Electron scattering experiment off proton at ultra-low Q 2

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1 Electron scattering experiment off proton at ultra-low Q 2 Toshimi Suda Research Center for Electron-Photon Science, Tohoku University, Sendai

2 Proton Radius Puzzle NEUROSCIENCE People Who Remember Everything MEDICINE A New Way to Tame Cancer INFOTECH FEBRUARY 2014 The Proton Problem Scientific American

3 Proton charge radius puzzle e-scatt. 1950~) μ-hydrogen (2000~) hydrogen (1990~) ( ) Proton Charge Radius (fm)

4 Proton charge radius puzzle many many discussions.. Data? Interpretation? μ-hydrogen Higher order effects? (2000~) QED calculation? ( ) e-scatt. 1950~) hydrogen (1990~) New Physics (beyond SM?) Proton Charge Radius (fm)

5 Proton charge radius puzzle many many discussions.. Data? Interpretation? μ-hydrogen Higher order effects? (2000~) QED calculation? ( ) e-scatt. 1950~) hydrogen (1990~) New Physics (beyond SM?) not Proton yet settled Charge Radius (fm) New experiments

6 Who are we?

7 Who are we? We are (low-energy) Electron Scatterers.

8 Who are we? We are (low-energy) Electron Scatterers. 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 F c ( q) = ( r)e i q r d r

9 Who are we? We are (low-energy) Electron Scatterers. 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 F c ( q) = ( r)e i q r d r Not for stable nuclei,,,,, BUT never-yet-performed Short-Lived Exotic Nuclei! Hofstadter s experiments for exotic nuclei

10 Who are we? We are (low-energy) Electron Scatterers. 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 F c ( q) = ( r)e i q r d r Not for stable nuclei,,,,, BUT never-yet-performed Short-Lived Exotic Nuclei! Hofstadter s experiments for exotic nuclei we are currently operating the World s first electron scattering facility dedicated for exotic nuclei.

11 SCRIT electron scattering facility RIKEN Aug. 3, 2016

12 SCRIT electron scattering facility RIKEN Aug. 3, 2016

13 SCRIT electron scattering facility RIKEN Aug. 3, 2016 sr -1 )] 2 s -1 )(cm -2 [(cm d d Ω σ L Xe(e,e) Ee = MeV Nions ~ 10 7 /s [fm q eff -1 ]

14 Electron scattering off proton e+p, e+a elastic scattering R. Hofstadter 1961 e+p deep inelastic scattering J. Friedman, H. Kendall and R. Taylor 1990 electron scattering eh spec. μh spec.

15 Proton charge radius RMS radius <r 2 >= Z r 2 (~r )d~r Z =4 r 4 (r) dr ρ(r) ~ exponential

16 Proton charge radius by e-scattering RIKEN Aug. 3, 2016 e e θ d d =(d d ) Mott G 2 E (Q2 )+ G2 M (Q2 ) 1+ momentum transfer energy transfer ~q = ~e ~e 0! = e e 0 4 momentum transfer Q 2 = q 2! 2 =4ee 0 sin 2 ( /2) ( d d ) Mott = z2 2 = 4e (1 + )tan 2 2 = Q2 4m 2 p cos 2 ( /2) sin 4 ( /2) / e2 q 4 high Q 2 : charge density ρ(r) Electric Form FactorGE ρ(r) Z <r 2 >= r 2 (~r )d~r (r) e r low Q 2 G E (Q 2 ) 1 <r 2 > 1/2 6 Q 2 + <r4 > 1/2 120 <r 2 > 6 dg E(Q 2 ) dq 2 Q2!0 Q 4... ill problem : higher order contribution radius is sensitive to ρ(r) at large distance ( even at r ~ 4 fm ) lower Q 2 as possible

17 Electron scattering at Low Q 2 J. C. Bernauer et al., Phys. Rev. C90 (2014)

18 Electron scattering at Low Q 2 G E (Q 2 ) 1 <r 2 > 6 Q 2 + <r4 > 120 Q4 <r 6 > 5040 Q J. C. Bernauer et al., Phys. Rev. C90 (2014)

19 Electron scattering at Low Q 2 G E (Q 2 ) 1 <r 2 > 6 Q 2 + <r4 > 120 Q4 <r 6 > 5040 Q <rp> = (5) fm J. C. Bernauer et al., Phys. Rev. C90 (2014)

20 Electron scattering at Low Q 2 G E (Q 2 ) 1 <r 2 > 6 Q 2 + <r4 > 120 Q4 <r 6 > 5040 Q <rp> = (5) fm but there are discussions about the fitting how to treat higher order? <rp> fm J. C. Bernauer et al., Phys. Rev. C90 (2014)

21 What are we going to do??? Reduction of the higher order contribution Q 2 = (GeV/c) 2

22 What are we going to do? Mainz Tohoku Q 2 min (GeV/c) Ee (MeV) 180 ~ ~ 60 absolute dσ/dω GE/GM separation

23 Electron scattering at Lower Q 2 Lab. Ee θ absolute dσ/dω GE, GM separation JLAB (USA Ultraforward GeV 1-4 deg. X Mainz Germany lower Ee by Bremsstrah lung 195, 330, 490 MeV X X TOHOKU low Ee MeV deg.

24 Research Center for Electron Photon Science Tohoku Univ., Sendai, JAPAN Exp. Hall 2 OLD Low-Energy Electron Linac GeV γ beam NKS II 1.3 GeV booster synchrotron Ee : 20 ~ 60 MeV variable Ie : 0 ~ 150 ua γ/e beam Exp. Hall 1 e-beam GeV γ beam FOREST GeV-γ Hall 90 MeV e-linac (injector) 60 MeV e-linac

25 e-scattering off proton at ultra-low Q 2 Goal of our experiment GE(Q 2 ) measurements in Q (GeV/c) 2 Our experiments Low energy electron beam ( 20 Ee 60 MeV) Absolute cross section measurement Rosenbluth separation (GE(Q 2 ), GM(Q 2 ) separation) <r 2 > 6 dg E(Q 2 ) dq 2 Q2!0 Q 2 = (GeV/c) 2

26 Rosenbluth separation (GE/GM) Elastic cross section d d / G2 E(Q 2 )+ ( )G 2 M (Q 2 ) Q 2 =4ee 0 sin 2 ( /2) change ( ) under fixed Q 2 different electron beam energies q = 30 MeV/c sys. err. of 0.3% Rosenbluth separation G 2 M (Q 2 ) G 2 E(Q 2 )

27 A key of the e+p experiments at ULQ 2

28 A key of the e+p experiments at ULQ 2 only ~ 2%

29 A key of the e+p experiments at ULQ 2 only ~ 2% Uncertainty of GE(Q 2 ) must be controlled to be an order of ΔGE/GE ~ 10-3

30 A key of the e+p experiments at ULQ 2 only ~ 2% Uncertainty of GE(Q 2 ) must be controlled to be an order of ΔGE/GE ~ 10-3 dn evt d = d d N target N beam target thickens beam dose spectrometer acceptance Statistics : at least > 10 6 for each (Ee,θ) measurements Target thickness Beam dose at various intensities Acceptance at various scattering angle accuracy of ~ 10-3 not obvious!

31 CH2 target for absolute cross section measurement Relative measurement for 12 C(e,e) 12 C and p(e,e)p dn e12c /d dn ep /d = d e 12C /d d e12c /d d ep /d N 12 C target N H target dn evt d = d d N target N beam Canceled out in relative measurements 1) RMS charge radius (or ρ(r) ) of 12 C?? 2) 12 C(e,e) 12 C, p(e,e)p by kinematics?? 3) change of C/H ratio by beam irradiation??

32 CH2 (e,e ) experiment 1) 12 C : standard nucleus for (e,e ) μ-xray electron scattering <r 2 12 C >1/2 <r 2 12 C >1/ ) 12 C(e,e) 12 C, p(e,e)p by kinematics ΔE = MeV for q = MeV/c Δp/p ~ ) no severe damage of target is expected large cross section : Ie ~ 1 na - 1 μa d d / 1/q4

33 Experimental setup at ULQ 2 exp. 22 m Radioactive Isotope Production Station Spectrometer A Spectrometer B Ee = 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 MeV Electron Linac

34 Rosenbluth-Separated GE(Q 2 ) at ULQ 2 Absolute cross section Rosenbluth separation GE(Q 2 ) Q 2 = (GeV/c) 2

35 Summary 1) elastic e+p scattering at ultra-low Q 2 region 2) GE(Q 2 ) at Q (GeV/c) 2 3) GE is extracted by the Rosenbluth separation 4) absolute cross section measurement relative to 12 C(e,e) 12 C : sys. err. ~3x10-3 5) Ee = MeV, θ = ) constructing of new beam line, and spectrometers 7) the experiments will start in 2019