Post on 01-Mar-2021
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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