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f photoproduction with linearly polarized photons at SPring-8

f 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. Outline. Search for exotic production mechanism in f photoproduction

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f photoproduction with linearly polarized photons at SPring-8

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

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

  3. q g r, w _ q N Vector Meson Photoproduction • Vector Meson Dominance • Meson Exchange • Pomeron Exchange _ qq = r, w, f ... Dominant at low energies g r, w f (~ss) Slowly increasing with energy Almost constant around threshold N uud

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

  5. f photoproduction near threshold Titov, Lee, Toki Phys.Rev C59(1999) 2993 (q=0 degree) Natural parity exchange Unnatural parity exchange Data from: SLAC('73), Bonn(’74),DESY(’78) P2: 2ndpomeron ~ 0+glueball (Nakano, Toki (1998)) Important to distinguish natural parity exchanges from unnatural ones

  6. Decay angular distribution of f meson f meson rest frame (Gottfried-Jackson(GJ) frame) eg K+ K+ y=fK+-Fpol p’ Fpol z-axis qK+ Production plane fK+ z g K- K- Decay plane eg : direction of linear polarization

  7. Decay Plane // g natural parity exchange (-1)J (Pomeron, Scalar mesons) Decay Planeg unnatural parity exchange -(-1)J (Pseudoscalar mesons p,h) 2p p 0 2p p 0 Decay asymmetry as a parity filter f meson rest frame y=0 K+ Yield eg Polarization vector of g y=p/2 K- Yield y

  8. g f P , glueball, p,h lg p lf g f + p lg lf=lg lf=0 Spin conserving and non-conserving processes A.I. Titov, T.-S.H. Lee nucl-th/0305002 W(cosqK) ≈ 1-cos2q Spin conserving process Pomeron, meson exchange Yield cosqK W(cosqK) ≈ 1 + b cos2q Spin non-conserving process Non-perturbative 2-gluon exchange Yield cosqK

  9. Published data in 1972 J. Ballam et al. PLD 7 (1972)3150 “Natural-parity exchange in the t channel seems to be the major process.” cos(qK+) 53 events in Eg=2.8,4.8 GeV Precise measurements near threshold at LEPS @Spring-8 (pol) CLAS @J-lab (unpol,pol) SAPHIR@Bonn (unpol) fK+ - Fpol(degree)

  10. Summary of data taking • Trigger condition : TAG*STA*AC*TOF • Run period I (50mm-long LH2) 2000,Dec. – 2001, June II(150mm-long LH2) 2002,May - 2002.July • Total number of trigger 1.83*108 trigger (~50% Horizontal, ~50% Vertical pol.) • Number of events with charged tracks 4.37*107 events Present analysis

  11. Event selections for g+p → f+p • f →K+K- decay mode (KK or Kp detected) • PID cut • Track quality cuts (to reject decay-in-flight) • Vertex position cut • -1100 < z < -910 mm (production from LH2) • Invariant mass cut • |M(KK)-Mf |< 10 MeV • Missing mass cut • |MM((g,K+K-)X)-Mproton|< 30 MeV (KK mode) • |MM((g,K-p)X)-MK|< 30 MeV (Kp mode)

  12. Reconstructed f events (K+K- track) Proton events /2.5MeV f(1019) s =10 MeV events /2.5MeV mass (g,K+K-)X (GeV) f mass2 (K+K-) (GeV2) mass (K+K-) (GeV) mass2(K-p) (GeV2)

  13. Reconstructed f events (K-p track) K+ f(1019) events /2.5MeV events /2.5MeV Background from L(1520) Missing mass (g,K-p)X (GeV) L(1520) f mass2 (K+K-) (GeV2) f mass (K+K-) (GeV) Background subtracted from sidebands (0.989<M<0.999,1.029<M<1.059 GeV) mass2(K-p) (GeV2)

  14. Kinematical coverage for f events KK event Kp event t -|t|min(GeV2) Eg (GeV)

  15. High Eg and Most forward angles(2.2<Eg<2.4,-0.12<t-|t|min) Decay angular distribution in GJ frame w/o Acceptance Correction K+K- detected t -|t|min(GeV2) Raw data Number of event Eg (GeV) Acceptance cosqK+ Dominance of spin conserving process cosqK+

  16. t -|t|min(GeV2) Eg (GeV) High Eg and Most forward angles(2.2<Eg<2.4,-0.12<t-|t|min) Decay angular distribution in GJ frame w/o Acceptance Correction Vertically polarized beam Horizontally polarized beam Raw data Number of event/30 deg. K+K- detected p p 0 0 2p 2p y(degree) Major contribution from natural parity exchange.

  17. gp rp gp fp High Eg and Most forward angles(2.2<Eg<2.4,-0.12<t-|t|min) M.A. Pichowsky and T.-S. H. Lee PRD 56, 1644 (1997) • Dominance of spin conserving process • Pomeron, meson exchange in t-channel • Major contribution from natural parity exchange • Contradiction with the model which predicts large amount of meson exchange at W ≈ 2.3 GeV. • Compensation by natural parity exchange processes (Pomeron, glueball, scalar mesons). Titov, Lee, Toki Phys.Rev C59(1999) 2993 W=2.3 GeV

  18. Analysis of lower Eg sample 1.8 < Eg < 2.0 GeV, -0.20< t -|t|min GeV2 Validity of BG subtraction and acceptance correction must be checked. K+p K-p Acceptance K+K- Preliminary Nf(corrected) Preliminary Nf(corrected) cosqK cosqK

  19. Summary • f photoproduction at low energies provides unique information about Pomeron and exotic components (glueball or/and scalar meson trajectories). • An angular distribution of f decay shows major contribution from spin conserving amplitudes, a larger fraction of natural-parity exchange at Eg =2.2-2.4 GeV,-0.12 <t-|t|min. • Differential cross section at forward angles will be extracted from the data. (q=0 degree) Titov, Lee, Toki Phys.Rev C59(1999) 2993 Nucl-th/0305002 Our data

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