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

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

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 Total cross section  (t)=  (0)+  ’(0)t A simple power of s J(=  (t)) M 2 (=-t)(GeV 2 ) Reggeon 1 3 Scattering amplitude

Total cross sections Donachie and Landshoff Phys.Lett. B296(1992)227 Flavor blind Additive-quark rule  trajectory  =a(0)-1 = Pomeron trajectory  =a(0)-1 = Pomeron Glueball ? Total cross section (mb) pp -p-p +p+p K-pK-p K+pK+p pp

Tensor glueball (J pc =2 ++ ) candidate f 2 (1950) pp→pp         WA91, PLB 324 (1994)509  (2230) J/  radiative decay Mark-III(SLAC),PRL56(1986)107 BES, PRL76(1996)3502 Lattice QCD: M(2 ++ ) = 2400 ±25±120 MeV (SDQCD) * Pomeron trajectory J(=  (t)) M 2 (=-t)(GeV 2 ) 1 3  (t)= t Scalar glueball (J pc =0 ++ ) candidate f 0 (1500), f 0 (1710) Lattice QCD: M(0 ++ )= 1730 ±50±80 MeV (SDQCD) * 1622 ± 29 MeV (IBMQCD) ** Daughter trajectory for J=0 glueball ?  (t)= t Lying on the Pomeron trajectory ! * Morningstar, PRD60(1999) ** Weingarten, PLD60(1999)014015

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

 p  p  p  p 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)

 photoproduction near production threshold P 2 : 2 nd pomeron ~ 0 + glueball (Nakano, Toki (1998)) Titov, Lee, Toki Phys.Rev C59(1999) 2993 Data from: SLAC('73), Bonn(’74),DESY(’78) Natural parity exchange Unnatural parity exchange 1.Important to detinguish natural parity exchanges from unnatural ones 2.Contribution of P 2 depends on threshold behavior of P 1 ??? P 2 : 2 nd pomeron ~ 0 + glueball (Nakano, Toki (1998))

Polarization observables with linearly polarized photon Decay Plane //  natural parity exchange (-1) J (Pomeron, Scalar mesons) Polarization vector of  K+K+ K+K+ K-K- In  meson rest frame Decay Plane  unnatural parity exchange - (-1) J (Pseudoscalar mesons  )   Relative contributions from natural, unnatural parity exchanges 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

Decay angular distribution W 0,W 1,W 2 are parameterized by the 9 spin density matrix elements.     Re(    )                    Im(    ) and  Im(    ) Unpolarized part Polarized part K.Schilling et al. Nucl. Phys. B15(1970) 408

Helicity conserving amplitudes Prediction (D+ps+N,N*) E  = 2.2 GeV by A. Titov |t|=      K+ -  pol Yield(Arbitary Unit) Pomeron, 0 + glueball, scalar meson (natural parity) pseudoscalar meson exchange (un-natural parity) Pure natural parity exchange Pure unnatural parity exchange 0   0 

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) P   p   p        +  W(cos  ) ≈ sin 2  W(cos  ) ≈ 1 + b cos 2 

Helicity flip amplitudes Single spin-flip,  0 00 (  →   |t|= Double spin-flip,  (  →     |t|= No helicity flip mechanism for the 0 ++ glueball and scalar meson trajectories Helicity flip amplitudes may give an information on the threshold behavior of the Pomeron Prediction (D+ps+N,N*) with T Pomeron ~(s/s 0 ) E  = 2.2 GeV (A. Titov)

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)

The LEPS beamline 

Linearly polarized Photon Backward Compton scattering by using UV laser light Intensity (typ.) : 2.5 * 10 6 cps Tagging Region : 1.5 GeV< E  < 2.4 GeV Linear Polarization : 95 % at 2.4 GeV E  (Tagger) (GeV) E  (GeV) Counts Linear polarization

Charged particle spectrometer 1m1m TOF wall MWDC 2 MWDC 3 MWDC 1 Dipole Magnet (0.7 T) Liquid Hydrogen Target 50mm-long (2000 Dec.-2001June) 150mm-long (2002May-July) Start counter Silicon Vertex Detector Aerogel Cerenkov (n=1.03) 

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

Event selections PID Decay-in-flight cut Vertex position cut Invariant mass cut Missing mass cut Decay angular distribution of  meson in  meson rest frame

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

Vertex distribution z vertex (mm) Events ToF start counter LH 2 target (50mm) Vacuum Window Vertex distribution (KK,Kp tracks) z vertex (mm) x vertex (mm) LH 2 target : < z < -910 mm BG from target cell : ! (z<-960mm, x<-15 mm) BG from target cell

Reconstructed  events (K + K - event) Missing mass ( ,K + K - )X (GeV) events /2.5MeV Proton(938)  =10 MeV Invariant mass (K + K - ) (GeV) events /2.5MeV  Invariant mass square (K + K - ) (GeV 2 )  Invariant mass square (K - p) (GeV 2 ) Selections for  event (KK mode) |M(KK)-M  |< 10 MeV |MM(( ,K + K - )X)-M proton |< 30 MeV

Reconstructed  events (K - p event) Missing mass ( ,K - p)X (GeV) events /2.5MeV K + (494) Invariant mass (K + K - ) (GeV) events /2.5MeV  Invariant mass square (K + K - ) (GeV 2 )  Invariant mass square (K - p) (GeV 2 ) Background from  (1520)   Background study is underway. Selections for  event (Kp mode) |M(KK)-M  |< 20 MeV |MM(( ,K - p)X)-M K |< 60 MeV

Kinematical coverage for  events High acceptance at forward angles ~5000  ’s (2000,Dec- 2001,June) Golden region (High polarization, acceptance ～ flat) 2.2 < E  < 2.4 GeV (P  ~0.95) -0.2 < t < |t| min E  (GeV) t (GeV 2 ) E  (GeV) KK eventKp event E  (GeV) t (GeV 2 ) Real data Phase space (Monte Carlo) Present analysis High acceptance at forward angles ~5000  ’s (2000,Dec- 2001,June) Present analysis 2.2 < E  < 2.4 GeV (P  ~0.95) -0.2 < t < -|t| min

Geometrical acceptance  K+ (lab) (degree) t (GeV 2 ) Present analysis Monte Carlo

cos  K+ distribution in GJ frame -0.2< t < -|t| min GeV 2, 2.2 < E  < 2.4 GeV w/o Acceptance Correction Raw data cos  K+ Number of event Dominance of spin conserving amplitudes

 K+ -  pol distribution in GJ frame -0.2< t < -|t| min GeV 2, 2.2 < E  < 2.4 GeV w/o Acceptance Correction Raw data Number of event/30 deg. Horizontally polarized beam Vertically polarized beam  K+ -  pol (degree)

Status at most forward angles (2.2<E  <2.4,-0.2<t<|t| min ) 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).  p  p  p  p M.A. Pichowsky and T.-S. H. Lee PRD 56, 1644 (1997) Titov, Lee, Toki Phys.Rev C59(1999) 2993 W=2.3 GeV

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 LH 2 target run –Nuclear target (Li, C, Al, Cu) run –LD 2 target run (Data taking underway)

Statistical significance (short LH 2 run) Estimate of statistical errors on spin density matrix elements |t| (GeV 2 )          E  =2.3 GeV w/ linearly polarized beam Diff.+PS+N,N*(A. Titov) SPring-8 (2.2<E  <2.4 GeV) JLAB w/ pol. or unpol. beam

Statistical significance (short LH 2 run) Estimate of statistical errors on differential cross section d  /dt (  b/GeV 2 )  (degree) E  =2.0 GeV E  =1.7 GeV Bonn(1974) (E  =2.0GeV) SPring-8 (1.9<E  <2.1 GeV) SPring-8 (1.6<E  <1.7 GeV) JLAB (?)JLAB Diff.+PS+N,N*(A. Titov)

Summary   photoproduction at low energies provides unique information about Pomeron and exotic components (glueball or/and scalar meson trajectories).  ~5000  photoproduction events have been identified with linearly polarized photon beam from E  = 1.6GeV(threshold) to 2.4GeV at LEPS/Spring-8.  An angular distribution of  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.