Production of Mesons on Protons near Threshold by Linearly Polarized Photon

at SPring-8/LEPS

Wen-Chen Chang for LEPS collaboration

Institute of Physics, Academia Sinica Taipei 11529, Taiwan

XVI Particles and Nuclei International ConferenceSeptember 30 - October 4, 2002, Osaka, JapanPaNic02

Outline

• Photo-production of mesons at high energy and near production threshold.– Pomeron exchange.– Pseduo-scaler particle exchange.

• How linearly polarized photon beam can help us in distinguishing different sources of contribution?– Spin density matrix element.– Decay asymmetry in Helicity Frame.

• Measurement by LEPS experiment at SPring-8.– Reconstruction of mesons in KK modes.– Angular distribution of K+ in Helicity Frame at forward direction.

• Summary.

Total Cross Section of Hadronic Interaction

XsYsT

Universal Scaling : = 0.5, = 0.08

A. Donnachie and P.V. Landshoff

Photo-Production of Mesons

at Forward Region (small |t|)

• Pomeron: – Positive power-law scaling of s.

– Dominating at large energy.

– Natural parity (=+1).

– Exchange particles unknown; likely to be glueball : P1(J=2+), P2 (J=0+, negative power-law scaling of s, Ref: T. Nakano and H.Toki, 1998).

• Pseudo-scaler particle: – Negative power-law scaling of s.

– Showing up at small energy.

– Un-natural parity (= –1).

– Exchange particles like ,.

– OZI suppressed.

Differential Cross section of p p

A.I.Titov et. al.PRC 59, R2993 (1999)

(t=0

)

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

p p

p p

Pomeron

Meson

With Linearly-Polarized Photon Beam

• W0,W1,W2 can be parameterized by the 9 spin density matrix elements.

Re(

)

Im() andIm(

)

),(cos2sin),(cos2cos

),(cos),,(cos21

0

HHHH

HHHHL

WPWP

WW

H : polar angle of K+ in Helicity frame H : azimuthal angle of K+ in Helicity frame : angle between the photon polarization vector and CMS production plane.

Spin Density Matrix Elements

at small |t| regions

•Spin-conserving processes:•Pomeron exchange: 1

1-1= –Im 21-1 = +0.5, and all

other ’s = 0 at =0., exchange: 1

1-1= –Im 21-1 = – 0.5, and all oth

er ’s = 0 at =0.•Azimuthal angle distribution:

A.I.Titov et. al., PRC60, 035205

)))(2cos(21(4

3),( 1

11

HH PW

Simulated Azimuthal Angle Distribution of K+ in Helicity Frame

=0, 11-1=+0.5 =1, 1

1-1= – 0.5

2

21

2

||||

1

2221

11

2

UN

UN

TT

TTT

SLAC MeasurementJ.Ballam, et. al, PRD 7(1973), 3150

LEPS Collaboration

RCNP, Osaka University, JapanH. Fujimura, M. Fujiwara, T. Hotta, H. Kohri, T. Matsumura, N. Matsuoka,T. Mibe, M. Morita, T.Nakano, T. YoritaOsaka University, JapanN. Nomachi, A. Sakaguchi, Y. Sugaya, M. SumihamaAcademia Sinica, TaiwanW.C. Chang, D.S. Oshuev, C.W. Wang, S.C. WangChiba University, JapanH. Kawai, T. Ooba, Y. ShiinoIHEP, RussiaP. ShaginJAERI, JapanY. Asano, N. Muramatsu, R.G.T. ZegersJASRI, JapanS. Date, N. Kumagai, Y. Ohashi,H. Ookuma

Konan University, JapanH. AkimuneKyoto University, JapanK. Imai, T. Ishikawa, M.Miyabe, M.Niiyamma ,M. YosoiNagoya University, JapanS. Fukui, T. Iwata, Y. Miyachi, A. WakaiOhio University, U.S.K. HicksPusan National University, S. KoreaJ.K. AhnSaskatchewan University, CanadaC. RangacharyuluTohoku University, JapanH. ShimizuWakayam Med. University, JapanS. Makino

LEPS detectors

1m

TOF wall

MWDC 2

MWDC 3

MWDC 1

Dipole Magnet (0.7 T)

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

Start counter

Silicon VertexDetector

AerogelCerenkov(n=1.03)

Charged particle identification

Mass(GeV)

Mo

men

tum

(G

eV

)

K/ separation (positive charge)

K++

Mass/Charge (GeV)

Eve

nts

Reconstructed mass

d

p

K+

K-

+-

Signal of K+K

Reconstructed events

Reconstruct photo-production of from both K+K- events and Kp events.

Large acceptance at forward angles ~5000 ’s (Dec,2000 - June,2001)

KK event Kp event

Simulation at -0.2< t < |t|min GeV2 2.2 < E < 2.4 GeV

=0 =0.5 =1

2222 :)1(|:||| UNN TT

Decay angular distribution of K+ in rest frame (Helicity frame)

|M(KK)-M |< 10 MeV , |M((KK)X)-Mproton|< 30 MeV

-0.2< t < |t|min GeV2 , 2.2 < E < 2.4 GeV

w/o Acceptance Correction

Raw Data

Vertically polarized beamHorizontally polarized beam

Summary

• About 5000 events of photo-production of mesons by linearly polarized photons from E= 1.6GeV(threshold) to 2.4GeV are measured by LEPS experiment at SPring-8/Japan.

• The preliminary results show that the contribution of natural-parity exchange still composes a larger fraction in the total scattering amplitude of at photo-production of mesons E=2.3 GeV and |t|<0.2 region.

• With the ongoing studies of the acceptance correction and systematic errors, the cross section, differential cross section and spin density matrix elements at the forward regions will be reported in the near future.

A presentation of detailed results will be shown in the poster session [ 6B-26]:“Polarization observables in the \phi(1020) meson photoproduction withlinearly polarized photons” by T. Mibe (RCNP, Osaka University).