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

CPHI @ Yerevan, Sep. 24-28, 2018 Elastic Electron Scattering for Proton Charge Radius Determination Toshimi Suda Tohoku University Sendai, Japan for ULQ 2 (Ultra-Low Q 2 ) Collaboration 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

CPHI @ Yerevan, Sep. 24-28, 2018 Ee = 20 - 60 MeV !!

CPHI @ Yerevan, Short-Lived Exotic Nuclei Sep. 24-28, 2018

CPHI @ Yerevan, RIKEN RI Beam Factory Sep. 24-28, 2018 world’s highest intensities of exotic beams ( 2007 ~ ) in-flight fragmentation of U E = 350 MeV/A I ~ 1 p μ A

CPHI @ Yerevan, size and shape of neutro- and proton-rich nuclei Sep. 24-28, 2018 Z < r 2 r 2 ⇢ c ( r ) d ~ c > = r X ⇢ c ( ~ r ) = ∗ ( ~ r ) ( ~ r ) p size shape electron proton isotope shift scattering reaction cross proton matter section scattering

CPHI @ Yerevan, Electron scattering o ff short-lived exotic nuclei Sep. 24-28, 2018 Nuclei targeted so far Short-lived Exotic Nuclei for electron scattering Production-hard + Short-lived Elastic electron scattering d Ω = d σ Mott d σ | F c ( q ) | 2 d Ω � r ) e i ⇧ q ⇧ r d ⌥ F c ( q ) = � c ( ⌥ r X ⇢ c ( ~ r ) = ∗ p ( ~ r ) p ( ~ r ) p SCRIT ( Self-Confining RI ion Target ) L ~ 10 27 /cm 2 /s with only ~10 8 target nuclei Expected low luminosities Charge density distribution H.deVries, C. deJager and C. deVries Charge radius Atomic Data and Nuclear Data Tables 36 (987)495

electron beam trapped ions scattered electron an external ion source ions from Electrodes for mirror potential CPHI @ Yerevan, Luminosities Sep. 24-28, 2018 SCRIT (Self-Confining RI Ion Target) : ion trapping ~10 8 ions are trapped on e-beam (~ 1 mm 2 ) N t ~10 8 /mm 2 => 10 10 /cm 2 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. …. ρ ・ t Ee N beam L Hofstadter’s ~ 1nA ~10 19 /cm 2 ~10 28 /cm 2 /s 150 MeV era (1950s) (~10 9 /s) ~100 μ A JLAB ~10 24 /cm2 ~10 38 /cm 2 /s 6 GeV (~10 14 /s) ~200 mA 150 - 300 SCRIT ~ 10 10 /cm 2 ~10 27 /cm 2 /s (~10 18 /s) MeV

CPHI @ Yerevan, SCRIT facility in RIKEN/RI Beam Factory Sep. 24-28, 2018 world’s first electron scattering facility for exotic nuclei

CPHI @ Yerevan, Sep. 24-28, 2018 the latest “Nuclear Physics News”

CPHI @ Yerevan, Sep. 24-28, 2018 Proton Charge Radius by Elastic Electron Scattering

r p uncertainty Lepton Universality (e <-> μ）?? CPHI @ Yerevan, Why is the proton radius a hot topics ? Sep. 24-28, 2018 1) the radius is one of the basic properties of the nucleon 2) the radius is strongly correlated to the Rydberg constant Δ E = R Rydberg ( 1 n 2 − 1 m 2 ) ∆ E = α · R Rydberg + β · < r 2 > R ∞ = 10973 731.568 539 ± 0.000 055 m − 1 3) possible new physics beyond Standard Model (??) 4) the neutron-skin thickness of neutron-rich nuclei => EOS of neutron matter

CPHI @ Yerevan, Charge radius and charge density Sep. 24-28, 2018 Z Z < r 2 > = r 2 ⇢ ( ~ r 4 ρ ( r ) d r r ) d ~ r = 4 π Proton （ ~0.8 fm) Mainz (2014) Proton Ee ≥ 180 MeV ~ exponential PRC 90 (2014) 015206. < r 2 > 1 / 2 R r r 2 ⇢ ( r )d ~ r R ∞ r 2 ⇢ ( r )d ~ r G E ( Q 2 ) ∼ 1 − < r 2 > 1 / 2 Q 2 + < r 4 > 1 / 2 Q 4 − ... 6 120 < r 2 > ≡ − 6 d G E ( Q 2 ) Ratio = 98 % | Q 2 → 0 d Q 2

1)no absolute G E (Q 2 ) (“floating”) 2) χ 2 is quite similar “floating” ABSOLUTE G E (Q 2 ) at lower Q 2 region !! CPHI @ Yerevan, Absolute G E (Q 2 ) at lower Q 2 region Sep. 24-28, 2018 < r 2 > ≡ − 6 d G E ( Q 2 ) | Q 2 → 0 d Q 2 a toy model for larger radius I. Sick, Atoms 2018, 6, 2

CPHI @ Yerevan, electron scattering under Ultra-Low Q 2 Sep. 24-28, 2018 The goal of this project G E (Q 2 ) measurements at 0.0003 ≤ Q 2 ≤ 0.008 (GeV/c) 2 Absolute cross section measurement with 10 -3 precision Rosenbluth separated G E (Q 2 ), G M (Q 2 ) Exp. @ Tohoku Low-Energy Electron Linac (Ee = 20 - 60 MeV) only ~ 2% Mainz (2014) Ee ≥ 180 MeV PRC 90 (2014) 015206. ULQ 2

1.3 GeV synchrotron 60 MeV e-linac CPHI @ Yerevan, ULQ 2 @ Sendai Sep. 24-28, 2018 ULQ 2 collaboration (Ultra-Low Q 2 ) Tohoku Univ. Sendai RIKEN RI Beam Factory

CPHI @ Yerevan, Research Center for Electron-Photon Science, Tohoku University Sep. 24-28, 2018 1.3 GeV Booster Ring 60 MeV electron linac tagged photons (~ 1 GeV) ~10 kW electron beam (150 uA) meson photoproduction, hypernucleus Radioactive Isotope photo-production Exp. Hall 2 GeV γ beam Exp. Hall 1 1.3 GeV booster synchrotron NKS II γ /e beam GeV γ beam 90 MeV e-Linac 60 MeV e-Linac FOREST (injector) GeV- γ Hall

CPHI @ Yerevan, e-scattering o ff proton at ultra-low Q 2 region Sep. 24-28, 2018 Goal of our experiment G E (Q 2 ) measurements in 0.0003 ≤ Q 2 ≤ 0.008 (GeV/c) 2 Our experiments Low-energy electron scattering Absolute cross section measurement Rosenbluth separation (G E (Q 2 ), G M (Q 2 )) accelerator, instruments Tohoku low-energy electron linac + experimental hall 20 ≤ Ee ≤ 60 MeV 30 ≤ θ ≤ 150° Δ p/p ~ 10 -3 new beam line + double-arm spectrometer Challenges Absolute cross section (G E (Q 2 )) with 10 -3 accuracy experimental challenges for measurement theoretical challenges for interpretation

One Photon Exchange Approx. 物理学会シンポジウム Proton charge radius by e-scattering 2018.03.22 e’ e G 2 E ( Q 2 ) + ⌧ ✏ G 2 M ( Q 2 ) θ d Ω = ( d σ d σ d Ω ) Mott 1 + τ e − ~ d Ω ) Mott = z 2 α 2 cos 2 ( θ / 2) sin 4 ( θ / 2) ∝ e 2 ( d σ momentum transfer q = ~ ~ e 0 4 e 2 q 4 ω = e − e 0 energy transfer 1 Q 2 = q 2 − ω 2 = 4 τ = Q 2 4 momentum transfer ✏ = 1 + 2(1 + ⌧ )tan 2 θ 2 = 4 e e 0 sin 2 ( θ / 2) 4 m 2 2 p -Q measurable ] 2 ° Beam Energy [(GeV/c) ° 150 ° 140 ° 130 60MeV ° 120 − 110 50MeV 2 ° 10 100 ° 40MeV 90 ° 30MeV 2 80 Q ° 70 20MeV ° 60 ° 50 ° 40 ° 30 − 3 10 − 4 10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 ∈

CPHI @ Yerevan, Challenges …. Sep. 24-28, 2018 Absolute cross section (G E (Q 2 )) with 10 -3 accuracy relative measurement to well-known (established) cross section Moeller cross section : PRAD@JLAB large scattering angle coverage for GE/GM separation 12 CH 2 (e,e’) cross section ULQ 2 @Tohoku Low energy electron detection with high resolution no tracking, frequent spectrometer setting changes ,,, Ultra Relativistic Limit : m e -> 0 ?? finite e ff ects : up to a few % depending on kinematics Coulomb distortion e ff ects not negligible ( ~ 0.2 % level )

CPHI @ Yerevan, New beam line and spectrometers Sep. 24-28, 2018 Exp. Hall 2 2 m new beam line GeV γ beam + new spectrometer(s) Exp. Hall 1 1.3 GeV booster γ /e beam synchrotron NKS II e-beam GeV γ beam 90 MeV e-Linac 60 MeV e-Linac FOREST (injector) GeV- γ Hall

1175 910 CPHI @ Yerevan, Electron spectrometer (P = 20 - 60 MeV/c) Sep. 24-28, 2018 Low energy : Ee = 20 - 60 MeV high-resolution without tracking “old-fashioned” spectrometer Electron spectrometer radius 500 mm bending angle 90° max. B 0.4T@60MeV gap 70 mm dispersion 850 mm Δ p/p 8 × 10 -4 momentum bite 10% Δθ 5 mrad solid angle 10 mSr

CPHI @ Yerevan, Summary Sep. 24-28, 2018 1) elastic e+p scattering at ultra-low Q 2 region 2) G E (Q 2 ) at 0.0003 ≤ Q 2 ≤ 0.008 (GeV/c) 2 3) G E is extracted by Rosenbluth separation 4) Absolute cross section measurement relative to 12 C(e,e) 12 C : 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