Elastic Electron Scattering for Proton Charge Radius Determination - - PowerPoint PPT Presentation

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CPHI @ Yerevan,

• Sep. 24-28, 2018

Elastic Electron Scattering for Proton Charge Radius Determination

Toshimi Suda

Tohoku University Sendai, Japan

Tohoku Univ.：K. Tsukada, Y. Honda, T. Tamae. T. Mutoh, K. Takahashi,

• K. Nambu, M. Miyabe, A. Tokiyasu, K. Nanba, T. Aoyagi

Miyazaki Univ.： Y. Maeda

for ULQ2 (Ultra-Low Q2) Collaboration

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CPHI @ Yerevan,

• Sep. 24-28, 2018

Ee = 20 - 60 MeV !!

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CPHI @ Yerevan,

• Sep. 24-28, 2018

Short-Lived Exotic Nuclei

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CPHI @ Yerevan,

• Sep. 24-28, 2018

RIKEN RI Beam Factory world’s highest intensities of exotic beams ( 2007 ~ )

in-flight fragmentation of U E = 350 MeV/A I ~ 1 pμA

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CPHI @ Yerevan,

• Sep. 24-28, 2018

size shape proton

isotope shift electron scattering

matter

reaction cross section proton scattering

size and shape of neutro- and proton-rich nuclei

⇢c(~ r) = X

p

∗(~ r) (~ r)

< r2

c >=

Z r2⇢c(r) d~ r

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CPHI @ Yerevan,

• Sep. 24-28, 2018

Electron scattering off short-lived exotic nuclei

L ~ 1027 /cm2/s with only ~108 target nuclei

SCRIT ( Self-Confining RI ion Target )

dσ dΩ = dσMott dΩ |Fc(q)|2

Fc(q) =

• c(⌥

r)ei⇧

q⇧ rd⌥

r

Elastic electron scattering

⇢c(~ r) = X

p

∗

p(~

r) p(~ r)

Short-lived Exotic Nuclei

Production-hard + Short-lived

Nuclei targeted so far for electron scattering

Charge density distribution Charge radius

Expected low luminosities

H.deVries, C. deJager and C. deVries Atomic Data and Nuclear Data Tables 36 (987)495

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CPHI @ Yerevan,

• Sep. 24-28, 2018

Ee Nbeam ρ・t L

Hofstadter’s era (1950s)

150 MeV ~ 1nA (~109 /s) ~1019 /cm2 ~1028 /cm2/s

JLAB

6 GeV ~100μA (~1014 /s) ~1024 /cm2 ~1038 /cm2/s

SCRIT

150 - 300 MeV ~200 mA (~1018 /s) ~ 1010 /cm2 ~1027 /cm2/s

Luminosities

Electrodes for mirror potential ions from an external ion source scattered electron trapped ions electron beam

SCRIT (Self-Confining RI Ion Target) : ion trapping

• Nucl. Inst. Meth. A532 (2004) 216.
• Phys. Rev. Lett. 100 (2008) 164801.
• Pbys. Rev. Lett. 102 (2009) 102501.
• Phys. Rev. Lett. 118 (2017) 262501.

Prog.Part.Nucl.Phys. 96 (2017) 1. ….

~108 ions are trapped on e-beam (~ 1 mm2) Nt ~108 /mm2 => 1010 /cm2

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CPHI @ Yerevan,

• Sep. 24-28, 2018

SCRIT facility in RIKEN/RI Beam Factory

world’s first electron scattering facility for exotic nuclei

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CPHI @ Yerevan,

• Sep. 24-28, 2018

the latest “Nuclear Physics News”

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• Sep. 24-28, 2018

Proton Charge Radius by Elastic Electron Scattering

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• Sep. 24-28, 2018

Why is the proton radius a hot topics ?

1) the radius is one of the basic properties of the nucleon 3) possible new physics beyond Standard Model (??)

Lepton Universality (e <-> μ）??

2) the radius is strongly correlated to the Rydberg constant

∆E = α · RRydberg + β· < r2 >

ΔE = RRydberg( 1 n2 − 1 m2 )

R∞ = 10973 731.568 539 ± 0.000 055 m−1

rp uncertainty

4) the neutron-skin thickness of neutron-rich nuclei => EOS of neutron matter

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CPHI @ Yerevan,

• Sep. 24-28, 2018

< r2 >= Z r2⇢(~ r)d~ r = 4π Z r4 ρ(r) dr

Charge radius and charge density

R r r2⇢(r)d~ r R ∞ r2⇢(r)d~ r

Proton < r2 >1/2

~ exponential

Proton（~0.8 fm)

Ratio = 98 %

GE(Q2) ∼ 1 − < r2 >1/2 6 Q2 + < r4 >1/2 120 Q4 − ...

< r2 >≡ −6 dGE(Q2) dQ2 |Q2→0

Mainz (2014) Ee ≥ 180 MeV PRC 90 (2014) 015206.

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CPHI @ Yerevan,

• Sep. 24-28, 2018

Absolute GE(Q2) at lower Q2 region

1)no absolute GE(Q2) (“floating”) 2) χ2 is quite similar

< r2 >≡ −6 dGE(Q2) dQ2 |Q2→0

a toy model for larger radius

“floating”

• I. Sick, Atoms 2018, 6, 2

ABSOLUTE GE(Q2) at lower Q2 region !!

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CPHI @ Yerevan,

• Sep. 24-28, 2018

electron scattering under Ultra-Low Q2

The goal of this project GE(Q2) measurements at 0.0003 ≤ Q2 ≤ 0.008 (GeV/c)2

• Exp. @ Tohoku Low-Energy Electron Linac (Ee = 20 - 60 MeV)

Absolute cross section measurement with 10-3 precision Rosenbluth separated GE(Q2), GM(Q2) ULQ2

Mainz (2014) Ee ≥ 180 MeV PRC 90 (2014) 015206.

• nly ~ 2%

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CPHI @ Yerevan,

• Sep. 24-28, 2018

Tohoku Univ. Sendai

ULQ2 @ Sendai

ULQ2 collaboration (Ultra-Low Q2)

RIKEN RI Beam Factory

60 MeV e-linac 1.3 GeV synchrotron

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CPHI @ Yerevan,

• Sep. 24-28, 2018

Research Center for Electron-Photon Science, Tohoku University

60 MeV electron linac ~10 kW electron beam (150 uA) Radioactive Isotope photo-production

1.3 GeV booster synchrotron

• Exp. Hall 2

GeV-γ Hall NKS II FOREST 90 MeV e-Linac (injector)

GeV γ beam

60 MeV e-Linac

γ/e beam GeV γ beam

• Exp. Hall 1

1.3 GeV Booster Ring tagged photons (~ 1 GeV) meson photoproduction, hypernucleus

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CPHI @ Yerevan,

• Sep. 24-28, 2018

e-scattering off proton at ultra-low Q2 region

Goal of our experiment GE(Q2) measurements in 0.0003 ≤ Q2 ≤ 0.008 (GeV/c)2 Our experiments Low-energy electron scattering Absolute cross section measurement Rosenbluth separation (GE(Q2), GM(Q2)) Challenges Absolute cross section (GE(Q2)) with 10-3 accuracy experimental challenges for measurement theoretical challenges for interpretation 20 ≤ Ee ≤ 60 MeV 30 ≤ θ ≤ 150° Δp/p ~ 10-3 accelerator, instruments Tohoku low-energy electron linac + experimental hall new beam line + double-arm spectrometer

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物理学会シンポジウム 2018.03.22

e e’ θ

momentum transfer energy transfer 4 momentum transfer

Q2 = q2 − ω2 = 4

~ q = ~ e − ~ e0

ω = e − e0

2 = 4 e e0sin2(θ/2)

dσ dΩ = ( dσ dΩ)Mott G2

E(Q2) + ⌧ ✏ G2 M(Q2)

1 + τ

✏ = 1 1 + 2(1 + ⌧)tan2 θ

2

τ = Q2 4m2

p

( dσ dΩ)Mott = z2α2 4e2 cos2(θ/2) sin4(θ/2) ∝ e2 q4

Proton charge radius by e-scattering

One Photon Exchange Approx.

∈ 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 ]

2

[(GeV/c)

2

Q

4 −

10

3 −

10

2 −

10

Beam Energy 60MeV 50MeV 40MeV 30MeV 20MeV

°

30

°

40

°

50

°

60

°

70

°

80

°

90

°

100

°

110

°

120

°

130

°

140

°

150

measurable

• Q

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CPHI @ Yerevan,

• Sep. 24-28, 2018

Absolute cross section (GE(Q2)) with 10-3 accuracy

Challenges ….

relative measurement to well-known (established) cross section

Moeller cross section : PRAD@JLAB

Ultra Relativistic Limit : me -> 0 ?? finite effects : up to a few % depending on kinematics

12CH2(e,e’) cross section ULQ2@Tohoku

large scattering angle coverage for GE/GM separation Coulomb distortion effects not negligible ( ~ 0.2 % level ) Low energy electron detection with high resolution no tracking, frequent spectrometer setting changes ,,,

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CPHI @ Yerevan,

• Sep. 24-28, 2018

1.3 GeV booster synchrotron

• Exp. Hall 2

GeV-γ Hall NKS II FOREST 90 MeV e-Linac (injector)

GeV γ beam

60 MeV e-Linac

γ/e beam GeV γ beam

• Exp. Hall 1

e-beam

2 m

New beam line and spectrometers

new beam line

+ new spectrometer(s)

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CPHI @ Yerevan,

• Sep. 24-28, 2018

Electron spectrometer (P = 20 - 60 MeV/c) Low energy : Ee = 20 - 60 MeV high-resolution without tracking “old-fashioned” spectrometer

1175

910

Electron spectrometer radius 500 mm bending angle 90°

• max. B

0.4T@60MeV gap 70 mm dispersion 850 mm Δp/p 8×10-4 momentum bite 10% Δθ 5 mrad solid angle 10 mSr

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CPHI @ Yerevan,

• Sep. 24-28, 2018

Summary

1) elastic e+p scattering at ultra-low Q2 region 2) GE(Q2) at 0.0003 ≤ Q2 ≤ 0.008 (GeV/c)2 3) GE is extracted by Rosenbluth separation 4) Absolute cross section measurement relative to 12C(e,e)12C : sys. err. ~3x10-3 5) Ee = 20 - 60 MeV, θ = 30 - 150° 6) the new beam line, and spectrometer are under construction 7) the experiments will start in 2019