photoproduction with linearly polarized

photons at SPring-8SENDAI03 16th June, 2003

Tsutomu Mibe(Research Center for Nuclear Physics, Osaka univ., Japan)

for the LEPS collaboration

Search for exotic production mechanism in photoproductionExperiment at LEPS/Spring-8Decay angular distribution of mesonSummary

Outline

Vector Meson Photoproduction

• Vector Meson Dominance

• Meson Exchange

• Pomeron Exchange

N

N

(~ss)

q

_q

_qq =

Dominant at low energies

Slowly increasing with energyAlmost constant around threshold uud

p p

p p

M.A. Pichowsky and T.-S. H. LeePRD 56, 1644 (1997)

Prediction from Pomeron exchangePrediction 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 formpseudo scalar meson exchangenear threshold

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

P2: 2ndpomeron ~ 0+glueball

(Nakano, Toki (1998))

photoproduction near threshold

=0

de

gre

e)

Decay angular distribution of meson

K+

K+

K-

p’

meson rest frame (Gottfried-Jackson(GJ) frame)

K+

K+

K-

polProduction

planez

Decayplane

z-axis

K+-pol

direction of linear polarization

Decay asymmetry as a parity filter

Polarizationvector of

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 Y

ield

Yie

ld

Spin conserving and non-conserving processes

P , glueball,

p

p

+

W(cos) ≈ 1-cos2

W(cos) ≈ 1 + b cos2

Spin conserving process

Spin non-conserving processNon-perturbative 2-gluon exchange

Pomeron, meson exchange

cosK

cosK

A.I. Titov, T.-S.H. Lee nucl-th/0305002

Yie

ldY

ield

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 measurementsnear threshold at

LEPS @Spring-8 (pol) CLAS @J-lab (unpol,pol)

SAPHIR@Bonn (unpol)

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

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

• -1100 < z < -910 mm (production from LH2)

• Invariant mass cut• |M(KK)-M |< 10 MeV

• Missing mass cut• |MM((,K+K-)X)-Mproton|< 30 MeV (KK mode)• |MM((,K-p)X)-MK|< 30 MeV (Kp mode)

mass (,K+K-)X (GeV)

eve

nts

/2

.5M

eV

Proton

=10 MeV

mass (K+K-) (GeV)

even

ts /2

.5M

eV

mas

s2 (

K+K

- ) (G

eV2)

mass2(K-p) (GeV2)

Reconstructed events (K+K- track)

Missing mass (,K-p)X (GeV)

eve

nts

/2

.5M

eV

K+

mass (K+K-) (GeV)

even

ts /2

.5M

eV

mas

s2 (

K+K

- ) (G

eV2)

mass2(K-p) (GeV2)

Backgroundfrom (1520)

Reconstructed events (K-p track)

Background subtracted from sidebands(0.989<M<0.999,1.029<M<1.059 GeV)

Kinematical coverage for events

E (GeV)

t -|t|

min(G

eV2 )

KK event Kp event

High E and Most forward angles(2.2<E<2.4,-0.12<t-|t|min)

2sin)(cosW

Decay angular distribution in GJ frame

w/o Acceptance Correction

Raw data

cosK+

Num

ber

of e

vent

Dominance of spin conserving

processcosK+

Acc

epta

nce

K+K- detected

E (GeV)

t -|

t| min(G

eV

2)

High E and Most forward angles(2.2<E<2.4,-0.12<t-|t|min)

Decay angular distribution in GJ frame

w/o Acceptance Correction

Raw data

Num

ber

of e

vent

/30

deg

. Horizontally polarized beam Vertically polarized beam

(degree)Major contribution fromnatural parity exchange.

E (GeV)

t -|

t| min(G

eV

2)

K+K- detected

0 0

High E and Most forward angles(2.2<E<2.4,-0.12<t-|t|min)

• 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).

p p

p p

M.A. Pichowsky and T.-S. H. LeePRD 56, 1644 (1997)

Titov, Lee, Toki Phys.Rev C59(1999) 2993

W=2.3 GeV

Analysis of lower Esample

1.8 < E < 2.0 GeV, -0.20< t -|t|min GeV2

Validity of BG subtraction and acceptance correction must be checked.

cosK

Acc

epta

nce

N(

corr

ecte

d)

K+p K-p

N(

corr

ecte

d)

cosK

K+K- PreliminaryPreliminary

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 =2.2-2.4 GeV,-0.12 <t-|t|min.

Differential cross section at forward angles will be extracted from the data.

Our data

=

0 d

eg

ree

)

Titov, Lee, Toki Phys.Rev C59(1999) 2993Nucl-th/0305002