Upload
bob
View
24
Download
0
Tags:
Embed Size (px)
DESCRIPTION
PaNic02. XVI Particles and Nuclei International Conference September 30 - October 4, 2002, Osaka, Japan. Production of Mesons on Protons near Threshold by Linearly Polarized Photon at SPring-8/LEPS. Wen-Chen Chang for LEPS collaboration - PowerPoint PPT Presentation
Citation preview
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 Exchange Pseudo-scaler Exchange
(OZI Suppressed!)
Exotic knock-out process
Photo-Production of Mesons
at Backward region (large |t|)
Emission from Nucleon Exotic shake-off process
At Forward region:
• 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)
– Successful phenomenology for diffractive process.
• 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
with un-polarized photon beams
A.I.Titov et. al., PRC 59, R2993
(t=0
)
With Linearly-Polarized Photon Beam
• Experimentally we measure W’s functions and density matrix
could be determined by spherical harmonics decomposition.
• The contributions of natural and un-natural parity exchange in the t-channel are represented by the matrix element of Re(0), Re(1).
),(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
011
000
2211
210
2111
110
2100
2111
2011
010
2000
000
21
)]2sinsinImsin2sinIm2(
2sin
)2cossincos2sin2cossin(
2cos
2cossincos2sinRe2
cos)13(2
1)1(
2
1[
4
3
),,(cos
HHHH
HHHHHH
HHHH
H
HHL
P
P
W
K.Schilling et. al., Nucl. Phys. B15 (1970) 397
The Spin Density Matrix Elements at small |t| regions
•Two important spin-conserving processes:•Pomeron exchange: 1
1-1= –Im 21-1 = +0.5, and all diagona
l ’s = 0 at =0., exchange: 1
1-1= –Im 21-1 = – 0.5, and all diagonal ’
s = 0 at =0.
A.I.Titov et. al., PRC60, 035205
.1when ,5.0 ;0when ,5.0
2
21
2
||||
1
111
111
2221
11
2
UN
UN
TT
TTT
Angular Distribution of K+ in Helicity Frame
=0, 11-1=+0.5 =1, 1
1-1= – 0.5
)))(2cos(21(4
3),( 1
11
HH PW
SLAC MeasurementJ.Ballam, et. al, PRD 7(1973), 3150
LEPS CollaborationRCNP, 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
Large acceptance at forward angles ~5000 ’s (Dec,2000 - June, 2001) Runs with 150mm-long LH2 target (May-July, 2002 ).
KK event Kp event
Experimental Acceptance at -0.2< t < |t|min GeV2
2.2 < E < 2.4 GeV
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.
• In comparison with measurement at high energy, our preliminary results show that the contribution of natural-parity exchange still composes a larger fraction in the total scattering amplitude while that of un-natural parity component becomes more significant at 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:“Polarization observables in the \phi(1020) meson photoproduction withlinearly polarized photons” by T. Mibe (RCNP, Osaka Univ.).
Decay Angular Distribution in p p
Example
Super Photon Ring 8 GeV (SPring-8)