### Conveners

#### QCDHS / PPHI: Parallel 9 — The Proton Radius Puzzle

- Seamus Riordan (Argonne National Laboratory)

Prof.
Gerald Miller
(University of Washington)

6/2/18, 4:10 PM

QCDHS

Parallel

A new scalar boson which couples to the muon and proton can simultaneously solve the proton radius puzzle and the muon anomalous magnetic moment discrepancy. Using a variety of measurements, we constrain the mass of this scalar and its couplings to the electron, muon, neutron, and proton. Making no assumptions about the underlying model, these constraints and the requirement that it solve both...

Mr
Lothar Maisenbacher
(Max Planck Institute of Quantum Optics)

6/2/18, 4:40 PM

QCDHS

Parallel

Precision measurements of atomic hydrogen (H) have long been successfully used to extract fundamental constants and to test bound-state quantum electrodynamics. Both the Rydberg constant $R_\infty$ and the proton root mean square charge radius $r_\mathrm{p}$ can be determined by H spectroscopy, requiring the measurement of at least two transition frequencies. With the very precisely measured...

Weizhi Xiong
(Duke University)

6/2/18, 5:10 PM

PPHI

Parallel

In order to investigate the proton radius puzzle, the PRad experiment (E12-11-106) [1] was performed in 2016 in Hall B at Jefferson Lab, with both 1.1 and 2.2 GeV unpolarized electron beams. The experiment aims to measure the $e$-$p$ elastic scattering cross section at unprecedented low values of the momentum transfer squared region ($Q^2 = 2\times10^{-4} - 0.06$ (GeV/c)$^2$), with a...

Dr
Paul E Reimer
(Argonne National Laboratory)

6/2/18, 5:30 PM

QCDHS

Parallel

The mean charge radius of the proton has been measured with elastic electron scattering and through spectroscopy of atomic hydrogen with consistent results. Recent results based on spectroscopic measurements of muonic hydrogen, however, have found a notably smaller charge radius with extremely high precision. This difference, known as the Proton Radius Puzzle, raises interesting issues...

Prof.
Sergey Syritsyn
(Stony Brook University)

6/2/18, 5:50 PM

QCDHS

Parallel

With the continuing discrepancy in experimental measurements of the proton radius, $\textit{ab initio}$ determination of this quantity from QCD is urgently needed. At present, QCD calculations on a lattice are performed with physical values of light and strange quarks and adequate lattice volumes to permit credible control of systematic errors. One particular obstacle to computing the nucleon...

Christian Weiss
(Jefferson Lab)

6/2/18, 6:10 PM

QCDHS

Parallel

We present a new method for calculating the nucleon electromagnetic form factors (EM FFs) combining Chiral Effective Field Theory (ChEFT) and dispersion analysis [1]. The FFs are expressed as dispersive integrals over the two-pion cut at timelike $t > 4 M_\pi^2$. The spectral functions are computed using elastic unitarity, chiral pion-nucleon amplitudes (LO, NLO, partial N2LO), and timelike...