The reaction studied with an electromagnetic calorimeter FOREST

Yusuke TSUCHIKAWAR. Hashimoto, Q. He, T. Ishikawa, S. Masumoto, M.

Miyabe, N. Muramatsu, H. Shimizu, Y. Tajima, H. Yamazaki, R.

Yamazaki,and FOREST collaboration

Research Center for the Electron Photon Science, Tohoku UniversityY. Tsuchikawa 12014/2/21

Outline

• Motivation• FOREST experiment– 4 electromagnetic calorimeter FOREST

• Analysis– Outline– Event selection– Kinematical fit– Results

• Summary and Future plan

The reaction studied with an electromagnetic calorimeter FOREST

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Motivation

• Baryon resonances have been experimentally studied by means of meson production reactions for understanding Quantum Chromo Dynamics.

• πN and ηN photoproduction reactions have been intensively investigated until now

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photoproduction reactions are well-studied until nowHOWEVER, few data on

-> KY channel…

Motivation

• photoproduction– Only NEUTRAL particles are implicated in this reaction

→ no charged particle (e.g. ) exchange term → few Born term contribution? -> study of Baryon

Resonance

𝑁 𝐾 𝑌

Born terms

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NKS data - photoproduction

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K. Tsukada et al., PhysRevC.78.014001, PhysRevC.83.039904

Research Center for Electron Photon Science (ELPH)

STretcher-Booster Ring:1.2 GeV electron synchrotron

Layout of ELPH ( ～ 2012)

GeV- Beam line:0.5-1.2 GeV photon

Linac

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Experiment

MeV

𝛾

Energy resolution

(for 1 GeV )～ 3 % ～ 7 %

～ 5 %

192 Pure CsI PS 24 × 3 layers

252 Lead/SciFi mod.sPS×12

PS×18 62 Lead/Glass

Liquid H2/D2 target

4 electromagnetic calorimeter complex FORESTExperiment

(Forward) (Backward)

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Analysis – Outline

• The final state: 　

　　　 Branching ratio(BR)s: : 30.69%, : 63.9% (PDG value)

• The proton in target deuterium is assumed as a spectator: not involve with the reaction

The neutron in target deuterium is assumed as a rest particle

• identification– Hit informations of calorimeter

(and front hodoscope) – Energy and timing informations

Assumed as a spectator

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• 4 neutral hits (expected ):– At least 4 neutral clusters are measured at same time– Selection of the combinations decayed from the same

→ test .

Analysis – particle identification

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𝛾 𝑑→𝐾𝑆0 Λ𝑝→ (𝜋 0 𝜋0 ) (𝑝𝜋−)𝑝→ ( 4𝛾 ) (𝑝𝜋−)𝑝

Timing difference of 2 pions

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• Charged hits (expected ):– Charged cluster(s) @ Forward Calorimeter & Hodoscope– ID -> method

𝑝

𝜋

Analysis – particle identification

𝜋

𝑝

𝑛

𝛾→ reject

4γ average timing

𝛾 𝑑→𝐾𝑆0 Λ𝑝→ (𝜋 0 𝜋0 ) (𝑝𝜋−)𝑝→ ( 4𝛾 ) (𝑝𝜋−)𝑝

Analysis – Kinematical fitting

Kinematical fitting with 3 constraints invariant mass 」 ２✕ 1. 2.

「 missing mass 」 3.

13 variables: Photon beam energy

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Analysis yield estimation

invariant mass distribution Fitting function:

4th polynomial + gaussian– yield: ～ 8,500 events

S/N ～ 10%

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Analysis – KinematicsRanges of CsI

Emission angle @ Lab. frame (deg)

Mom

entu

m (G

eV)

𝐾 0

𝑝

𝜋−

𝐸𝛾=1.15GeV

the maximum emission angle of proton < 40°→ hit pattern of hodoscopes:　　 Forward (): 2 & Central: 0

• Azimuthal angle difference between system and system

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Analysis – Kinematics

(deg)

Accidental coincident events are subtracted by sideband

Analysis – Kinematics

Emission angle @ Lab. frame (deg)

Mom

entu

m (G

eV)

𝐾 0

𝑝

the maximum emission angle of proton < 40°→ hit pattern of hodoscopes:　　 Forward (): 2 & Central: 0

𝜋−

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(Monte Calro simulation)𝐸𝛾=1.15GeV

Energy dependence of K0 emission angle

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Analysis – Yield

invariant mass

Real Data

GEANT4 Simulation

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Analysis – Yield

reaction threshold ～ 1050MeV

Analysis – total cross section

invariant mass

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Very Preliminary

A preliminary result of the total cross section

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Analysis – Background study

4 background candidates

✕ B.R. → mixed

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Analysis – Background study

Invariant Mass

a.u.

𝐾 0

Summary and Future plan

• The photoproduction reaction is studied with an EM calorimeter FOREST at ELPH

• About 8,500 events are confirmed in the reaction analysis• The reaction total cross section is estimated order of 1μb at

GeV region

• Future plan– Event selection – Differential cross section– Background event study

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