum bias trigger Virtual laboratory :