Photoproduction of Λ (1405) and Σ (1385) p ( ) ( ) at LEPS/SPring8 (II) DEUK SOON AHN R E S E A R C H C E N T E R F O R N U C L E A R P H Y S I C S O S A K A U N I V E R S I T Y R E S E A R C H C E N T E R F O R N U C L E A R P H Y S I C S, O S A K A U N I V E R S I T Y D E P A R T M E N T O F P H Y S I C S , P U S A N N A T I O N A L U N I V E R S I T Y F O R T H E L E P S C O L L A B O R A T I O N F O R T H E L E P S C O L L A B O R A T I O N 1. Physics Motivation 2. Experimental Setup E i l S 3. Data Analysis 4. Summary and Outlook Strangeness Workshop@Atami, 2009.2.27 DeukSoon Ahn
Physics Motivation Physics Motivation Λ (1405) : Meson-baryon resonance or 3-quark System ? ( ) y q y Λ (1405) with J P =1/2 - , I=0, and S=-1 ~20 MeV Σ (1385) with J P =3/2 + , I=1, and S=-1 LEPS data LEPS data, PRC78,035202(2008) , PRC78,035202(2008)M.Niiyama M.Niiyama γ p � K+ Λ (1405) � K+ Σ + π – K+ Σ - π + Λ∗/Σ∗ = 0 . 54 ± 0 . 17 0 . 084 ± 0 . 076 γ p � K+ Σ (1385) � K+ Λ π 0 Strong Energy dependence! Strong Energy dependence! High Statistics ! Hi h St ti ti Hi h St ti ti High Statistics ! ! ! γ p � K+ Λ (1405) / Σ (1385) To understand the production Mechanism, To understand the production Mechanism, : Using missing mass of K+ - Differential Cross section Differential Cross section - Photon Beam Asymmetry Photon Beam Asymmetry Photon Beam Asymmetry Photon Beam Asymmetry 2 Strangeness Workshop@Atami, 2009.2.27 DeukSoon Ahn
Photon Beam Photon Beam Asymmety Photon Beam Photon Beam Asymmety Asymmety for Asymmety for for for Λ (1405) @ S.I. Nam et al. Λ (1405) @ S.I. Nam et al. arXiv:0806.4029 arXiv:0806.4029 ;Strong contribution of electric coupling from the K exchange coupling from the K- exchange Data Data; ; T T. . Azemoon Azemoon et et al al. . NP NP B B95 95 ( (1975 1975) ) Nucl. Phys. A 748 (2005) 499 Nucl. Phys. A 748 (2005) 499 77 by M.F.M.Lutz & M.Soyeur by M.F.M.Lutz & M.Soyeur @ E γ ≈ 2 GeV (t-m K 2)-2 (t-m K 2)-1 Rapid fall-off suggesting a t-channel exchange process 3 Strangeness Worksho@Atami, 2009.2.27 DeukSoon Ahn
Experimental Setup ; LEPS Detector Experimental Setup ; LEPS Detector TOF Aerogel Dipole Magnet wall Cerenkov (0.7 T) ( (n=1.03) 1 03) Start counter Liquid hydrogen target γ MWDC 3 Silicon Vertex MWDC 2 Detector MWDC 1 W C 1m 1m Trigger condition ; TAG x UPveto x TRG x AC x TOF 70 Hz for 800 kHz@Tagger Charged particle spectrometer with forward acceptance g p p p Particle Identification from momentum and Time of Flight measurement 4 Strangeness Workshop@Atami, 2009.2.27 DeukSoon Ahn
Data Data analysis analysis γ + p γ + p K + Λ （ 1405) / Σ (1385) K + + Λ （ 1405) / Σ (1385) K+PID with 3 σ tum Moment Λ （ 1116) Counts Σ (1193) C Λ （ 1405) Λ （ 1405) Kinematical region Mass 2 Σ (1385) Λ （ 1520) Ф K+ hal angle Ф Missing Mass (K + ) Azimuth Momentum Transfer 5 Strangeness Workshop@Atami, 2009.2.27 DeukSoon Ahn
Photon Beam Asymmetry Photon Beam Asymmetry K+ K+ ε γ Σ >0 ; V>H ; γ γ p p Σ <0 ; V<H Λ (1405)/ (1405)/ Σ (1385) (1385) Preliminary results Σ (1385) dominant ( 3 5) - K* exchange ? Λ (1405) dominant - K - exchange ? 6 Strangeness Workshop@Atami, 2009.2.27 DeukSoon Ahn
Particle Identification for Particle Identification for Kaon Kaon – – π + contamination + contamination K+ PID with 3 σ K+ PID with 3 σ K+ PID with 2 σ K+PID with 1 σ M Mass 2 2 Missing Mass (K + ) 7 Strangeness Workshop@Atami, 2009.2.27 DeukSoon Ahn
Photon Beam Asymmetry Photon Beam Asymmetry K+ PID with 3 σ K+ PID with 2 σ K+PID with 1 σ 8 Strangeness Workshop@Atami, 2009.2.27 DeukSoon Ahn
Photon Beam Asymmetry Photon Beam Asymmetry as a function of as a function of MissngMass MissngMass 1.50<E γ <2.40 1.65<E γ <1.80 2.25<E γ <2.40 Missing Mass (K + ) π +/proton contamination and Missing Mass (K + ) Missing Mass (K ) other background channel should be studied. 9 Strangeness Workshop@Atami, 2009.2.27 DeukSoon Ahn
Background Background Ns+N Ns+N BG BG : w/o sideband subtraction N Ns Ns =(Ns+N BG )-(N S1 +N S2 ) (N N ) (N N ) : w/ sideband subtraction Ns Production Channel Production Channel γ + p K + Λ （ 1405) / Σ (1385) γ + p K + + Λ （ 1405) / Σ (1385) N N S1 N N BG N S2 N Possible Background Channels Possible Background Channels + γ γ + → + Λ + π 1.28 1.33 1.43 1.48 p p K γ + → + + Σ + π πΣ mass Kp threshold p K γ + → φ + → + + − + p p K K p γ + → + Λ Λ * p K K γ + → + Σ * p K ……………….. 10 Strangeness Workshop@Atami, 2009.2.27 DeukSoon Ahn
Yields and Acceptance for Yields and Acceptance for Λ (1405)/ (1405)/ Σ (1385) (1385) 1.28<MM(K+)<1.48 ( ) 4 1.33<MM(K+)<1.43 1.33<MM(K+)<1.43 with Acceptance Yields sideband subtraction 11 Strangeness Workshop@Atami, 2009.2.27 DeukSoon Ahn
Differential Cross Section d Differential Cross Section d σ /dt dt 1.28<MM(K+)<1.48 1.33<MM(K+)<1.43 1.33<MM(K+)<1.43 with sideband subtraction P Preliminary results li i lt 12 Strangeness Workshop@Atami, 2009.2.27 DeukSoon Ahn
Summary and Outlook Summary and Outlook � To understand production mechanism, we measured the Differential Cross Section and Photon Beam Asymmetry for Differential Cross Section and Photon Beam Asymmetry for γ p � K + Λ (1405)/ Σ (1385) on the Liquid Hydrogen target at E γ =1.5-2.4GeV using linearly polarized photon beam. (@ Forward region) (@ F d i ) � The photon beam asymmetry increases above E γ ~1.7GeV and the sign of photon beam asymmetry was changed E γ ~2 0GeV the sign of photon beam asymmetry was changed E γ ~2.0GeV. � We expected production mechanism for Λ (1405)/ Σ (1385) is different. ( K- exchange @low E γ and K* exchange @high E γ ) � From the t-distribution, we can extract t-dependence is flat@low E γ and steep@high E γ � The Background study will be done for the Λ (1405)/ Σ (1385) . 13 Strangeness Workshop@Atami, 2009.2.27 DeukSoon Ahn
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