The Proton Radius Puzzle Angeli Istvn Budapest KFKI

The Proton Radius Puzzle Angeli István Budapest, KFKI, 2020 január 20.

Bohr’s hydrogen atom. Transitions: l l 1

1928: Dirac-equation H-atom V ~ 1/r E(n, j) j=l+s 2 S 1/2 and 2 P 1/2 energies equal!

1930 - … : Small anomalies in Balmer transitions

1933 Kemble: breakdown of the Coulomb-law 1935 Yukawa: „dynaton” ( -meson) field 1938 W. Lamb: Proton not point like ? V not ~1/r ? S electron weakly bounded

1939 – 45 World war II. Radar! 1946 – 47 Lamb, Retherford, experiment: 2 S 1/2 – 2 P 3/2 10 GHz! (not 11 GHz) But calculation: -meson cloud ~ 0. 02 MHz ! ? ? ?

June 1947, Shelter Island: QED ! Bethe, QED : 2 S self energy: DE ~ 1 GHz 1955: Lamb, Kusch: Nobel-Prize ----------------------------But: size of the proton?

1953: Hofstadter, „Project initiated …„ (Nobel Prize, 1961) Target: polyethylene foil, or H-gas (2000 psi) Spectrometer (on Navy gun mount): 1800 magnet, vertical to plane of scattering Cherenkov detector

at low q: slope sensitive to at high q: slope sensitive to model

Hand 1963, from 8 series: rp = 0. 805 (11) fm Simon 1980, from 2 series: rp = 0. 862 (12) fm New, independent method necessary!

1990 -… QED test Ln ~ 1/n 3 1 S shift L 1 to be measured. 2 S → 1 S UV line width ~1. 3 Hz Garching: Hänsch (Nobel Prize 2005)

Contributions to L 1 E (MHz) DE (k. Hz) Self energy 8396. 456 1 Vacuum polarization ‑ 215. 168 1 QED higher order 0. 724 24 Recoil corrections ‑ 10. 376 6 1. 167 32 L 1 theory 8172. 802 40 L 1 experiment 8172. 874 60 Proton size

Alternative approach Assume: QED valid, calculation correct. rp as free parameter L 1, theory = L 1, exp. is searched for rp = 0. 883(14) fm Moral:

Isola di San Servolo: QED test? Accurate proton radius -as input- necessary! Bernauer: e – p scattering „top” : low q, 1400 points! Pohl: Lamb shift in muonic H-atom, r 2003, high sensitivity to rp , but 6 pulses/h ! 2005: „No significant 2 S 2 P resonance was observed”

Isola di San Servolo: QED test? Accurate proton radius -as input- necessary! Bernauer: e – p scattering „extra”: low q, 1400 points! Pohl: Lamb shift in muonic H-atom, r 2003, high sensitivity to rp , but 6 pulses/h ! 2010: rp = 0. 84184(67) fm !

https: //indico. psi. ch/event/6857/contributions/18904/attachments /15291/20998/talk_antognini_PSI_2019. pdf

„Proton Radius Puzzle!”

Pohl: „Our result implies that either the Rydberg constant has to be shifted by 4. 9 , or the calculations of the QED effects are insufficient, ”

From H-spectra: h The new definition of the kilogram: „The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6. 626 070 15 × 10 -34 , when expressed in the unit Js, … ” But if R is shifted by 4. 9× , . . ? ? ?

2011, Zhan: polarized e- , polarized p, TPE cancel, rp = 0. 875(10) fm 2014, Bernauer: MAMI, 1400 data, from small Q, … rp = 0. 879(10) fm.

Bernauer, Pohl: Scientific American, 310/2 (2014) 32. „Four years after the puzzle came to life, physicists have exhausted the straightforward explanations. We have begun to dream of more exciting possibilities” (Beyond Standard Model)

2017: Beyer, H-spectroscopy rp= 0. 8335(95)fm 2018: Fleurbaey, H-spectr. rp = 0. 877 (13) fm 2019: Bezginov, H-spectr. rp = 0. 833 (10) fm A world of two poles?

2019: Xiong, e- -p scattering Target: cryo-cooled gas flow. Spectrometer: 1. 16× 1. 16 m 2 plane, high ( ) efficiency! 2 gas electron multipliers: 72 m X-Y resolution. Calorimeter: 580 Pb-glass, 1200 Pb. WO 4 crystals. Cross section: Normalized to e- + e- scattering M ller Xsect, QED accurately calculable. rp = 0. 831 (7) [12] fm !

Way out? 1) Search for undiscovered systematic errors. El-scatt: larger errors, does not resolve puzzle. H-spectroscopy: 4 3. Independent - H ? 2) Muse’s kiss: MUon Scattering Experiment collaboration (MUSE) 2012: „We propose to measure p scattering. We expect the experiment to last about late 2014 mid 2015. ” (PSI) 2017: Technical Design Report, PSI Exp. R-12 -01. 1 „they started collecting physics data only in 2019” from Aldo Antognini; Ronald Gilman: NIM (2020): target.

Some readings: R. Hofstadter: Rev. Mod. Phys. 28 (1956) 214. Ch. VIII. : The Validity of Electrodynamics. Fizikai Szemle, 2011/4, p. 118. (In Hungarian). Pohl, R. : Nature, 466 (2010), p. 213. Bernauer, J. C. , Pohl, R. : Sci. Am. , 310/2 (2014) 32. Arrington, J: J. Phys. Chem. Ref. D. 44/3 (2015)031203. Krauth, J. J. , et al: ar. Xiv: 170696 v 2; 19 Aug 2017. Xiong, W. : Nature, 575 (2019), p. 147. … and refs.

Thank you for your patience!