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 photoproduction with linearly polarized photons at SPring-8 SENDAI03 16 th June, 2003 Tsutomu Mibe (Research Center for Nuclear Physics, Osaka univ.,

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Presentation on theme: " photoproduction with linearly polarized photons at SPring-8 SENDAI03 16 th June, 2003 Tsutomu Mibe (Research Center for Nuclear Physics, Osaka univ.,"— Presentation transcript:

1  photoproduction with linearly polarized photons at SPring-8 SENDAI03 16 th June, 2003 Tsutomu Mibe (Research Center for Nuclear Physics, Osaka univ., Japan) for the LEPS collaboration

2 Search for exotic production mechanism in  photoproduction Experiment at LEPS/Spring-8 Decay angular distribution of  meson Summary Outline

3 Vector Meson Photoproduction Vector Meson Dominance Meson Exchange Pomeron Exchange  N   N  (~ss) q _q_q _ qq =  Dominant at low energies Slowly increasing with energy Almost constant around threshold uud

4  p  p  p  p M.A. Pichowsky and T.-S. H. Lee PRD 56, 1644 (1997) Prediction from Pomeron exchange Prediction from meson exchange Data from: LAMP2('83), DESY('76), SLAC('73), CERN('82), FNAL('79,'82), ZEUS('95,'96) Vector meson photoproduction Prediction : dominant contribution form pseudo scalar meson exchange near threshold

5 Titov, Lee, Toki Phys.Rev C59(1999) 2993 Data from: SLAC('73), Bonn(’74),DESY(’78) Natural parity exchange Unnatural parity exchange Important to distinguish natural parity exchanges from unnatural ones P 2 : 2 nd pomeron ~ 0 + glueball (Nakano, Toki (1998))  photoproduction near threshold  =0 degree)

6 Decay angular distribution of  meson  K+ K+K+ K-K-  p’  meson rest frame (Gottfried-Jackson(GJ) frame)  K+ K+K+ K-K-   pol Production plane z Decay plane z-axis  K+ -  pol    direction of linear polarization

7 Decay asymmetry as a parity filter Polarization vector of  K+K+ K-K-  meson rest frame Decay Plane  unnatural parity exchange -(-1) J (Pseudoscalar mesons  ) Decay Plane //  natural parity exchange (-1) J (Pomeron, Scalar mesons)   0   0  Yield  

8 Spin conserving and non-conserving processes P, glueball,    p   p        +  W(cos   ) ≈ 1-cos 2  W(cos   ) ≈ 1 + b cos 2  Spin conserving process Spin non-conserving process Non-perturbative 2-gluon exchange Pomeron, meson exchange cos  K A.I. Titov, T.-S.H. Lee nucl-th/ Yield

9 Published data in 1972 J. Ballam et al. PLD 7 (1972)3150  K+ -  pol (degree) cos(  K+ ) 53 events in E  =2.8,4.8 GeV “Natural-parity exchange in the t channel seems to be the major process.” Precise measurements near threshold at (pol) (unpol,pol) (unpol)

10 Summary of data taking Trigger condition : TAG*STA*AC*TOF Run period I (50mm-long LH 2 ) 2000,Dec. – 2001, June II(150mm-long LH 2 )2002,May July Total number of trigger 1.83*10 8 trigger (~50% Horizontal, ~50% Vertical pol.) Number of events with charged tracks 4.37*10 7 events Present analysis

11 Event selections for  +p →  +p  →K + K - decay mode (KK or Kp detected) PID cut Track quality cuts (to reject decay-in-flight) Vertex position cut < z < -910 mm (production from LH 2 ) Invariant mass cut |M(KK)-M  |< 10 MeV Missing mass cut |MM(( ,K + K - )X)-M proton |< 30 MeV (KK mode) |MM(( ,K - p)X)-M K |< 30 MeV (Kp mode)

12 mass ( ,K + K - )X (GeV) events /2.5MeV Proton  =10 MeV mass (K + K - ) (GeV) events /2.5MeV  mass 2 (K + K - ) (GeV 2 )  mass 2 (K - p) (GeV 2 ) Reconstructed  events (K + K - track)

13 Missing mass ( ,K - p)X (GeV) events /2.5MeV K+K+ mass (K + K - ) (GeV) events /2.5MeV  mass 2 (K + K - ) (GeV 2 )  mass 2 (K - p) (GeV 2 ) Background from  (1520)   Reconstructed  events (K - p track) Background subtracted from sidebands (0.989

14 Kinematical coverage for  events E  (GeV) t -|t| min (GeV 2 ) KK event Kp event

15 High E  and Most forward angles (2.2

16 High E  and Most forward angles (2.2

17 High E  and Most forward angles (2.2

18 Analysis of lower E  sample 1.8 < E  < 2.0 GeV, -0.20< t -|t| min GeV 2 Validity of BG subtraction and acceptance correction must be checked. cos  K Acceptance N  (corrected) K+pK+p K-pK-p cos  K K+K-K+K- Preliminary

19 Summary   photoproduction at low energies provides unique information about Pomeron and exotic components (glueball or/and scalar meson trajectories).  An angular distribution of  decay shows major contribution from spin conserving amplitudes, a larger fraction of natural-parity exchange at E  = GeV,-0.12


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