Production of Mesons on Protons near Threshold by Linearly Polarized Photon at SPring-8/LEPS
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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
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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.
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Total Cross Section of Hadronic Interaction
XsYsT
Universal Scaling : = 0.5, = 0.08
A. Donnachie and P.V. Landshoff
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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.
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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
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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.
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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
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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
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SLAC MeasurementJ.Ballam, et. al, PRD 7(1973), 3150
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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
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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)
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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-
+-
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Signal of K+K
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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
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Simulation at -0.2< t < |t|min GeV2 2.2 < E < 2.4 GeV
=0 =0.5 =1
2222 :)1(|:||| UNN TT
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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
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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).