𝜋0𝜋± photoproduction on the deuteron at ELPH

Univ. of Tokyo, ELPH Tohoku UnivA, KEKB, Yamagata Univ.C

Shin’ichi Masumoto, Takatsugu IshikawaA, Kyoichiro OzawaB ,

Hajime ShimizuA, Yasuhisa TajimaC , Yusuke TsuchikawaA, Ryo HashimotoC , Qinghua HeA, Manabu MiyabeA, Norihiti MuramatsuA, Hirohoto YamazakiA, Ryuji YamazakiA, and the Forest Collaboration

YITP workshop on Hadron in Nucleus

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Contents

• Introduciton• Study of baryon resonances in the reactions 𝛾𝑁 → 𝜋0𝜋±𝑁

• Analysis of 𝛾𝑁 → 𝜋0𝜋±𝑁• Experimental setup ELPH FOREST• Event selection and acceptance correction• Total and differential cross section of 𝛾𝑁 → 𝜋0𝜋±𝑁• Monte-Carlo simulation of Fermi motion on the deuteron

• Summary

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Introduction

• We investigate the highly excited states of baryon resonances by using photon beam.

• The properties of baryons were mainly derived from partial-wave analysis of single π and η production.

• The highly excited baryons do not strongly couple to the πN channel. ⇒multi-meson photoproduction process provides important information on highly excited baryon states.

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Focus on baryon resonances couple to 𝜌𝑁and 𝜋Δ channel using 𝛾𝑁 → 𝜋0𝜋±𝑁 reaction

𝜌±𝑁

𝜋Δ

𝛾 𝛾

𝛾 𝛾

𝑁

𝑁

𝑁𝑁 𝑁

𝑁𝑁 𝑁

𝜌±

Δ

𝜌±

N∗, Δ∗ Δ

N∗, Δ∗

𝜋±𝜋0𝜋𝜋

𝜌± contact term

Δ Kroll-Ruderman Resonance term

Resonance term

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Focus on baryon resonances couple to 𝜌𝑁and 𝜋Δ channel using 𝛾𝑁 → 𝜋0𝜋±𝑁 reaction

• The total and differential cross section of 𝜋0𝜋+ photoproduction for photon energies from 300 to 800 MeV have been reported by Mainz and DAPHNE.

• Measurement of 𝜋0𝜋−photoproduction has not been reported.

⇒The precise measurements of the 𝜋0𝜋± photoproduction for photon energies more than 800 MeV are important to study the properties of 2nd

and 3rd resonance region.

Total cross section of 𝜋0𝜋+

photoproduction obtained at Mainz and DAPHNE.

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Analysis of 𝛾𝑁 → 𝜋0𝜋±𝑁 on the proton and deuteron

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Experimental setup

• Bremsstrahuling tagged photon beam : 570～1150 MeV (Δ𝐸 =1～2 MeV)

• Hydrogen/deuteron target

• Three type of calorimeters : acceptance ～ 90%

• Plastic scintillation counters are placed in front of each calorimeters. 7

Analysis procedure of 𝛾𝑁 → 𝜋0𝜋±𝑁

1. Particle identificationDetection of all emitted particles (𝜋0 → 𝛾𝛾, 𝜋±, proton/neutron) are required. • 𝜋0 → 𝛾𝛾 selection. • Proton/charged pion identification.• Neutron identification.

2. Kinematical Fitting• Event identification using Chi-square probability test. • improve intermediate mass resolution.

3. Acceptance & Efficiency correction• Evaluate detection efficiency of proton/neutron/charged pion• Total cross section and differential cross section

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1. Particle identification

𝜋0 → 𝛾𝛾 selection・Two neutral particles ・Timing difference of 𝛾𝛾 < 1.5 nsec. ・90 ≤ 𝑀𝛾𝛾 < 190 MeV/c2

Proton/𝜋± identification ・Identified by means of Δ𝐸and E correlation.

Neutron identification・Delayed neutral particle from 𝛾𝛾 timing [1.5, 15) nsec

𝛾𝛾 invariant massTiming difference between 𝛾𝛾 and delayed neutral particle

Measured energy of calorimeter (MeV)

Mea

sure

d e

ner

gy o

f p

last

ic s

cin

tilla

tio

r(M

eV)

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2. Kinematical Fitting (4C-fit)

• Event selection using Chi-square test.

Constraints : 𝛾𝛾 invariant massEnergy and momentum conservation

Measurement variables : photon beam energyMomenta of the 𝛾𝛾Emitted nucleon momentumEmitted angle of 𝜋±

𝜒2 probability ≧ 0.110

3. Acceptance & Efficiency correction

• We evaluate proton, neutron and charged pion detection efficiency of pure CsI and Lead/SciFi calorimeters.

• Proton efficiency is evaluated using missing proton kinematical fit of 𝛾𝑝 → 𝜂𝑝 and 𝛾𝑝 → 𝜋0𝑝 reaction on the hydrogen.

• Neutron (charged pion) efficiency is evaluated using missing neutron (charged pion) kinematical fit of 𝛾𝑝 → 𝜋0𝜋+𝑛 reaction on the hydrogen.

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proton

neutron

𝝅+

neutron

𝝅+

Det

ecti

on

eff

icie

ncy

(Lea

d S

ciFi

)

proton

Det

ecti

on

eff

icie

ncy

(pu

re C

sI)

Efficiency Evaluation

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𝐸𝛾 (MeV/𝑐2)

𝛾𝑁 → 𝜋0𝜋±𝑁 cross section

• Acceptance correction using Geant4 based Monte-Calrosimulation with obtained detector efficiency.

• Those plots with higher energy above 800 MeV are newly obtained.

• Our data covers 2nd and 3rd

resonance region.

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𝜋Δ

𝛾𝑁 → 𝜋0𝜋±𝑁 cross section

(MeV/𝑐2)

𝜌±𝑁

𝛾 𝛾

𝛾 𝛾

𝑁

𝑁

𝑁𝑁 𝑁

𝑁𝑁 𝑁

𝜌±

Δ

𝜌±

N∗, Δ∗ Δ

N∗, Δ∗

𝜋±𝜋0𝜋𝜋

𝜌± contact term

Δ Kroll-Ruderman Resonance term

Resonance term

Deviation of the experimental data from

the phase space distribution are evidence

for meson intermediate states.

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Cross section on the deuteron

• Cross section on the deuteron target is affected by Fermi motion and Final state interaction.

• We evaluate Fermi motion effect using 𝛾𝑝 → 𝜋0𝜋+𝑛 reaction on hydrogen and deuteron.

• Fermi motion effect is evaluate by Monte Calro simulation using nucleon momentum distribution and effective mass of participant.

• In this work, 𝜋𝑁 and 𝑁𝑁 rescatterings in the final state are neglected.

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Cross section

𝐸𝛾 (MeV/𝑐2)

: Estimated 𝛾𝑝∗ → 𝜋0𝜋+𝑛 cross section on the deuteron using 𝛾𝑝 →𝜋0𝜋+𝑛 cross section on the hydrogen.

• Fermi momentum distribution is determined by atomic density and Hulthen’s wave function.

• Effective mass of participant

𝑚(𝑝)′ = 𝑚𝑑 −𝑚(𝑠)

2− 2𝑚𝑑(𝐸(𝑠) −𝑚(𝑠))

assuming the spectator nucleon is on-shell in the initial state.

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Summary

• We have measured 𝜋0𝜋± photoproduction on the hydrogen and deuteron for 570 < 𝐸𝛾 < 1150 MeV. • Obtained cross section is consistent with Mainz and DAPHNE data (𝛾𝑝 →𝜋0𝜋+𝑛).

• Our data covers 2nd and 3rd resonance region. • An enhancement of 𝜌N intermediate state is observed near 2nd resonance

region. • Fermi motion effect on the deuteron is evaluate by toy Monte-Calro

simulation.

• Future plan• We need more detail study for Fermi motion effect and final state interaction.

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