Photoproduction of (1405) and (1385) p ( ) ( ) at - - PowerPoint PPT Presentation

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

E i l S

• 2. Experimental Setup
• 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 JP=1/2- , I=0, and S=-1 Σ(1385) with JP=3/2+ , I=1, and S=-1 ~20 MeV γ p K+ Λ(1405) K+ Σ +π – LEPS data LEPS data, PRC78,035202(2008) , PRC78,035202(2008)M.Niiyama M.Niiyama K+ Σ -π + γp K+ Σ(1385) K+ Λ π 0 Λ∗/Σ∗ = 0.54 ± 0.17 0.084 ± 0.076 Strong Energy dependence! Strong Energy dependence! Hi h St ti ti ! Hi h St ti ti ! γp K+ Λ(1405) / Σ(1385) : Using missing mass of K+ High Statistics ! High Statistics ! To understand the production Mechanism, To understand the production Mechanism,

• Differential Cross section

Differential Cross section Photon Beam Asymmetry Photon Beam Asymmetry

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DeukSoon Ahn

• Photon Beam Asymmetry

Photon Beam Asymmetry

Photon Beam Photon Beam Asymmety Asymmety for for Photon Beam Photon Beam Asymmety Asymmety for for Λ Λ(1405) @ S.I. Nam et al. (1405) @ S.I. Nam et al. arXiv:0806.4029 arXiv:0806.4029 ;Strong contribution of electric coupling from the K exchange

• Nucl. Phys. A 748 (2005) 499
• Nucl. Phys. A 748 (2005) 499

by M.F.M.Lutz & M.Soyeur by M.F.M.Lutz & M.Soyeur Data Data; ; T T. . Azemoon Azemoon et et al al. . NP NP B B95 95 ( (1975 1975) ) 77

@ Eγ ≈ 2 GeV

coupling from the K- exchange (t-mK2)-2 (t-mK2)-1

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DeukSoon Ahn

Rapid fall-off suggesting a t-channel exchange process

Experimental Setup ; LEPS Detector Experimental Setup ; LEPS Detector

TOF wall Dipole Magnet (0.7 T) Aerogel Cerenkov ( 1 03) Start counter (n=1.03) Liquid hydrogen target

γ

1m

MWDC 2 MWDC 3 MWDC 1 Silicon Vertex Detector

1m

W C

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

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Strangeness Workshop@Atami, 2009.2.27

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Data Data analysis analysis

γ + p K+ + Λ（1405) /Σ(1385) γ + p K + Λ（1405) /Σ(1385)

tum

K+PID with 3σ Counts

Λ（1116) Σ(1193)

Moment

C

Λ（1405) Λ（1405) Σ(1385) Λ（1520)

Mass 2 ФK+

Kinematical region Missing Mass (K+)

hal angleФ Azimuth DeukSoon Ahn

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Momentum Transfer

Photon Beam Asymmetry Photon Beam Asymmetry

K+ K+ εγ γ p Σ >0 ; V>H

Λ(1405)/ (1405)/Σ(1385) (1385)

γ p ; Σ <0 ; V<H Σ(1385) dominant Preliminary results ( 3 5)

• K* exchange ?

Λ(1405) dominant

• K- exchange ?

DeukSoon Ahn

Strangeness Workshop@Atami, 2009.2.27

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Particle Identification for Particle Identification for Kaon Kaon – – π+ contamination

+ contamination

K+ PID with 3σ K+ PID with 3σ K+ PID with 2σ K+PID with 1σ M 2

DeukSoon Ahn

Strangeness Workshop@Atami, 2009.2.27

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Mass 2 Missing Mass (K+)

Photon Beam Asymmetry Photon Beam Asymmetry

K+ PID with 3σ K+ PID with 2σ K+PID with 1σ

DeukSoon Ahn

Strangeness Workshop@Atami, 2009.2.27

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Photon Beam Asymmetry Photon Beam Asymmetry as a function of

as a function of MissngMass MissngMass 1.50<Eγ<2.40 1.65<Eγ<1.80 2.25<Eγ<2.40 Missing Mass (K+) Missing Mass (K+) π+/proton contamination and

DeukSoon Ahn

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Missing Mass (K )

• ther background channel should be studied.

Background Background

N (N N ) (N N ) Ns+N Ns+NBG

BG : w/o sideband subtraction

Ns Ns =(Ns+NBG)-(NS1 +NS2) : w/ sideband subtraction

N N N Ns γ + p K+ + Λ（1405) /Σ(1385)

Production Channel Production Channel

NS1 NBG NS2

1.28 1.33 1.43 1.48

γ + p K + Λ（1405) /Σ(1385)

π γ + Λ + → +

+

K p

Possible Background Channels Possible Background Channels

πΣ mass Kp threshold

p K K p p + + → + → +

− +

φ γ γ p Λ

*

K

π γ + Σ + → +

+

K p

Λ + → + K p γ Σ + → +

*

K p γ

………………..

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Strangeness Workshop@Atami, 2009.2.27

Yields and Acceptance for Yields and Acceptance for Λ(1405)/ (1405)/Σ(1385) (1385)

1.28<MM(K+)<1.48

Acceptance

( ) 4 1.33<MM(K+)<1.43 1.33<MM(K+)<1.43 with

sideband subtraction

Yields

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Strangeness Workshop@Atami, 2009.2.27

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Differential Cross Section d Differential Cross Section dσ/dt dt

1.28<MM(K+)<1.48 1.33<MM(K+)<1.43 1.33<MM(K+)<1.43 with

sideband subtraction

P li i lt Preliminary results

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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 γp K+Λ(1405)/Σ(1385) on the Liquid Hydrogen target at Eγ=1.5-2.4GeV using linearly polarized photon beam. (@ F d i ) (@ Forward region)

The photon beam asymmetry increases above Eγ~1.7GeV and

the sign of photon beam asymmetry was changed Eγ~2 0GeV the sign of photon beam asymmetry was changed Eγ~2.0GeV.

We expected production mechanism for Λ(1405)/Σ(1385) is

• different. ( K- exchange @low Eγ and K* exchange @high Eγ)

From the t-distribution,

we can extract t-dependence is flat@low Eγ and steep@high Eγ

The Background study will be done for the Λ(1405)/Σ(1385).

DeukSoon Ahn

Strangeness Workshop@Atami, 2009.2.27

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