Electron scattering experiment oﬀ proton at ultra-low Q2...ULQ2@JPARC Nov. 1, 2016 Electron...

ULQ2@JPARCNov. 1, 2016

Electron scattering experiment off proton at ultra-low Q2

Toshimi Suda

Research Center for Electron-Photon Science, Tohoku University,

Sendai


Proton Radius Puzzle Proton Radius Puzzle A New Way

to Tame Cancer

MEDICINE

People Who

Remember Everything

NEUROSCIENCE

INFOTECH

The Proton Problem

© 2014 Scientific American

FEBRUARY 2014

2010 2013

“Proton Radius Puzzle”


４％(７σ)

e-scatt. （1950~)

hydrogen (1990~)

μ-hydrogen (2000~)

Proton Charge Radius (fm)

“ Proton charge radius puzzle”

so far, not yet settled (2016)

Data ? Interpretation ?

QED calculation ?

New Physics (beyond SM ?)

Higher order effects ?

many many discussions ..

ULQ2@JPARCNov. 1, 2016Who are we ?

We are “ Electron Scatterers”.

we are currently operating the World’s first electron scattering facility dedicated for exotic nuclei.

Not for stable nuclei,,,,,BUT never-yet-performed Short-Lived Exotic Nuclei !

“Hofstadter’s experiments” for exotic nuclei

“classical” elastic electron scattering to study the charge density distributions pioneered by R. Hofstadter in 1950s !

d�

d⌦=

d�Mott

d⌦|F

c

(q)|2

Fc(⌥q) =�

�(⌥r)e�i⇧q·⇧rd⌥r

ULQ2@JPARCNov. 1, 2016Nuclei studied by electron scattering

prot

on n

umbe

r

neutron number

126

82

50

282082

82

50

28

20

82

82

50

28

20

82

126

82

50

282082

208Pb

40,48Ca

16O

○　Most of stable nuclei (except noble gases such as Kr, Xe) ○　some example for unstable nuclei such as 3H, 14C, 41Ca etc...

strictly limited to stable nuclei never applied for exotic nuclei (short-lived)

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

ULQ2@JPARCNov. 1, 2016Electron Scattering

1. point particle 2. electromagnetic interaction i) coupling : charge and current => el.mag. structure ii) “weak” -> probing whole volume perturbation theory iii) exp. data => structure information 3. variable q for fixed ω

~e ~e0

! = e� e0

~q = ~e� ~e0

Electron scattering provides direct and unambiguous structure information of atomic nuclei including proton

ULQ2@JPARCNov. 1, 2016Elastic Electron Scattering

d�

d⌦=

d�Mott

d⌦|F

c

(q)|2

Fc(⌥q) =�

�(⌥r)e�i⇧q·⇧rd⌥r

⇢c(~r) =ZX

i=1

| i(~r)|2⇢c(~r) =ZX

i=1

| i(~r)|2

For 0+ nuclei

For non-0+ nuclei

d�

d⌦=

d�Mott

d⌦|F

c

(q)|2[Charge+Magnetic]

ULQ2@JPARCNov. 1, 2016SCRIT electron scattering facility

the world’s first facility dedicated for exotic nuclei

ULQ2@JPARCNov. 1, 2016SCRIT facility at RIKEN RIBF

LuminosityMonitor

RTM : Race Track Microtron injector + ISOL driver 150MeV/0.5 mA peak/2 μs

Electron energy： 150 - 700 MeV stored current： 300 mA (as of today) beam life time：2 hours

WiSES (Window-frame Spectrometer for Electron Scattering) Δp/p ~ 10-3 ΔΩ ~ 100 mSr long target acceptance ~ 50 cm

ISOL (ERIS) photofission of 238U132Sn : 3x105 @ 20W

ULQ2@JPARCNov. 1, 2016SCRIT（Self-Confining RI Target)

Problematic ion trapping phenomena @

electron storage ring

ionized residual gases are trappedby the circulating electron beam

ill problem of e-storage ring

Idea

vacuum chamber

electron beam

residual gas ions

scatteredelectron

electrontrapped RI

electrode

e-beam

manipulating injection,trapping and ejection

for short-lived RI

e-ring

RIs from an external ion source

trapping RIs on electron beam 　　（automatic e-scattering off trapped RIs)

new ion trap for e-RI scattering

M. Wakasugi, T. Suda and Y. YanoNucl. Instrum. and Method A278 (2004) 216.

electrode

ULQ2@JPARCNov. 1, 2016SCRIT system


50 cm


110 120 130 140 150 1600

200

400

600

800

160 170 180 190 200 2100

500

1000

1500

2000

2500

260 270 280 290 300 3100

100

200

300

Scattered electron energy (MeV)

Cou

nt (/

MeV

)

132Xe(e,e’)

a) b) c)

Ion IN - Ion OUT for comparative measurements

132Xe(e,e’)

Ee = 150 MeV Ee = 200 MeV Ee = 300 MeV


]-1 [fmeff

q0.4 0.6 0.8 1 1.2 1.4

)]-1

sr2)(c

m-1 s

-2 [(

cmΩdσd L

-310

-210

-110

1

10

210

First Data from the SCRIT facility

132Xe is a stable nucleus but has never been targeted.

The facility started its full operation, and the first physic run was carried out since April, 2016.

Luminosity, 1027 cm-2s-2, is achieved with only ~107 target nuclei

132Xe(e,e) Ee = 150, 200, 300 MeV θ = 30 - 60° Nions ~ 107 /s

First experiment for exotic nucleus, 138Xe (14 min.), this autumn. and to be followed by doubly magic nucleus, 132Sn (50s).

Ee = 150 MeV

Ee = 200 MeV

Ee = 300 MeV

Preliminary


]-1 [fmeff

q0.4 0.6 0.8 1 1.2 1.4

Mot

tΩdσd /

Ωdσd

-410

-310

-210

-110

1

PWIA

d�

d⌦=

d�Mott

d⌦|F

c

(q)|2

DWBA

|FDWBAC

|2 ⇠ d�d⌦

/d�

Mott

d⌦

Ee = 150 MeV

Ee = 200 MeV●○▼ Ee = 300 MeV

Preliminary

ULQ2@JPARCNov. 1, 2016Luminosities and Number of target nuclei

Ee Nbeam ρ・t LHofstadter’s era

(1950s) 150 MeV~ 1nA

(~109 /s) ~1019 /cm2 ~1028 /cm2/s

JLAB 6 GeV ~100μA (~1014 /s) ~1022 /cm2 ~1036 /cm2/s

SCRIT 150 - 300 MeV~200 mA (~1018 /s) ~ 10

9 /cm2 ~1027 /cm2/s

~107 ions are trapped on the electron beam of ~ 1 mm2 cross section

~107 /mm2 -> 109 /cm2


Proton Charge Radius


４％(７σ)

e-scatt. （1950~)

hydrogen (1990~)

μ-hydrogen (2000~)

Proton Charge Radius (fm)

Proton charge radius puzzle

ULQ2@JPARCNov. 1, 2016Proton charge radius determination

Spectroscopy Scattering

e-

μ-

me = 0.511 MeV mμ = 105.6 MeV

0.8770(60)0.8758(77)

0.8409(4) MUSE@PSI

ULQ2@JPARCNov. 1, 2016μH spectroscopy

P. Randolf et al., Nature 466 (2010) 213


1960 1970 1980 1990 2000 2010

e+p, e+A elastic scattering R. Hofstadter （1961）

e+p deep inelastic scattering J. Friedman, H. Kendall and R. Taylor

（1990）

eH spec.

μH spec.

electron scattering

Electron scattering off proton


< r2 >=

Zr2⇢(~r)d~r

RMS radius

ρ(r)~ exponential

Proton charge radius

= 4⇡

Zr4 ⇢(r) dr


GE(Q2) =

1

(1 + Q2

↵2 )2

↵2 = 0.71(GeV/c)2

Q2 1/2=2p3

↵

< r2 >1/2= 0.81fm

(r > 0)

Fourier transformation

GE(Q2) ! ⇢(r)


GE(Q2) ⇠ 1� < r

2 >1/2

6Q2 +

< r4 >1/2

120Q4 � ...

２）low Q2

ill problem : higher order contribution

lower Q2 as possible

< r2 >⌘ �6 dGE(Q2)

dQ2|Q2!0

< r2 >=

Zr2⇢(~r)d~r

１）high Q2: charge density ρ(r)

radius is sensitive to ρ(r) at large distance ( even at r ~ 4 fm )

Electric Form FactorGE

ρ(r)

⇢(r) ⇠ e�↵r

ee’θ

momentum transferenergy transfer4 momentum transfer Q2 = q2 � !2 = 4EeEe0sin2(✓/2)

~q = ~e� ~e0! = e� e0

Q2 = q2 � !2 = 4 e e0sin2(✓/2)

d�

d⌦= (

d�

d⌦)Mott

G2E

(Q2) + ⌧✏

G2M

(Q2)

1 + ⌧

✏ =1

1 + 2(1 + ⌧)tan2 ✓2

⌧ =Q2

4m2p

(

d�

d⌦

)

Mott

=

z2↵2

4e2cos

2(✓/2)

sin

4(✓/2)

/ e2

q4

Proton charge radius by e-scattering

ULQ2@JPARCNov. 1, 2016Density distribution and RMS radius

< r2 >=

Zr2⇢(~r)d~rCharge radius

R rr2⇢(r)d~rR1r2⇢(r)d~r

208Pb

< r2 >1/2

RMS radius（5.499(1) fm)

Ratio = 98 %


5.503±0.002 fm (4x10-4)


Proton

< r2 >1/2

~ exponential

RMS radius（~0.8 fm)

Ratio = 98 %

0.895±0.018 fm (2x10-2)


J. C. Bernauer et al., Phys. Rev. C90 (2014) 015206.

= 0.879 (5) fm

but …there are discussions about the fitting

how to treat higher order ?

Electron scattering at Low Q2

GE(Q2) ⇠ 1� < r

2 >

6Q2 +

< r4 >

120Q4 � < r

6 >

5040Q6 + ...


Q2 = 0.0003 (GeV/c)2

Reduction of the higher order contribution

What are we going to do ???

GE(Q2) at lower Q2 region


Mainz 2014 Tohoku

Q2min (GeV/c)2 0.004 0.0003

Ee (MeV) 180 ~ 850 20 ~ 60

absolute dσ/dΩ ｘ〇

GE/GM separation ｘ〇

What are we going to do ?


Lab. Ee θ absolute dσ/dΩGE, GM

separation

JLAB (USA）

Ultra-forward

1.1 - 2.2 GeV

1 - 4 deg. 〇 X

Mainz （Germany）

lower Ee by Bremsstrah

lung

195, 330, 490 MeV X X

TOHOKU low Ee 20 - 60 MeV30 - 150

deg. 〇〇

Electron scattering at Lower Q2

ELPH, Tohoku Univ. : only a electron scattering facility.

experimental GE separation at ultra-low Q2


Research Center for Electron Photon ScienceTohoku University

Sendai

Where are we ?


1.3 GeVbooster

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

Research Center for Electron-Photon Science


1.3 GeVbooster

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

Ee : 20 ~ 60 MeV variable Ie : 0 ~ 150 uA

“OLD” Low-Energy Electron Linac

Low-energy branch

ULQ2@JPARCNov. 1, 2016e-scattering off proton at ultra-low Q2

Goal of our experimentGE(Q2) measurements in 0.0003 ≤ Q2 ≤ 0.008 (GeV/c)2

Our experimentsLow energy electron beam ( 20 ≤ Ee ≤ 60 MeV)Absolute cross section measurementRosenbluth separation (GE(Q2), GM(Q2) separation)

Q2 = 0.0003 (GeV/c)2

< r2 >⌘ �6 dGE(Q2)

dQ2|Q2!0


d�

d⌦/ G2E(Q2) + ↵(✓)G2M (Q2)

Rosenbluth separation (GE/GM)

Elastic cross section

Q2 = 4ee0sin2(✓/2)

change under fixed Q2↵(✓) different electron beam energies

Rosenbluth separation

G2M (Q2)

G2E(Q2)

sys. err. of 0.3%q = 30 MeV/c

ULQ2@JPARCNov. 1, 2016A key of the e+p experiments at ULQ2

only ~ 2%

っっっっｚ

dNevtd⌦

=d�

d⌦Ntarget Nbeam �⌦target thickens

beam dose

spectrometer acceptance

Statistics : at least > 106 for each (Ee,θ) measurements Target thickness Beam dose at various intensities Acceptance at various scattering angle

accuracy of ~ 10-3 not obvious !

Uncertainty of GE(Q2) must be controlled to be an order of ΔGE/GE ~ 10-3

ULQ2@JPARCNov. 1, 2016CH2 target for absolute cross section measurement

Relative measurement for 12C(e,e)12C and p(e,e)p

dNevtd⌦

=d�

d⌦Ntarget Nbeam �⌦

Canceled out in relative measurements

dNe12C/d⌦

dNep/d⌦=

d�e12C/d⌦

d�ep/d⌦·N

12Ctarget

NHtargetd�ep/d⌦

d�e12C/d⌦

1) RMS charge radius (or ρ(r) ) of 12C ??2) 12C(e,e)12C, p(e,e)p by kinematics ??

3) change of C/H ratio by beam irradiation ??


っっっっｚ

っっっっｚ

μ-Xray electron scattering

2) 12C(e,e)12C, p(e,e)p by kinematics

Δp/p ~ 10-3

1) 12C : “standard” nucleus for (e,e’)

� < r212C >1/2

< r212C >1/2

⇠ 3⇥ 10�3

CH2 (e,e’) experiment

ΔE = 0.2 - 4 MeV for q = 20 - 90 MeV/c

っっっっｚ

3) no severe damage of target is expectedlarge cross section : d�

d⌦/ 1/q4

Ie ~ 1 nA - 1 μA


Experimental setup at ULQ2 exp.

Spectrometer A

Radioactive Isotope

Production Station

60-MeV Electron Linac

Spectrometer B

22 mEe = 20 ~ 60 MeV Ie ~ 1 nA - 1μA

1) new beam line 2) two magnetic spectrometers Rosenbluth measurements Luminosity monitoring

CH2 target ( ~0.1 mm t) Δp/p ~ 1 x 10-3

ULQ2@JPARCNov. 1, 2016Rosenbluth-Separated GE(Q2) at ULQ2

Q2 = 0.0003 (GeV/c)2

Absolute cross section Rosenbluth separation GE(Q

2)

ULQ2@JPARCNov. 1, 2016How rp has been determined ??

Spectroscopy Scattering

e-

μ- MUSE exp. @PSI is coming …

ULQ2@JPARCNov. 1, 2016Summary

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 the 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) constructing of new beam line, and spectrometers

7) the experiments will start in 2019

科研費・基盤（S）　2016 ~ 2020

Electron scattering experiment oﬀ proton at ultra-low Q2...ULQ2@JPARC Nov. 1, 2016 Electron...

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