Spring-8 LEPS seminar 5 th February, 2003 Tsutomu Mibe †‡ for the LEPS collaboration

1. Measurement of polarization observables in f photoproduction with linearly polarized photons at BL33LEP/SPring-8 • Spring-8 LEPS seminar • 5th February, 2003 • Tsutomu Mibe†‡ • for the LEPS collaboration • † Research Center for Nuclear Physics • ‡ Advanced Science Research Center, JAERI

2. Outline • Physics probed by f photoproduction with linearly polarized photons • Experiment at LEPS • Current status of data analysis • Future plan • Summary

3. 2 1 4 3 Regge theory • T. Regge Nuovo Cimento 14, 951 (1950) • Soft processes in two-body elastic/quesi-elastic scattering Exchange of a family of particles on Regge-trajectories Reggeon a(t)=a(0)+a’(0)t J(=a(t)) Scattering amplitude 3 2 Total cross section 1 3 1 A simple power of s M2(=-t)(GeV2)

4. Total cross sections • Donachie and Landshoff Phys.Lett. B296(1992)227 rtrajectory e =a(0)-1 = -0.4525 Pomeron trajectory h =a(0)-1 = 0.0808 p-p pp pp p+p Total cross section (mb) Flavor blind Additive-quark rule K-p gp K+p Pomeron Glueball ?

5. Pomeron trajectory Tensor glueball (Jpc=2++) candidate f2(1950) pp→pp p+p-p+p- WA91, PLB 324 (1994)509 x (2230) J/y radiative decay Mark-III(SLAC),PRL56(1986)107 BES, PRL76(1996)3502 Lattice QCD: M(2++) = 2400 ±25±120 MeV (SDQCD) * J(=a(t)) 3 2 Lying on the Pomeron trajectory ! a(t)=1.08 + 0.25t 1 Scalar glueball (Jpc=0++) candidate f0(1500), f0(1710) Lattice QCD: M(0++)= 1730 ±50±80 MeV (SDQCD) * 1622 ± 29 MeV (IBMQCD) ** 3 1 M2(=-t)(GeV2) Daughter trajectory for J=0 glueball ? * Morningstar, PRD60(1999)034509 ** Weingarten, PLD60(1999)014015 a(t)=-0.75 + 0.25t

6. 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

7. 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 Data from: LAMP2('83), DESY('76), SLAC('73), CERN('82), FNAL('79,'82), ZEUS('95,'96)

8. f photoproduction near production threshold Titov, Lee, Toki Phys.Rev C59(1999) 2993 P2: 2ndpomeron ~ 0+glueball (Nakano, Toki (1998)) Natural parity exchange Unnatural parity exchange Data from: SLAC('73), Bonn(’74),DESY(’78) P2: 2ndpomeron ~ 0+glueball (Nakano, Toki (1998)) Important to detinguish natural parity exchanges from unnatural ones Contribution of P2 depends on threshold behavior of P1 ???

9. Polarization observables with linearly polarized photon In f meson rest frame K+ Decay Plane // g natural parity exchange (-1)J (Pomeron, Scalar mesons) g Polarization vector of g K- Decay Planeg unnatural parity exchange -(-1)J (Pseudoscalar mesons p,h) g K+ Decay angular distribution of f meson Relative contributions from natural, unnatural parity exchanges

10. Decay angular distribution of f meson f meson rest frame (Gottfried-Jackson(GJ) frame) eg K+ K+ p’ fK+-Fpol z-axis qK+ Fpol Production plane fK+ z g K- K- Decay plane

11. Decay angular distribution K.Schilling et al. Nucl. Phys. B15(1970) 408 • W0,W1,W2 are parameterized by the 9spin density matrixelements. • r000 , Re(r010), r01-1 • r111 , r100 , r110 , r11-1 , Im(r210 ) andIm(r21-1) Unpolarized part Polarized part

12. lf =lg lg Helicity conserving amplitudes • Pomeron, 0+glueball, scalar meson (natural parity) • pseudoscalar meson exchange (un-natural parity) Prediction (D+ps+N,N*) Eg = 2.2 GeV by A. Titov Pure unnatural parity exchange Pure natural parity exchange Yield(Arbitary Unit) |t|= 2p p 2p 0 p 0 fK+-Fpol fK+-Fpol

13. g f P p g f p Helicity flip amplitudes • Diffractive ‘soft’ Pomeron exchange • Helicity is conserved • Non-perturbative 2-gluon exchange • Different from ‘soft’ Pomeron exchange at larger angles • Helicity flip mechanism due to spin-orbital interaction (A. Titov) lf lg W(cosq) ≈ sin2q + lf=0 lf=lg lg W(cosq) ≈ 1 + b cos2q

14. Helicity flip amplitudes Helicity flip amplitudes may give an information on the threshold behavior of the Pomeron No helicity flip mechanism for the 0++ glueball and scalar meson trajectories Prediction (D+ps+N,N*) with TPomeron~(s/s0) Eg = 2.2 GeV (A. Titov) |t|= |t|= Double spin-flip,r01-1(lg → lf = -lg) Single spin-flip,r000(lg → lf = 0)

15. 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)

16. The LEPS beamline g

17. Linearly polarized Photon • Backward Compton scattering by using UV laser light • Intensity (typ.) : 2.5 * 106 cps • Tagging Region : 1.5 GeV< Eg < 2.4 GeV • Linear Polarization : 95 % at 2.4 GeV • Counts • Linear polarization • Eg(GeV) • Eg(Tagger) (GeV)

18. g Charged particle spectrometer Dipole Magnet (0.7 T) TOF wall Start counter Liquid Hydrogen Target 50mm-long (2000 Dec.-2001June) 150mm-long (2002May-July) Aerogel Cerenkov (n=1.03) MWDC 3 Silicon Vertex Detector MWDC 2 MWDC 1 1m

19. 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

20. Event selections • PID • Decay-in-flight cut • Vertex position cut • Invariant mass cut • Missing mass cut Decay angular distribution of f meson in f meson rest frame

21. K/p separation (positive charge) Reconstructed mass p- p+ p+ p K+ K+ Events d Momentum (GeV) K- Mass(GeV) Mass/Charge (GeV) Charged particle identification s(mass) = 30 MeV(typ.) for 1 GeV/c Kaon 4 s cut for K+/K-/proton PID

22. Vertex distribution Vertex distribution (KK,Kp tracks) ToF start counter Events x vertex (mm) LH2 target (50mm) Vacuum Window BG from target cell z vertex (mm) z vertex (mm) LH2 target : -1100 < z < -910 mm BG from target cell : ! (z<-960mm, x<-15 mm)

23. Reconstructed fevents (K+K- event) Proton(938) f(1019) events /2.5MeV events /2.5MeV s =10 MeV Missing mass (g,K+K-)X (GeV) f Invariant mass (K+K-) (GeV) Invariant mass square (K+K-) (GeV2) Selections for f event (KK mode) |M(KK)-Mf |< 10 MeV |MM((g,K+K-)X)-Mproton|< 30 MeV Invariant mass square (K-p) (GeV2)

24. Reconstructed fevents (K-p event) K+(494) f(1019) events /2.5MeV events /2.5MeV Background from L(1520) Missing mass (g,K-p)X (GeV) L(1520) f Invariant mass (K+K-) (GeV) Invariant mass square (K+K-) (GeV2) f Selections for f event (Kp mode) |M(KK)-Mf |< 20 MeV |MM((g,K-p)X)-MK|< 60 MeV Background study is underway. Invariant mass square (K-p) (GeV2)

25. Kinematical coverage for f events KK event Kp event • High acceptance at forward angles • ~5000 f’s (2000,Dec-2001,June) • Golden region (High polarization, acceptance ～flat) • 2.2 < Eg < 2.4 GeV(Pg ~0.95) • -0.2 < t < |t|min Real data t (GeV2) t (GeV2) Present analysis Eg (GeV) Eg (GeV) • High acceptance at forward angles • ~5000 f’s (2000,Dec-2001,June) • Present analysis • 2.2 < Eg < 2.4 GeV(Pg ~0.95) • -0.2 < t < -|t|min Phase space (Monte Carlo) t (GeV2) Eg (GeV)

26. Geometrical acceptance Present analysis t (GeV2) Monte Carlo fK+(lab) (degree)

27. cosqK+ distribution in GJ frame -0.2< t < -|t|min GeV2 , 2.2 < Eg < 2.4 GeV w/o Acceptance Correction Raw data Number of event Dominance of spin conserving amplitudes cosqK+

28. fK+-Fpol distribution in GJ frame -0.2< t < -|t|min GeV2 , 2.2 < Eg < 2.4 GeV w/o Acceptance Correction Raw data Vertically polarized beam Horizontally polarized beam Number of event/30 deg. fK+ - Fpol(degree)

29. gp rp gp fp Status at most forward angles(2.2<Eg<2.4,-0.2<t<|t|min) M.A. Pichowsky and T.-S. H. Lee PRD 56, 1644 (1997) • Major controbution 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

30. On-going analysis • Acceptance studies • Decay angular distributions at larger |t| • Extraction of full spin density matrix elements (Maximum likelihood fit) • Differential cross section • Analysis of other data set • Long LH2 target run • Nuclear target (Li, C, Al, Cu) run • LD2 target run (Data taking underway)

31. Statistical significance (short LH2 run) w/ pol. or unpol. beam • Estimate of statistical errors on spin density matrix elements Eg=2.3 GeV r000 w/ linearly polarized beam JLAB r11-1 r01-1 Diff.+PS+N,N*(A. Titov) JLAB SPring-8 (2.2<Eg<2.4 GeV) |t| (GeV2) |t| (GeV2)

32. Statistical significance (short LH2 run) • Estimate of statistical errors on differential cross section Eg=2.0 GeV Eg=1.7 GeV Bonn(1974) (Eg=2.0GeV) SPring-8 (1.6<Eg<1.7 GeV) SPring-8 (1.9<Eg<2.1 GeV) Diff.+PS+N,N*(A. Titov) ds/dt (mb/GeV2) JLAB JLAB (?) Q (degree)

33. Summary • f photoproduction at low energies provides unique information about Pomeron and exotic components (glueball or/and scalar meson trajectories). • ~5000 f photoproduction events have been identified with linearly polarized photon beam from Eg= 1.6GeV(threshold) to 2.4GeV at LEPS/Spring-8. • An angular distribution of f decay was studied at forward angles (-0.2 <t<-|t|min) . • The major contribution from spin conserving amplitudes, a larger fraction of natural-parity exchange were observed.