Diffractive φ photo-production off the deuteron near the threshold

in LEPS/SPring-8

M. Miyabe, K. Horie, S. Shimizu, W. C. Chang and LEPS collaboration

Kyoto Univ.

Φ photo production of proton near the threshold

• High energy– Pomeron exchange– Positive energy

dependence.

• Low energy– Pseudo scalar meson

exchange– Negative energy

dependence.

P, glueball, , f2’

p

Pure naturalparity exchange

Pure unnaturalparity exchange

0 0

Decay angular distribution

φ-Φ

φ : photon pol. AngleΦ : K decay angle.

Results of proton target

Peak structure around 2GeV.Natural parity exchange is dominant　→　 0+ glueball ?T. Mibe, et al

Interest of Deuteron target

1. Coherent production– Interact with deuteron

itself.

2. Incoherent production– Interact with proton or

neutron in deuteron.

Coherent production• Deuteron is isoscalar target

– π exchange is strongly suppressed• Very steeper t-slope in differential cross section dσ/dt .1. There are no coherent production data near the production threshold.

– Really exist?2. If coherent process is truly exist,

which mechanism is dominant ?

Incoherent production

• Due to isospin effect,– gπnn and gηnn has opposite sign. →unnatural parity exchange process is suppressed in

neutron case. Information of unnatural (π/η) exchange process

Experiment at Spring-8

•8GeV electron storage ring Harima Hyogo

BCS photon beam

LEPS (Laser Electron Photon at Spring-8)Backward Compton scattered photon beam

→ 2.4GeV maximum energy→ high polarization photon > 90%

Detectors setup

1m

TOF wall

MWDC 2MWDC 3

MWDC 1

Dipole Magnet(0.7T)

Liquid Hydrogen or Deuteron Target50mm-long (2000 Dec.-2001June)150mm-long (2002May-July)

Start counter

Silicon VertexDetector

AerogelCerenkov(n=1.03)

Summary of data taking

• Trigger condition : charged hadron track 1≧• Run period

1. (50mm-long LH2) 2000,Dec. – 2001, June

2. (150mm-long LH2) 2002,May - 2002.July

3. (150mm-long LD2) 2002,July – 2003 Feb, Apr-Jun

• Total number of trigger 1. 180M trigger (~50% Horizontal, ~50% Vertical pol.)

2. 170M trigger ( same )

3. 460M trigger ( same )

φ event selection

Total φ event ~ 20K

Existence of CoherentMissing Mass distribution of D(γ,φ)X

•Red : coherent(MC)•Blue : incoherent(MC)•Black : experiment data

E2~E9 : 2.423~1.723(GeV) → 0.1(GeV) divided

Extract coherent process

• Black– Experiment data

• Blue– Incoherent mode (MC)

• Red – (Black) – (Blue)

→　 Coherent component ?

E2~2.423(GeV)

↓ 0.1(GeV) divide

E9~1.723(GeV)

Prelim

inary

Cross section of coherent

• Fit with exp(b*t)• Slope b is very steep

– Larger than 10

Very P

relim

inary

Summary

• First find coherent production off deuteron near the threshold region.

• Very steep t-slope > 10 (GeV-2)– agreement with theoretical prediction.