22 September 2005 Haw05 1  (1405) photoproduction at SPring-8/LEPS H. Fujimura, Kyoto University Kyoto University, Japan K. Imai, M. Niiyama Research Center for Nuclear Physics, Osaka University, Japan T. Nakano for the LEPS collabration Collaborators 1.Physics Motivation 2.Mechanical Design of TPC 3.Experiment Setup at SPring-8/LEPS 4.Current status of Analysis 5.Summary and Prospects Contents

22 September 2005 Haw05 2 Physics Motivation structure of Λ*(1405) J P =1/2 - Chiral perturbation theory describe  (1405) as a meson-bariyon resonance and predict its lineshape to be different in different decay channel    ,    +. → J.K.Ahn et al They predict the modification of invariant mass distribution of  (1405) in nuclear matter. E. Oset et al., Nucl. Lett. B455 55(1999) Lutz…, 3-quark state or KN bound state ? Large mass difference between  (1520) J P =3/2 - and  (1405) J P =1/2 - cannot be explained by quark model. KN threshold 3/2 - 1/2 -  )  ) 30 MeV

22 September 2005 Haw05 3 Physics Motivation Experimental Data Thomas et al. Nucl. Phys. B56 15 (1973) 470 events Hemingway et al. Nucl. Phys. B (1985) J.K.Ahn et al. Nucl. Phys. A721 (2003) It is necessary to detect  to identify  (1405) develop Time Projection Chamber (TPC) as 4  detector to detect decay topology Σ + π events Σ - π events

22 September 2005 Haw mm 585 mm Up stream Solenoid Magnet Down stream view 600mm TPC is designed to be installed in Solenoid Magnet. Hexagonal cylinder 880mm in length 585 mm in diameter Design of TPC E // B 700mm Target holder High voltage plane Wire & pad plane Drift field cage Beam Active volume (cylindrical shape) 700 mm in length 400 mm in diameter Drift time → z position To detect trajectory as close as a few cm from target, target holder is mounted in TPC.

22 September 2005 Haw05 5 Design of TPC Pad Plane Signals from TPC are read out through cathode pads and anode wires. The position resolution (required value) Drift direction : 550  m (700  m) Pad plane : 340  m (350  m) Invariant mass of (1405) → 1% accuracy # of Cathode pads : 1055 # of Anode wires : 95 Beam E // B 400mm Large pads 8mm x 13mm Small pads 4mm x 8mm 3-dimentional position information pad-plane → x-y position drift time → z position dE/dX, momentum → PID

22 September 2005 Haw05 6 Experimental setup at SPring-8/LEPS  E // B

22 September 2005 Haw05 7 Solenoid Magnet Dipole Magnet TPC Buffer Collimator 24Φ Collimator 2 １ Φ Beam TPC

22 September 2005 Haw05 8 Beam Time CH 2 113Mtrig : 110k K + in spectrometer 500  (1405) in  K +  - TPC  + ) 600  (1405) in  K + spec  +  - ) C 60 Mtrig : 60k K + in spectrometer Cu 41 Mtrig : 12k K + in spectrometer Jan – Mar Commissioning run Apr – Jul Physics run Sep – Dec Physics run 2004 How to Identify  (1405) events Missing Mass of p ( , K +  +  - ) Spectrometer TPC            nK K Kp )1405( Missing mass of p ( , K +  +  - ) → n Missing mass of p ( , K +   ) →   ± Select decay mode ( ) by the kinematical fit. In this talk, missing mass spectrum of p( , K + )X is shown by selecting  +  - in TPC to extract  (1405) events.

22 September 2005 Haw05 9 Proton ++++  dE/dx (arbitrary unit) Momentum×charge (GeV/c) PID by TPC p K+K+ K-K- ++ -- Mass x Charge (GeV/c 2 ) Particle Identification PID by Spectrometer TOF, Momentum → Mass

22 September 2005 Haw05 10 Missing mass of p ( , K + ) X CH 2 C  (1116)   (1193)  (1520)  (1405) /  (1385) CH 2 - C p ( , K + ) X (GeV/c 2 ) K + were detected by Spectrometer  PDG: ± GeV  0 PDG: ± GeV  (1502  PDG: ±0.006 GeV E  and Momentum calibration of LEPS Spectrometer system have been done.

22 September 2005 Haw05 11  (1385) events Spectrometer TPC Invariant mass of (p,  - ) (GeV/c 2 ) Select  (1116) by TPC CH 2 C p ( , K + ) X (GeV/c 2 )

22 September 2005 Haw05 12 CH 2 C CH 2 - C neutron Missing mass p ( , K +  +  - ) (GeV/c 2 ) Event Selection by TPC Missing mass of p ( , K +  +  - ) Missing Mass p ( , K +  +  - ) Spectrometer TPC            nK K Kp )1405( Selection - Spectrometer 1 track, K +  2 prob ≧ TPC 2 tracks,  +  - scattering angle of  +  - > 40 ° Momentum calibration of TPC is underway

22 September 2005 Haw05 13 CH 2 C p ( , K + ) X (GeV/c 2 ) Missing mass of p ( , K + ) X selected by  +  - in TPC CH 2 - C  (1520) Next step: select decay mode by identifying  in p ( , K +  )X.

22 September 2005 Haw05 14 Summary and Prospects  (1405) is an unique object to study the dynamics of QCD. Some theoretical models describing  (1405) as meson-baryon molecular state あ and predict the different lineshape in different decay channel and the modification of lineshape of  (1405) in nuclear matter. We have performed hyperon photoproduction experiment at SPring-8/LEPS. The CH 2, C, and Cu targets were used. The energy range of the backward compton scattering photon was 1.5 – 2.4 GeV. To identify the  (1405) from  (1385), we have constructed a TPC as a 4  detector to measure decay topology. The physics run has been done in the year We identified 100K of K + production events measured by forward spectrometer from CH 2 target. Among K + events tagged by spectrometer, 600 events of  (1405) are expected. LEPS forward spectrometer system was used to detect forward going particles. E  and momentum calibration of LEPS spectrometer system was finished. Momentum calibration of TPC is underway. We will extract  (1405) lineshape from different decay mode by identifying  in p ( , K+  )X. The modification of invariant mass shape of  (1405) in the nuclear matter will be studied.